50mm eyepiece S@N special.

[cotterless45]

Those who have the July issue will note the "how to make a 50mm eyepiece". I found a Mamiya 50mm camera lens at our local boot fair for a pound. I epoxied a 1.25" ep nose on the front of the lens, got an old bino fold up ep surround from LeeB and viola !

Eye relief is great as the lens was originally designed to focus on the film. I've tried it on a refractor and await

clear skies,

Nick.

[KevUU]

Hey, now that sounds fun! Will be interested to hear how it performs

[MattGoo]

I've read the article in the mag, looks interesting and would like to know how it performs. Will keep a look out at car boots in the meantime...

[Lux1]

I've used a 80mm camera lens with some success. It provides excellent eye relief but as expected is more suited to low power sky sweeping. I've even used a 200mm lens reversed and had a degree of success, however in my f5 Newtonian such a big eyepiece only offers 3x magnification so pretty pointless....

[cotterless45]

Very sharp, used it in my £11 refractor, gives a useful x14 .

Nick.

[michael.h.f.wilkinson]

Interesting project. Just one question. The lens was designed with optimal performance when the image is at the lens-mount side, and parallel rays coming from the filter-thread side. Should the optimal performance be reached with the bayonet side facing the telescope? This might mess-up exit pupil, but usually not for long focal lengths such as the 50mm. Many 50mm have a more-or-less Zeiss Planar-type design, which is near symmetrical, so it would not matter. At the camera side, the image is corrected up to a field-stop size of about 43mm, so it could be used with a 2" mounting.

[russellhq]

Just an idea (maybe a daft one), but would this work with a zoom lens?

[Adrian]

Just a quick reminder that some old lenses (inc Asahi super Takumar lenses) used Thorium glass that are radioactive through alpha decay.

This is not normally an issue through normal use on a camera as alpha particles are easily stopped, but if you are sticking your eye up to the element for extended periods then it may be more of an issue - medical/dental x-ray levels of radiation for extended periods doesn't sound good for the eyes.

[michael.h.f.wilkinson]

Alpha particles will be stopped by the epidermis (which consists of dead skin cells). I gather there is also a gamma component which is a real problem. Many of these lenses tended to yellow with age, I gather, so that might be a tell-tale.