Longest FL Largest AFOV 31.7mm EP?

[25585]

What is the EP which would give best low power wide field views for a long fl Mak such as the Skymax 180 Pro, given it would not give full FOV using a 2 inch ep?

[michael.h.f.wilkinson]

I assume you are mainly interested in the maximum true FOV, which depends on the field stop diameter and the focal length of the scope. A 24mm 68 deg EP and a 32mm 50 deg both have the maximum diameter field stop (27.3mm) for a 1.25" EP. A 16 mm Nagler gives about the same. The true FOV is identical, but the apparent FOV is very different. A MaxVision 24mm 68 deg EP would be a nice choice. Very good quality for the price (if it still available), comfortable and it gives a smaller exit pupil (and therefore darker background) than the 32mm Plossl.

[Moonshane]

If you add a 2" adapter what is the effective diameter ? I.e. what is the maxium field stop usable with the scope?  If it's more than 27.3mm you will benefit from a 2" eyepiece albeit not by the full field.

[Louis D]

I put a 2" visual back on my 127mm Mak and can't really detect vignetting visually with a 40mm Meade 5000 SWA.  However, if I put a bright star in the center and move it to the edge, it develops a weird ellipsoid reflection the moment it passes the edge of the rear baffle tube.  If you can live with that, it is remarkable how much wider a 2" eyepiece lets you go than a 1.25" eyepiece.

[Stu]

Some discussion here. Generally as Louis says, 2" eyepieces work surprisingly well with minimal detectable vignetting.

https://stargazerslounge.com/topic/291866-2-inch-diagonal-should-i-shouldnt-i/?tab=comments#comment-3197943

[John]

I think the main 1.25" candidates have been mentioned. I'd add the Celestron Ultima 35mm which has an AFoV of 49 degrees. The Orion Ultrascopic is the same eyepiece. Another option might be to consider a Baader Aspheric 36mm and use it with the 1.25" barrel which is supplied. You loose field width of course but there is no field stop within the 1.25" barrel so you get the benefit of the full internal width of the barrel at the expense of a less than sharp field edge.

I used to have a KK Widescan III 20mm which delivered an 84 degree AFoV from a 1.25" format and that worked well in F/10 scopes.