Which are the best 2in Wide Field Eyepieces, avoiding excessively Big and Heavy Eyepieces.

[Tiago Ferreira]

I was looking for explore 2" scientific 30mm 82º but was, and still is, out of stock everywhere so i decided to give a try to the 2" Omegon SWA 70º. I like that rubber eye guard and i didn't want to go for ES62º. I have the 100º ES 9mm and i love wide fields. Well, i'm quite happy with that Omegon at f/5. I was worried about coma but from Astroshop they said if i didn't like it i could return it without costs. Today i open a place for that eyepiece in my foam case. I was happy, almost no coma at all. Sometimes a litlle on borders but in my ES i can see the same. Not so heavy (comparing with the ES), cheaper and good performance also with the 2x ES barlow/ FocExt i have. And i really really love that kind of strong adjustable rubber. Now i only would buy the 100º from ES but it's too much expensive for my taste. So, here you have another option.

[radian]

How critical is it to avoid slightly oversize exit pupil?

I just bought a GSO 250mm f/5 Dobsonian and a ES 52º 40mm eyepiece for it. It'll have 8mm exit pupil. Is this going to be an issue... or are there more severe issues with this scope-eyepiece combo? I wear glasses so a decent eye-relief is an issue.

[Louis D]

5 minutes ago, radian said:

How critical is it to avoid slightly oversize exit pupil?

I just bought a GSO 250mm f/5 Dobsonian and a ES 52º 40mm eyepiece for it. It'll have 8mm exit pupil. Is this going to be an issue... or are there more severe issues with this scope-eyepiece combo? I wear glasses so a decent eye-relief is an issue.

As long as the central obstruction doesn't become so large as to cause a distracting shadow, you'll be okay.  You'll just have part of the light from the primary truncated by your pupil, so you won't make full use of your aperture.  You'll also have a more washed-out background making it more difficult to locate faint fuzzies.  If you're just taking in bright star fields, it shouldn't be an issue.

[vlaiv]

12 minutes ago, Louis D said:

As long as the central obstruction doesn't become so large as to cause a distracting shadow, you'll be okay.  You'll just have part of the light from the primary truncated by your pupil, so you won't make full use of your aperture.  You'll also have a more washed-out background making it more difficult to locate faint fuzzies.  If you're just taking in bright star fields, it shouldn't be an issue.

Have you ever seen shadow of secondary?

I'm not sure how that is supposed to work? As far as I can tell from optics - you should not be able to actually see shadow itself - only some sort of "vignetting cone" - opposite from regular vignetting where brightness falls of towards the edge - here it would fall off towards the center of the FOV but it would never be completely dark unless "pencil of the shadow" is larger than dilated iris.

Something like this:

(as far as I can tell - above is actual image of shadow of secondary).

[John]

I just preferred the darker background sky that a 21mm or 31mm eyepiece gave me over a 40mm in my F/5.3 12 inch dob. I let my 40mm Aero ED go to a new home recently for this reason - each time I tried it, I much preferred the views with the shorter focal length eyepieces in terms of background sky and the contrast of deep sky objects against it

When I have seen the "secondary shadow" it has been a vague and ill defined darker patch rather than anything firmer than that. Not that I used the 40mm in the 12 inch dob very often for the reasons described earlier in this post.

 

Edited December 9, 2020 by John