At 23:35 5/22/01, Mike Williamson wrote (in part):
I've researched in the archives plus used google to search the newsgroups,
but I'm still at a loss as to which macro to obtain.
My first thought was to get one of the 50mm macros. I already have a 1.2,
1.4 (high serial nbr), and several 1.8 lenses, so I don't plan on using a
50mm macro as my "normal" lens. Most of my reasoning here is that a 50mm
would be easier to hand hold than the 90. Can a 50 be successfully hand
held in daylight conditions and take an adequately sharp photo, assuming
focusing on a flower at minimum focusing distance (without extension
tubes)? I don't have a clue about depth of field with a macro, so I could
imagine a small f-stop requiring a shutter speed that wouldn't be
advisable hand held. If I've got to use a tripod anyway, I assume I would
be better off with the 90mm. True? False? Care to comment?
At macro levels (generally defined as 0.25X magnification and higher [on
film]) the steadiness or stability required to rid camera shake is related
to image magnification, not focal length. Stating the obvious, you can
have the same magnification by using a longer focal length and moving
farther away, or by using a shorter focal length and getting closer. At
the same magnification, going longer or shorter changes "standoff"
(distance from subject), perspective and what the different perspective
does to image depth (unless you're doing copy stand work with zero subject
depth).
I've also used lenses such as the 50/1.2 (without extension tube)
deliberately at its minimum focus position at apertures of f/2.8 and
f/2. The challenge is keeping critical focus on the spot where I want it .
. . camera shake in the image "z-axis" versus the "x- or y-axes."
For field macro work, many like the 90mm and 135mm Macro lenses for the
standoff they offer at the same magnification level compared to using the
50/2 or 50/3.5 Macro. I've used the 85/2, 135/2.8 and 200/4 lenses with
extension tubes for this very reason. The standoff makes it easier to keep
from blocking natural lighting or disturbing insects/spiders/chinchillas
(sorry Erwin, couldn't help that). I've also used extension tubes with
everything from the 18/3.5 through the 35/2 for making macros.
DOF is *also* determined by aperture and magnification, *not* the focal
length. What does this mean? Switching from a 135mm to an 85mm and moving
closer to the subject to maintain the same magnification does nothing to
gain a larger depth of field (at the same aperture); it remains the
same. BTW, this applies whether or not you're making a macro.
One of the things that has helped me with close macros is using a sliding
plate between the camera and normal tripod head that allows moving the
camera a few centimeters closer or farther. Some even use two stacked at
right angles so they can make minor adjustments left and right also.
Hope this helps some with your decision.
-- John
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