RE: [APML] 2 inch camera adapter question

["Frank Parrotta (Navy Yard)" <FParrotta@TSC.COM>]

Brian,

As John has said, you really can't use the 1.25" if you want to illuminate
as much of the 35mm frame as you can.  However, you're still not home free.
The camera T-ring will also vignette the frame as well - the amount
depending on the focal ratio.  I find that the corners get pretty dark but
the central core of the frame is usable with some vignetting removal
processing.  If you want to get an idea of just how much light falloff
you'll have to content with, set up your scope with the camera attached and
aim it at an evenly illuminated source (e.g., blue sky, white painted wall,
etc.).  Set the shutter to "B" and open the camera back.  Fire the shutter
and look through the camera back opening (where the film would be) and
notice the illuminated circle produced by the objective.  Move your eye
around to the frame's edges and corners - the amount of the illuminated
circle that is obscured at each location will be proportional to the amount
of vignetting you will get at those locations.  Hope this helps.

Frank

-----Original Message-----
From: Brian Larmay [mailto:astrobri@ameritech.net]
Sent: Sunday, March 02, 2003 3:40 PM
To: astro-photo@seds.org
Subject: [APML] 2 inch camera adapter question


Hi!

What are the advantages photographically of a 2 inch camera adapter over a
1.25.

Thanks,
Brian


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