100mm macro + full set of kenko tubes = manual focus only?

[maximus96]

when i put my 100mm macro with the full kenko tubes, i find that i can't auto focus anymore. the lens just goes back and forth and doesn't lock onto anything. by itself with no tubes the lens autofocus perfectly but mounted on the tubes AF becomes useless. is this the norm? or maybe because i'm in a poor lighting environment?

[LordV]

AF on macro lenses can be marginal at 1:1 - put on extension tubes and you lose another 2 stops of light so AF becomes even more marginal.
Most macro shooters use MF when shooting near 1:1 or above. Even if the AF works, the DOF is so thin that the AF does not know what part of the subject you want in focus.
I suggest you start getting used to MF - easiest way is to set the focus and then focus by moving the camera.
Brian V.

[hobbes2112]

As Brian said, AF is more trouble than it is worth at that level. It takes a while to get used to it but moving the camera back and forth to focus is the best way. Use Live View on your Xsi if you have the light.

[kevinso]

When you use the Kenko Tubes do you lose the f2.8? I was thinking about getting the tubes. and another question adding all the tubes gives you a 2:1 ratio right?

Kevin

[John_B]

maximus96,
With that magnification and tiny DOF, sorry but AF just doesn't cut it ;)

[John_B]

kevinso,
Yes a full set of Kenko tubes with the 100mm f/2.8 gives you 2:1 as I show here in Macro Variations <-- click to see (http://photography-on-the.net/forum/showthread.php?t=578274)
Oh and your lens will still allow f/2.8 :)

[maximus96]

i've been doing "setting focus at 1:1 with lens on manual focus, then moving back and forth while holding the * button (set to focus) and hope that the center point beeps" thing. i find that sometimes it doesn't beep at all, or that i still moved slightly after it beeps. i found my sharpest shots have been with just the lens at AF...i find it hard to judge if the bug is in perfect focus looking thru the viewfinder.

with liveview, my screen is completely black when the camera is set to manual because i set the ss to 1/200 and at f/8 or f/11. the image comes back on if i switch to any other mode, like Av. but the problem is if i get it just right when handholding the camera, i inevitably will have shifted it by the time i adjust it back to manual again. i find it much better on the tripod, but carrying it around is troublesome.

i really need a lot of work on my technique.

[hobbes2112]

That's a good point about live view being so dark. I forgot about that part, normally if I am doing live view shooting I am also doing natural light (av mode) with a tripod.

[krb]

Isn't there a camera setting that makes liveview bright regardless of exposure settings?

[kevinso]

Isn't there a camera setting that makes liveview bright regardless of exposure settings?
Yea there is when your shooting from the computer. forgot what its called but i will look and get back to this.

[krb]

Just checking on my 40D and there's a custom function setting for "Live View exposure simulation".

[maximus96]

appears to have no such function in my XSi. oh well, i just sold the 100mm couple of days ago.