Designing a aux viewfinder for 80mm 6x6

D

drpops

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Guys,
This project is Waaaaaaaaaaaaay out there.

There has got to be a wealth of knowledge out there.
I am trying to design an aux viewfinder for my Ikonta with some eye relief. The rangefinder is not a big deal...but the viewfinder is.

I would like someone to help / confirm.

The design calculations using off-the-shelf lab lenses to get the viewfinder about a 1:1.
I think I have a handle on this section of the problem, but...
...how does one calculate the eye relief prior to the prototype build. Is the eye relief a function of the diameter of the optics used? if so where could I find the engineering background so that I can solve the problem.


thanks,
David
 
What about using the finder from a disposable or 35mm finder for 35mm cameras. Paint/tape off the the edges. Might not get "enough" eye relief or 1:1 but useful and clear enough.

Also why not try something similar to the Ikodot design?

Cheaper too.
 
I think the best solution would be what companies like Horseman and Fotoman have done. Find a finder and simply put a mask on it. The mask can be made with a little trial and error and should be fairly easy if you can see the image at the film gate--try a piece of frosted plastic as the ground glass. Also, a finder is made for a specific distance so make sure you are focused at that object distance.

You can make a very simple finder without optics. Cut out a framing square and then place a peep hole at a distance in proportion to the focal length. For 6x6, a 56mm x 56mm frame (the size of a 6x6 image area) would be used and the peep hole would be placed at the lens focal length. You can also use a 28mm x 28mm frame with a peep hole half the focal length. The frame is accurate for infinity. You can make the frame good for other distances by compensating for the change in magnification/image distance.
 
Last edited:
Kontur

Kontur

drpops said:
Guys,
This project is Waaaaaaaaaaaaay out there.

There has got to be a wealth of knowledge out there.
I am trying to design an aux viewfinder for my Ikonta with some eye relief. The rangefinder is not a big deal...but the viewfinder is.

I would like someone to help / confirm.

The design calculations using off-the-shelf lab lenses to get the viewfinder about a 1:1.
I think I have a handle on this section of the problem, but...
...how does one calculate the eye relief prior to the prototype build. Is the eye relief a function of the diameter of the optics used? if so where could I find the engineering background so that I can solve the problem.


thanks,
David
Click to expand...

Much easier to search for a Voigtlander Kontur Sports finder - they made them for 24x36mm, 6x6 and 6x9. At one time I had a good example of each and used the 6x6 on my Perkeo 6x6 which had an 80mm lens.
 
To answer your question, the size of the optics is not related to eye relief, at least not as a clear relationship as it depends on the design. Also, your finder will not form a real image, not unless you want to have an upsidedown image or you are going to have an erect prism in there, but it will use a virtual image, a Galilean finder. Here you are not dealing with eye relief in the sense of binoculars, but rather you need to worry about whether the field will be visible.

http://www.patentstorm.us/patents/4348090/description.html

You can also find information at Google books. Search for Galilean Viewfinder.
 
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