On Tue, 13 Nov 2001, Steve Goldstein wrote:
Some really quick comments - I've got to get some other stuff done.
> So assuming a perfect bellows which never gets in the way,
> it seems to me that the front opening will ultimately limit
> the amount of relative shift between the front and rear - at
> some point the bellows frame will start blocking light, thus
> imposing the primary limit on movements.
Are you are thinking about rays of light coming from the entire front
standard surface or just from the lens. You do need to remember that the
lens is mounted typically near the center of the front standard, is
usually smallish, and projects a cone of light towards the film plane.
Often the bellows themselves are tapered to make use of this observation.
You'd have to have enough shift to move the lens until part of the film
plane can't see it. I think that the lens coverage would have been
exceeded before you'd get this condition in most cameras.
In other words, it isn't so much the light that gets blocked by the edge
of the box in your example as it is whether or not the opposite edge of
the cone of light has entered the film plane. Even if the bellows blocks
some of the light, that just means that this part of the image doesn't
fall on the film plane. If the lens still covers enough area you could
still compose on the ground glass. If however, half of the image falls on
the internal bellows, and the other half on the ground glass you will only
get half a frame on the film. It won't matter if you make the bellows
bigger. I'll try an ASCII diagram below (you'll probably need to turn off
proportional text to see this correctly):
lens
*
/ \
/ \ <-------- cone of light
/ \
/ | \ |
/ | \ | <---- Box
|---=======---|
film
You could make the box and/or the bellows bigger, but the film size still
stays the same. Any light falling outside the box isn't going to hit the
film in any case unless you move the film too. Did I completely miss the
point?
> It occurs to me in typing this that a possible solution is to
> arrange that the bellows mounts towards the rear of the box,
> perhaps even at the film plane. In this case the problem is
> lessened - now the front edge of the box will eventually hit
> the bellows and block the inbound light, but this happens
> later than in my originally-assumed case.
Often the bellows is attached to the back of the box. I'm
assuming this is a field camera we are talking about? In this case the
so-called rear standard "box" is usually the container into which the
bellows compresses when you fold the camera. The depth of the box needs
to be on the order of the height of the compressed bellows.
> Is this how it's normally done, i.e. mount the bellows closer
> to the back and not the front?
I'd say usually.
> In the case of a removable bellows it seems one would then have to
> remove the back to change the bellows.
Hmmm ... you can glue the bellows to a frame that can be disconnected
from the back. That "could" be done using a quick release mechanism. On
my camera I didn't figure I'd replace the bellows often so this board,
which serves as the back of the box, is attached with screws.
> Maybe this isn't a big penalty since swapping bellows is done far less
> frequently than changing film, or even lenses...
This all depends on your use.
I guess I'd suggest that the usual advise for selecting a view camera
definitely applies to view camera design. You need to decide what kind of
shooting you plan to do, and what lenses you want to use. THEN you can
start making more meaningful choices about what kind of camera you need to
buy, or in this case build. For instance, you probably don't need the
extreme movements like you are talking about if you are shooting
landscapes.
- Wayde
([EMAIL PROTECTED])
_______________________________________________
Cameramakers mailing list
[EMAIL PROTECTED]
http://rmp.opusis.com/mailman/listinfo/cameramakers
