Eric Smith <eric RemoveThis @brouhaha.com> wrote:
>I'm considering buying a Canon Digital Rebel XSi for a project involving
>macro photography, and I'm looking for advice regarding macro lenses,
>reverse mounts, etc.
You are getting a lot of wonderful information... almost
all of which is correct, but totally useless for your
needs!
Given what you have said you want to photograph, you
CANNOT do it with typical "macro" techniques.
>Basically I'm trying to photograph a flat subject such that an area
>about 1 mm on a side will be full-frame. It would be better yet if
>I could do that for an area 0.5 mm on a side.
>
>The camera has an APS-C size sensor (22.2 x 14.8 mm).
Okay, that means between 14.8:1 and 29.6:1 magnification.
To put it simply: You can't do that with a macro lens on
a DSLR.
You need a microscope. You might also want to look at
other types of cameras, because while it can be done
with a DSLR that may not be the most reasonable in terms
of either convenience or price.
>I have a precision X-Y stage with stepper motors and microstepping
>control, so I can position the subject in increments of less than
>0.1 mm. I plan to take many photos with a small shift, and stitch them
>together, probably using Hugin. Because I expect there to be a lot of
>overlap between the images, I think I can tolerate some amount of
>vignetting, spherical abberation, etc.
Do you want _each_ image to be even higher magnification
than stated above, and for the resulting final product
to be as described above???? Or do you mean each
exposure will capture 0.5 to 1.0 mm of a larger object?
If you mean that each exposure will capture 1mm of an
object, then a typical dissecting microscope would be
appropriate (and would be very convenient to mate with
your X-Y state). Another possibility is a toolmakers
metallurgical microscope.
If the total object is 1mm, you need even greater
magnification. In that case the metallurgical
microscope is what you'll need. And even if you want
1mm portions of a larger object, you might want to look
at this technique anyway, as it offers more flexibility
than a dissecting scope.
The feature you'll want to look for is the ability to
mount it in a way that you can use your X-Y stage (which
is not true of all metallurgical scopes). Another
feature, which is almost universal though there is a
chance you don't need it, is episcopic (or "epi" for
short) illumination. That uses a beam splitter to
illuminate the object through the same optical path that
you view it. (That is probably _very_ useful to you.)
Metallurgical microscopes also use special objective
lenses that allow a greater lense to object distance.
Microscopes can be very expensive, but it is unlikely
that you need a fancy one. It should be fairly easy to
find an older used model that will do fine. They often
are available on eBay at reasonable prices, as are the
parts and pieces such as objectives and "relay lenses"
for photography. Keep in mind that objective lenses are
matched to the eye pieces (and to the relay lenses used
for projecting into a camera), and hence should not
necessarily be mixed and matched between manufacturers.
>Is this feasible with some macro lens, combination of lenses, reversing
>ring, extension tube, etc?
>
>I'm hoping to avoid the need to buy a microscope and adapter, due to
>the cost, though that's obviously an option. I'm not sure how to tell
>whether a particular microscope would be suitable without trying it;
>for instance, I've looked at a 7x-90x microscope, but apparently 10x
>or 20x of that magnification is due to the magnification of the
>eyepiece, which I wouldn't have with the camera adapter.
This is a *large* topic, which will take a good deal of
research for you to get a handle on the perspective.
Here is a set of tutorial articles on photography through
a microscope:
http://www.microscopyu.com/articles/digitalimaging/index.html
One thing to note is that due to the optical limitations
of a microscope, the resolution of photographed images
is limited. The practical effect is that high
resolution cameras are *not* necessary, and might even
be less useful! A very fancy DSLR is not going to get
any better an image that some of the nicer, much less
expensive, webcam's available! And adapting/using a
web cam with a microscope may be much less expensive and
easier to operate than mounting a DSLR on the same
scope! In the end, the images are not different.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd RemoveThis @apaflo.com
>> Stay informed about: Newbie question about macro with DSLR 
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