Regarding extension tubes

[(Ghastly) Krueger]

Hello all,

I'm pretty much convinced on getting some extension tubes to do some macro (close to macro? w/e). I'll eventually save for a true macro lens, but that will take a long while.

I'm considering buying Kenko tubes for my Canon Xt and will use them with 28mm, 50mm and a 75-300mm lenses.

What I need to decide now is whether to buy one tube or the complete set (due to $).

I understand that longer tubes give higher magnification and that they can be stacked (with some light loss) to get it even higher.

If all that is correct, why would I need the smaller ones (12mm, 20mm) except to stack them with the 36 mm? I mean, wouldn't it be enough to get the 36mm and back a bit farther from the subject?
Is the 36mm even sold by itself?

Thanks for any info on the subject

 

[Big Mike]

The shorter lengths would give you less magnification...which might beneficial in some situation. I can see it being possible that some lenses wouldn't be able to focus with a 36mm tube.
That's just a guess anyway.

 

[(Ghastly) Krueger]

Thanks for your answer

The shorter lengths would give you less magnification...which might beneficial in some situation.

Cant' I just get the camera a bit farther from the subject to get less magnification?

I can see it being possible that some lenses wouldn't be able to focus with a 36mm tube.
That's just a guess anyway.

Not able at all or just not able to autofocus?

 

[Big Mike]

Well sometimes, too much magnification means that your focus range is an inch or so in front of your lens...and I'm guessing that you don't have infinity focus with one of these on.

So (it's my guess) that when you use an extension tube...your focus range that used to be 3 feet to infinity...might change to 4" to 10"...or something like that.

So if you have too much magnification....your focus range might be 1/4" to 2"...which might be way too close for many subjects.

 

[(Ghastly) Krueger]

Great, thanks!