150mm G-Claron the WRONG lens for Over 25" Paintings?

"Dr. Slick" <radio913.TakeThisOut@aol.com> wrote in message
news:1d15af91.0402151446.350947bb@posting.google.com...
 > Hi,
 >
 > I got a hold of a brochure for the G-Claron:
 >
 > "The normally used range of linear magnification
is between
 > 5:1 and 1:5. ...the G-Claron may also be used for
distances up to
 > infinity by stopping down to f/22 or less."
 >
 >
 > Ok, so if i understand this correctly, the reduction
is 1:5, so if
 > you take the largest side of 4x5, this would be a maximum
of 5x5=25"
 > on the largest side of the painting.
 > So i was taking about 35" images @f16, so perhaps this
was out of
 > the range of the lens? Or perhaps i really needed f22,
even at this
 > size, and not just for infinity?
 >
 > One fellow at KS said that the G-Claron is mainly for
really up
 > close marco work, like product pics of wallets and purses
and stuff
 > like that. And that some people use it for landscape work
when
 > stopped down more than f/22, because it's a very light
shutter and
 > lens.
 >
 > Then he recommended a 150mm Rodenstock Apo-Sironar-N,
and didn;t
 > charge me for the rental because the pics i took with the
G-Claron
 > didn't turn out (nice, eh?).
 >
 > Said this would be good for 8.5"x11" up to 3'x4', as
well as
 > infinity.
 >
 > The brochure says the optimum aperture for 4x5 is
f16-22.
 >
 > I'll try f16, f22, and f32 tonight!
 >
 >
 > Slick

It should work fine for the paintings. They are not much
out of the optimum correction range. The main aberation
picked up when outside of the optimum object to lens
distance is coma. Coma is proportional to the f/stop so
stopping down gets rid of it. You should be able to work at
f/16 without any loss of quality at the corners.
The APO Sironar-N may or may not be a better lens but its
optimised essentially for infinity (actually for around 20
feet) so the G-Claron is actually more nearly in its optimum
range.
To find the widest f/stop you can use look at the corners
of the image. Check using a small bright highlight, even a
pen light at the corner. When wide open the image may have a
slightly tear-drop shaped smear. As you stop down it will
shrink and finally disappear. That's the largest stop you
should work with. Symmetrical and semi-symmetrical lenses
are automatically corrected for coma when the entire system
is symmetrical but have very substantial cancellation of
coma even at infinity focus. Field flatness and other
aberrations should not be a problem.


--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk.TakeThisOut@ix.netcom.com<!-- ~MESSAGE_AFTER~ -->
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