The Bobbs wrote:
Hi All,
Some questions about macro photography. My pardons if this has been discussed
recently. I did some searching of the archives (haven't been keeping up with
the mail list in some time) but didn't really find an answer.
Goal: Shooting insects, flowers, etc. at 1:1 to 1:2 ratios.
Equipment: A relatively inexpensive Vivitar 100mm f3.5 macro lens, with matched 1:1 close-up lens.
Used in combination with either OM2n or OM-2000. Both with "stock" split-prism focus
screen. Problem: At 1:1, I often find it difficult to avoid "dark semi-circle" syndrome.
You know, where the top or bottom half goes dark and wiggle as you might, you can't quite seem to
keep your eye at that exact point where it stays clear. I don't seem to get it as bad at 1:2 or
smaller ratios, but at the limit, is quite a problem. I'm surprised by it, as I wouldn't think the
matched close-up ring would be robbing much, if any light.
The aux. lens isn't robbing a lot of light. You are running into 2
things. First, the optical design of split image focusing aids in SLR
focusing screens means they darken below a certain f-stop. Second, the
effective speed of a lens declines as it is focused closer, so the light
available to the screen declines quite a bit as you go from 1:2 to 1:1.
This is true of all macro lenses.
I really prefer the working range I get with the 100mm, so using my 50mm with
tubes is usually not desired.
Nor desirable, from a technical perspective. You should note that the
aux. lens changes the focal length to about 70mm.
I'm expecting answers along these lines:
a) Well duh! That's why we all bought the VWXmm, fY.Z macro lense! Just to
avoid that problem! And to empty our bank accounts. :-)
The Modern Photography tests of this lens showed it to be excellent,
including with the auxiliary close-up lens. No need to spend more unless
you need more speed (but, of course, lack of speed in the lens is part
of your problem).
b) You need to be using focus screen XYZ. (Hmm, bear in mind I can't switch
the screen on in the OM-2000 and for all other shooting, I really like the
stock, split prism in the OM2n. The thought of my fumbling fingers switching
these screens in and out leaves me mighty cold ...
Well, there are certainly screens specifically designed to deal with
this problem. The thought of one body, either existing or acquired, with
the proper screen installed and dedicated to macro crosses my mind. Of
course, you ask for a solution that involves no cost and no
inconvienience, a tough call when you are up against the laws of optical
physics.
c) Learn to focus with the collar and ground glass. You don't really need the
split image. (Hmm, I've not had good luck here. My eyesight isn't exactly the
keenest, even with glasses).
It costs money, but you might consider the Varimagni. It gives 1.2x and
2.5x magnification of the viewfinder image, which makes focusing on the
matte surface easier and includes diopter correction to assist eyesight.
If possible, increasing the light on the subject should take care of
most of your problems. Oly makes special TTL flashes for just this use,
but they cost money.
Finally, a related question. Are there any "reasonably cheap" (< $50) tripod
attachments that would help with small movements for this kind of work? Trying to bump the
tripod up or back by an inch or less is really an annoying experience. I've seen the fancy
rail setup, but that seems more like a copy stand kind of thing, not something easily tossed
in the fanny pack and taken on a hike.
Let me know if you find one!
Moose
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