On EF telephoto and 25mm extension tube (teleplus, AF)

[Jeff]

I tried coupling the teleplus 25mm tube to my 400/5.6 and found that the lens has serious problems AF at close range and can only MF. I tested with a 200/2.8 and the AF improves dramatically although still more to be desired.

Is this normal? Cause thought of selling the tube away as must MF. I have the habit of HH with telephoto lenses so MF is quite troublesome.

Thanks.

 

[mervlam]

no personal experience in this aspect, but want to add my 2 cents

i think it's the way Canon programs its AF algorithm for that lens. thus the lens fails to achieve focus with a extension tube. there are certain macro lenses that can be used with extension tubes

adding an extension tude shortens the minimum lens working distance but you can achieve focus at infinity, right? :dunno:

 

[Jeff]

no personal experience in this aspect, but want to add my 2 cents

i think it's the way Canon programs its AF algorithm for that lens. thus the lens fails to achieve focus with a extension tube. there are certain macro lenses that can be used with extension tubes

adding an extension tude shortens the minimum lens working distance but you can achieve focus at infinity, right? :dunno:

infinity lost

 

[weg]

infinity lost

yup with extension tube focus at infinity is lost...
but normal AF at closer distances shld be ok?? heh unless tt extension tube is not compatible for AF

 

[Jeff]

yup with extension tube focus at infinity is lost...
but normal AF at closer distances shld be ok?? heh unless tt extension tube is not compatible for AF

Will hunt ALOT on the 400/5.6. Quite useless actually with that tube.

 

[Bluestrike]

Will hunt ALOT on the 400/5.6. Quite useless actually with that tube.

well given the len 3.5M MFD, it quite hard for it to focus at very close range. The tude, I think, shorten the MFD to abt 1.8m-2.5m.

A good way to use it is, MF until abt there, aim on a contrasty area then use AF.

 

[Jeff]

Thanks folks. Just sold the tube a minute ago.