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Thread: High magnification eyepiece for planetary, lunar, and solar observation

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    jbweimar's Avatar
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    Default High magnification eyepiece for planetary, lunar, and solar observation



    Some please help me sort out my inner struggles. I own a SW 100ED f/9 APO on a sturdy AZ mount (no tracking, mount can handle 22lbs) and I currently have 3 quality EPs:

    • 1.25" ES 82° 6.7mm (134x, 0.6° AFOV)
    • 1.25" ES 82° 11mm (82x, 1° AFOV)
    • 2" ES 68° 28mm. (32x, 2.1° AFOV)


    I've heard some people argue that pushing beyond 150x magnification on a 4" APO doesn't make sense. So I'm interested to hear thoughts on this as it effects my choices below.

    I'm looking to expand mainly for my SW 100ED for more detail on planetary/lunar/solar observations, so higher power, preferably up to 250x/300x. My thoughts are all over the place so maybe can help me focus.

    The least important factor, but worth mentioning, is that at some point I want to get into binoviewing. I'd like to keep that in the back of my head when making my decision, so as not to get anything redundant. But again, it's the least important factor, so if I get something I can't use later, it's not the end of the world.

    1) I've been looking at the Baader Mark IV (shipping Feb 1) with 2.25 Barlow which would give me 37x (1.35°) through 253x at (0.27°). Of course for lower powers I would use my 2" EP but this setup seems very nice. I could find my target with the 2" EP, put on the Baader + Barlow and I would be all set. But of course this also gives quite a bit of redundancy with my existing EPs. Would I still use the ES 11mm or ES 6.7mm?

    2) The other option is to just extend my EPs on the higher end by buying the NZ 3-6mm. I could use the 2" EP to find my target, and the use either the 6.7mm or 11mm to hone in. Then finally put in the NZ 3-6mm as a finishing touch. If the seeing conditions are right it still allows me to zoom in to get more detail.

    3) Another option (if one feels one should avoid zoom EPs) is to get, for example, the TV 3.7 Ethos. In case the viewing is good, I can replace my 6.7mm with the 3.7mm to get more detail. The main worry I have with non-zoom pieces is that I would have trouble keeping my targets in view. Suppose I have Mars in view and I switch to the 3.7mm. Then Mars moves out of view and I lose it. I have to now switch back to 6.7mm to locate it again. In the process of replacing EPs I also might bump the scope.

    4) An cheaper alternative to the above solution is to get a 3x ES Barlow which would give me 2.7mm, 3.6mm, 6.7mm, 11mm.

    Hope to get some input.

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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    If you're happy with the ES 6.7mm, why not go for the 4.7mm which will give you 191x. I think the 100ED will handle this is on a night with great seeing without any problem.
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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    And my concerns about losing targets while changing EPs? Do you have experience with the zoom pieces?

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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    For high magnification a exit pupil of 0.5 is a good reference which with your scope is a 4.5mm eyepiece. Higher than that you may start getting floaters from your eye in the FOV.
    The 6.7mm gives you an exit pupil of 0.75 and a mag of 134x, the 3.7 gives you an exit pupil of 0.41mm and a mag of 243x which is a very large jump as you can see.
    The limits of high power are what the atmosphere is allowing at the time.
    Personally getting a Ethos for high power viewing is money spent on an eyepiece that will rarely be used.
    If you are intending to get the barlow, keep your fixed focal lengths longer so you can barlow them and you will not end up with a bunch of eyepieces you may only use once a year.
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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    Quote Originally Posted by jbweimar View Post
    And my concerns about losing targets while changing EPs? Do you have experience with the zoom pieces?
    As long as you have your finder well setup... for planetary if you lose the object just point the finder back at central and it should be in the field of view. For the Moon - well it's a bit difficult to lose that one I think approaching 200x will be pretty good though for other objects like some bright planetary nebulae and globular clusters!
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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    If I do end up getting a Barlow, should I get the 2x, or the 3x?

    2x would give me 3.35mm, 5.5mm, 6.7mm, 11mm
    3x would give me 2.23mm, 3.6mm, 6.7mm, 11mm

    Given the comments above, I assume it's the 2x

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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    The 2x barlow is always a good place to start.
    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    Hello again JB, thank you for a well written inquiry in your post #1.

    Being a user of an 8" 1200mm f/6 Dobsonian on an alt-azim base, I understand your concern about losing your target while changing eyepieces without a tracking mount. In my formative weeks this was an issue for me as well.

    As you are well aware, the orientation of the star-field image in the FOV on our scopes is quite unlike that on our star-charts.

    To my delight however, I quickly found that if I was to make a mental note of how the target was moving in the FOV, I could make allowances for it before stepping away from the eyepiece to change it out, or any other reason.

    You can think of this like a sniper might when aiming ahead of a moving target. The marksman doesn't aim at the position where the target is presently, rather he aims ahead of the target, towards the position where he thinks that the target might be when the bullet gets there. Slower, heavy bullets lobbed in a high curved arc will require more lead time. Faster, lightweight bullets moving in a flatter trajectory will require less lead time.

    You can apply this model to your observing as well. You have a manually driven alt-azim mount that you will use to find and then follow your target as it moves through the sky. The speed and direction with it moves thorough your FOV will depend on the altitude and azimuth of your target at your location.

    Clearly, if you're observing a target that is due south of your location and its altitude puts it somewhere near the celestial equator, it will be moving E-W a whole lot faster through your FOV than anywhere else. On the other hand if you're observing a target that is somewhat north of your location and its altitude puts it very high in the sky, up near the pole star Polaris, then you're faced with a target that moves considerably slower but possible in mind confounding directions as it might even appear to be moving W - E or even vertically up or down, in what appears to be a straight line.

    All this to say that if train yourself to become aware of the movement of the object in the FOV, you'll soon be able to predict to where it will move in the time that it takes you to swap out an eyepiece or pour another drink.

    Using higher power eyepieces that have a wider AFOV really does help as well and this, by virtue of your 6.7mm and 11mm 1.25" ES82° eyepieces, you already know.

    I use the wider AFOV of my small stable of ES82° eyepieces in much the same manner. I use the excuse that I prefer to view the object, say a binary star that I have just managed to resolve, in the context of its surroundings. In other words I opine that I want to see Space and lots of it around my target. The truth however is more practical. The larger TFOV of the ES82° eyepiece allows me more time and 'real estate' in which to determine the speed/direction that the target is moving in the FOV. I can then shift the aim of the scope such that the target is right at the edge of the FOV. Knowing which way it is then going to move, and how long it will take to cross that expanse of Space, I can then guesstimate how much time I have to step away from the eyepiece or be busy swapping it out.

    I think that I am being Captain Obvious here, but my point is that it does not take you very long to figure out how your targets translate in your FOV and how to provide for that when manually steering your scope.

    Something else that assists me greatly is my Telrad with its three-ringed reticle being projected on the sky. If necessary, I can adjust the aim of the scope such that the target is out of view and then simply wait for it to move back into view during the time that I am absent at the eyepiece. In like manner, the 9x50 finder-scope is useful for locating my reference stars amongst which I will again find the elusive target.

    I have no experience with zoom-eyepieces to expound on.
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    Default Re: High magnification eyepiece for planetary, lunar, and solar observation

    Thanks again for your detailed post, Philip. I actually just pulled out my Orion XT10 an hour ago to get a view of Venus which is especially bright tonight (and clear skies!). I used the 6.7mm giving me a 180x magnification. It took about 6 to 7 seconds for Venus to cross from the lower-right to the upper-left (in reality going from upper-left to lower-right) and when I put in a filter (to reduce the brightness somewhat) I indeed intuitively applied the trick that you mention above.

    I still have to attach my Telrad to the tube but I first want to be sure where I'm going to put it. The EZ Finder II is not that great. The battery already died, even though I don't think I ever turned it on!

    I'm currently tending towards getting the Mark IV + Barlow. That way I get to compare both situations (I can use the 2.25x Barlow also with my ES EPs). I can always get rid of the Mark IV in case I don't like them.

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    Default

    One thought on the EZ finder - if you've never turned it on, check to see if there's still a plastic shipping tab preventing the battery from making contact. some red dot finders ship with one to prevent accidental discharge, that you have to pull out before use.

    On the main question - a lot depends on the quality of your scope and the seeing conditions. On a night of near perfect seeing, I've had my FSQ106ED up to around 340x and still getting sharp results (running at f8 with the extender, and a 2.5mm Nagler). However, at that sort of extreme magnification, the exit pupil is tiny, and floaters in your eye become very obvious. And on an undriven mount, the planet drifts across the field of view very quickly - so a lot depends on how quickly your scope settles down after nudging it - otherwise, with a narrow AFOV eyepiece, by the time the view settles you may need to nudge the scope again.
    So although it worked - and gave me some of my best views of Mars so far - most of the time it's probably more sensible not to push things so hard. The seeing may not cooperate, and dropping the magnification down gives you a more reasonable exit pupil with fewer floater issues (and a brighter image, and longer between nudges).

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