Re: Sinar creates adapter to mount DSLRs as digital backs

Started Jul 29, 2010 | Discussions thread
Joseph S Wisniewski
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The aerial image is very small...
In reply to jeffcpix, Aug 8, 2010

jeffcpix wrote:

I remember something about drilling a hole in the center of
a ground glass and using a loupe to focus on the 'aerial image'.

Would it be possible to replace the loupe with a DSLR?

Unfortunately, it's only possible to take a picture of where there's actually light. The light rays move in reasonably straight lines from the lens's exit pupil to the focal plane. The reason the "hole in the glass" trick works is because the hole (the entrance pupil of the "viewing system" is smaller than the exit pupil of the view camera's lens, as seen from well behind the hole.

To light up a larger area, you need to somehow turn the rays inward, towards the DSLR's lens.

That can be done with a "condenser lens" at the focal plane. Unfortunately, a solid lens of such a short focal length is heavy, and introduces a ton of aberrations, so you'd have to make it a macro lens. Maybe 6 elements, at 6.5 inches in diameter. Suddenly, the large format scanning back seems like the "low cost" solution...

A fresnel lens introduces aberrations and severely limits resolution. A holographic lens might be possible, it's a well defined problem...

I think that any optical system that would couple the two lenses is going to lower the optical quality so badly that you'd really be better off with a Nikon or Canon tilt/shift lens.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

http://www.swissarmyfork.com

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