Re:Superimposing 2 images taken with 2 FL lenses

Colin,
We could start writing all sort of lens equations, but there is a word in
your questions that is "key" for any answer, the word is "SUPERIMPOSE",
there is another word -sort of- intrinsic in the word superimpose and that
is "PERSPECTIVE". If you make 2 images of the same object or scene
(tri-dimensional) using 2 different focal length (FL) lenses and you make
them in such a way that the 2 images have roughly the same dimensions, let's
say the scene contains a building and you make the height of the building to
be the same in both images taken with different lenses, when you
superimposed these 2 images you will notice that altho the height
superimposed nicely, any other side of the building does not, this is due to
the change in perspective as you would have to get closer to the building
with your shorter FL and you may have to point the lens up at a greater
angle from the horizontal (compared with the longer FL lens) in order to get
all the building in the image. To get the same perspective, both images
will have to be made from the same distance from the object and with the
same camera angle. Obviously, when you go to superimpose these 2 images,
the one taken with the shorter FL lens shows the object very small and will
not superimpose with the one taken with the longer FL lens. The solution is
to either reduce the size of the image showing a larger object to match the
other image or (better, perhaps) to enlarge the image taken with the shorter
FL lens to match the size of the object of the other one. When you do, you
will see that their perspectives are the same and should match nicely, at
least nicely for "government work"!!. If on the other hand, what you are
trying to superimpose is 2 dimensional (flat) and it will be placed parallel
to the image plane, meaning no perspective involved, then there are ways
(equations) to find out the distance from lens to object so the
magnification is the same in both images, if so, let me know and I will see
if my brain still lucid enough to answer that.

Happy 2007 to everyone!

Guillermo

----- Original Message -----
From: "Colin Talcroft" <ctalcroft@yahoo.com>

> Good to see some activity on the list again. I have a
> technical question I was hoping someone might be able
> to answer.
>
> I have an idea for a photographic project that will
> require exposing two negatives of the same subject,
> one with a lens camera and one with a pinhole (or zone
> plate) camera. I want the two images to be roughly of
> the same size so that one can easily be superimposed
> on the other. Given information such as camera-subject
> distance, focal length (for the lens camera),
> pinhole-to-film distance, etc. Is there any simple way
> to calculate how to create images of equal sizes on
> the film using these two very different cameras?
>
> I suspect that the question may not be clear. An
> example might help: My pinhole cameras generally are
> very wide angle, but my lens cameras are not (usually
> a 50mm lens on a 35mm SLR, an 80mm lens on a 6x4.5
> medium format camera, or a 200mm lens on a 4x5 view
> camera). Say I'm in a studio setting. I want to take a
> picture of a reclining figure with my 4x5 camera from
> Zernike using two frames, making it 50mm from
> pinhole/zone plate to film. I take a picture. Now, I
> want to take another picture of the same subject with
> my 4x5 view camera so that the two fiimages of the
> figure are the same size on the film. With the lens
> camera I can see how big the figure is. With the
> pinhole camera, I can't. I guess what I'm asking is
> this: given the specs of a pinhole camera, can you
> easily calculate the size of the image of the subject
> formed on the film?
>
> Hope this makes sense
>
> Thanks
>
> Colin
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Received on Fri Dec 29 08:17:08 2006