Re: Wide angle question

use pinhole body cap not cap on lens
skippy

At 08:31 AM 7/12/01 -0400, you wrote:
>
>----- Original Message -----
>From: "Johanna Zamora" <jjjulep@yahoo.com>
>
>
>> If my body cap pinhole lens has the same field of view
>> as a 50mm lens, will I have a wider angle if I make a
>> lens cap pinhole lens to fit on my 28mm lens?
>
>No lens cap or a lens cap with pinhole on your 28mm lens still gives you
the same 28mm lens, you just went to a smaller f/stop and -yes- you'll get
more DOF at expenses of difraction (model builders do this all the time).
But a picture made with such set up can't be considered PINHOLE IMAGE 'cause
the glass lens is actually making the image and not just the small aperture.
>
>> I hate to sound like uber dork...but it's further from
>> the film. Or am I answering my own question if I say
>> that it has to do with the optics of the lens?
>
>Yes, it has to do with the optics of the lens.
>
>As you know, the image in the film plane is inverted (left to right, up
side down), in a pinhole camera you can consider that the "invertion" hapens
at the actual pinhole point, the distance from the "invertion" point to the
film is your focal length. Your 28mm glass lens is thick (has many lens
elements) and you can consider it as having an "invertion" point that has 2
parts, the front part and the rear part (they are called principal or nodal
points), you could consider that the image "enters" through the front point
and is inverted only when it leaves the rear point, well, the distance from
the rear "invertion" point to the film for your 28mm lens is 28mm from the
film, even if the front portion of your lens is further away from the film.
>
>When we talk about "wide angle" we are saying that the angle formed by
connecting the "invertion" point (as explained above) and the edges of the
film is some 60 degrees or more, that for 35mm format can only be obtained
if the "invertion" point is at a distance 35mm or under.
>
>There are 2 ways to increase the angle of view: by leaving the pinhole
where it was and increase the size of the film or by getting the pinhole
closer to the film.
>
>Hope I didn't confuse you.
>
>Guillermo
>
>
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Received on Thu Jul 12 19:40:47 2001