Recommend me a wide-angle EP between 26-30mm.

[emadmoussa]

Will be used on an 8" SCT and a 4" achro...

Ideally, Explore Scientific 30mm 82-deg - but too expensive for my current budget. 

I was also looking at the Skywatcher Nirvana 28mm 82-deg, but it's also expensive-ish, although I can swallow the bullet and get it. But perhaps buy a 2x ED barlow with it and save me a 14mm eyepiece? 

Any suggestions? 

[rwilkey]

Hi there Emad, the Sky Watcher 32mm PanaView is a great performer I have found, but depending on your achro focal length, it does suffer a bit at the edges in fast scopes, however, the on-axis view is stunning at any speeds.  At 70 º AFoV it performs well above its relative cost of £72, found here:
https://www.firstlightoptics.com/ovl-eyepieces/panaview-2-eyepieces.html

[Louis D]

I would go with the 30mm APM UFF.  I replaced my 27mm Panoptic with it.

[emadmoussa]

On 06/12/2018 at 14:47, Louis D said:

I would go with the 30mm APM UFF.  I replaced my 27mm Panoptic with it.

Erm, these don't seem to exist in the UK?

[Jforson]

1 hour ago, emadmoussa said:

Erm, these don't seem to exist in the UK?

I think that you can order them direct from APM, I have had my eye on the 24mm UFF for a while.  

Might be worth checking but I think altair astro may do a similar Eyepiece. 

[Louis D]

1 hour ago, Jforson said:

I think that you can order them direct from APM, I have had my eye on the 24mm UFF for a while.  

Might be worth checking but I think altair astro may do a similar Eyepiece. 

The 24mm APM UFF is no where near as good as the 30mm.  First off, it's not actually flat of field.  I have to refocus for the edge, if you can believe it!  It is wider than a 32mm plossl at the expense of some edge vignetting and indistinctness (a 27.5mm effective field stop based on my measurements relative to said plossl).  It's as if they pushed the design a bit too far.  I measured it to have a 63 degree visible AFOV, but an effective AFOV (eAFOV) of 66 degrees due to magnification differing across the field.  With the eyecup folded down, it does have 17mm of usable eye relief, so it's quite easy to use with eyeglasses.  I haven't encountered blackouts or exit pupil finickiness.  There might be some edge astigmatism, but I would need to double check that before I say anything more on that point.  Stars definitely don't remain pin sharp to the edge.  The last 5% becomes mushy.  In the central region, I'm still evaluating it.  So far, it's no better or worse than a plossl in that region based on my limited time with it under the stars.  I haven't written much about it because I'm still developing my opinions about it.  I'm mostly disappointed it isn't flat of field as claimed and yet costs a lot compared to other 24mm options out there.  The 30mm APM UFF is definitely flat of field, so I don't know what happened with this eyepiece's design.

[Jforson]

59 minutes ago, Louis D said:

The 24mm APM UFF is no where near as good as the 30mm. 

That's good to know I had not heard much about the 24mm.   Like the OP a 30mm for my long achro a 102 f11 may be nice. 

[Piero]

I have the 30mm APM UFF mentioned by Louis. Great eyepiece in my opinion. You can get one from APM telescope.

[Louis D]

On 08/12/2018 at 10:51, Louis D said:

The 24mm APM UFF is no where near as good as the 30mm.  First off, it's not actually flat of field.  I have to refocus for the edge, if you can believe it!  It is wider than a 32mm plossl at the expense of some edge vignetting and indistinctness (a 27.5mm effective field stop based on my measurements relative to said plossl).  It's as if they pushed the design a bit too far.  I measured it to have a 63 degree visible AFOV, but an effective AFOV (eAFOV) of 66 degrees due to magnification differing across the field.  With the eyecup folded down, it does have 17mm of usable eye relief, so it's quite easy to use with eyeglasses.  I haven't encountered blackouts or exit pupil finickiness.  There might be some edge astigmatism, but I would need to double check that before I say anything more on that point.  Stars definitely don't remain pin sharp to the edge.  The last 5% becomes mushy.  In the central region, I'm still evaluating it.  So far, it's no better or worse than a plossl in that region based on my limited time with it under the stars.  I haven't written much about it because I'm still developing my opinions about it.  I'm mostly disappointed it isn't flat of field as claimed and yet costs a lot compared to other 24mm options out there.  The 30mm APM UFF is definitely flat of field, so I don't know what happened with this eyepiece's design.

Okay, I had the time and sky conditions last night to spend more time evaluating the 24mm APM UFF.  It is very sharp and well corrected across the majority of the field.  There is only a small amount of edge astigmatism and edge defocus.  If you only look in the center, you would never see it.  It's only noticeable when allowing objects to drift across the field.  The edge indistinctness mentioned above was only present when using my GSO coma corrector.  The field stop was sharply defined when used natively in my f/6 Dob or with a 1.25" long barlow.  I can't recall seeing another eyepiece behave like this.  Usually, they clean up at the edge with a CC due to the field flattening effect.  I'll have to investigate this further in my 72ED and 127 Mak sometime since they don't use CCs.  Unfortunately, I didn't note how well it did without a CC or with a barlow.  I was just so shocked by the sharp edge that I kept swapping around intermediate optics trying to identify the soft edge culprit to no avail.  I did note the AFOV felt distinctly wider with the 2x barlow than without.  As for why, I could not figure out that either.  I'll have to shine a flashlight through the combination to see if that is actually the case, or if it was merely the sharp field stop fooling my brain.  It would be nice if some other folks reported their critical evaluations of this eyepiece to see if they're seeing similar results with their equipment, or if it is just me and my old eyes.

So far, I'd say that if you need long eye relief and a well corrected, widest field 1.25" eyepiece, the 24mm APM UFF is a good choice.  Just be aware it may not play nice with some coma correctors at the edge.