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Thread: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces.

  1. #11
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces



    Ritchey-Chrétien Telescopes (R-Cs)


    1. The Ritchey-Chrétien telescope should probably be thought of as a relatively high-end astrophotography telescope. I debated not even discussing this telescope since it has been of limited interest to the amateur market. However, the price seems to have come down a little and my perception is that they are increasingly popular within the amateur community.
    2. Why you might want a Ritchey-Chrétien telescope?
      1. Photographic excellence. The R-Cs don't have the same problem which some other scopes have with coma (there is an issue, but it is not the same) and it has no issues with spherical aberration. Astigmatism and field curvature can be a significant problem but most people who use the R-C like them for AP.
      2. Some of the R-C mirrors are getting dielectric coatings. This is a relatively durable coating and is more highly reflective meaning you get a little more from your mirror.
      3. For some imagers the most compelling reason for getting an R-C would be that they tend to have a lot of back-focus. In this case that means that you could put a focal reducer, a filter wheel, as well as an OAG and a camera on the thing and still likely have no trouble achieving focus. A lot of other designs result in a lot of difficulty achieving focus if you are hanging a bunch of stuff off the back-end of the telescope.
      4. Not very sensitive to dewing problems since the mirror is recessed in the tube.
      5. You can use them with an eyepiece for visual purposes. I just don't know of anyone who has bought one for this reason. The relatively large size of the central obstruction is likely the primary reason for dis-favoring it for visual use as the central obstruction is likely to be visually disturbing at magnification levels which would be no problem with an SCT.
      6. Faster final cool-down than with the SCT design – no corrector plate means faster cooling. But again, getting an SCT cooler will largely remove the R-C advantage.
      7. Bragging rights. . . Yup, the really big telescopes for professionals are virtually all (maybe all?) using some variant of the Ritchey-Chrétien design. I believe the last of the big ones which did not use the R-C design was the Hale (200-inch) and the reason it didn't get the R-C design could be argued to have been a logistical/timing decision.

    3. Why you might not want to get a Ritchey-Chrétien Telescope?
      1. Expensive. They still tend to be more expensive than a good EdgeHD or ACF Schmidt-Cassegrain Telescope. It is possible that the R-C design is better for photographic purposes than is the SCT, but I'm not convinced the R-C is generally better for the amateur astronomer than are the EdgeHD and ACF SCT designs.
      2. Bigger secondary obstruction.
        • Since the R-Cs have relatively large secondary obstruction (as compared to those of the SCTs) one would expect better light-gathering from a good SCT with the ACF or EdgeHD optics (a dielectric mirror coating would help the R-C but likely would not allow it to equal the SCT).
        • The larger secondary obstruction will also increase the amount of diffraction and reduce perceived contrast. If, however, the R-C has a dielectric coating I would expect a little less scattering from the mirrors and that might reduce the SCT advantage in this regard.

      3. You are somewhat more likely to get messed up mirrors. Since there is no corrector plate you can get dust, pollen, bugs, etc. on your mirrors and that may be harder to clean up than the corrector plate of the SCT.
      4. Collimation. I hear/read varying reports on this. Some say that the collimation is easy but I also read of the need for special equipment for collimating the R-Cs and some people have had difficulty acquiring the equipment. I do not know the validity of the concern.
      5. That big advantage of having a really long back-focus? If you start hanging a lot of stuff on the focuser you can actually have flexure in the optical train and significant aberration as a result.
      6. Relatively large image circles. I have repeatedly read that the image circle of an R-C is relatively large resulting in the ability to use larger sensors. I have difficulty verifying this as the people making and selling them don't seem eager to tell you the size of the image circle. Telescopes sold for imaging purposes should specify the image circle size.
      7. Field curvature and astigmatism. Some folk have flatteners for their instruments but I've also seen situations where they could not find a field flattener for their instrument – and with larger sensors field curvature can be a significant issue.
      8. Diffraction spikes from the secondary mirror support. Some people like the diffraction spikes and some do not.


    Yes, there is no free lunch, but the Ritchey-Chrétien suits an increasing number of people quite well. I suspect, however, that for most amateurs getting an SCT with EdgeHD or ACF optics will be a more pleasing choice.
    Last edited by OleCuss; 08-14-2016 at 10:32 PM.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Miscellaneous Telescope Designs


    There are a lot of various designs with various strengths which are custom-made or are available commercially. I have no hope of listing them all but there are some which I'd like to mention since they have caught my eye or fired my imagination for some reason. None of the ones I'll list seem to have captured much of the market but that does not necessarily mean that they are not better – or that they are not worse.


    1. Ed Jones has made a pretty amazing solar projector. This device is unusually safe as it never concentrates the sunlight. It also projects a relatively large image onto a screen (or side of a truck. . .) so that many folk can observe at the same time.
      1. Here is a link to it if you are interested: https://opticaleds.com/unusual-teles...lar-projector/
      2. At the time this is written we are about one year away from the total solar eclipse here in the USA so I'll mention sort of parenthetically that I plan to take mine to the eclipse and set it up with a screen and with a regular video camera aimed at the screen. And I will otherwise enjoy the eclipse visually.

    2. Tilted Component Telescopes (TCTs). These are intended to eliminate the diffraction from the secondary mirror and give better views. Examples are the Yolo design and the Schiefspiegler. I believe Ed Jones' Chiefspiegler is a Schiefspiegler variant – and I'd really like to have one (I'm just not willing to pay for it).
    3. Dall-Kirkham and Corrected Dall-Kirkham (CDK). These seem to be pretty popular in larger sized telescopes.
    4. There are lots of others which have been made/enjoyed. I intend no offense by not mentioning (or in some cases not even knowing of) them.
    Orion XX12G and XT8; 10 inch LX200GPS; Celestron NexStar 8SE; Tele Vue NP-101is (Petzval apochromat); Meade LS-8; WO GT-71; AVX and Losmandy G-11 mounts.

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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Eyepieces

    I hesitate to address this issue once again, but in order to make this thread a convenient place to get an overview of equipment choices I guess we really need to touch on this. I'm going to try to stay with the broader characterizations to help you choose rather than trying to tell you what is best for you or for your equipment.

    It is really important to understand that personal likes and dislikes are extremely important when it comes to eyepiece choices. There is simply no accounting for taste in the matter – some people really like what others detest and I've not come up with a way of telling what others will like. I will, however, make one statement right up front. . .

    I personally find the Delos line made by Tele Vue to be completely unobjectionable. They are optically excellent. Their great eye relief means that you can enjoy them with or without glasses. Their field of view is big enough to make those of us who really like very wide fields of view fairly happy. Their field of view is not so big as to be irritating to those who do not like very wide fields of view. I think they are excellent eyepieces!

    People tend to obsess over the magnification. I barely mentioned that at first because it generally isn't a priority in amateur astronomy. But it is easy to calculate because you simply divide the effective focal length of telescope by the focal length of the eyepiece.

    Just don't try to push your magnification too much. Start with lower magnification and wider fields of view for locating your target and then you can push up the magnification if you wish. But you must remember that the magnifications advertised for some scopes are just ridiculous/unusable. Your useful magnification is going to be limited by the size of your objective, the quality of your optics, and by environmental conditions. Some nights you may not be able to use 100x even if you've got great optics - and in some locations people can seldom usefully use even 100x. Some nights I've found 60x was the most I could do. But lots of nights I don't really even want to get 100x - I'm looking for how low a magnification I can use.


    OK, now we need to get down to the basics.


    1. Your dark-adapted pupil. It is important to remember that you eye and brain are a very important part of the system you will use in order to observe the stars. There are some things which must be remembered/considered.
      1. Size of the dark-adapted pupil:
        • The size of the dark-adapted pupil tends to vary inversely with age. This means that an old guy like myself cannot expect to have a dark-adapted pupil as large as when I was young.
          • You cannot predict the pupil size based on age. There is a lot of variation in pupillary size within age brackets and you might be young with a small dark-adapted pupil and you might be old and have one which is relatively generous (I reach 6 and 6.5mm with my eyes which is better than I should expect).

        • The size of the dark-adapted pupil varies with extraneous light. If you are in a heavily light-polluted area your pupil will likely not dilate to the degree it would dilate if you were under very dark skies.
          • In a city you are likely to have less dilation.
          • The Moon is light pollution. It makes the skies brighter and could cause some pupillary constriction (I've not seen a study to show how much).
          • If you are looking at the Moon using a telescope without a good filter you are going to have a lot of issues with pupillary constriction.


      2. How do you measure your dark-adapted pupil? There aren't all that many great options.
        • My eye doctor does some Lasik procedures. At one time it was considered very important to measure pupils prior to that procedure so some of the Ophthalmologists still have pupillometers. So one time when I went for my exam and he'd used drops to dilate my pupils I asked him to measure – and he did. You might be able to make that happen as well.
        • Ifyou can get some small rods or hex keys (aka Allen wrenches) and go out on a very dark night. You look at a bright star and hold one rod after the other up close to your eye (make sure you do not poke your eye). When the rod is directly between your pupil and the star, if the rod is thinner than your pupil's diameter then you will still be able to see some of that star above or below the rod (or both above and below depending on alignment). If the rod is larger than the pupillary diameter it will completely block your view of the star. The rod which just barely blocks all the star's light is exactly the size of your pupillary diameter.
        • Telescope manufacturers and some optical gurus assume a 7mm dark-adapted pupil. This is very optimistic for most of us.

      3. OK, now consider trashing all the above information on pupillary diameter. Realistically you probably shouldn't count on more than about a 5mm pupil due to age, various ambient lights, etc. If you are young you still may wish to play with it for some reason, but it likely won't matter too much.

    2. What is the exit pupil (aka Ramsden disc) and why should you care?
      1. The exit pupil is sort of an image of the objective of your telescope.
        • If you aim your telescope (with an eyepiece) at a bright wall and then run a piece of white paper back and forth near the eyepiece there will be a spot where the illuminated circle on the paper is minimized – and the diameter at that point is the exit pupil size.
        • You can calculate the diameter of the exit pupil by dividing the diameter of your objective by the magnification of the telescope/eyepiece combination. So for a 10x50 binocular you will have an exit pupil of 50mm divided by 10x – and find that you have an exit pupil of 5mm.

      2. Why should we care about the exit pupil?
        • Generally speaking, a larger exit pupil is going to deliver more light to your eye. Think of it this way, that larger exit pupil means that the image of your objective is larger – and a larger objective gathers/delivers more light.
          • If your exit pupil is larger than is your dark-adapted pupil you will not see all the delivered light but you will still benefit from the relatively wide field of view delivered by the combined optics of the telescope and eyepiece.
          • Given the same telescope, an eyepiece which delivers lower magnification will tend to provide a larger exit pupil.

        • Generally speaking, a smaller exit pupil is going to deliver less light to your eye since it is providing a smaller image of the objective.
          • This means that on dim objects going with a smaller exit pupil will make it more difficult to see your target. On very bright objects the loss of brightness will not be an issue.
          • Given the same telescope, an eyepiece which delivers higher magnification will tend to provide a smaller exit pupil.
            • Note that the two preceding bullet points suggest that as you increase the magnification of your system you are also decreasing the brightness of your target.

          • If your exit pupil is less than about 0.5mm you will begin to have degradation of your view due to imperfections we all have in the structure of our eyes. If you think about it, 0.5mm is a very small area. . .

        • For most of us under most conditions keeping the exit pupil no smaller than 0.5mm and no larger than 5mm will work well (0.5-5mm). Larger may prove beneficial but smaller is unlikely to be beneficial.




    3. Telescope Design Limitations on Eyepiece Focal Length:
      1. For a refractor or other telescope which has an unobstructed design (e.g. no secondary or diagonal mirror) there is no solid limit to the focal length you might be able to use. If you use an eyepiece with a long enough focal length to result in an exit pupil larger than your dark-adapted pupil, then you will have some light loss/wastage but you may not find this objectionable.
      2. For a telescope such as a Newtonian reflector, SCT, etc. which has an obstructed design (e.g. there is a secondary or diagonal mirror) then using an eyepiece with an excessively long focal length may result in the obstruction being visually disturbing. This is a bigger problem in bright conditions (such as daylight) than in dark conditions.

    4. Eyepiece Optical Designs
      1. Not going to list all these. Seriously, there are a whole lot of designs out there and some of them are confusingly labeled. Generally speaking, you get what you pay for. If you buy cheap you will likely have a worse view. If you are paying more you are probably getting a better view.
      2. Are premium (generally expensive) eyepieces worth the expense? Maybe.
        • If you get a pretty good eyepiece it might get you 90% of the view which the best eyepiece will get you – and it may cost you only 1/3 the price. A simple view of this would suggest that the premium eyepieces just may not be worth their cost – but it may not be that simple.
          • Yup, if you just want to see something, a premium eyepiece may be a waste of your money.
          • If you want to see the finest detail with the truest color then anything but the finest eyepiece may be a total waste of your money. In this scenario you should save up the money and get the best eyepiece on the market.



    5. General technical parameters for choosing an eyepiece:
      1. Focal length.
        • The focal length of your telescope divided by the focal length of your eyepiece gives you the magnification of the system.
        • Generally, given a particular optical design, a longer focal length for your eyepiece will likely result in a wider field of view (FOV).

      2. Field Of View (FOV). Typically the eyepiece manufacturer will list the AFOV (Apparent Field Of View) for the eyepiece. A bigger number means you see a larger portion of the sky and a smaller number (of course) means you see a smaller portion of the sky.
        • Pay attention to this and to the Field Stop. One of my pet peeves is the pretty readily available (and popular) 40mm Plossl which may show you less of the sky than will the 30mm Plossl.

      3. Field stop. The field stop is an inherent characteristic of every eyepiece. It is the effective diameter of the optics of the eyepiece and (combined with the characteristics of the telescope) determines the TFOV (True Field Of View).
        • The field stop may be the barrel of the eyepiece itself, it could be a ring of material which fits up against the optics of the eyepiece pointing into the telescope, or it could be nestled up between the various lenses of the eyepiece.
        • Ideally, the telescope manufacturer will publish the size of the field stop. In some cases you can grab a pair of calipers and simply measure it.
        • You can calculate your TFOV. TFOV=(Eyepiece Field Stop)x57.3°/(Telescope Focal Length).

      4. Eye relief. This is the distance from the eyepiece to where you will be positioning the your eye. Very short eye relief can make for an unpleasant viewing experience since you are having to put your eye uncomfortably close to the eyepiece.

    6. Eyeglasses.
      1. If you have no astigmatism you may be able to take off your eyeglasses and focus to use almost all the eyepieces on the market. You can use an eyepiece with relatively short eye relief.
      2. If you have significant astigmatism you will:
        • Want to wear your eyeglasses while using an eyepiece (contact lenses which correct for astigmatism tend to have issues if you are gazing at the angles we frequently use for eyepieces). This means you will want an eyepiece with at least 15mm of eye relief and you will likely be happier if you have 20mm of eye relief.
        • Alternatively, you can purchase an eyepiece compatible with the Tele Vue Dioptrix system. I have not yet seen anyone using this, but Tele Vue makes quality products so I'm going to assume it works very well. Tele Vue Optics: DIOPTRXâ„¢


    7. Some commonly asked questions.
      1. Should I buy an eyepiece kit which has multiple Plossl eyepieces? There are two different opinions and you get to choose.
        • The first camp would say that you should first use the eyepiece(s) which came with your telescope and learn what you value in an eyepiece and then purchase precisely the eyepieces which will suit your needs/wants. Going to star parties and looking through other peoples' eyepieces can help with this approach.
        • The second camp would suggest that buying that eyepiece kit is a great idea! You are getting a selection of decent eyepieces in a nice and convenient case. It is a relatively low-cost way to learn what various eyepiece focal lengths will do for you. Getting the case is a significant consideration since you may choose to sell the eyepieces and use the case with the new eyepieces you chose to replace the old ones – and having a good case is not insignificant.

      2. Which eyepiece is the best one for my telescope? There is no good answer. It all depends on what you like, what you want to observe, how you want to observe, whether you need to wear glasses, etc.
      3. Is the more expensive eyepiece worth the cost? This is a question only you can answer for yourself. The best corrected eyepieces require an expert to spend a lot of time putting together the proper design, glass, and eyepiece structure. Getting it just right is not cheap.

    Last edited by OleCuss; 08-14-2016 at 11:49 PM.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Two Primary Types of Mounts for Telescopes

    1. What, exactly, is the mount? Actually, as we discuss the matter in amateur astronomy this is not exactly clear.
      1. Most typically the mount should be thought of as the device to which the telescope is attached and which allows the telescope to be usefully pointed in the desired direction.
      2. We often refer to the tripod and the mount combination as the “mount” as they are very frequently sold together.
        • I have an Advanced VX (AVX) mount made by Celestron. It is sold with a good tripod and when someone refers to an AVX it is assumed to be an AVX mount perched atop the supplied tripod.

      3. We often refer to a mount/tripod/telescope combination with the name/model of the telescope. This is particularly true for many telescopes such as SCTs and MCTs which are frequently sold with a fork-mount. I'll give three illustrations.
        • I currently have an LX200 telescope. Broadly experienced amateur astronomers will immediately understand that I have a double-fork mounted SCT which was sold with a tripod. In our communications I do not separately reference the OTA (Optical Tube Assembly), the mount, and the tripod as they are all a package.
        • I also own a Celestron NexStar 8SE. Amateur astronomers acquainted with that instrument will know which OTA, which mount, and which tripod are in use as they are all typically sold as one package.
        • I also own an 11” SCT OTA which was removed from its double-fork mount (it was de-forked) prior to my purchasing it. When it was in its original configuration it was a Compustar system. In order to avoid confusion I will not refer to it as an 11” Compustar but I may reasonably refer to it as a de-forked Compustar or as a Compustar OTA.
        • This can be a bit confusing but you'll get used to it.

      4. We frequently need to specify the mount alone. And then it stays confusing. . .
        • Some mounts were either not sold with a tripod (or telescope for that matter) and when we refer to them it doesn't imply the use of a particular tripod (or telescope). I find this to be more true with the more expensive/high-end mounts.
        • Some mounts are no longer used with the tripod which was initially provided. This may be because a different tripod has been purchased or maybe the mount is now on a pier.
          • I plan to put in a pier in the next few months and then put my Losmandy G-11 mount on that pier. At that point it will be best if (when relevant) I refer to my pier-mounted G-11. If no one is going to care whether it is on the supplied tripod or on a pier then there is no need to specify that it is pier-mounted.

        • Just to make things less clear? The Losmandy G-11 is used without any computerization/GoTo system or with the Gemini-1 system, or with the Gemin-2 system.
          • Since much of the time when a G-11 is being discussed the presence of absence of a GoTo system is relevant it is frequently necessary to specify whether it is a G-11 with a Gemini-1 or with a Gemini-2. Yes, mine has the Gemini-1 system.
          • To make things worse (or much better) for me? I plan to eventually purchase the Avalon Instruments StarGo system to put on my G-11. At that time it will frequently be necessary to specify that I have a StarGo-equipped G-11 on a pier.

    2. What types of mounts must we discuss? Generally speaking we will be discussing two broad categories: Altitude-Azimuth and Equatorial Mounts.
      1. Altitude-Azimuth mounts. These are frequently referred to as Altazimuth, Alt-Az, or A-Z, or even AZ mounts.
        • These mounts move in Azimuth (roughly speaking, horizontally) and in Altitude (roughly speaking, vertically).
          • Alt-Az mounts are typically relatively inexpensive and are intuitive. Especially if it is not a computerized mount you can just sort of set it up and point it where you want to look.

      2. Equatorial mounts.
        • These mounts are designed to have one axis of the mount pointed directly at either the Celestial North Pole (if in the Northern Hemisphere) or at the Celestial South Pole (if in the Southern Hemisphere).
          • These mounts are a little more difficult to use and are not as intuitive to use – but once you are familiar with them you will generally not find them much more difficult than the Alt-Az mount.


    It is tempting to directly launch into a detailed discussion of these two types of mounts but it is probably too daunting to do this all as a single topic so I'm going to do separate discussions of Alt-Az and Equatorial mounts.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Altitude-Azimuth Mounts
    There are many Alt-Az mounts on the market today and they have their strong points and their weak points.

    It is sort of common to think of Alt-Az mounts as being for visual use only and there is some merit to that opinion – but it also falls apart under certain conditions.

    If you are not at the equator or at the North or South Pole then without additional special equipment the photographic use of an astronomical telescope will likely result in a problem called “field rotation” and may be quite bothersome. This means that in astrophotography most of us do not want to use an Alt-Az mount.

    Let's try this approach to Alt-Az mounts.

    1. Variants of the Altitude-Azimuth (Alt-Az) mounts.
      1. Computerized Alt-Az mounts. These are especially valuable in light-polluted areas since light pollution can make it very difficult to find targets.
        • Computerized without drive motors. These are instruments such as the Intelliscope which are typically designed to help you point your telescope at a target and then you nudge your telescope along to track your target of choice. Frequently referred to as PushTo scopes.
          • Valuable for finding stuff but it will not track for you.

        • GoTo Alt-Az mounts have drive motors and after your system is properly aligned with the sky you can command the mount to point the telescope at a particular target and it will both find the target for you and then it will track the target.
          • Tracking is often under-estimated. If you are really concentrating in order to get your best view, tracking can help you to see considerably more than if you were distracted by having to keep nudging your telescope along. The distraction may feel insignificant but it is not.

      2. Non-computerized Alt-Az mounts.
        • No computers involved. You find the target and you track it.
        • Whoops! There are actually non-computerized Alt-Az mounts which have been sold by Sky-Watcher which are not computerized but can be set up to track. I think there is also a kit of sorts which will do limited tracking but I don't remember the name.

      3. One very popular Alt-Az mount is the Dobsonian mount – except maybe it should not be called a mount at all. The reason for this is because John Dobson popularized the idea of using large Newtonian reflectors on an Alt-Az base. That “Dobsonian” design does imply an Alt-Az mount along with the Newtonian reflector but sometimes the typical Dobsonian rocker-box Alt-Az mount is referred to as a Dobsonian mount.

    2. Why you should want an Alt-Az mount.
      1. Inexpensive.
        • These Alt-Az mounts can be made ridiculously inexpensively in some cases. Inexpensive is taken too far in some cases and can result in a wobbly and/or shaky mount.
        • A very stable Alt-Az mount can also be made relatively inexpensively and the mounts used as part of the Dobsonian design are usually examples of this.

      2. Simple. Sometimes a very simple and easily understood design where you just point the telescope/mount where you want is just the ticket. No complicated process – set it down and you are ready to go!
      3. Needed for astrophotography at some latitudes. Yup, this is often forgotten by many of us who do astrophotography.
        • Many equatorial mounts cannot be readily aligned with the celestial poles if you are near either the equator or one of the poles.
          • So near the equator or the poles an equatorial mount may not be desired – you actually may need an Alt-Az mount.

        • If the mount is high-quality then use with a quality de-rotator can allow for superb astrophotography.
          • I have an LX200 (mentioned elsewhere as well). This is a double-forked SCT which is designed (at least in part) for astrophotographic use.
            • Meade has sold a de-rotator for use with this instrument (I've read varying reports about its quality) so I can use it for astrophotography in Alt-Az mode.
            • I could also purchase a wedge for the instrument/mount and use it as an equatorial mount.

        • If the Alt-Az mount is not designed for use in astrophotography you may still be able to use it for astrophotography, but mounts designed for visual use generally do not have very smooth tracking and you will likely have a lot of exposures messed up by jerkiness in the mount which you would never notice with your eye. You could put a nice de-rotator on the scope and still have lots of issues.

      4. You are leading a group making a very large professional telescope. There are a number of design concerns which mean you will probably find it more practical to build an Alt-Az mount and use a de-rotator for your imaging.

    3. Why you don't want an Alt-Az mount.
      1. Astrophotography! For most of us not near the equator or the poles will find a good equatorial mount more suitable for astrophotography.
      2. Simple manual tracking is better done with an equatorial mount. You get that mount polar aligned and you can just slowly turn one knob to beautifully track your target.

    4. Jazzing up your Alt-Az mount!
      1. Dobsonian mounts.
        • You can get a riser to move the thing up in the world a bit if you are taller than average.
        • You can get or make digital setting circles along with leveling devices in order to allow you to use celestial coordinates to point at targets which are difficulty to find.
        • You can get the Astro-Fix NMS: https://sites.google.com/site/astrofixdeepsky/ and use that to locate your target.

      2. You can, of course, make or purchase a buggy or dolly to wheel the mount and tripod around.



    The upshot is that Alt-Az mounts can be good choices depending on your needs and your likes.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Equatorial Mounts


    I'm going to try to continue to stay away from some of the technical terminology as I'm writing this mostly for folk starting out and making their choices. If you get an equatorial mount there are lots of aids for getting you started with one.


    Suffice to say, the equatorial mount is designed to be aligned with the Celestial Pole(s) and to easily track the stars and other celestial targets as the Earth rotates below them. Once this mount is set up it is relatively easy to track whether manually or by using a motor drive.


    One little secret to Equatorial mounts? They may also be Altitude-Azimuth mounts. If you do not orient the correct axis toward the Pole but aim it vertically it is effectively an Alt-Az mount. There are some mounts which are specifically designed to operate either as an Alt-Az or as an Equatorial mount.


    OK, down to business!


    1. There are several variants on the equatorial mounts. What they all share is the ability to be aligned with the Pole and then to rotate on one axis to track the chosen point in the sky.
      1. German Equatorial Mount (GEM). This is sort of the classic equatorial mount. It is designed to operate only in equatorial mode and does that quite well. Conceptually simple but the best are highly engineered. Quite a number of the best astrophotographers seem to believe that these are the best mounts for astrophotography at most latitudes.
      2. Non-German Equatorial mounts. This will include instruments such as the double-forked SCTs, MCTs, etc. which can be placed on a wedge and used in an equatorial mode. There are other designs as well such as the Equatorial Horseshoe mount.
      3. Equatorial Platforms. The equatorial platform may not fit easily into this category but I'm putting it here anyway.
        • This is an equatorially aligned platform upon which can be placed an Alt-Az tripod and mount. The most common use is with a Dobsonian telescope system but just about anything could be put on it – including a camera with its lens.
        • This equatorial platform can normally be expected to track for up to one hour. The dual-axis equatorial platforms are favored for astrophotography purposes.

      4. Tracking mounts for use primarily with cameras. This would include (but is not limited to) the current Polarie and the SkyTracker. They are light-weight and have limited capacity but can have a polar alignment done and produce credible results.

    2. Computerized, not-computerized, motorized., manual.
      1. Given the current favored use of GEMs for most astrophotographers it is not surprising that computerized, motor-driven mounts are quite popular. They allow you to align the mount, have the mount find targets for you within the limited FOV of your telescope, and then precisely track that target and allow you to use a guidescope to further refine the tracking. This is immensely valuable to astrophotographers.
      2. At the low-end it is common to find the relatively wimpy/shaky EQ-1 and EQ-2 GEMs which are usually not motorized and do not have any computerization and typically require you to manually track.
      3. You can get some really good mounts which are motorized and can therefore track but have no computer and that brings up a point I wish to make which relates to some of the above.
        • It is common for someone to get a computerized and motorized mount and to roughly align the mount with the Celestial Pole and then go through an electronic alignment process – and then expect precise tracking. The Celestron All-Star Polar Alignment process sort of reinforces this misapprehension. Let's separate things out a little:
          • Unguided tracking of stars is dependent upon two things:
            • Precise alignment of the mount with the proper pole. This is a mechanical and non-electronic alignment. You need to get this right. You can use a polar scope to assist. You can use electronics to assist. You can use cameras and software to assist. But in the end it is mechanically/manually adjusting the mount to bring it into alignment with the Pole.
            • Mechanical excellence of the mount and of the motor driving it. The mount should not wobble and the motor and gearing should cause rotation at exactly the correct rate.
            • You will notice that neither of the above points require a computer. If you have everything just right that mount should precisely track an object for hours. Unfortunately, things are never quite perfect.

          • Building a model of the sky. This is where you use the mount's computer to align on a number of stars and develop an understanding of where things are in the sky. Once this is done your mount will find things for you. But note that this does not assist you in correct tracking.


    High-end mounts are generally more about precision and a robust build than they are about the electronics/computerization.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Special Considerations in Choosing a Mount

    If you've read through everything so far it could be almost bewildering because I'm deliberately not trying to tell you what you should get. I've not been trying to guide you to a specific choice but to let you understand what choices are available and what they mean.

    Now I'm going to deviate from that just a little and discuss some specific choices and give you some Rules-Of-Thumb (ROTs) or just suggestions for thought.


    1. If you can transport and afford the mount it can never be too good. Great tracking and a robust build will mean that minor gusts will not disturb your tracking and your view or image. Also, discovering that your mount just isn't that good may mean that when you upgrade your telescope you will also have to pay for a new mount. If you can buy a great mount to begin with it can save you money in the long-term because you already have a great mount for whatever new scope you decide to purchase.
    2. Some of us find a Newtonian reflector on a GEM (German Equatorial Mount) to be a pain in the neck or in the back. Rotating the OTA may reduce the pain but is still not acceptable to some of us. Others have no issue with this.
    3. If you have any physical limitations you should think long and hard about the size and configuration of your equipment choices. If you are wheelchair bound and get a 24” Dobsonian with a focal ratio of 10 – you may never see through that eyepiece. Some thoughts which may be useful?
      1. Consider going with a smaller telescope and use an astronomical video camera such as those sold by Astro-Video Systems, Atik, ZWO, Mallincam, and Starlight Express. You will be able more easily handle the equipment and you can put the computer or monitor/TV in a location of convenience and view to your heart's content. So far as light-gathering is concerned, this kind of viewing makes your equipment look like it is much larger. There is, however, more of the equipment since you have to have to hook up power to several devices and supply the camera and the monitor at a minimum.
      2. Do look at the Universal Astronomics EasyView Arm. This will allow for good sky access with short refractors and smallish catadioptric OTAs and since it moves the scope out beyond the legs of the tripod you can get a wheelchair or walker right up to the eyepiece at a reasonably convenient height.
      3. Putting a pier under your mount will potentially make access easier.
      4. If you have the resources you can look at something like this: http://planewave.com/products-page/telescopes/0-7m-cdk-telescope-system/#.VZiN30aMHMs It is really expensive, but it also has dual Nasmyth foci which emerge from the mount at a height which is convenient for wheelchairs. There are also designs which use a Coudé focus.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Some Thoughts About Accessories

    This is sort of difficulty to properly categorize. Do consider these thoughts to be semi-random but somewhat responsive to questions which have been asked by many (or should have been asked).


    1. Finder scopes and related.
      1. Finder scopes.
        • Many of us find these preferable to almost everything else for finding targets. They can be very precise as well as giving you additional light-gathering which is especially beneficial in light pollution.
        • Consider getting a RACI finder scope. These can feel more intuitive with less irritation finding things and can be considerably more comfortable to use as well.

      2. Red-dot finders (RDFs). I don't like these all that much. They can be used, but usually when you align the RDF with your target star you can no longer see the star! They also always seem to me to be too bright or too dim.
      3. Reflex finders. I am using the term in distinction to RDFs.
        • Can range from slightly modified pistol sights (I'm serious, some really are pistol sights with slight modification) to specially designed finders.
        • The two reflex finders you really should know about are the Telrad and the Rigel QuikFinder. If you stay in astronomy for long you will likely end up owning one or both:
          • Telrad. This ugly thing has been around for decades.
            • I greatly dislike its looks but the thing works and you can find charts and software designed for use with the thing.
            • You can vary the intensity of its concentric circles and you can also modify it with a pulser. When looking at a dim section of the sky this is a very valuable asset.
            • Arguably the single most popular finder in amateur astronomy.


          • Rigel QuikFinder.
            • This is much smaller and fits better if you have limited space on your OTA.
            • Smaller size means less generous aiming circles but they really are quite adequate for most purposes.
            • The ability to vary the intensity and to pulse the illumination is built into the thing with no extra cost or need for modification to your finder.



    2. The essential accessories (which are not included).
      1. An observing chair. This is first on the list because you will see better if you are seated and comfortable. Among experienced and skilled observers this is pretty much a universal belief. You don't have to buy something expensive, you can build a good LYBAR chair for a low cost.
      2. A rug. Eventually you are going to drop something.
        • If you are on a hard surface this may mean that your expensive eyepiece or telescope is dented/bent and the optics are broken. Seriously, I've held someone's $600 eyepiece and heard it tinkle as I carefully held and moved it – not a pleasant sound. . .
        • If you are on a soft surface (like grass) it means you may never find that dropped essential screw or other item. A rug which isn't too deep/thick means you have a chance of finding that item.

      3. An eyepatch. Yup, you want that cool piratical astronomer look!!! Or maybe you just realize that if you wear that eyepatch on your observing eye while you make a run indoors for a drink of water that you won't lose all your dark adaptation.
      4. A hooded piece of apparel or even a towel thrown over your head can block extraneous light and make your viewing much better.
      5. A dew shield will improve your view through most instruments. They are built into many refractors but are especially advisable for scopes such as MCTs and SCTs – and yes, even for Newtonian reflectors.
      6. If you have a telescope which will need collimation you need to bring gear to accomplish that.
        • For a Newtonian a Cheshire sight tube is actually very good and is relatively inexpensive and easy to use.
        • Lasers can also be helpful if they are properly collimated themselves and they are especially useful if Barlowed or used with a TuBlug.
        • Installing Bob's Knobs or the equivalent (from ScopeStuff) will mean you don't need tools in order to do your alignment of the diagonal of your Newtonian OTA or secondary mirror of your SCT or MCT. This may sound like a minor detail until you drop that Allen wrench onto the primary mirror, corrector plate, or meniscus. It also reduces fumbling in the dark (or daylight).

      7. Red light. OK, if you are observing by yourself you may actually be better off getting a very dim white light. But for a variety of reasons (including misunderstanding) red lights are accepted in astronomical circles while dim white lights are not.
        • IMHO, the absolute best light I have seen/used for amateur astronomy is a white Zebralight. You can set it up for very dim light which will not seriously damage your night vision and which will allow you to properly distinguish colors on your star chart.
        • People pull out their bright red lights and destroy their night vision and don't notice it because they have had it drilled into their heads that if it's red it is fine. A dim red light is fine. A dim light of any color is fine. The key is dim light.
        • Consider a headlamp. This is very convenient but you have to be careful that it doesn't inadvertently aim into the space or eyes of others.
        • Something like a flashlight can be more controlled. That is one of the beauties of the Zebralight. You can use it as a headlamp or as a little angled-head flashlight. IMHO you can't beat it.
        • Conventional wisdom is moving toward the idea that 590nm amber light is actually the best for amateur astronomy.


      8. If your equipment must be powered, bring extra batteries for any that just might need to be replaced.
        • If you have to supply a lot of power then if you are at a remote site where you cannot operate off wall current, be sure to bring a big enough battery (or batteries) to run your equipment.
          • Several astronomy vendors sell battery power packs. Don't buy them! They are usually over-priced and relatively unreliable. You can get better value if you buy a very simple jump starter with the appropriate power socket and use that or buy a good lithium power pack/battery after shopping around a bit.
          • Consider a deep-cycle battery with plenty of power. These can be your best buy and tend to be more reliable than most other power sources you could bring.
          • For relatively low power demands you may want to consider a Lithium Ion or similar battery. These are relatively light and can be quite adequate. They are especially convenient for GoTo Dobsonians of modest size – you can put the battery on the base of the mount and not have to worry about the power cord wrapping around the scope/base until it pulls the power out of the socket.


      9. Food and drink.
        • You will do best if you are not hungry or dehydrated.
        • Don't bring food or drink if you are going to certain locations. In bear country, bringing food and anything but water will run a significant risk of having your observing session seriously disturbed.

      10. Adequate clothing. If the evening is going to be even a little chilly you need to prepare like you are going to be spending the evening in sub-zero temperatures. Sitting or standing still at an eyepiece does not generate much heat and you can be quickly very chilled. Bring more than you need and if you don't need it just don't wear it.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Amateur Astrophotography is not Amateur Astronomy – or Scientific.
    Nowadays professional astronomy is primarily astrophotographic or otherwise computerized and is not utilizing an eyepiece. Seriously, there are professional astronomers who have never looked through the eyepiece of a telescope!

    At best, amateur (visual) astronomy and amateur astrophotography have important differences in emphasis. There are important relationships and certain commonalities of knowledge and equipment, but they are still quite different.

    Being good at astrophotography does not mean you are good at visual astronomy – or vice versa.

    If you want to do astrophotography really well you should plan to spend a year or more both studying the seeing conditions in the location from which you will be doing astrophotography and also studying information from the masters to learn just what the various equipment choices will mean in terms of the targets you are imaging and how you will choose to image. Unless you take this approach it is highly likely you will make suboptimal choices in terms of camera, mount, and OTA – and this can be costly.

    IMHO at this time the best books for learning what you should know for astrophotography are “Astrophotography” by Thierry Legault and “The Deep-Sky Imaging Primer” by Charles Bracken. The Legault book is more beautiful and has had some very high-powered editing. I've found as time goes on that I find myself referring more to the Bracken book.

    Jerry Lodriguss also has some very good books out and he is a master of the craft, but I don't like the e-book approach. It may be a superb choice for others, however. It should also be noted that many amateur astrophotographers are using computers during imaging and an e-book can thus be immediately available to them – a good thing!

    If you have relatively modest equipment or want to do your imaging unguided (like me) then I think you should read one of the above books and also read “Astrophotography On the Go” by Joseph Ashley. IMHO his insights on how to make this stuff work with modest equipment are just without substitute.

    Next we'll delve just a little into some of the issues with amateur astrophotography. The intent is mostly to help you identify some of the issues and questions you need to address.
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    Default Re: A Brief Guide to Choosing Equipment for Astronomy. Telescopes, Mounts, Eyepieces

    Emphases in Amateur Astrophotography

    Importance of the mount.

    In amateur AstroPhotography (AP) people will often say that the mount is the most important part of the requisite system. I disagree since you can do limited astrophotography with a consumer camera on a tripod. The camera is the most important part.

    But the point at which they are driving is valid. The priority purchase in most forms of DSO astrophotography is the mount. It is often said that you should plan to spend about ½ your AP budget on the mount and the rest on your telescope, camera, etc. - and I would not disagree for most purposes.

    You can do pretty good AP using a great mount and a marginal telescope and a marginal camera. You will not do good AP with a marginal mount with a great telescope and a great camera (at least not without great determination and tolerance for set-backs).

    If at all possible get a really good mount.

    We're not doing scientific work

    Don't worry whether the professionals will approve of what you do. Few of them will even take notice of what you've done under normal circumstances. Occasionally we amateurs will do something very significant in the eyes of the professionals but you should not be planning for that to be the case.

    So you pursue your personal goals and artistic endeavors and let everyone else think what they may. In the end it should not matter if anyone else approves of what you are doing, it matters whether it is bringing you insights and/or pleasure.


    Planetary AP is very different from DSO AP.

    The best quality amateur planetary AP is done using lucky imaging. Since the planets are really very tiny targets but yet are far brighter than DSOs we can minimize the effects of turbulence by taking a whole lot of images over a short period of time and then select the best of the images and stack them.

    We do this by using video cameras with fast frame rates and short exposure times. You then use something like Autostakkert 2 or Registax 6 to select and stack the best of the images. At this time Autostakkert 2 uses a better de-Bayering algorithm and will give you better detail and should be preferred for this part of the task.

    After the image is stacked you can use other photo processing software to improve the image.


    Astrophotography of DSOs.

    I'm going to ignore what can be done with minimal equipment as that is not what most of us want to do and if it is what you want to do, you really need to read “Astrophotography On the Go” by Joseph Ashley.

    What I want people to get from the following are the primary issues and concerns as they relate to choosing equipment.


    1. What mount choice should be made?
      1. If you are not at latitudes near the poles or near the equator – get a GEM (German Equatorial Mount). Overall you can get the more robust mount with more options available.
        • To sort of illustrate? It is not the highest-end mount by any means but the Losmandy G-11 mount which I own can be upgraded to a better worm gear, the electronics can be upgraded, and it will handle anything from my camera with a telephoto to my C11 OTA. This means that if I started out with the G-11 I'd not have to first purchase a smaller mount for smaller scopes – cheaper in the long-run to buy the final mount at the beginning.

      2. If you are near the equator or near one of the poles you will need to look for the unusual equatorial mount which can handle those latitudes – or get an Alt-Az mount (possibly with a de-rotator).
      3. More capacity is better if you can afford it. Not only can you never have too good a mount, if you get a very capable mount now then when you get a bigger scope you won't have to sell your first mount at a loss and then buy the better mount.


    2. What factors should be considered for other elements? This is where it gets complex.
      1. What kind of target do you want to image?
      2. Do you want to guide or do you not wish to guide?
      3. What is your budget. And yes, this is a huge question because pretty much whatever your budget we can spend it and wish we had more to spend. Remember that in another module of this series I linked a $200,000 CDK system?
      4. Under what conditions do you wish to image?
        • Are you going to be traveling to sites?
        • What are the seeing conditions? You did, of course, spend a year or two studying the seeing conditions so that you can match your equipment to the actual conditions you will encounter so that you are getting your sampling right?
        • Will you be in an observatory?
        • Do you want to do a lot of imaging? If so, focal lengths under about 700mm is probably where you should concentrate. The shorter focal lengths means you will have less difficulty with “seeing” conditions and minor tracking issues will not be as bothersome either.
        • Will you have sufficient power available? Yeah, that camera will be using electricity along with your mount, your autoguider, your computer, your dew control system, etc.

      5. Consider what you will be doing with all those cables? They can get tangled and cause all kinds of problems.
      6. What kind of resolution do you want from your system?
      7. What FOV do you want/need?
      8. Do you want to do monochrome imaging?
      9. Do you want to go with a monochrome camera and use filters? If so, are you going to be doing luminance with RGB or are you going to do some narrowband imaging?
      10. Are under-sampling or over-sampling things you think you won't tolerate?
      11. What do you wish to do in terms of processing?
      12. Are you willing to deal with amp-glow?
      13. How will you be doing your darks (may not be needed with a CMOS sensor), flats, and bias shots?
      14. If you want to do imaging which is relatively immune to light pollution, then you should consider narrowband imaging – and remember that an achromat can be great for narrowband imaging.
      15. You will likely read that with a DSLR you need to keep your ISO down to around 800. This is significantly based on the idea of Unity Gain which you should ignore for modern cameras. A lot of superb astrophotographers use an ISO of 3200 for some of their work.
      16. A specialized cooled CCD camera is likely to do the best work. A DSLR can do great work as well but you need to understand and utilize dithering to make it work well – and dither by something like 9 pixels.


    3. Some general Look and Feel Stuff
      1. Focal ratio and aperture.
        • Remember, you change your focal ratio to change your photographic speed. A tiny telescope with a very low focal ratio will image most of our preferred targets faster than will an enormous scope with slower optics. There are cases where this is not exactly true but those mostly apply to point sources and generally don't become an issue in amateur astrophotography.
        • You increase the aperture of the scope so that you can get a longer focal length at the chosen focal ratio.

      2. How a low focal ratio benefits you:
        • You get an image very quickly and don't necessarily need to spend as much time out on a cold night.
        • Unless you have a large telescope, a fast focal ratio means a short focal length.
          • Short focal length will translate into wider fields of view for a given sensor.
          • A short focal length means your system will not be as significantly affected by turbulence in the atmosphere and you are more likely to have good sub-images with which to work.
          • The short focal length will result in less sensitivity to tracking errors. Since we are typically using relatively inexpensive mounts which necessarily compromise quality we are generally plagued by tracking errors and that short focal length is a boon.



      3. Forget “Magnification”!
        • In imaging the idea of magnification doesn't really work. You may be displaying the image on bigger or smaller screens and thus changing the perceived size. Magnification is relevant for visual use - not for imaging
        • If you are planning to print the image then you need to think about the desired pixel density and the paper size you will be using – and note whether or not your sensor size and likely cropping will actually give you a pleasing appearance at the likely viewing distance.



    My apologies for being rather brief in the above but my point was not to discuss them in detail but to raise awareness of potential issues which you may research if you find them relevant.
    Orion XX12G and XT8; 10 inch LX200GPS; Celestron NexStar 8SE; Tele Vue NP-101is (Petzval apochromat); Meade LS-8; WO GT-71; AVX and Losmandy G-11 mounts.

  20. The Following 8 Users Say Thank You to OleCuss For This Useful Post:

    AMCD300 (01-09-2017),bladekeeper (08-15-2016),carter2002 (09-03-2017),DeeFitz (09-24-2017),Eagleheaf (04-04-2017),Gaff (12-21-2017),Macrob1 (03-11-2017),Shabadoo (10-29-2018)

 

 
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