U of S | Mailing List Archive | alt-photo-process-l | RE: more 15x15 camera

RE: more 15x15 camera

The "normal" (length-of-the-diagonal) lens for 15"x15" would be about
21-1/4" (~540mm) so your 610mm (24") is going to be just a tad long for
normal, but well within the range of 4x5 folks debating whether 210mm or
180mm is better.

To focus a 1:1 lifesize image (image on film the same size as the object)
you need to be at twice the infinity focus, so, 610 x 2 = 1220mm, or darn
close to 48".  If you started photography using smaller large formats, you
probably had a bellows that, like neal said, would go to between 2 and 2-1/2
times normal.  You probably need length that if you're going to get closer
than ~6' to your subjects with your lens.

Maybe a good rule of thumb if you're only going to shoot landscapes without
extreme movements or those little foreground objects, is that you want at
least 25% longer than your focal length, which would be 30".  But that is
really limiting, creatively speaking.

But say you want to do occasional lifesize work, and you want some movements
and some squish for focal length inaccuracy (That "610" has an accuracy
attached to it, but I'm not sure what it is for Nikon lenses.).  In that
case, go above 48" (say 50" or 52")...on up to 60" inches of bellows.

If you go for a 5' bellows, you may run into a sagging bellows vignetting
your image, so you may have to design a stiffener or middle lifter.

Oh yeah, the mount displacement...all the focal lengths are from the nodal
point of the lens...so, assuming you're using the 610 f9 APO Nikkor, your
nodal point is somewhere around your shutter's leaf plane or iris plane.  If
this is back in the camera from the front standard, you need to add that
depth to the bellows...if the lens is out in front, you could subtract it.
But if it's only an inch or so, just make the bellows a bit long so you can
make movements on a lifesize image, and you should be fine.

Like neal said, "heavy".

	- Dan

-----Original Message-----
From: Neal Wilson [mailto:wilsonneal@hotmail.com] 
Sent: Thursday, September 11, 2008 11:07 AM
To: alt-photo-process-l@usask.ca
Subject: RE: more 15x15 camera

you'd need a little more than 23 inches to focus at infinity, and more than
that if you want to focus closer than infinity.  8x10 cameras commonly have
30" of bellows extension, which is about 2 1/2 times what's required for a
'normal' lens at infinity.  So something like 48" max bellows extension
would not be unrealistic. heavy.
Join me

> Date: Thu, 11 Sep 2008 13:51:24 -0400
> From: zeesme@gmail.com
> Subject: more 15x15 camera
> To: alt-photo-process-l@usask.ca
> Hello guys
> So I've built the back of my camera and am now at the front standard  
> and building my bellows. The lens is a 610mm Nikon with the mount 1"  
> from the back of the lens. Now the question is, how long do I have to  
> build my bellows?
> Thanks