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Old February 2nd, 2008, 06:53 PM   #1
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Optical viewfinder discussion

I'd like this to be a general discussion, but to quickly sum up my project:
I've made an optical viewfinder on the Elphel 353 cmos camera. Because of the small size of the sensor, I was able to use most parts from a super8 camera.
So far, it all seems to work really well. I still have to fine adjust everything though.
I posted some pictures of my first sketch and the result. here

I think this could be useful for any DIY HD camera projects.

One thing I'd like to improve, or have as an option, is a viewfinder-extension. It would be much more comfortable to position your head behind the camera :)
Does anyone know how such an extension tube works?

Another option I'd like to add, is an inverted(rotated) image when using the 35mm adapter. (Maybe by skipping the flipping tube in my setup?)

Any thoughts?
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Old February 4th, 2008, 11:39 AM   #2
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Hi Oscar,

I have a few thoughts on this.

If the viewfinder is working as you would like it to, there may be no need to extend the tube. The camera itself isn't much larger than video taps that are installed in other viewfinder systems on larger 16mm and 35mm cameras. This being the case, couldn't your solution be treated as being the viewfinder component of a larger system (mini-itx pc, battery, audio mixer, etc)? If so, you can mount it on your rails and adjust it to meet your eye comfortably, while the rest of the system is farther back on the rails to provide balance.

Just my $.02.

What is your viewfinder built from? You mentioned the other day that you are using a super-8 VF to match the sensor size. Did you pull these components out of a S8 camera, or is it all fabricated from scratch?

-Brandt
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Old November 13th, 2009, 06:57 PM   #3
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This is a very old thread, but still... I'd like to reopen the topic.

I recently took up my hobby again: wrecking and taking apart an old camera :-)

This time it was a nice Olympus Camedia C-1400L
This camera had a fairly large CCD and a real optical viewfinder. It was not using a flipping mirror like a SLR camera though, but a beamsplitter.
This beamsplitter was a 45 deg prism (roof prism??) that directs the image straight to a simple eyepiece, and also 45 deg downwards to the CCD that is placed directly to the prism. Can't be simpler. A little bit like this image. The CCD would be on the bottom plane.

So the idea came to mind about the Elphel camera 45 deg front end . Although using the 45 deg front end, the sensor would remain in it's normal place with a roof prism type beamsplitter between the sensor and the lens and an eyepiece in 45 deg on top of the camera.

Just an idea to think about.

BTW, I remember there used to be a SLR camera that used a 35mm sized beamsplitter in stead of a mirror for high speed continuous shooting. Does anyone remember the camera type and brand?
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Old December 5th, 2009, 08:43 AM   #4
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I was thinking about those beamsplitter attachments made for telescopes or microscopes, so you can see the image through the eyepiece, but simultaneously capture the image with an attached camera.
Something like this: http://www.versacorp.com/vlink/produ...x/vacams33.jpg
or: http://www.traderscity.com/board/use...er-video-1.jpg

Anyone know if the added beamsplitter will increase the focal lenth?
It could be a way to make an optical viewfinder between the lens and the Elphel.
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Old April 17th, 2010, 01:03 AM   #5
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Spinning shutter

Several years ago, Dan Vance built a mechanical shutter to achieve a deinterlaced image from a full frame CCD camera. I have a CP16-RA that uses a mirrored butterfly shutter to intermittently transmit light to the film plane or to the viewfinder. I also have a Kinoptic orientable viewfinder for the Eclair ACL. I wonder how difficult it would be to use something like an ARDUINO board to control a small servo motor and the sensor read-reset timing.

Crude design of the basics of the optical path:
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Old April 17th, 2010, 01:11 AM   #6
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Link to Dan's circuit design:
VC25P Shutter Drive Circuit
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Old April 18th, 2010, 05:31 AM   #7
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Nice, thanks for the input.

A mechanical shutter would at the same time as being used for an optical viewfinder solve any rolling shutter issues.

But the mechanical and electronic efforts to build a proper one are not to be underestimated.
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Old April 19th, 2010, 09:52 AM   #8
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There are many surplus parts on the camera support market, and I expect that the market for these will drop off precipitously, making them more affordable. They are already balanced, so the details to be worked out are in the electronics and the housing to hold them in registration with the CMOS and VF optics. If all of this is done using CAD/CAM software, such as SolidWorks, it ought to be pretty accurate. The key would be the sync circuit, and making sure that the shutter locks in the VF position, which I think can be aided by the poles of the motor.
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