Reverse teleconverter

[eos650]

I shoot Canon, both APS-C and Full Frame and consider them complimentary to each other. The recent rumors about a possible 7D upgrade have got me wondering...

Why doesn't someone create a reverse teleconverter? Something that you can put between your Canon EF lenses and an APS-C body. It could be something like a -1.6X or whatever. Since this would squeeze all of the light from the full frame image into a space the size of an APS-C sensor, I'm assuming you would gain approximately one stop plus of light. You would also have the advantage of having the same FOV on an APS-C body as you have on a full frame body and I'm assuming the same DOF.

If someone were to build this and it actually worked as described, I can see a huge market for it.

Is something like this possible? Am I nuts (don't answer this)? What do you think?

[jhaces]

You should check out the Metabones Speed booster.   There's a review over on LR's blog.  http://www.lensrentals.com/blog/2013/01/metabones-magic

So, it does exist and apparently works. Unfortunately it is currently only available CanonEF>SonyNEX but we can hope...

[emag]

In the astrophotography world it's known as a focal reducer or less commonly a telecompressor.  Often it is optically figured to also reduce field curvature; hence, another name - field flattener/focal reducer or FF/FR.  I use an f/6.3, it reduces my scope's effective focal length from 2350 to 1480mm and from f/10 to f/6.3. 

As for camera lenses:  http://www.sansmirror.com/newsviews/focal-reducer-lens-adapter.html

[Axilrod]

I shoot Canon, both APS-C and Full Frame and consider them complimentary to each other. The recent rumors about a possible 7D upgrade have got me wondering...

Why doesn't someone create a reverse teleconverter? Something that you can put between your Canon EF lenses and an APS-C body. It could be something like a -1.6X or whatever. Since this would squeeze all of the light from the full frame image into a space the size of an APS-C sensor, I'm assuming you would gain approximately one stop plus of light. You would also have the advantage of having the same FOV on an APS-C body as you have on a full frame body and I'm assuming the same DOF.

If someone were to build this and it actually worked as described, I can see a huge market for it.

Is something like this possible? Am I nuts (don't answer this)? What do you think?

Yeah I was gonna say it but the other poster beat me to it, the Metabones Speed Booster is essentially exactly what you are describing.  But it's only Sony E or A mount to EF and maybe a few other variations, and then they are doing an MFT to EF.  I want the MFT to EF so I can use it on the Blackmagic Design Cinema Camera and reduce the crop from 2.4 to around 1.6x or 1.5, effectively giving you a Super 35mm 12-Bit RAW Cinema Camera for $3600.

I haven't heard anything whatsoever about plans to do a Canon version.  It's not a new thing, Stanley Kubrick used it way back in the day to modify a Zeiss 50mm and give it a max aperture of f/.7.  That's the beautiful thing about a reverse teleconverter, while you lose a stop with an extender you actually gain one with the reverse extender.  So an f/2.8 becomes an f/2 and an f/1.4 becomes a f/.9 (Or maybe it's f/1.2 becomes f/.9, not sure).

[eos650]

Wow! I never know these existed. Assuming they had favorable optical quality, that would be fantastic.

I can see why Canon might be reluctant to make one of these. It certainly wouldn't eliminate all of the advantages of Full Frame, but it would make it a lot closer for those shooting APS-C.

Here's hoping that Metabones, Sigma, Tamron, Tokina or someone comes out with one of these for EF to EF-S, in the not too distant future.