Bad teleconverter idea... How bad?

JohnRog

Ok here's my dumb question... I have a vivitar (canon mount) 1.4x teleconverter that has AF confirmation that works fine, but no lens I've tried will get a lock on focus....it continually hunts even in bright light. If I focus manually I will get confirmation that is accurate. I know that teleconverters are for longer focal length lenses, but I've tried it on everything just to see if I could get actual auto focus on anything including my 50 1.8 and 85 1.8 as well as the 70-200 2.8 II that I rented last summer. Occasionally something will lock, but usually not. Optically it doesn't seem so great anyway, so unless there is some wisdom to be shared about how to get it to work, my idea was to remove the optics to make it into an extension tube with AF confirmation... so aside from possibly making a big mess, how bad is this idea, and does anyone know what length extension tube it would equate to (or can I just measure the outside dimensions)? Thanks

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time2smile

this focus issue is common with tele"s at least cheap ones. I have 3 and they all do the same, except my tamron 1.4 works most the time. use manual focus.

if you remove the glass, and i am only guessing, no expert, but i think you will not have what you are looking for, the converter should have electronic chip inside, and i believe it will be confused without the glass, and may not confirm focus anymore.

let us know if you try it,

ziggy53

Your best option, IMO, is to sell the teleconverter. Use the proceeds towards purchasing a Canon teleconverter for the 70-200mm. A Canon converter won't work on the shorter primes because of the protruding element of the converter, but for longer lenses the quality improvement (vs the Vivitar) is considerable, even using the older converters. Even Canon teleconverters will affect AF acquisition.

Regarding removing the optical elements, if the converter has simple pass-through then the resulting tube should work fine. If the converter has a "reporting" circuit then the exposure may, or will, be affected. Yes, you can just measure the length of the tube minus mount in order to measure the extension.