RF diopter engineering history

[ruben]

Now that I have made my mind to go to the optician to make a few diopters for my Kievs, I find the best place to put them is on the front part of the viewing window, instead of the flat crystal whose sole task seems to be to defend the prism from dirt scratches etc.

But from time to time I have seen at eBay original diopter housings for Kiev RF, which you insert on the rear side of the viewing window, i.e, the one close to the eye. Very obviously these attachments make a very undesirable protrusion.

Can anyone explain me why the Contax/Kiev diopters were designed for the rear side ? I am very curious.

(I am submitting this thread starter to the General Discussion as I suppose this has more to do with general RF engineering history)

Cheers,

Ruben

 

[jlw]

All eyepiece correction lenses (diopters) are designs for attachment on the rear side because this is the easiest location for correcting both the viewfinder and rangefinder images.

If you placed a correction over the front of the viewfinder lens only, the rangefinder lens would be out of focus. You might be able to attach some sort of correction device to the front of the camera that would cover both the front viewfinder and rangefinder lenses (it would look something like the "goggles" for a Dual-Range Summicron) but this would be a larger and more awkward device.