Bellows factor

[Steve M Hostetter]

Can anyone give me the bellows factor for 4 and 6 feet of bellows length.. thx

[aduncanson]

Depends on the focal length of the lens used.

required exposure time/metered exposure time = (image distance/focal length)^2

[Steve M Hostetter]

405mm..lens

[cjbroadbent]

Maybe you could just put a 2-inch object in the set and read the factor off the Kodak BF strip on the groundglass. I mentioned elswhere that I keep a copy of the strip rolled up un a 2" tube.

[Joanna Carter]

405mm..lens
4ft is around 1200mm

6ft is around 1800mm

for 4ft - 1200^2 / 405^2 = 1440000 / 164025 = 8.8x or just over 4 stops

for 6ft - 1800^2 / 405^2 = 3240000 / 164025 = 19.75x or around 5 1/3 stops

[Steve M Hostetter]

Lets say If I used a probe and an 18% gray card would that give me basicly the same reading as an incident reading might ?

[aduncanson]

Steve,

If by probe, you mean the Sinar through the lens meter doohickey, then that automatically compensates for bellows factor (because it is through-the-lens.)

[Joanna Carter]

Lets say If I used a probe and an 18% gray card would that give me basicly the same reading as an incident reading might ?
That depends on whether there is enough light to activate the sensor.

As you can see, the calculation really isn't that difficult :

Bellows length (squared) divided by the focal length (squared) gives you the exposure factor.

So, e.g. for & 210mm lens and a bellows of 420mm, the exposure factor is 4x, thus use 2 stops.

[BradS]

4ft is around 1200mm

6ft is around 1800mm

for 4ft - 1200^2 / 405^2 = 1440000 / 164025 = 8.8x or just over 4 stops

for 6ft - 1800^2 / 405^2 = 3240000 / 164025 = 19.75x or around 5 1/3 stops

Joanna got the first part (the multiplicative factor) correct. However, the conversion to stops is incorrect...

8.8x is 3.1 stops
19.75x is 4.3 stops

[Mark Sawyer]

It's much easier to just measure the aperture diameter through the front element, measure the bellows extension, and divide the latter by the former to get the actual f/stop. Much simpler than squaring one thing, then squaring another, then dividing, then translating the factor.

It keeps you in touch with the simplicity of the focal length/aperture relationship. I never understood why so many large format photographers prefer the longer formula...

[Joanna Carter]

Joanna got the first part (the multiplicative factor) correct. However, the conversion to stops is incorrect...

8.8x is 3.1 stops
19.75x is 4.3 stops
Ooops!! I started counted on the wrong finger :D

[Eric Woodbury]

Here's yet another 2-bit option on how to convert. 405mm is about 16", so call that f/16 and 4 feet is 48 inches, so call that f/45. From f/16 to f/45 is 3 stops. 6 feet is 72 inches which is closest to f/64 (and some change), so a little more than 4 stops difference. You get the idea. It's not very metric, but you can do it with a piece of string.

[aduncanson]

... Much simpler than squaring one thing, then squaring another, then dividing, then translating the factor.


Well I suggested dividing and then squaring, it gets you the same thing and saves a step.

But I just created a table and pasted it into my shooting notebook along with tables for filter factors and reciprocity corrections for my usual film.

Use a tape measure to measure in inches the bellows extension, and find that extension down the first column of the table, then go across to find the f-stop compensation required under the focal length of the lens I'm using in top row of the table.

I have to admit that my table would not go to a 48 or 72 inch extension.

[Steve M Hostetter]

the lens will be a Kodak 405mm 4.5 which is the aperture I'd like to shoot at

film is iso 400

[Joanna Carter]

the lens will be a Kodak 405mm 4.5 which is the aperture I'd like to shoot at

film is iso 400
Neither the aperture nor the film speed have any effect on the bellows factor, it is purely based on the relative length of the bellows to the focal length.

When people use f/stops in the calculation, it is purely a simple mnemonic to help you do the calculation without too much complex maths.

[Kevin Crisp]

Google "salzgeber disc bellows," which takes you to the quick disc .pdf. Print it out and use it, problem solved.

[Steve M Hostetter]

I understand Joanna,,, I thought I might include that info I got a reading at f32.7 so I'll shoot at f11 for iso 400 which is a 4 stop difference..

[Shen45]

ExpoDev.

[Steve M Hostetter]

steve, that a program?

[Steve M Hostetter]

Google "salzgeber disc bellows," which takes you to the quick disc .pdf. Print it out and use it, problem solved.

thx Kevin everyone

[Kevin Crisp]

Just remember to take the disc out of the photo before you take the picture. Unless you're really good at retouching.

[Steve M Hostetter]

Kevin, well I downloaded it and used it and the disc is measuring 3 1/2 times the on the dipstick thingy and that comes to 7 stops ,, bellows are 68" long

does that sound right

[Steve M Hostetter]

I happen to download Jason Brunner's bellows thingie and it says 4 1/3 stops ..

thx again Jason,,, and to everyone else that responded

[Dan Fromm]

Um, Steve, what is your lens? I ask because I took a quick look at Brian Wallen's pages and couldn't find a 16"/4.5 Kodak Anastigmat. Or anything else Kodak 16" long, for that matter. Which proves nothing but does raise interest.

I don't know how you're measuring bellows length but if the lens is a 16 incher and extension (diaphragm to film plane is a good approximation) is 68" then magnification should be 3.25, not the 3.5 you measured using the disc. The difference is pretty trivial, though.

Effective aperture is (1 + m) * aperture set. So if you set the aperture to f/4.5, at 3.5:1 effective aperture would be 4.5*4.5 = f/20. Counting on my fingers (6.3, 9, 12.7, 18) says 4.5 stops down, not 7 as you reported.

Another point, and not a fine one. For best results at that magnification you should reverse the lens. Most f/4.5 Kodak Anastigmats (that is what you have, isn't it?) are tessar types, i.e., very asymmetrical and are designed for shooting at distance. You're doing the opposite of shooting at distance (subject is near the lens, film is relatively far from it; at distance things are the other way 'round) so to get the best your lens can give you should reverse it.

Good luck, have fun,

Dan

p.s., if you need an education on photomacrography, buy a copy of Lester Lefkowitz' book The Manual of Close-up Photography. Amphoto. Garden City, NY. 272 pp. ISBN 0-8174-2456-3 (hardbound) and 0-8174-2130-0 (softbound).

[Steve M Hostetter]

Thx Dan for taking the time to explain that ,,, my lens is a Kodak 4.5 405mm portrait lens

[Steve M Hostetter]

Do to f stop needed of f11 the soft focus effect should be non existant.. from what I can see on the GG anyway.. dof is still shallow but interesting
very fun configuation I'll have to post a demo
I have taped bellows in a coat of gaffers tape but shoot in a totally dark room (no shutter) and also cover bellows with 4 yard x 1 yard strip of black velvet cloth.
works great so far , my one film holder is old and flemzy but I try to keep it in the dark from darkroom to studio..

[Kevin Crisp]

Steve: You lost me. I printed it out here at the office. You put the disc in the photo and measure on the ground glass with the little ruler. The left side of the disc is put on the first line, marked "xt f-stop," not on the edge of the ruler. If you measure and get 3.5 in the first column with the lines next to it, then you are shooting almost but not quite 1:1. You would compensate for the bellow factor (read second column) by giving 1.8 more stops of exposure. Since the disc maxes out at 2.0 stops I have no idea how you got to 7 stops.

[Shen45]

steve, that a program?

Yes Steve it is a Palm Pilot programme for BTZS which take full account of Bellows, DOF, Exposure, Filter factors, Reciprocity and development times per each individual sheet based on full and correct film tests.

http://www.viewcamerastore.com/default.php?cPath=27_75

[Kevin Crisp]

If you're using a 16" lens with 6 feet of bellows then I guess you are way beyond the range of the disc and my suggestion was inappropriate to your question. Still a handy tool though. I don't know if multiplying out the exposure factor on the ruler (is that what you are doing, 3 1/2 of the rulers?) would still allow you to get an accurate stop from this tool.

Out of curiosity, what is the object being photographed?

[Steve M Hostetter]

Steve: You lost me. I printed it out here at the office. You put the disc in the photo and measure on the ground glass with the little ruler. The left side of the disc is put on the first line, marked "xt f-stop," not on the edge of the ruler. If you measure and get 3.5 in the first column with the lines next to it, then you are shooting almost but not quite 1:1. You would compensate for the bellow factor (read second column) by giving 1.8 more stops of exposure. Since the disc maxes out at 2.0 stops I have no idea how you got to 7 stops.

Kevin,, No what I mean't is when I place the disc in the scene and view through the camera the disc is 3 1/2 times larger then the ruler ..

[Steve M Hostetter]

antique salt shakers

[Steve M Hostetter]

as far as the BTZS tubes go,,,, it takes 8 ounces for each 8x10 tube, thats 16 ounces of chems to do just two sheets.. The Jobo uses 120ml to do the same two sheets

[Steve M Hostetter]

Film is out of the soup and I have detail ,,, looks like my red duck is red, so they say.

I'm doing a series on small objects. Not just just any small objects but only small objects you expect to see small ,,, balls of steelwool, the inner workings of a pocket watch, toothbrush,,, give me some ideas:D

[climbabout]

Here's yet another 2-bit option on how to convert. 405mm is about 16", so call that f/16 and 4 feet is 48 inches, so call that f/45. From f/16 to f/45 is 3 stops. 6 feet is 72 inches which is closest to f/64 (and some change), so a little more than 4 stops difference. You get the idea. It's not very metric, but you can do it with a piece of string.

Eric has the simplest formula - I used it for years with the most demanding of all photography, in terms of having the correct exposure - tabletop commercial photography on reversal film - before the age of computers and photoshop correction. Works every time.
Tim

[Steve M Hostetter]

I got the answer from the bacon guy :D scroll back

[Steve M Hostetter]

just checking the pan gasket,,, once they start leaking ,, well you know

[Steve M Hostetter]

Hello,, does anyone know what happened to the wisner co.? I can't seem to locate their web page

[Tracy Storer]

The Wisner website seems to have been down for a week or so....maybe I'll give him a call tomorrow and see what's up?

[Steve M Hostetter]

I heard Ron has closed the doors for good..

[Tracy Storer]

FWIW, I emailed RW about the website and he responded "changing servers"

[Don7x17]

The 'inch method' of lens and bellows length is a lot simpler than those hand held computers and all the math formulas. Quick and easy. Even more so if you use a level that has a tape measure.

Even better -- go to a cloth supply store. Buy one of those fiberglas yard long measuring tapes....sew onto the edge of your darkcloth. you'll always have it available and no fumbling around looking for it when you are in a hurry.

[Steve M Hostetter]

Even better -- go to a cloth supply store. Buy one of those fiberglas yard long measuring tapes....sew onto the edge of your darkcloth. you'll always have it available and no fumbling around looking for it when you are in a hurry.

excellent idea Don,, this I can do thx