1980's Vixen Plossls

[Franklin]

I really like these Plossls, so sharp and clear with a well defined field stop and have been trying to put a collection together for some time now. The 15mm and 5mm are still proving elusive and I'm not quite sure what focal lengths beyond the 26mm in 1.25" fitting were actually available. I've seen a 45mm and have read about a 40mm and 35mm and possibly a 30mm??? I've also read that beyond the 26mm the eye relief becomes quite extended which can cause kidney beaning when viewed off axis???

[Don Pensack]

Extended eye relief can cause blackouts when the eye drifts inside the exit pupil, too close to the eyepiece.

This occurs on axis as well as off axis if the eye drifts in and out or side to side.

That is not what "kidney bean" blackouts are caused by.  They are caused by spherical aberration of the exit pupil, or SAEP, which is when the exit pupil is curved and eye relief is not the same in the center as it is at the edges.

It is possible for a simple eyepiece to have too long an eye relief AND SAEP, but anything that eclipses light in the field is simply called blackouts, and "kidney bean" blackouts have a special cause.

Here is a better, illustrated, explanation:

http://www.handprint.com/ASTRO/ae4.html#SAEP

and, a more technical explanation go down the page to see a full explanation of SAEP:

https://www.telescope-optics.net/eyepiece_aberration_2.htm

[Louis D]

See the following post of mine below for more on SAEP vs. blackouts.  It has some nice animations of each type of blackout by @Ruud.

 

[LongJohn54]

I sometimes have a wee look through my Vixen 26mm and 7.5mm eyepieces.  They are sharp and clear.

The TV Panoptic 24mm gives a slightly greater magnification (41x verses 38x) and a wider field of view to the Vixen 26mm. I really prefer the Panoptic on a 3x Teleconverter (125x) than struggling with the Vixen 7.5mm (133x).  That 6mm diameter top lens and tight eye relief can be a pain.

 

 

[kev]

Hi. I have a set of these!  From Luton, with my SP102m that i bought at the same time.  Love them.  Used them regularly with my f5 newt as well. For planetary they are hard to beat.