Toronto Photography Meetup Group

Sabesh's M4/3 thread has really got me thinking about the E-PL1 to make use of my Canon FD glass. While thinking about it, it got me dreaming of the possibilty of a wide angle behind the lens converter. With a 0.5 converter on a FF lens adapted to a M4/3 camera would make a FF 24mm lens an effective 24mm lens on the cropped sensor. So why bother. Well as the behind the lens telecoverter loses 4 times the light for every halfing of the field of view, this wide behind the lens converter would do the reverse. Thus a 2.8 lens would effectively become a 1.4 lens, and that precious 50mm 1.2 prime would become an effective 50mm 0.6 prime. Of course this adapter would only work with full frame lens adapted to a cropped sensor. If this is the first time this idea has been publicly expressed and is patentable I declare it public domain.

Browsed around a bit and apparently it has been thought about. and implemented in some special applications.

Apparently Kodak is just sitting on the patents doing nothing with them right now. But patents can eventualy expire, I believe. Six more years in this case.

I don't think the physics of this makes sense. How can you make a lens gather more light by adding an optical element behind it? If this were possible why wouldn't all the manufacturers do this to all their lenses so that we'd all be walking around with f1.4 zoom lenses instead of f2.8..?

This type of converter does the opposite of a teleconverter. The TC takes the image coming out of the back of the lens and magnifies it. If you do a 2 times image mag. only a 1/4 of the image area gets to the film thus 1/4 of the light. A two times TC loses at least 2 stops of light, + plus a bit more for lose through the TC lens element. What I am talking about is a wide converter, but only a wide converter for FF lens going to cropped sensors. Take a 50mm lens and put it on a m4/3 camera say (the most affordable adaptable body available) you get 100mm equiv. No unit light per unit image area is gained or lost because you are just cropping. However 3/4 the image area and light that would have hit the FF sensor or film, that the lens was designed for, is not used. The converter that I am talking about (lets call it a 0.5 converter) takes all of the image and light that was targeted for the FF sensor or film and concentrates it on the smaller m4/3 sensor resulting in 2 stops more light minus the bit that is lost in the conversion lens. It is called a wide converter because it bring the effective fl back to the lens fl. on the cropped sensor. These could be used FF but you a get a smaller usable image, but still get more light where you have an image.

Interesting, I see what you're getting at. Coincidentally I've asked a related question in the past and this is what one person who seemed to know what he was doing said:

http://www.velocityreviews.com/forums/s ... ostcount=8

The problem of resolution is not a problem of the app. I was talking about, ff to 4/3 and even less of a problem with 1.5 or 1.6 cropped sensors. That is if there is a problem I have not thought through the geometery in that way, but believe that good legacy glass should be up to it if there is a problem. Kodaks patent probably has a lot to do with the complexity of the optical design and Nikon may not of been able to get around Kodak with a design of their own that would not infringe on Kodaks patent. But I'm just guessing here. I would think that there would be big bucks here if Kodak's patent resolved all the issues. We will have to wait for the Kodak patent to expire and see if someone else has the will to start where Kodak left off. Really really big guessing here.

This link shows one person's implimentation when using a full frame circular fisheye on a (crop) Nikon D1 and thus explains what is actually involved, and what a pain in the ass it really is: http://www.naturfotograf.com/D1_fisheye_1,html.htm

even just reading the first 3 paragraphs, there is hell of a lot more involved with this fisheye conversion than dealing with say a standard 50mm legacy prime.