"Jon Anderson" wrote in message
...
On 5/26/2012 1:26 PM, anorton wrote:

I do not think the apparent multiple images are reflections. I think it
is just due to the waviness of the filter across the aperture. Each
image is formed by a different area of the filter that has a slightly
different wedge angle. The film works because even though it is wavy,
the front and back surfaces remain very parallel and do not deviate the
light.

What I hadn't noticed, being behind the camera, was that things got warm
enough for the little bits of duct tape to start slipping. By the end of
my shoot, the welding lens was a couple degrees out, far exceeding any
possible waviness in the filter itself.
In any case, a proper machined holder for the Baader filter is still a
nice thing to have and beats the rolled and glued paper tube the
instructions show...


Jon

But if you you have a flat, parallel piece of glass at an angle in front of
your lens it will not cause any aberration at all for reasonably distant
objects. Even the very dim, double reflection off the inside of the back
surface and then inside of the front surface will overlap perfectly with the
original image for distant objects.