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GSO 50mm 2 Inch EP - Opinions?


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I'm hoping to gain a little more TFOV with the 8 inch SCT - and looking to do the same IF I can ever stretch to a 10 inch SCT.  

This 50mm/60 degree EP looks like the best chance, at a sensible price, so I wondered if anyone with experience of it could tell me:

# is it really a 60 degree EP?  I know figures can be exaggerated!  (E.g. in the case of the 50mm Rev.)

# might it need an extension to achieve focus?  (The 50mm Rev didn't.)

Doug.

 

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A little algebra shows that a 50mm with a 60 degree AFOV would require a 50mm field stop, which isn't possible in a 2" barrel: the 2" filter thread already has an outer diameter of 48mm (on the male side) so 47mm is the most that can be done. This yields a 56 deg AFOV (I have seen 55 deg quoted. Having said that, it should give the largest true FOV possible with a 2" visual back. One problem may be the 5mm exit pupil, which can result in rather washed out backgrounds. I personally use either a Nagler 31mm, which at 3.1mm exit pupil is a lot better in keeping the background dark, or the Vixen LVW 42 if I want the widest view possible. Now these are rather expensive pieces of kit, but in a slow scope like your F/10 SCT (I also have one), a cheaper option should be possible. I have heard the Moonfish 30mm 80 deg is rather good, value for money on a slow scope. On fast scopes they fail miserably. There's a review here:

Alternatively, you could look at the (more expensive) 40mm MaxVision 68 deg EP:

https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-68-degree-maxvision-eyepieces.html

I have the 24mm and it is superb in my F/10 and F/6 scopes, works very nicely down to F/5, and is OK over the majority of the field in an F/4.2 scope.

 

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Thanks, Michael.  That reminded me of the equation, and yes, the absolute max TFOV would be very close to 57 degrees.  

Exit pupil considerations aside, I probably can't do better than with the range of EPs I already have!

Thanks again,

Doug.

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It's exactly the same eyepiece as the 50mm Revelation, I had GSO one before replacing it with 50mm revelation (TelescopeHouse agree to shortened the exessive long nosepiece ofr me).

The measured field stop (both drift-timed and dayime measure) is 40.5mm, AFOV is 47.9°.

This EP is just for larger exit pupil in my scopes, not for wider FOV.

For the widest 2" FOV, there's Skywatcher 40mm Aero too, in addtion to the ones mentioned by Michael.

 

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I had the TMB Paragon 40mm, and the Aero is apparently a clone. It is an excellent EP, and I was foolish enough to sell it because it didn't get that much use after the Nagler 31T5 arrived. I bought the Vixen LVW 42mm as a replacement, but still feel the Paragon was more comfortable to look through. The Paragon/Aero is much lighter than the MaxVision, which is important if the balance of the scope is an issue.

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