Designing a aux viewfinder for 80mm 6x6

[drpops]

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

 

[Hamster]

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.

 

[Finder]

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.

 

[Leigh Youdale]

Kontur

Kontur

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

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.

 

[Finder]

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.

 

[drpops]

great ideas and comments, I
knew asking was a smart thing to do....