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-   -   optical viewfinder extension.. DIY? (https://www.dvinfo.net/forum/apertus-open-source-cinema-project/140712-optical-viewfinder-extension-diy.html)

Oscar Spierenburg January 2nd, 2009 10:32 AM

optical viewfinder extension.. DIY?
1 Attachment(s)
Hi everybody,

Some time ago I built this optical viewfinder on my Elphel Cmos camera (see Elphel 333 thread)
One thing I'd like to improve, if possible, is to make some sort of extension. (similar to this, but a lot smaller of course (the viewfinder I use is adapted from a 8mm camera. It would be very nice to enlarge the image too, because it's quite small now.
All ideas are welcome!

Here is an image of the Elphel with viewfinder.

Sebastian Pichelhofer January 10th, 2009 05:36 AM

Great idea!

Could these be of any use: Prism mirror, precision grade

Oscar Spierenburg January 11th, 2009 05:28 AM

2 Attachment(s)
Sebastian, I have used such a mirror prism in the viewfinder. First, the beamsplitter in front of the sensor mirrors the image into the tube that sticks out of the camera. Then the image is mirrored again through the mirror prism into an eyepiece. See the original drawing attached.
From that eyepiece I need the extension tube. Here is a quick drawing of what I mean.
Now if I make the same kind of tube that comes from the beamsplitter, I'd flip the image 180 deg. Is there another setup possible?

Brandt Wilson January 18th, 2009 08:08 PM

Oscar, are you using a longer focal length lens and diopter to extend the optical path?
If I remember correctly (and I may be way off, so don't go by my figures) wouldn't a longer FL lens be of value? If so, I found a really long PCX here: PRECISION PCX 21MM CLEAR DIA X 300MM FL MTD - Surplus Shed. It's 21mm diameter mounted by 300mm FL. A hair under $16 plus shipping.

You can then use a diopter to bring your eye closer to the focal plane, which should effectively perceptually enlarge the image.

Oscar Spierenburg January 20th, 2009 07:26 AM

I'm not sure. I hope it would work like you describe it. The first tube is actually creating the distance to the focal plane. So what is left is the eyepiece, I don't know if you can extend it..

Right now I've done a huge compromise, but I need to have this working: I've put a tiny cmos pinhole camera (without the lens of course) in place of the eyepiece. The output of the camera is displayed on a separate B/W viewfinder from an old TV camera.
The advantage is that I can flip the whole thing when I'm using a 35mm adapter.

This is just temporarily a quick solution, because of the quality loss, so I'll continue to make it totally optical.

Brandt Wilson January 20th, 2009 11:02 PM

I think a diopter at the eyepiece end would bring the eye closer to the imaging plane. Perhaps someone more knowledgable about optics can time in here, but I think that's right.

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