From: S Wang (stwang@direcTVinternet.com)
Date: 12/17/02-10:10:49 PM Z
Shannon,
Pinhole or lens, there is no difference between images made with a
telephoto or with a long focus, as long as the focal lengths are the
same. That is, the perspective is determined by the focal length.
Period.
Technically, as someone else pointed out also, you cannot make a
pinhole into "telephoto", because by definition a telephoto has a
shorter physical length for its focal length.
At long focal length, a pinhole certainly CAN give you the same
Giacomelli-like flattening effect. I wonder whether you can obtain as
good sharpness as wide angle pinhole images though. Try it and let us
know.
By the way, it is critical that the camera does not move during the
long exposure. Not even a little bit. Which may not be that easy with
the bellows completely extended and the exposure going to be so long.
Remember all the talk about reciprocity failure? Let's see, f/750 is
about 12 stops from f/16, so going by "sunny 16" rule, it's 8 seconds
in bright sun with ASA 400 film, before reciprocity correction.
Looking forward to your results.
Sam Wang
> > At 2:23 PM -0800 12/17/02, Shannon Stoney wrote:
>>>Katherine wrote:
>>>
>>> One interim solution I've come up with
>>>> is to fix a pinhole to a lensboard and stretch the bellows out as far as
>>>> it will go, which is around 30".
>>>
>>>That's interesting. So, in effect that makes a pinhole telephoto aperture?
>>>
>>>--shannon
>
>Sam wrote:
>>
>> No, Shannon. Not a telephoto. Just a long lens. A telephoto lens of
>> 30" focal length will physically measure maybe just 10".
>>
>> If you load your 8x10 holder with a piece of 35mm film and put it
>> behind your 12" lens, you'll get a narrow field of view, but the 12"
>> lens would not have transformed into a telephoto lens.
>
>But, what if you change the pinhole aperture to have a focal length that
>matches the bellows extension of 30"? I'm looking at the chart in Eric
>Renner's book on p. 124 where he gives different pinhole sizes for different
>focal lengths. My pinhole camera is six inches deep, takes 8x10 film and
>has an aperture of f352. That's the "correct" pinhole aperture for
>sharpness at six inches focal length. So it's wide angle and it's in focus.
>If you wanted it to be telephoto and in focus, couldn't you increase the
>bellows length to say 30" as Katherine says, and make an aperture that would
>cause the image to be in focus, ie the "correct" aperture for a 30" focal
>length? (Eric's chart would say 1.0267 mm, or f750.) Wouldn't that be like
>making a pinhole telephoto image, in the same way that my camera makes a
>wide angle image? I wonder if the image would look like a telephoto image,
>sort of, taken with a lens.
>
>--shannon
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