From: Shannon Stoney (shannonstoney@earthlink.net)
Date: 12/17/02-09:58:47 PM Z
>
> 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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