All I want for XMAS is a 0.67X teleconverter

Started Dec 16, 2012 | Discussions thread
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rpenmanparker Contributing Member • Posts: 645
All I want for XMAS is a 0.67X teleconverter

I floated this idea on another forum a while ago, but the response was very disappointing, basically just, "The lens manufacturers do what they want without listening to us."  I thought I would give it another go here.

My idea is for a fractional "tele" converter at 0.67X to be used with FF lenses on APS-C.  The pupose would be to erase the tele effect of the cropped sensor relative to FF as well as to eliminate the DOF disadvantage of the APS-C format.  It wouldn't work with APS-C specific lenses, because there is no image information outside of the sensor that can be placed back on the sensor by shrinking the image.  But with FF lenses, the 1/3 of the FF image that spills off the cropped sensor could be recovered by widening the angle of the lens

Here are the advantages of this idea:

  • Original intent and utility of FF lenses would be preserved or restored when used with the teleconverter on APS-C.
  • DOF of the lens/converter combination on APS-C would be equivalent to the DOF of the lens alone on FF.
  • Speed of the lens/converter combination would be more than one stop faster than the lens alone.

The obvious drawback would be the potential for loss of IQ.  How much would depend upon the quality of the converter.

A couple of examples:

Supposing you shoot a Sony APS-C but own one of the highly revered old FF Minolta AF 100mm f/2.0 portrait lenses. On APS-C the 100 is too long for traditional portrait use, and the DOF at 2.0 is more than 1 stop defensive to what it is on FF.  The lens might have some short telephoto uses, kind of like the old 135mm lenses on FF.  By and large I think it would sit in the camera bag and not see much use. But with the 0.67X converter, the original intent and utility of the lens for portraiture would be preserved.  At 67mm on APS-C it would give an image equivalent in coverage to the 100mm lens on FF.  The bonus advantage would be the more than one stop increase in speed to a very attractive f/1.3 just for the price of the converter.  And the 67 mm f/1.3 combination of lens and converter on APS-C would exactly preserve the DOF of the 100mm lens alone on FF.

Now what about that FF 50mm f/1.4 FF lens you paid so much for.  On APS-C it is neither fish nor fowl, a little too short for portraits or telephoto, too long to use as a normal.  50mm is a fine focal length when included in a zoom lens range on APS-C, but it is just not the base case normal lens that it was on FF.  (Don't get me wrong, I know lots of folks still use their 50s on APS-C, but it just doesn't have the same utility it did on FF.) With the 0.67X converter, however, the 50mm 1.4 becomes a 33mm f/0.94.  Wow, it is once more a normal lens, but now with blazing fast speed.  And it would have the same DOF on APS-C as the 50 did alone on FF.  That is tough to beat.

I think such a product would be a tremendous addition to the camera bag of every APS-C shooter. So where is this 0.67X teleconverter?  I haven't seen any.  What is wrong with my analysis?  Why doesn't Tamron or Sigma have one out there? Or where is Canon's version, which would be more likely 0.625X to match with the 1.6 tele factor on their APS-Cs.

Your thoughts?


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