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TML74
05-30-2013, 08:02 AM
How long should be a bellow on a 20x24 camera if I want to take portrait in a studio ?
I know that it depend on the lens I will use and that I should have a bellow that is twice longer than the lens, so that I can use the 1:1 ratio...
but what would you consider a good lens to make portrait on this kind of camera ?
In fact at the biginning I will only use 16x20 sheet film in vertical position inside the 20x24 film holder that would be in horizontal position...

Sorry if my english is not so good, I hope my questions are clear ?

Thank you, T. Moenne-Loccoz.

Dan Fromm
05-31-2013, 07:28 AM
Well, the normal focal length for 20x24 inches is approximately 800 mm. The normal focal length for 20x24 cm is around 300 mm. A portrait lens would be as much as twice as long as normal.

There are very few 1600 mm lenses available, you might have to settle for a 1200, e.g., Apo-Ronar or Apo-Nikkor. There are more, but not many, choices at 600 mm.

To get a better idea of your choices, see, e.g., http://www.cameraeccentric.com/html/info/goerz_3.html . Rodenstock and Nikon process lenses were made in a similar range of focal lengths and have similar coverages.

TML74
06-08-2013, 03:59 PM
I have asked for a bellow 2,2 meter long, I think that it should be enough if I use a 42" lens. hope so !
Thierry M.L.

TimFox
06-08-2013, 05:28 PM
Note that with ULF such as 20x24 inches, the scale of reproduction (inverse magnification) is going to be small. For example, if you are doing a head and shoulders shot with a field-of-view that equals 20x24 inches (not unreasonable), the magnification is x1 and the required bellows draw is 2x the focal length of the lens. With smaller formats, we only use bellows > 110% of focal length with "macro" shots, but "macro" is with reference to the film size and can be hit easily even at a measly 8x10 inches of film.

Reinhold
06-14-2013, 08:27 PM
I did some testing with my new, soon to be released, 790mm f:5.4 meniscus lens.
I wanted to verify the bellows draw needed to focus at 3 meters (10') and at 1.5 meters (5').
When focused at infinity the bellows draw is 790mm, as expected.
When focused at 3 meters, the bellows draw is 1000mm.
When focused at 1.5 meters, the bellows draw is 1400mm.
I converted a spare bedroom into a camera obscura for evaluating monster lenses.
Unfortunatly, I can't evaluate the field of view with my set-up.
Tim's post gives some insight on what to expect under similar conditions.
Here's a data sheet on the new lens...

Reinhold
www.re-inventedphotoequip.com

TML74
06-15-2013, 04:09 PM
This meniscus lens could be an alternative, but if possible I would like to find a lens that would be a bit soft when wide open and pretty sharp when stopped down. In the 1000 - 1200 mm range what could be possible ? Of course if it could be mounted in a shutter it would be very nice. Perhaps I want too much ? Any idea of that dreamed lens that could cover 20x24 also at infinity ?

Hope that what I said is correct ?

Thank you for your answers. Thierry M.L.

Dave Wooten
06-15-2013, 07:54 PM
Use a 450 mm lens and pull bellows to 800the mm, or the less :)

Dave Wooten
06-15-2013, 07:55 PM
...pull to 800 mm or less:)

Dave Wooten
06-15-2013, 07:59 PM
At 1:1, the human head will fit in an 11 x 14 inch area on your film.

Dave Wooten
06-15-2013, 08:07 PM
You do not need an 800 mm lens or 1600 mm bellows to do 1:1 portrait on 20 x 24 film.

Reinhold
06-16-2013, 07:13 PM
I agree about designing around a sliding box with short bellows for focusing.
A while ago I sketched up a telescopung box with bellows scrounged from a junk 8x10 camera.
In This case the bellows were to be out front, focusing the lens (smaller, lighter, easier to make).
The only downside is you need looooong arms to reach the focus knobs...

After I created a camera obscura in the wife's sewing room, I set this idea aside.
Here's my original sketch...

Reinhold
www.re-inventedphotoequip.com

jb7
08-02-2013, 06:08 AM
Well, the normal focal length for 20x24 inches is approximately 800 mm. The normal focal length for 20x24 cm is around 300 mm. A portrait lens would be as much as twice as long as normal.

There are very few 1600 mm lenses available, you might have to settle for a 1200, e.g., Apo-Ronar or Apo-Nikkor. There are more, but not many, choices at 600 mm.

To get a better idea of your choices, see, e.g., http://www.cameraeccentric.com/html/info/goerz_3.html . Rodenstock and Nikon process lenses were made in a similar range of focal lengths and have similar coverages.

Given that it's conceivable that a portrait taken on 20x24 might be close to life size, then the question becomes much simpler. Since the perspective is determined by the distance between the lens and the sitter, then half that distance will give you the focal length. If the distance between the lens and the sitter is 1.6m, then the bellows draw at 1:1 will be equal to that, and the focal length will be 800mm.

TheToadMen
08-02-2013, 07:09 AM
Given that it's conceivable that a portrait taken on 20x24 might be close to life size, then the question becomes much simpler. Since the perspective is determined by the distance between the lens and the sitter, then half that distance will give you the focal length. If the distance between the lens and the sitter is 1.6m, then the bellows draw at 1:1 will be equal to that, and the focal length will be 800mm.

I'm not used thinking like this and want to understand the theoretics of this logic. Reading your posts leads me to this conclusion. Am I correct?

Size 1:1 means that the object on the negative is the same size as the original. To do so the distance between the object and the lens must be the same as the distance between the negative and the lens.
An other factor is the lens size. But what is the relation here? Why 800 mm lens for 1.6 m bellow draw? This is a factor of 1/2 for an aspect ratio of 1:1. Is this a constant? So a bellow draw of 400 mm would need a lens of 200 mm (besides any image circle problems)?

And what if I use a 1000 mm lens on a distance of 1.6 m? Will this make the ratio 1000:16000 = 1/1.6 giving an aspect ratio of 1:0.8? This would mean a linear relation in the formula. And using a 500 mm lens on 1.6 m will give an aspect ratio of 1:2?

How does this works?

Bert from Holland

BTW: I ordered the 790mm f:5.4 meniscus lens lens from Reinhold this week. My first real ULF lens I want to use for building a large camera. My only experience up to now is only with an old Russian FKD field camera (negative size 18x24 cm, lens 300 mm). See also: http://thetoadmen.blogspot.nl/2012/09/making-dry-plate-glass-negatives-with.html

I also have a Kodak Commercial Ektar 10" (like Ansel Adams used) but I haven't used it yet since I don't have a 8x10" camera yet to put it on.
72354

jb7
08-02-2013, 07:47 AM
I think you might want to replace 'Aspect Ratio' with 'Magnification'. A search will provide simple formulae for magnification and focal length- try http://www.physicsclassroom.com/Class/refrn/u14l5f.cfm

Regarding your 1000mm lens at 1.6m, your magnification will be less than the 800mm example, but your bellows draw will be longer.

You have some nice lenses there, you'll get an idea about magnification by playing with them- a small window in a darkened room will tell you a lot about magnification and coverage...

jb7
08-02-2013, 07:50 AM
Also, due to the inverse square law, which is very strict, you'll lose two stops at 1:1 magnification, so an f/8 lens becomes f/16... Nice portraits on your blog...