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Old June 22nd, 2008, 10:26 PM   #1
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Join Date: Oct 2005
Location: Long Island, NY
Posts: 208
My mini35 for the XL2

I just finished this and thought I'd share. I built it over about 3 weeks. Much of the design was based loosely on a prototype from over a year ago.

It uses a vibrating ground glass (which I got to be very quiet), first surface mirrors to invert the image (much cheaper than prisms), and a 28mm Canon fd lens as a relay lens.

Sample/Test footage:

http://www.justine-haupt.com/movies/testmontage.MOV

(Note that the sharpest footage is near the end when the sun was out and I was able to stop down the relay lens a bit more. Also, the very last shot I show the ground glass off and on for comparison.)


Pics:

http://www.justine-haupt.com/images/DSC00665.JPG

http://www.justine-haupt.com/images/DSC00672.JPG

http://www.justine-haupt.com/images/DSC00655.JPG

http://www.justine-haupt.com/images/DSC00656.JPG

http://www.justine-haupt.com/images/DSC00658.JPG


Sample screens:

http://www.justine-haupt.com/images/Image0.jpg

http://www.justine-haupt.com/images/Image2.jpg


:)
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~Justine

"We are the music makers, and we are the dreamers of dreams" -Arthur O'Shaunessey (as quoted by Willy Wonka)

Last edited by Justine Haupt; June 22nd, 2008 at 11:45 PM. Reason: forgot stuff
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Old July 1st, 2008, 03:54 AM   #2
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ik like the use of the 28 mm relay lens. I have some different types around here. How did you attach the relay lens to your camcorder?
It could maybe work as an relay for a letus or a redrock.
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Old July 23rd, 2008, 10:30 PM   #3
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Sorry I took so long to respond... haven't checked the board.

The FD relay lens is attached to the XL mount via an adapter I machined myself from aluminum. Though, I'll never do that again... it would work just as well to get an extra body cap for the XL2 and a rear lens cap for the FD lens, and glue them together (with a big hole drilled through the optical axis). The important thing is the spacing between the two lens mounts (caps, lets say). Changing this distance effectively alters the flange focal distance of the FD lens, which affects both how "zoomed in" the relay is and how far away the ground glass has to be. There's a very simple formula which I forget at the moment, but it's probably easiest just to experiment with the spacing. My ground glass winds up having an optical distance of about 21 cm to the front of the relay lens (thats with the distance it takes for the light to get through the mirror array). With this, the spacing between the back of the relay and the XL2 is1.6cm. This resolves a cinema 35mm frame on the ground glass.

To get the sharpest focus of the ground glass, I usually keep the relay stopped down to f/4 if I can help it (it's an f/2.8 lens). Between that and the f/2.8 zoom lens (28mm~70mm) I use as a prime, the light loss IS significant, but it still works very well.

I see no reason this shouldn't work on a Redrock or a Brevis... I actually was going to buy a Brevis for my XL2, knowing what I know about relay lenses, but decided there was too much money to be saved by going back to my old designs and making a second generation version. The *only* issue I can really think of of using a relay like this on a commercial adapter is the optical distance to the ground glass I just mentioned above. If it's too much different than about 20cm, a different focal length lens might have to be used as a relay... but no big deal.

One thing I should point out, is that this setup is only really practical *because* the adapter has an image erecting system. It's that array of mirrors that eats up the optical distance to the ground glass. If they weren't there, the adapter would have to be so long, you may as well use the Canon´s stock lens as the relay.

More questions are welcomed! I'll check the board more... it doesn't seem like anyone else is doing what I'm doing, and it seems like a fairly obvious solution for cams with detachable lenses.
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~Justine

"We are the music makers, and we are the dreamers of dreams" -Arthur O'Shaunessey (as quoted by Willy Wonka)
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