"Paul Jones" writes:
> I am looking at buying some k-mount extension tubes. I am
> wondering if there
> is any difference in the performance of different brands? As
> if there like
> the screw mount ones i have seen then there is no glass in the tube.
I don't know if there are differences between extension tube sets, but here
are a few things to lok for differences in:
A) build quality. For example, my (used) Vivitar extension tube set has
two flaws: the plastic lens-release handle on one of the tubes broke off
(there's a screw head there I can use, but it isn't as convenient). Also,
when one of the tubes was made, they didn't bend the tension tabs on the
lens mount part, resulting in a lot of slop when anything was mounted to
that tube; the other two tubes were just fine. This probably was a one-off
problem with the set I have.
B) useable with autofocus camera. My set had anodization on the lens mount
flange (sp?). Since that is an insulator, I couldn't use trap focus mode
with the tubes.
C) vignetting. This one is a biggie. The interior aperture of my tube set
is not large enough to prevent vignetting of the image even when using my
100/4 lens at full extension. Could be I'm stacking them in the wrong
order, but I thought I'd tried all the combos.
Another feature worth looking for is to have a tube with a tripod mount on
it that you can rotate around the tube. That makes tripod use more
conveinent and allows you to easily switch from horizontal to vertical
format without resetting up the tripod. Wish I had such a beast.
> Are there any other cons of extension tubes?
Length. The longer the lens, the more extension is needed to get to a
given magnification.
hope that helps,
patbob ([EMAIL PROTECTED], [EMAIL PROTECTED])
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