When using a bellows...

....where should one focus the lens at? I am using the minimum focussing
distance and then focussing with the bellows itself, but I'm wondering if
you always have to be at the minimum distance on the lens?

--
Dallas
www.dallasdahms.com

Dallas wrote:

...where should one focus the lens at? I am using the minimum focussing
distance and then focussing with the bellows itself, but I'm wondering if
you always have to be at the minimum distance on the lens?

It should be set to infinity, I believe. I could be wrong, it's been a few
months since I last checked the charts for my Pentax bellows, and the
100mm/f4 I use on it has no focusing ring. Can't seem to find the
instruction book at the moment.

- Matt White

Dallas wrote:
...where should one focus the lens at? I am using the minimum focussing
distance and then focussing with the bellows itself, but I'm wondering if
you always have to be at the minimum distance on the lens?

It doesn't matter, but if there is a distance scale on the bellows
it will be correct if the lens is set to infinity.

If your lens is one of the fancy kind with floating lens
elements which changes the lens to optimize it for the
focussed distance then it would probably be best to use
it fully extended.

If you are working at greater than 1:1 magnification, it is
usually better optically to mount the lens reversed. In that
case the focusing ring won't normally do anything.

Peter.
--

In article , Peter Irwin
writes
Dallas wrote:
...where should one focus the lens at? I am using the minimum focussing
distance and then focussing with the bellows itself, but I'm wondering if
you always have to be at the minimum distance on the lens?

It doesn't matter, but if there is a distance scale on the bellows
it will be correct if the lens is set to infinity.

If your lens is one of the fancy kind with floating lens
elements which changes the lens to optimize it for the
focussed distance then it would probably be best to use
it fully extended.

If you are working at greater than 1:1 magnification, it is
usually better optically to mount the lens reversed. In that
case the focusing ring won't normally do anything.

It will if the lens has floating elements, as these normally change the
focal length somewhat. Usually, the focal length is reduced as the focus
helix is racked out to close focus. This will give you a bit more
magnification for a given bellows extension, but will also reduce
working distance, and thus increase the lighting difficulties.

Otherwise I agree with what you say.
--
David Littlewood

On Sun, 29 Aug 2004 14:47:39 +0100, David Littlewood wrote:

In article , Peter Irwin writes
Dallas wrote:
...where should one focus the lens at? I am using the minimum focussing
distance and then focussing with the bellows itself, but I'm wondering
if you always have to be at the minimum distance on the lens?

It doesn't matter, but if there is a distance scale on the bellows it
will be correct if the lens is set to infinity.

If your lens is one of the fancy kind with floating lens elements which
changes the lens to optimize it for the focussed distance then it would
probably be best to use it fully extended.

If you are working at greater than 1:1 magnification, it is usually
better optically to mount the lens reversed. In that case the focusing
ring won't normally do anything.

It will if the lens has floating elements, as these normally change the
focal length somewhat. Usually, the focal length is reduced as the focus
helix is racked out to close focus. This will give you a bit more
magnification for a given bellows extension, but will also reduce working
distance, and thus increase the lighting difficulties.

Otherwise I agree with what you say.

Okay, I don't have a reversing mount adaptor, but as I discover more about
the versatility of the PB-4, the more I want to learn. Unfortunately I
don't have a manual, so if anyone is able to give me some kind of
grounding in using the bellows, I would be very appreciative!

--
Dallas
www.dallasdahms.com

Hi Dallas

I'm not a big specialist for bellows, but I think I can learn you some
basics.
First of all, to answer your question: you should focus at infinity,
to get the right magnification and to know the right extention factor.

To know the magnification, you need this: magn. = "bellows
distance"/focal length(of lens you're using).
"bellows distance" (I don't know the right name for it) can mostly be
seen on the bellows: it is the distance between the lens and the film
plane. (there should be a scale on the bellows).

The exposure is also important. You should measure the normal exposure
time with a gray card (18% gray, from kodak). and multiply this time
with the "bellows extention factor".
This factor is: [focal length (of lens) + bellows distance (see
above)]^2 / focal length (of lens)^2.

A small example: bellows distance: 50mm, focal length: 35mm
magnification of the negative will be: 50/35 = 1,43. So something of
1mm in real life will be 1,43mm on the negative!
The "bellows extention factor" will be: [35 + 50]^2 / 35^2 = 5,9
Assuming you have a 'normal' exposure (measured with gray card) of
1/10 second, you will have a new exposure of 0,6s (take 1/2).

You should use a very small diaphragm: 1/16 or 1/22! 'cause you have
an extreme low sharpness distance.

If you use a telelens (200mm) you can go further away from the
subject, so you get increasing sharpness depth. Ideal for flowers or
so.

I hope this will help you out a bit.
Don't hesitate to ask more questions. You may always email me too.

Have fun
Pieter

Dallas wrote in message news:pan.2004.08.29.17.32.11.857000@southafrican ...
On Sun, 29 Aug 2004 14:47:39 +0100, David Littlewood wrote:

In article , Peter Irwin writes
Dallas wrote:
...where should one focus the lens at? I am using the minimum focussing
distance and then focussing with the bellows itself, but I'm wondering
if you always have to be at the minimum distance on the lens?

It doesn't matter, but if there is a distance scale on the bellows it
will be correct if the lens is set to infinity.

If your lens is one of the fancy kind with floating lens elements which
changes the lens to optimize it for the focussed distance then it would
probably be best to use it fully extended.

If you are working at greater than 1:1 magnification, it is usually
better optically to mount the lens reversed. In that case the focusing
ring won't normally do anything.

It will if the lens has floating elements, as these normally change the
focal length somewhat. Usually, the focal length is reduced as the focus
helix is racked out to close focus. This will give you a bit more
magnification for a given bellows extension, but will also reduce working
distance, and thus increase the lighting difficulties.

Otherwise I agree with what you say.

Okay, I don't have a reversing mount adaptor, but as I discover more about
the versatility of the PB-4, the more I want to learn. Unfortunately I
don't have a manual, so if anyone is able to give me some kind of
grounding in using the bellows, I would be very appreciative!