Re: Nikon extension tube with teleconverter
- From: Paul Furman <paul-@xxxxxxxxxxxxx>
- Date: Fri, 28 Sep 2007 17:58:42 GMT
C J Campbell wrote:
Nikon's AF-S TC series of teleconverters can only be used with a small number of lenses because the teleconverters are designed in such a way that the rear element of most lenses will contact the front element of the teleconverter, possibly breaking them. You can only use the teleconverters with lenses that have deeply recessed rear elements, such as the 70-200mm AF-S VR.
Suppose, though, you put an extension tube between the teleconverter and the lens, so that the lens elements cannot contact each other. What would be the effect on picture quality and exposure?
Those AF-S teleconverters are optimized for longer focal lengths so it may not work well for shorter lenses. I believe the way extension tubes effect exposure is that they increase the focal length so the aperture becomes smaller relative to the focal length and the f/stop becomes a larger number. a 50mm f/1.8 has an aperture diameter of 50/1.8=27.7mm and if you add 50mm of extension it's a 100mm lens with an f/stop of 100/27.7= f/3.6
Also, you may have to grind off a metal tab on the teleconverter because they are designed not to mount to some things. That modification has no effect on performance. I did this in order to be able to stack my 1.4 & 2x teleconverters.
--
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