From: Steve Shapiro (sgshiya@redshift.com)
Date: 12/19/02-07:34:41 PM Z
----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: <shannonstoney@earthlink.net>; <alt-photo-process-l@skyway.usask.ca>
Sent: Tuesday, December 17, 2002 7:15 PM
Subject: Re: pinhole telephoto
> 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
>
The telephoto lens, 'compresses' the distant view because of the set of
elements [usually] in the rear element set that don't render the light to
the film plane. That same thing could be, perhaps, accomplished with a
double pin hole housed behind the "normal" focal length hole. That way, the
light would be 'stoped' without an effect upon the f- stop.
Some telephoto lenses have a mirror to reflect the distant image and
remagnify it again, so the pinhole could be placed with a mirror behind it,
with another hole, mirror facing the film and an third pinhole for the
mirror to reflect a second, possibly magnified image upon the film.
Sounds good to me, but who's me?
:)
Steve Shapiro
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