A TC20E becomes an electrified extension tube

Started Sep 26, 2012 | Discussions thread
OP mmalkin15 Regular Member • Posts: 290
Re: Electrical mod

Hi Marianne

You are correct that the aperture is reported correctly when pin 10 is cut but autofocus hunts rapidly back and forth around the proper focal point and cannot lock in at all with my 70-200 - likely too much gain in the motor feedback loop. Restoring pin 10 does restore focus lock operation but yes it is slower. I guess that there is more than meets the eye in the TC20ii electronics - perhaps this is part of the reason that we have not seen electrified tubes from Nikon. I would surmise that the AF algorithm is partly lens specific and may employ distance and lens focus motor characteristic information to control the feedback and work optimally. I should have realized this because I already knew that using the Kenko 36mm tube on the 70-200 has the same AF problem - the lens hunts badly and does not AF. Short extension tubes like the kenko 12mm tube are less problematic but still have a touch of hunting before lock-on. I have previously used the TC14e along with a Kenko12mm tube and was able to get decent butterfly photos. So - using a telconverter or an extension tube seems to require modification and slowing down of the AF operation for AF-S motor lenses .

Still - modifying the converter by removing the optics does work properly but at some cost of AF Performance.

The quest for professionally viable macro AF performance - two steps forward, one step back.....

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