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Thread: 38mm, 32mm or both?

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    Default 38mm, 32mm or both?



    I am looking to upgrade from my current set of EPs (Plossls received when I purchased my first telescope and current telescope) to something with a wider FOV and in the 2" format. Right now, I find that I use the 1.25 32mm quite often and switch down to a 25m or 17mm as needed. Agena offers the 2" Super Wide View EPs in a 38, 32, and 26 mm focal length.

    With the small magnification difference between the 38 and 32, is it worth getting both? I'd like to also find a shorter focal length in a 2", and saving money in purchasing only one of the two to use towards a shorter focal length seems desirable. I'm still trying to understand the different between fields of view and apparent fields of view, but I'm not sure I see much of a difference between these two.
    Tony
    Telescope: Celestron 8SE OTA
    Mount: Celestron Advanced VX
    EPs: 1.25":2X Barlow Lens, 32mm, 25mm, 17mm, 10mm Plossls / 2": 38mm, 32mm, 26mm Agena SWA 70*
    Imaging: ZWO ASI385MC

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    Default Re: 38mm, 32mm or both?

    Hi Tony!

    You typically won't see a 2" eyepiece shorter than around 18mm unless it is a very expensive wide-field, such as the ES 100 series. In most cases, all that extra glass and material simply adds to the cost of the eyepiece and adds nothing to the quality or the field of view. Thus, by and large the shorter focal lengths are in the 1.25" format.

    SCT scopes are very tolerant of most eyepiece designs. I would say the Agena SW's you are considering would work well in your scope, but please do wait for some opinions from others with SCT experience. That is one scope design I have little experience with.
    Bryan

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    Default Re: 38mm, 32mm or both?

    A good 32mm, 1.25" eyepiece is about the perfect low-power eyepiece for a typical 8-inch SCT. I sold the 32mm University Optics I had because the apparent field of view was only about 52 degrees, but the true field of view was around 0.8 degrees. Crisp optics, except near the edge.

    My low power ep now is an Explore Scientific 24mm 68 degree, which is excellent, but I do miss the 32mm at times. If ES made a 32mm 68* ep in a 1.25" format I'd snap it up in a second!
    Last edited by Arctic; 04-25-2018 at 01:04 AM.
    Gordon
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    Default Re: 38mm, 32mm or both?

    Quote Originally Posted by Arctic View Post
    A good 32mm, 1.25" eyepiece is about the perfect low-power eyepiece for a typical 8-inch SCT. I sold the 32mm University Optics I had because the apparent field of view was only about 52 degrees, but the true field of view was around 0.8 degrees. Crisp optics, except near the edge.

    My low power ep now is an Explore Scientific 24mm 68 degree, which is excellent, but I do miss the 32mm at times. If ES made a 32mm 68* ep in a 1.25" format I'd snap it up in a second!
    Thanks Gordon. I enjoy the 32, but was hopeful the 38 would better fit some of the larger objects (double cluster, andromeda, etc).

    Bryan, thanks for the info. I have been trying to figure out if they even made 2” EPs with that short of a focal length. I haven’t seen many, though I have seen 2/1.25 “dual” body EPs.

    Tony
    Tony
    Telescope: Celestron 8SE OTA
    Mount: Celestron Advanced VX
    EPs: 1.25":2X Barlow Lens, 32mm, 25mm, 17mm, 10mm Plossls / 2": 38mm, 32mm, 26mm Agena SWA 70*
    Imaging: ZWO ASI385MC

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    Default Re: 38mm, 32mm or both?

    What should I be looking for if I’m wanting to avoid the “peephole” that I have with my 10mm EP? I much prefer the large piece of glass of the 32mm and ability to see an object without my eyeball making contact with the glass *
    Tony
    Telescope: Celestron 8SE OTA
    Mount: Celestron Advanced VX
    EPs: 1.25":2X Barlow Lens, 32mm, 25mm, 17mm, 10mm Plossls / 2": 38mm, 32mm, 26mm Agena SWA 70*
    Imaging: ZWO ASI385MC

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    Default Re: 38mm, 32mm or both?

    Hi Tony, if I was going to try for wider field in that scope I would certainly go for the 38mm rather than the 32mm. You already have a 32mm 1 1/4", which as noted above is excellent for your scope; but the 38mm will give a much wider fov (about 1.3 degrees vs around 0.8 degrees for your 32mm). With the f10 optics as Bryan noted it should give quite a sharp field too. If you bought the 32mm wide-field it wouldn't have that dramatic an improvement (around 1.1 degrees vs 0.8) for you.

    The reason you don't get 2" eyepieces in the shorter fl's is that their effective field stop (ie: the diameter of the circle for the maximum amount of light that comes into the eyepiece) is smaller than 32mm (which is the maximum for a 32mm eyepiece), so there is no advantage in going bigger. Al Nagler has some good articles on eyepieces that you might find interesting here: Tele Vue Optics: Advice (you don't have to buy TV's though!: a lot of what he says applies to all eyepieces).

    I have the 42mm GSO wide-field, and it works well in the SCT, giving a fov of around 1.4 degrees.

    All the best,

    Dean
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    Default Re: 38mm, 32mm or both?

    Quote Originally Posted by Childersa View Post
    What should I be looking for if I’m wanting to avoid the “peephole” that I have with my 10mm EP? I much prefer the large piece of glass of the 32mm and ability to see an object without my eyeball making contact with the glass ��

    I just saw this one. You need an eyepiece with a longer eye-relief to avoid this, like the Orion "edge-on" planetary series, with 20mm eye-relief: https://www.telescope.com/Orion-Edge...ieces/e/68.uts
    These are branded by a number of other companies, like Williams and Long Perng- so if you want one, it is worth shopping around. I have the Long Perng 9mm (a retailer gave it to me in apology for stuffing me around with something else! ), and it works very well.

    - Dean
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    Default Re: 38mm, 32mm or both?

    PS: for some reason the link I copied above doesn't seem to work properly. It just takes you to the general site. If that is the case, try this one https://www.telescope.com/Orion/Acce...sc/47/e/68.uts - try a cut and paste, don't click on it as a link- or just click on the "Accessories" and "Telescope eyepieces" window...
    Stupid computers...
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    Default Re: 38mm, 32mm or both?

    Quote Originally Posted by DeanD View Post
    Hi Tony, if I was going to try for wider field in that scope I would certainly go for the 38mm rather than the 32mm. You already have a 32mm 1 1/4", which as noted above is excellent for your scope; but the 38mm will give a much wider fov (about 1.3 degrees vs around 0.8 degrees for your 32mm). With the f10 optics as Bryan noted it should give quite a sharp field too. If you bought the 32mm wide-field it wouldn't have that dramatic an improvement (around 1.1 degrees vs 0.8) for you.

    The reason you don't get 2" eyepieces in the shorter fl's is that their effective field stop (ie: the diameter of the circle for the maximum amount of light that comes into the eyepiece) is smaller than 32mm (which is the maximum for a 32mm eyepiece), so there is no advantage in going bigger. Al Nagler has some good articles on eyepieces that you might find interesting here: Tele Vue Optics: Advice (you don't have to buy TV's though!: a lot of what he says applies to all eyepieces).

    I have the 42mm GSO wide-field, and it works well in the SCT, giving a fov of around 1.4 degrees.

    All the best,

    Dean
    Thanks for the information! From what I have read, the Agena Superwide Angle EPs have good reviewed for an F/10 SCT. I think I'll probably order the 38, 32, and 26. Saves about $45.00 as a package deal and comes with bolt cases for each. As for a shorter focal length, I took a look at the ES 82s, which will likely be my next investment.
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    Telescope: Celestron 8SE OTA
    Mount: Celestron Advanced VX
    EPs: 1.25":2X Barlow Lens, 32mm, 25mm, 17mm, 10mm Plossls / 2": 38mm, 32mm, 26mm Agena SWA 70*
    Imaging: ZWO ASI385MC

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    Default Re: 38mm, 32mm or both?

    I'd like to suggest that you go even longer. An f10 SCT needs a good 50mm eyepiece. The reason is that you need a 5mm exit pupil to get the most difficult objects like the Horsehead Nebula and it's low contrast brethren. Now the Agena SW series doesn't have a 50mm player but Agena also has this guy:

    https://agenaastro.com/gso-50mm-superview-eyepiece.html

    Now you won't get any wider TFOV because a 2" visual back maxes out TFOV at 42mm focal length. But you get a 5mm exit pupil and in detecting faint fuzzies exit pupil is king, not aperture!

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