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Old January 31st, 2005, 10:39 PM   #1
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Flipping image by lens

A main problem handling the homebuilt 35mm-adapter is the flipped image, upside down as well as right to left. I'd like to discuss a simple idea that seems to be a possible solution.

www.bodyhey.com/big_screen.gif

I would avoid a hotspot by using a glasscreen:

www.glasscreen.com

By blowing up the picture from 35mm diameter to about 60mm you maybe don't even need a diopter and have increased resolution.

cheers,
martin
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Old January 31st, 2005, 11:30 PM   #2
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one thing i have been wondering is if theres an element in the 35mm lens that flips the image... i havent got an old broken lens to take it apart and find out... but im guessing its mirrors? but maybe glass? if so is there a way to adapt to a mini35 of anykind?
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Old February 1st, 2005, 01:54 AM   #3
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Well, there is no mirror inside a 35mm objective, it's the lens itself. With a convex, magnifying lens parallel rays of light are focused in one point (until then the picture is upright) After that point, the picture you'll get is upside down.

This linke explains it by the method, a telescope works.

http://members.shaw.ca/quadibloc/science/opt01.htm
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Old March 5th, 2005, 12:36 PM   #4
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Martin D-
I've considered this option as well. The problem with this scherme (http://www.bodyhey.com/big_screen.gif) is that the DOF will be affected. More DOF, less DOF... I don't know. Secondly, this will probobly make the lens adaptor quite long and not very efficient in terms of light loss.
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Old March 5th, 2005, 01:00 PM   #5
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I don't see any reason the DOF would have to be affected. If you placed the lens inbetween the GG and the 35mm lens you would inevitably affect the focal length. However, if you placed it behind the ground glass you would get the same affect without the problems associated with the other method.

Adding a single element shouldn't affect light loss much at all - assuming you use a decent coated element.
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Old March 5th, 2005, 02:14 PM   #6
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"I don't see any reason the DOF would have to be affected. If you placed the lens in between the GG and the 35mm lens you would inevitably affect the focal length."
Yes, I agree. Martin D's drawing shows the "field" lens between the 35mm format lens and the GG. Placing the field lens after the GG would be a better option.
I doubt that you can use just one single element. Multiple elements would have to be used to achieve this task. In this process you're bound to loose at least a stop and a half at least.
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Old March 5th, 2005, 03:50 PM   #7
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One should be enough if you get the right focal length and distance from the GG and the video cameras lens. It would take some intentional design though. It wouldn't be as simple as most stuff.
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Old March 6th, 2005, 11:55 AM   #8
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Wouldn't it need to be at least a doublet, to reduce chromatic abberation?
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Old March 7th, 2005, 12:25 AM   #9
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Oh absolutely. I mean, just one lens should be enough (a muli-element lens but only one of them). I hope that made sense.
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