6 replies to this topic

[GTom]

Which one should be the better combo on a c8 with a Baader sct/t2 prism? Using the Celestron reducer with a shorter Panoptic, the 35, or no reducer and going for the longest one in the set?

[rollomonk]

Personally, if I had to choose between your two options, it would be the Pan 41 without reducer. With every eyepiece decision I make, I look at the size of the exit pupil and try to stay in the 0.8mm to 4.0mm range. With the Pan 41 the exit pupil is 4.1mm, but with the Pan 35 and f/6.3 reducer it is 5.6mm. I typically observe in Bortle 4 skies  and a 5.6mm exit pupil would give me a bright background and low contrast (washed out) view. If your skies are darker than mine, this will be less of a problem. 

 

For me, a Pan 35 and no reducer (3.5mm exit pupil) would provide an even better view but, of course, narrower. I use a Pan 35 with a Mewlon 180 and an exit pupil of 2.9mm — views are very nice and contrasty. 

Edited by rollomonk, 30 November 2024 - 12:45 PM.

[eblanken]

Hi All,

 

I'm following with interest. 

 

Best,

 

Ed

 

P.S. What is the use model: What objects ? Is this a finder eyepiece ? Filters involved ?

Edited by eblanken, 30 November 2024 - 01:04 AM.

[SeattleScott]

The 35 Panoptic with reducer would have some vignetting. How obvious, hard to say. The short diagonal would help somewhat. You are talking about a very unique setup that probably no one has used, and you are talking about vignetting which bothers some people more than others, so there is really no way to predict if you will like it or not. You would just have to try it and see. The 41 Panoptic is the safer route, although the 41 Panoptic is kind of a beast of an eyepiece. Personally I would go 40XW for the lighter weight. It isn't like it won't have good enough edge correction at F10.

[eblanken]

+1 on what Scott said . . . I own the Pentax XW 40mm and use with my Meade M8 SCTs . . . 

 

Best,

 

Ed

Edited by eblanken, 30 November 2024 - 02:06 AM.

[Spikey131]

Baader makes two T2 prisms diagonals.  The “Zeiss” model has a 34mm clear aperture and the other one 32mm.  The 35mm Panoptic has a 39mm field stop.  So all choices will vignette.

 

Furthermore, if you use a reducer, it will not fully illuminate a 2” eyepiece, so there will be more vignetting.

 

If your goal is to maximize your true field of view, there are two ways to do it.  Both yield about 1.3 degrees.

 

You can use a 2” diagonal and a maximum field stop 2” eyepiece like a 41mm Panoptic.

 

Or you can use a reducer and a maximum field stop 1.25” eyepiece like the 24mm Panoptic.  With this choice you could use a T2 diagonal or a 1.25” diagonal.

[SeattleScott]

Another issue is prism diagonals start having issues with chromatic abberation once you go below F7-8. A reducer is F6.3, and that assumes a 1.25" diagonal. With 2" diagonal it is more like F5.5. The Baader prisms are kind of between 1.25" and 2", and the prism has a little shorter light path, so probably closer to F6.3 than F5.5. But still looking at around F6. So chromatic abberation will be a factor. If you want to use a reducer in a SCT, you should really use a mirror diagonal.

 

With a 2" mirror diagonal, one can use a reducer and 35 Panoptic in an 8" SCT. I believe you lose a little bit of aperture, but maybe half an inch or something. The view will vignette fairly seriously, but it will be about 1.5 degrees wide. Whether or not you are sensitive to the vignetting is something you would just have to test out and see. The fairly extreme focus position would move the scope off optimal correction the lenses were designed for, but it should still deliver pretty good views. The reducer will generally reduce planetary contrast a little, and could introduce unwanted reflections when viewing the Moon.