Minus Teleconverter

94 sol eclipse 11
Originally uploaded by Bart Benjamin

It seems to me that any full frame lens could become a DX lens with a minus-teleconverter, if such a thing were constructed.  The advantage would be that full-frame lenses could be made faster on DX bodies.  Perhaps my 300-f/4 could become a 200-f/2.8 simply by reducing the image circle!

I'm sure that I'm not the first person to consider this.  My best guess is that the economics of this minus-teleconverter don't appear to pan out well enough for Nikon to make one.  Perhaps sports and wildlife photographers would consider another DX body for their existing lenses if it were faster?

Update: Somebody has built one, and they call it a "Speed Booster - adapter for mounting SLR lenses on APS-C and Micro Four Thirds cameras that reduces the focal length by a factor of 0.71x and increases the maximum aperture by 1 stop".  I see the term wideangle convertor also in use.

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