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(meteorobs) Normal lens



Ed,
I don't think your definition of what constitutes a normal lens is the same
as what it's normally referred to.  A normal lens for a 35mm camera is
accepted at 50mm.  A 4"X5"'s normal lens is accepted at 6". And for a 2
1/4"X2 1/4" should be 80mm(I don't use this format so I'm not that familiar
with what's normally made).  Anything less is considered Wide
Angle...anything more is considered telephoto. What determines what sized
lens is normal for any given format  is roughly based on the diagonal
dimension of the film used. This is not a precise number. It's often rounded
off to a convenient number, but the lens size is very close to the diagonal
film measurement in all cases...if it's to be considered the normal lens.  

The actual measurements are: 35mm comes out to 45mm.  4"X5" comes out to  6
3/8". 2 1/4"X2 1/4" comes out to 3 1/8" or 80mm.   With a 4X5, you can have a
6" normal lens. If you slide a 120 roll film holder in place of the standard
4X5 film holder, you no longer have a normal lens if you keep the 6". ...you
are using a telephoto then. 

You may be able to pick up Aero camera's or lenses, but it's not that easy.
I've looked already in all of San Diego County...haven't found one yet . The
biggest camera store in San Diego County is called Nelson's Photo. They seem
to have nearly everything...new and used. I buy all my used camera bodies and
lenses from this place.  I'm sure it's not impossible to find Aero lenses
from somewhere...but I wouldn't consider it an easy thing.  As for Press
camera's...yes you can find these in a lot of places still...and they are
relatively cheap compared to the newer models of 4X5's. 

Out of curiosity, how long are your exposures when you are trying to make
spectrographs?  Also, do you know of a source for large enough scientific
grade prisms that have angles at about 30 degrees?  You've already indicated
that diffraction gratings are quite expensive and difficult to find.