bellows extension factor - getting the hang of it - any suggestions : )!!! ??

[Ig Nacio]

Hi,

How are you guys doing? I hope doing very well : )!!!

I have used more a 75mm. lens. than another longer lens that
I also use sometimes. The other lens is a 135mm. lens

The 75mm. - I should perhaps be a bit embarrassed to say - is shot like a
point and shoot camera. I mean, I frame for and focus usually at a
distance of at least eighteen feet, and onwards, just depending on
what is photographed. (That is some six meters and onwards, and I
rarely frame or focus any shorter). My diafragm is set between f/11
and f/32, but recalling, I usually use it at f/16. Shutter speed is of 1/60tth
of a second or slower, depending on light conditions.

The 135mm., when used, is also used with the same characteristics as above,
more or less.

It is done in a way that both focal lenghts and the camera are used,
as I mentioned, almost like a point and shoot camera.

My negatives have come out ok. after developing. With more practice,
they can be better, I think, but are ok for the most part.

Being the photos framed and focused under the circumstances commented
above, the compensation needed, as you can see, is not much. I mean,
compared to wanting to shoot a 210mm. or 240mm. lens focused at
nine feet, (or some three meters), the compensation needed would be greater
for those longer focal lengths.

I like the way John A. Cook explains and uses the 'bellows extension factor'
method, here explained, (please scroll down once you have entered the link,
and please look for his name):
https://www.largeformatphotography.info/bellows-factor.html

The thing that for me stills feels a bit awkward is the fact that if I want to photograph
any longer focal length focused at shorter distances like three, six, or nine feet,
it can not yet be that easily done for me, like a point and shoot. Unless one uses
a flexometer or meausuring tape, one can not know how much to compensate.

It takes time and it can be boring part of the process. How did you get the hang of it?

It's ok if there are no 'shortcuts' to it. It is perhaps the 'inertia' down in me that kind of
comes back to me, and wants to inhabit me, and wants it to be easy-peasy in this sense,
like 35mm. and medium format where these steps are (almost) inexistent.

Thank you in advance, very kind regards!

Ig : )!!!

[xkaes]

The only short-cut I know of is to do the calculations ahead of time. For you, this is easy with two lenses. Figure out how much extension creates how much exposure change for each lens. Then transfer this exposure information to a tape measure or to the camera itself. This will depend on your camera. You can stick/etch/write/paint marks on your camera bed or rail for +1/2f, +1f, etc. A lot of people do this when they only use one or two lenses. Many 35mm bellows (that are designed for a specific lens) and macro lenses have the exposure compensation etched into the rail of the bellows or barrel of the macro lens -- (below is a Minolta bellows for example). You can do the same sort of thing.

Then, after you focus, look at your marks to see if adjustment needs to be made.

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[Mark Sawyer]

There is no such thing as "bellows extension factor". All those calculations are just a work-around for not being able to figure out your f/stop at any focusing distance other than infinity.

It's all in the word "f/stop". "f" is your focal length, from lens to ground glass. "stop" is the diameter of your aperture opening. Divide "f" by "stop" and that's your "f/stop".

Say you have an 8-inch lens with a 2-inch aperture opening. At infinity you have 8 inches of bellows draw. 8/2 = 4, so you're shooting at f/4. Focus a little closer and you have 10 inches of bellows draw. 10/2 = 5, so you're shooting at f/5. Focus closer still and you have 12 inches of bellows draw. 12/2 = 6, so you're shooting at f/6.

I don't know why people make it so complex...

[Maris Rusis]

....... I don't know why people make it so complex...

This is one of the best threads on exposure compensation for close focus work but much of it can be arithmetically challenging in countries that don't have inches and vulgar fractions of inches. That is nearly everybody except the good ol' USA. We who have only millimetres, and the metric camera and lens makers, are condemned to calculations that can look like numerical alphabet soup.
What's a 37.5mm entrance pupil in a 210mm lens? Answer: 5.6 of course but it didn't come as easy as Mark Sawyer's clear and instructive example of a 2 inch aperture in an 8 inch lens being f4.
Thank goodness I don't use my Wollensak 6 1/4 inch f9.5 lens with its aperture size of 21/32 inches for close-ups. But this fine thread shows me how to do it if I must.

[Alan9940]

I use a sewing tape measure to measure the distance from the film plane to the lens center. Convert the lens focal length and prior measurement to the closet f-stops and the difference is your exposure adjustment. For example, let's say you have a 150mm lens that's racked out 14". Convert the lens to f/8 (yeah. I know it's roughly a 6-inch lens), convert the measurement to f/16 and you're looking at +2 stops more exposure needed. This method certainly isn't exact, but it's close enough and easy.

[xkaes]

I have absolutely no idea what the actual maximum diameter is of any of my lenses is -- in mm or inches. I know I could figure it out, but I just have a ruler (the length of my bellows) marked with a line for each of my lenses, and the amount of compensation that I need to make according to the amount of extension. If you only use one lens, you can mark it on your camera in some way. If you use two lenses, mark one on one side, and the other on the opposite side.

[Ig Nacio]

Hello,

Thank you for your very nice answers to my message : )!!!

Please allow me a bit of time to write back to you properly.

I am also still 'digesting' some of the technical information
you have given me. I find it fascinating.

Thank you very much again!

Very kind regards,

Ig : )!!!

P.S. Thank you to the moderator for having placed this forum question in the correct subforum, that is this one.

[JMO]

Try the Reciprocity Timer app on your smartphone to determine your bellows extension factors and/or film reciprocity factors - 'easy peezy....

[Alan Klein]

Try creating this simple disk that will tell you what factor to use.
https://www.salzgeber.at/disc/manual.html

[xkaes]

One thing I like about this QUICK DISC is that it doesn't mess with magnification formulas, or INCHES (instead of mm), or knowing the physical diameter of each of my lenses. It just uses the two things you need that are easy to know -- focal length of the lens & amount of extension.

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[Kevin Crisp]

I'm with Alan. Once I got the quick disc, printed it out and laminated it and put it in the camera bag, I stopped worrying about this.

[Alan Klein]

I'm with Alan. Once I got the quick disc, printed it out and laminated it and put it in the camera bag, I stopped worrying about this.

Just remember to remove it from the camera view after using it. ;)

[Kevin Crisp]

That wouldn't be fun to spot out of the print....

[Doremus Scudder]

The calculations are not difficult. Make a table with exposure factors for each lens you own at different bellows extensions. Then keep that and a small tape measure with you. When working close-up, its as simple as measuring the bellows and consulting the table.

Best,

Doremus

[monochromeFan]

The calculations are not difficult. Make a table with exposure factors for each lens you own at different bellows extensions. Then keep that and a small tape measure with you. When working close-up, its as simple as measuring the bellows and consulting the table.

Best,

Doremus

THis is getting strange... its almost like the tables and scales that are found inside teh Time Life Library Photography book series when dealing with bellows and 35mm macro photography

[Doremus Scudder]

THis is getting strange... its almost like the tables and scales that are found inside the Time Life Library Photography book series when dealing with bellows and 35mm macro photography

It's exactly the same thing. Camera format or lens focal length make no difference to the inverse-square law. Once you extend the bellows away from infinity focus, the intensity of the light starts to weaken at the film plane. At twice the infinity focus, you get just 1/4 the light.

FWIW, I simply made a table that I carry with me that has columns for all my lenses; 75mm, 90mm 135mm 150mm 180mm 200/210mm 240mm and 300mm. That and a tiny tape measure are all I need to deal with bellows extension factors.

Best,

Doremus

[Robert Opheim]

I do the same thing as Doremus! I have calculated distances from the center of lens to film plane and shown that correction on a 3 1/2 x 5" cards that I keep in my camera case. I have a number of different lens lengths - So each lens has a different card. I measure with a very short tape measure the distance and refer to the card for that lens and length for bellows factor. I also look at the film info sheet for reciprocity correction if I am using a long exposure. Added correction for filters used. For black and white I make those corrections on the meter as I decide where to place the shadows and what development for highlights to give each negative. I mark the film holder for that development. For color I don't use a zone system process - so I place the exposure on the meter ring - with the corrections listed above.

[Mark Sawyer]

Okay, here's probably the simplest method for math-o-phobics:

Close down the aperture of your lens to 1 centimeter wide, measured through the front element. Put a little mark on your aperture scale there.

When photographing, just close to 1 centimeter mark and measure your bellows extension in centimeters. That's your actual f/stop. 25 centimeters bellows extension? That's f/25. 36 centimeters bellows extension? That's f/36.

Then you can open or close any number of stops using the positions of the conventional stops on the scale. The only math is reading the measurement of the bellows and counting stops up and down.

[maltfalc]

just convert your bellows extension to f-numbers. if you have a 140mm lens focused at a distance that adds 60mm of bellows extension, giving you an effective focal length of 200mm, that's f/1.4 to f/2.0, one stop darker.

[Kiwi7475]

But here's the real question... if I use a 200 mm lens focused at a bellows extension of 140mm, do I gain 1 stop? ;-) (ignore that whatever I photograph won't be in focus)

[Mark Sawyer]

But here's the real question... if I use a 200 mm lens focused at a bellows extension of 140mm, do I gain 1 stop? ;-) (ignore that whatever I photograph won't be in focus)

Yes. You've concentrated the same amount of light in a smaller area, regardless of focus.

[Kiwi7475]

Yes. You've concentrated the same amount of light in a smaller area, regardless of focus.

So Tele lenses, which require less extension than the focal length to focus at infinity, get a light advantage (“are faster”) than the theoretical equivalent non tele design (meaning for a constant diameter of the entrance pupil)?

[Mark Sawyer]

So Tele lenses, which require less extension than the focal length to focus at infinity, get a light advantage (“are faster”) than the theoretical equivalent non tele design (meaning for a constant diameter of the entrance pupil)?

Remember that calculating the f/stop means measuring from the rear nodal point of the lens to the focal point. On telephoto lenses, the rear nodal point is in front of the lens, while on conventional designs it's within the lens, so it's a wash. No advantage or disadvantage.

[Kiwi7475]

Remember that calculating the f/stop means measuring from the rear nodal point of the lens to the focal point. On telephoto lenses, the rear nodal point is in front of the lens, while on conventional designs it's within the lens, so it's a wash. No advantage or disadvantage.

Makes sense — there’s no free lunch I guess. Thanks!

[rodney@theloughroad.com]

Hope this is ok to ask here but…

Does anyone remember this thing?
The Quick Stick - For Large Format Bellows Camera Exposure Calculations