Manual Focus problem

[jaydee]

I've just received macro extension tubes for my canon 40D. The problem is that my 17-85 lens will not focus in manual mode with the tubes attached. If I use the 17-85 without the tubes, no problem focussing. I can also focus correctly with my 70-300 attached with the extension tubes connected!

Any advice? Help!

 

[StewartR]

The problem is that my 17-85 lens will not focus in manual mode with the tubes attached.

Did I read that right? What does happen when you try to focus manually?

 

[Chappers]

Rather than use the focus control try using the zoom control to " Focus" the image. It's not really focusing, but your depth of field is so small with tubes attached you may be outside the range of the focusing control. Using the zoom gets you to into " the ball court" so to speak. I use this technique with my 70-200, when using tubes

 

[jaydee]

StewartR - I am unable to focus at all!

Chappers - I have tried that and still cannot focus correctly.

 

[captain jack]

When using extension tubes or bellows the lens looses infinity focusing as chappers says you can get a focused image by using the zoom function of the lens , the focusing method when extension is used is to set magnification factor by altering the focal length of the lens & then focusing by altering the lens to subject distance. Magnification is given by dividing the extension length by the focal length of the lens.

 

[Chappers]

Jaydee

You may simply have to much extension on. I don't know what tubes you have but I just did a test with my 20D and the if you have a large extension tube on, you cannot focus at all.

Drop down to the shortest one and see if this helps.

 

[Canon Bob]

I suspect that this lens will not focus at much more than 25cm with 25mm of tube attached...even on the long end and will be much shorter at the wide.
Put your shortest tube on and hold your hand to the lens (focussed at infinity) and slowy move your hand away until you are focussed....very short distance I imagine.

Bob

Edit...if a lens has a large amount of internal extension then it's possible that infinity focus will actually end up inside the lens itself.

 

[Chappers]

Edit...if a lens has a large amount of internal extansion then it's possible that infinity focus will actually end up inside the lens itself.

!!!Painfull !!!

 

[jaydee]

Thanks to all for your feedback.

I'M SORTED. IT WORKS!

I have to place the camera really close to the subject in order to achieve focus, unlike the 70-300 where I need to move further away.

Thanks Again