From: Joe Smigiel (jsmigiel@kvcc.edu)
Date: 12/17/02-09:15:35 PM Z
Shannon,
I think the issue is getting confused by terminology. "Telephoto" refers to a lens design while "wide-angle" has to do with the circle of illumination and large angle of coverage of some lenses. Telephoto lenses focus at infinity at extensions from the film plane less than their focal length. Most photographers incorrectly call long lenses with narrow angles of view "telephotos" while in fact they are just longer than normal focal lengths. (The "normal" focal length depends on the diagonal measurement of the film format.) Likewise, "wide-angle" in common usage incorrectly refers to lenses with shorter than normal focal lengths. It too is actually a type of lens design.
One key point that I haven't seen discussed here is that*perspective* has nothing to do with lens focal length, telephoto design, etc. Your perspective only depends on your physical location in space. There is really no such thing as "wide-angle," "normal," or "telephoto" perspective. All lenses (or pinholes for that matter) will have the same perspective if located physically in the same point in space. A 6" lens or pinhole camera will have the same perspective as a 3" or 12" or 24" lens/camera if they are located at the same point.
In order to achieve a specific image size of an object, one might choose to use a certain focal length (at a certain point in space) or enlarge the negative format in the darkroom, but this really has nothing to do with physical perspective. Focal length choices may be limited by physical constraints (e.g., using short focal lengths in cramped interiors) but as long as you are in the same physical spot, all focal lengths will produce the same perspective. (You may not be able to include or exclude certain objects at that perspective point with certain focal lengths though.)
On the other hand, "psychological perspective" (for lack of a better phrase) is impacted by focal length, depth of field, physical perspective, subject distance, etc., and I think this is where the discussion has veered off.
In terms of pinhole cameras, I believe the limiting factor on whether the camera is actually a "wide angle," etc., has to do with the thickness of the pinhole shim. You could drill a small hole in a 1/4" thick piece of aluminum to use on a camera, but that pinhole would have a very narrow angle of view compared to the identical diameter hole drilled into a piece of aluminum foil, regardless of the focal distance of the camera.
Hope this helps.
Joe
<<< shannonstoney@earthlink.net 12/17 8:56p >>>
>
> 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
This archive was generated by hypermail 2.1.5 : 01/31/03-09:31:26 AM Z CST