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Old Wednesday 18th May 2016, 16:27   #1
PSBT
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32mm Plossl for PF80ED-A

Hey!

To explain my motivation, I currently own the Celestron SkyMaster 8x56 binoculars and the PF80ED-A. I was thinking it would be nice to have the following magnifications:

8x (binocular)
16x (PF80ED-A with 32mm Plossl)
21x-63x (PF80ED-A with SMC zoom).

So far I'm looking into the following two eyepieces:

Celestron Omni Series 32mm
It has really good reviews in Amazon and that's cheap compared to other brands (http://www.amazon.com/Celestron-Omni...=sr_1_1&sr=8-1).

Televue 32mm
It's much more expensive but the quality will also be better (http://www.amazon.com/Televue-32mm-P...=sr_1_1&sr=8-1)

Anyone has experience with any of those two? Will they reach focus in the PF80ED-A? Any other recommendations?

Related to the question above, is there any way to know if a given eyepiece will work in the PF80ED-A without having to try it first since the only way I have to get them is by ordering them online?

One of the benefits of the PF80ED-A is that it accepts 1.25'' astronomical eyepieces, but looking some of the forums here, seems that some eyepieces don't reach focus? Is that correct? Any way to know before hand?

Thanks!
Pedro
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Old Thursday 19th May 2016, 11:28   #2
jring
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Hi,

I would not recommend a 32mm Ploessl in your case. The Ploessl has an apparent field of view of 50 degrees which gives 3.1 degrees true field of view at 16x. A 24mm wide-angle eyepiece with 68 degree afov gives the same true field at 21x and does not give the tunnel view of the Ploessl - ok, your zoom is even worse at 24mm...

Warmly recommended are Explore Scientific 24mm 68 degree either in the current waterproof series or the older and cheaper Maxvision series.
Also not too shabby are Baader Hyperions. All those are in the same ballpark as the Televue Ploessl new (Maxvision cheaper at 90€). If you can get a used one, expect to pay 60-70% of new price.

Joachim
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Old Thursday 19th May 2016, 14:02   #3
PSBT
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Thanks Joachim!

I forgot to mention another motivation. Besides using the PF80ED-A for daytime observations I also use it for astronomy. The other night I was trying to find Mars, Saturn, and an open cluster in Scorpios, and it was really hard to do with the 21x and 1.8 RFOV provided by the Pentax zoom at the longest focal length (24mm), at least compared to finding them with the 8x56 (5.8) binoculars, which is a breeze...

So, using the 24mm eyepieces you recommend or even the XW20 with 70 AFOV and 2.6 TFOV (27x) make it easier to easily find objects in the sky, even if the magnification is much higher than with the binoculars?

That's why I thought that using a 16x magnification would be a good idea...
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Old Thursday 19th May 2016, 14:40   #4
jring
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Hi,

well the maximum possible afov of an eyepiece at a given focal length is dictated by the field stop diameter and this is usually a bit smaller than the outside diameter of the eyepiece (1,25" or 2"). For 1.25 " EPs that's ususally 27mm which is what your 32mm Ploessls and the 24mm 68 deg EPs have.

An XW20 shows a bit less field than the others mentioned but is a premium EP which I would compare with a Televue Panoptik or Delos (their 68 and 72 deg lines) - although the Explore 68 deg models are not too far behind...

For astro use there is another parameter to think about which is the size of the exit pupil (objective aperture / magnification). The ideal size is determined by two parameters - first your eyes ability to open wide enough at night (this varies between about 7mm for young adults and goes down to around 5mm for the elderly) and the quality of your sky (with really dark skies you can as high as your eyes can open, with lots of light pollution like close to a big airport where I live, 5mm can be too much and provide a too bright background).

With your 80mm Pentax and the 32mm Ploessl you get a 5mm exit pupil, with the 24mm EP you get 3.8mm. So if you live somewhere with a nice dark sky, the Ploessl might indeed be better at night despite of the tunnel view, if you live in a big city, 24mm all the way.

Joachim
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Old Thursday 19th May 2016, 19:25   #5
PSBT
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Ok great! Thanks Joachim for all the info!

In regards to 1.25 eyepiece compatibility with the PF80ED-A, any special considerations? Any way to know (e.g. by looking at dimensions, etc) if a given eyepiece will work (reach focus) with this spotting scope without having to try it first?

Thanks!
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Old Thursday 19th May 2016, 23:40   #6
jring
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Quote:
Originally Posted by PSBT View Post
In regards to 1.25 eyepiece compatibility with the PF80ED-A, any special considerations? Any way to know (e.g. by looking at dimensions, etc) if a given eyepiece will work (reach focus) with this spotting scope without having to try it first?
Hi,

having done some more research it seems that the Hyperions are better avoided in this case. The Zoom certainly does not focus to infinity with Pentax spotting scopes (unless it's modified) and the fixed ones seem to be marginal at best - depending on the EP focal length and your eyes if they will focus to infinity,

And no, it's unfortunately not easy to say if an EP will work on a a scope with a limited focus way, like most spotting scopes. It also depends on the users eyes...

Joachim
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