How important is it to be able to have the full aperture range?
For 3D objects, it’s pretty important, Andy. The whole question is
one of depth of field. If you were using the macro lens to photograph
flat documents or something, it wouldn’t matter, but for 3D things,
being able to stop down the lens to a smaller aperture, while it
increases the exposure time, also increases the depth of field.
That’s the range of distance from the lens within which things are in
acceptable focus. With a wide open lens, only a narrow plane will be
focused, and anything closer or farther is out of focus. Stopped
down, you can get much of a small object in focus. And example would
be a ring. If you want a close up shot where the top, like the stone,
is clearly focused, and you’d also like the shank and back of the
ring recognizably focused instead of being a dim blur, then stopping
down the lens to a smaller aperture is a requirement.
A suggestion. Try using your camera in full manual mode. Don’t worry
about it syncing up. You set the aperture to a small figure, as well
as the focus, manually, and the exposure time. Just like with your
old 35mm. If the camera doesn’t have the ability to give you exposure
suggestions when used like this, just use trial and error. Slow till
you get an idea of what exposures work, since you have to go and look
at each image to see how it looks, but with the in camera review of
digital images, this is a lot simpler than waiting till 35mm slides
come back. Once you get an idea of the usual exposure settings for a
given lighting setup and camera settings, just bracket several
exposures around that typical setting, and one or more should be
fine.
I bought a Pentax digital not long ago for a similar reason. Back in
the old film camera days I rather liked an old Vivitar 100 mm macro
lens I’d gotten that gave way better images than it’s price would
have suggested. My new camera only does limited things with this
totally manual lens, but it’s enough. The lens works as well as ever.
All I really give up is all the auto stuff the new camera does that
my old 35mm cameras didn’t. Otherwise, it’s still quite capable of
using the lens, and I’d bet your Canon can do most of this too. If
it cannot determine from the lens where your aperture is set, and the
camera doesn’t have a “depth of field preview” button, then simply
take the exposure reading with the lens wide open, which you say the
camera WILL do, right? Then use math to determine the approximate
setting for a smaller f stop. It’s straight linear math. If your f
stop (aperture is half the size (larger number), then the exposure
setting needs to be twice as long. thus, going from an f2 to f4
would double the exposure time. f4 to f8 would do it again, and so
on. Most likely, you’ll want to be shooting between f8 and f16 or so,
to get acceptable depth of field. Some items might need even smaller
apertures. That sometimes needs a quite long exposure (and a good
tripod), and then you run into oddities of the sensitivity of the CCD
sensor, so sometimes you have to make adjustments, but once you
figure out what settings to use, it will remain roughly the same if
the lighting is the same…
Hope that helps.
Peter