Adapted eyepiece correction lens for glasses wearers

[jcb4718]

In a recent thread ('Advice on Leica SBOOI...') I described how I adapted a old SLR eyepiece correction lens for my Leica IIIf eyepiece. I'm a glasses wearer and I'm sure any other wearers will be familiar with my problem! I though I would describe in a more general way the adaption in the case of the two cameras I use frequently: my Voigtlander Vito B and my Leica IIIf. The Vito B eyepiece is about 10mm dia. and sits about 6mm proud of the back of the camera. I therefore used 3mm thick aluminium sheet (the foam tape is about 1mm thick, see below). I drilled a 10mm hole and then cut it out using a hack saw. I carefully shaped it (using a vertically mounted belt sander) into a rectangle that just fitted inside an old Pentax SLR correction lens. I attached double sided foam tape to both sides, cut the 10mm holes, fitted the correction lens and slipped the assembly over the Vito B eyepiece. For the Voigtlander rangefinder I found two washers with the right inner and outer diameter and glued them together to make the right thickness. I had to belt-sand a flat on one side so they would not interfere with the rangefinder adjustment wheel. The lens I cut from an old pair of glasses using a fret saw. I cleaned it up and made the flat using the belt sander. Of course the lens was plastic! I have astigmatism so I had to keep the orientation of the lens. I can therefore only use the rangefinder with the camera held horizontally but since that is what I do anyway, that's not a problem for me. The eyepiece arrangement for the IIIf is similar to the VITO B arrangement but because the IIIf eyepiece surround is bigger than the SLR correction lens frame, I had to remove the sides of the frame and used thin strips of double sided tape to secure it (one down each side). For the SBOOI correction lens I dispensed with any washers: its just a single ring of double sided foam tape. Just comparing the cameras, in terms of viewing quality, the Vito B is the best because the viewfinder image is 0.7 magnification whereas the IIIf is only 0.5 magnification. Both are useable. The Vito B lens (a 50mm Color Skopar) is a very nice unit focussing Tessar. The IIIf of course accepts any LTM lens and is usually fitted with a Canon 50mm f1.5...so each camera has its place.

 

[john_s]

Good job.

I have very little astigmatism but enough shortsightedness combined with very little accommodation (eyesight focus range) that fairly precise diopter correction is needed. I have minimal problem with current Leica, as they have increments of 0.5 diopter in the low value part of the range, but other makes are usually whole 1.0 increments. I'm at the age where my shortsightedness is moving back towards neutral a bit (70 years approx) so at the moment I'm considering a similar project for my Mamiya 6 and 7. The manufacturer supplied diopters are push out lenses in a snap-in plastic frame so if I cut a plastic lens to just the right size it should fit the frame. I've kept my old specs so I should be able to find an ideal lens to cut up, bearing in mind that the ideal prescription for ordinary seeing is not necessarily the ideal for looking in a viewfinder if one is old. For the young who have much greater accommodation it's rarely a problem.

 

[jcb4718]

Yes, indeed, this whole camera viewfinder business has become a bit of a mission as I have got older. One thought about your project: most likely the snap out lens is glass and certainly the glasses lenses you intend to cut up are plastic. Plastic lenses are usually much thicker than the equivalent glass lens and may not fit.

 

[john_s]

Yes, indeed, this whole camera viewfinder business has become a bit of a mission as I have got older. One thought about your project: most likely the snap out lens is glass and certainly the glasses lenses you intend to cut up are plastic. Plastic lenses are usually much thicker than the equivalent glass lens and may not fit.

Yes, I had already thought of that. To make matters worse, the larger a lens the thicker it has to be to have the right curvature, and the glasses are a lot bigger than the little Mamiya eyepiece. I never expected it to snap in like the old one. What would be the best way to cut the glasses lens do you think. I have a Dremel tool so was thinking of looking at their range of rotary cutters.

 

[jcb4718]

I carefully outlined the lens shape I wanted and cut round roughly using a fine toothed fret saw. It took two attempts. My plastic lenses were a little brittle, maybe the effect of exposure to UV over many years use. So you have to go slowly. I finished off the shape using a vertically mounted belt sander. I worked it slowly down to the shape I had outlined. I don't see any reason why a Dremel would not work since a belt sander works. Using a ring (or any shape) of double sided foam tape around the edge of a shaped lens is an effective way of securing it. I'm not familiar with the Mamiya plastic frame but it may be possible to 'line' the frame with tape and then press on your shaped lens.

 

[john_s]

I carefully outlined the lens shape I wanted and cut round roughly using a fine toothed fret saw. It took two attempts. My plastic lenses were a little brittle, maybe the effect of exposure to UV over many years use. So you have to go slowly. I finished off the shape using a vertically mounted belt sander. I worked it slowly down to the shape I had outlined. I don't see any reason why a Dremel would not work since a belt sander works. Using a ring (or any shape) of double sided foam tape around the edge of a shaped lens is an effective way of securing it. I'm not familiar with the Mamiya plastic frame but it may be possible to 'line' the frame with tape and then press on your shaped lens.

Thanks. The Mamiya frame is very minimal because it fits inside the rectangular viewfinder and it's thin to avoid cutting off the effective size of the viewfinder any more than absolutely necessary. I am at the age where my short sightedness is reducing as a result of the common changes in the eye. My left eye has now a zero prescription. Unfortunately the right eye which is the one I want to use, has a fair way to go!

 

[dmr]

I made one out of a cheapo canera-show eye cup and one of those -2 diopter goggle lenses. I just unscrewed and removed the original (plano) lens and shaped the -2 goggle lens to fit with the dremel. Works fine on both the Pentax and the Mamiya.