Adapter for lens shortening

Started Jul 28, 2012 | Discussions thread
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Adapter for lens shortening
Jul 28, 2012

Please forgive me, this may exist already. It that case, this idea is not new and I apologize for being uniformed. Also, I apologize for putting this thread on NEX forum, but I guess NEX users are most advanced users of manual lenses with adapters.

I have just order NEX adapter for M42 lenses. I was also interested to buy extension tubes (rings) that I could use with the adapter and M42 lenses. So I have read couple of pages of them and find out that:

The tube contains no optical elements; its sole purpose is to move the lens farther from the image plane. The farther away the lens is, the closer the focus, the greater the magnification, and also the greater the loss of light (requiring a longer exposure time). Lenses classically focus closer than infinity by moving all optical elements farther from the film or sensor.

But, what happens if optical elements are closer to the film or sensor? Will it all go in reverse? I will never understand optics, huh. Anyhow,
Q: How can this be possible?

A: Adapter manufacturer may design NEX adapter for M42 lenses (or any other mount) shorter .
i.e. Dimensions of my adapter:
2.36 in x 2.36 in x 1.30 in (6.0 cm x 6.0 cm x 3.3 cm)
what if they are half of their lenght
2.36 in x 2.36 in x 0.65 in (6.0 cm x 6.0 cm x 1.65 cm)
My big question is: Will it make any sense to anybody?

 Jokica's gear list:Jokica's gear list
Sony Alpha NEX-5N
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