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Thread: 90's Celestron c8 + Super polaris mount, good starter

  1. #1
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    Question 90's Celestron c8 + Super polaris mount, good starter



    Hi everyone,

    I'm new to astronomy and am very interested in astrophotography. I have owned several digital camera's, with several lenses and am experienced in landscape and underwater photography, have taken several pictures of the moon with a simple telelens + extender set-up and I now want to have a go at getting pictures of galaxies, nebulea etc. through a scope set-up.
    I've looked into buying a new scope, but also found a third-hand c8 from the '90s with a super polaris motorized GEM mount + 3 eyepices, a 2" diagonal, a 2x breslow and dew sleve for a reasonable price of 600 euro's (approx 850$). Having read several comments on forums, it seems to me the general statement is that the bigger the appature, the better. Buying second or in this case third hand will allow me to get a 8" + simple motorized gem set-up instead of a 5" + goto az set-up.
    What is your advice, does this seem like a good starters set? What do you think of the price? What other option would you recommend?\
    Thanks in advance for your advice and clear skies to all

    Jos
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    1st off welcome to the forum.

    It could be a good deal.

    Used equipment is kind of iffy.

    Do you know the seller? If so how what the equipment treated? Can you get an opportunity to see it in use and view through it?

    Scary part is there is no warranty. So buyer beware.
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    hi and welcome to the forums,
    @ above.
    clear skies,
    andy
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    andy

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    Thanks for the warning, the selle seems ok, his story about how long he has had the scope and why he wants to sell checks out. I'm hoping to have a look tonight.

    Greetz,

    Jos
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    Jos,

    Welcome to the Astronomy Forum. A very large number of photographers like you successfully make the transition to Astrophotography. Before going out and purchasing a telescope and mount, take the time to read a few books on astrophotography, do a google on astrophotography and you will find several excellent internet sites where you can also get information.

    For photographing objects in space, the telescope is not that important ..... what is important is the telescope mount and its tripod. Next is the knowledge and skills of the photographer, followed by the camera (some people may reverse the photographer and the camera in importance). Least important is the telescope.

    The c8 from the '90s with a super polaris motorized GEM for 600 euros. Can you photograph with this setup? Yes but it will be difficult as you will be pretty much doing everything manually.

    The first problem you will face .... to photograph an object in space, you must first get the object in view of the telescope. With a non-computerized mount, you will need to know how to find the objects on your own; not impossible as many people do this but it is a set of knowledge and skills that you must develop first.

    While the motorized mount can track an object once you get the object in view of the telescope, it can not track it accurately enough for photography. You will need to correct tracking errors manually using either a guide telescope or a device known as an off-axis guider. Either way, the job is very tedious but many people still correct of tracking errors using this method.

    One way to simplify the object acquisition and guiding processes is to use a computerized telescope commonly called a goto telescope. With these telescopes the scope's computer will find objects for you and automatically track them. You can add a self guider and it will automatically correct tracking errors.

    For photography you need an equatorial mount. The AZ (azimuth) mount you mentioned is designed for visual observations and not photography. While you can photograph with an azimuth mount, you will have many limitations that will greatly restrict what you can accomplish.

    Aperture is king for visual observations. For photography, focal length is important. A telescope having a longer focal length will require longer exposure times but will produce a larger image. A telescope with a short focal length will need less exposure time but will also have a smaller image. With the resolution of today's digital camera, plenty of pixels are available to expand the size of a photograph.

    The C8 is a Schmidt Cassegrain Telescope (SCT). In many ways Schmidt Cassegrain Telescopes are the workhorse for amateur astronomy. They are popular because they are capable of both visual and photography work and can do both these task well; thus, give a person the capability of doing both tasks with one telescope. Their compact size is another reason for their popularity. But, if you are interested only in visual work, other designs offer more economical solutions and if you are interested only in photography, again, other designs offer a better option. Never the less, a very large, percentage, perhaps more than 50%, of amateur astrophotographiers use Schmidt Cassegrain Telescopes and are very successful at taking excellent images. Many SCT owners who use them for photography also use a focal reducer to shorten their effective focal length.

    Here are four alternatives that will provide an adequate "low cost" mount, tripod, and telescope for astrophotography. The mount is the important part of these four telescopes. To this you will need to add a self guider and either a guide scope or off axis guider .... another 500 euros or so. Add some other accessories (eyepieces, camera adapters, etc.) and your total cost is now approaching 1500 to 2000 euros. Other telescopes exist that will do as well or better that will fit upon the mount used by these telescopes.

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    http://firstlightoptics.com/proddeta...?prod=c6sgtxlt

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    Hi Sxinias,

    Thanks for your extensive and helpfull reply. Reading more and more each day, I understand that the mount is very important for astrophotography. My idea was to buy this set-up as first step to see if this is something for me and then spend more money if I get hooked on the hobby. I understand that go-to mounts with tracking makes life easier, and I can opt to buy a nice new CG 5 celestron goto GEM mount for 650 euro's. This would bring the total ammount of money spent to a similar region as the c6sgt that you propose, only having to spend less money now and ending up with a c8 + extra's instead of a 'bare' c6.
    It was my understanding that the apperture-focallength ratio determines the exposure time. This means that the c8, would be a F/10, just the same as the c6 you propose is a F/10, with the only difference being that the c8 has a higher magnification, am I correct? I have read about people using a focal reducer, but haven't seen examples of what this acutaly is. Could you give a popular example?
    You state that for pure photography purpose 'other designs' offer a better option. Could you be more precise; do you mean Newton's as you recommend some of these and why are they a better option (optically, costs)?
    Thanks again for your help and info, I really appreciate it!

    Jos
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    For photography, refractors tend to produce sharp images and are considered the best type of telescope. The Newtonians I mentioned provide perhaps the lowest cost entry not necessarily the best optics.

    When you attach your camera to a telescope lens, the telescope becomes the camera's lens. All the relationships that govern camera lenses .... focal length, exposure times, image size, etc. also apply with a telescope as a camera lens.

    A reducer is a lens that is inserted in the light path of a telescope. For a SCT it screws on the rear of the telescope then the scope's visual back screws on it. This lens effectively shortens the effective focal length. The ones used for SCTs typically change the focal ratio from f/10 to f/6.3 or f/3.3 here is a link to one: Reducers/Flatteners - Celestron f6.3 Focal Reducer

    The six inch f10 SCT has a focal length of 1500 mm and the 8 inch f10 SCT has a focal length of 2000 mm. The image size with the telescope with the longer focal length will be the larger image. This image size has little to do with the aperture of the telescope or its focal ratio but is related to the chip size of the camera and the telescope's focal length (divide the focal length of the telescope by the diagonal length of the camera chip).

    Regarding the mount you are thinking about purchasing. It was not too many years ago that the system you are considering was state of the art. I think your biggest challenge will be learning how to locate objects in the night sky. A book like "turn left at Orion" and an inexpensive pair of binoculars are a easy way to get started with this task.

    I'm pursuing a path I call minimalist astrophotography .... using lightweight equipment generally deemed unsuitable. I face a lot of challenges but it is fun. Here is a link to what I and others are doing. Minimalist Astrophotography
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    Hi Sxinias,
    Thanks again for your advice and information!

    Jos

 

 

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