Bellows extension

Alan Edward Klein said:

My cellphone has an app that shows a calibrated ruler on the screen. I suppose one could use that in a pinch.

Click to expand...

If you have a phone you have a calculator so use the formula d^2/f^2

I taught this for many years and learned it from a master photography many years ago. You need a small tape measure in inches.

You need to know your lens focal lengths in inches.

Get your composition and focus set.

Say you are using a 150mm lens. In inches 6". Measure the extension with your tape. Say 9" in this example.

Change the unit of the " to Apertures. 6" = F5.6 1/3. 9" = F8 1/3. What is the difference? 1 stop. Also the reproduction ratio is 1/2 life size.

You can fudge a tiny bit, but this works really well.

Focal length in inches for large format lens



FL Inches



47mm 1.8



65mm 2.7



75mm 3



90mm 3.5



100mm 4.0



115mm 4.5



120mm 4.7



125mm 5.0



135mm 5.3



150mm 6.0



162/165mm 6.5



180mm 7.0



200mm 8.0



210mm 8.25



240mm 9.4



250mm 10



300mm 12



360mm 14



400mm 16



450mm 18



500mm 20



600mm 24



Remember, most wide angle designs are quite poor up close,



as are telephoto design lenses.



With Telephoto lenses if you wish to try them, you must use the FFD(flange focal distance) as the focal length to calculate.

Hope some find this helpful.

Rod

Simple table:



So if bellows is out 120mm and you have 90mm FL lens in use, look up 1.3 ( 120/90 ) and increase time by 2.3EV

If you use the tape rule method, use a metric one. That simplifies calculations. And you need to measure between the nodal point of the lens and the film plane itself. With telephoto lenses, the nodal point is different from regular lenses. I put predetermined markings on my little pocket tape rule relative to specific favorite lenses. But then I found an even easier method, applicable to any lens :

Since long bellows extensions are mainly in relation to close-up subjects, I now use the little Calumet visual calculator. You put a square little target temporarily on the subject, then simply compare its size on the ground glass using a special little ruler marked in f-stop correction increments. Although these are no longer made, I believe there are still equivalent products available, or you might find a used Calumet one.

No math needed, nothing electronic or battery dependent needed.

I haven’t read the responses but what I did when I started with a 4x5 I did the formula and for each lens and f stop change I marked a small retractable tape measure with a different color marker for each lens. After composing and deciding the stop, I measure the bellows length and see what exposure adjustment is indicated on the tape for that lens. Did the math once and done.

Dan Henderson said:

simply put, the exposure reading from your light meter will only be accurate when the camera is focused at infinity. To focus on objects closer to the camera the lens must be moved farther from the film plane, and less light falls on the film. So additional exposure needs to be provided to make up for this light loss. The farther the bellows is extended, the more compensation is required.

Click to expand...

that's putting it into a nutshell. Unless you are moving in close, the bellows extension can be largely ignored. I'll attach a free PDF that has a whole section about it.

jeffreyg said:

I haven’t read the responses but what I did when I started with a 4x5 I did the formula and for each lens and f stop change I marked a small retractable tape measure with a different color marker for each lens. After composing and deciding the stop, I measure the bellows length and see what exposure adjustment is indicated on the tape for that lens. Did the math once and done.

Click to expand...

That's what I did as well, but I used a wider strip of paper -- as long as my bellows & top-hat (16.5"), and used both sides -- and laminated it.

One more point. Lots of lenses have flange focal lengths significantly different from their optical focal lengths. That needs to be taken into account when making your calculations.

DREW WILEY said:

If you use the tape rule method, use a metric one. That simplifies calculations. And you need to measure between the nodal point of the lens and the film plane itself. With telephoto lenses, the nodal point is different from regular lenses. I put predetermined markings on my little pocket tape rule relative to specific favorite lenses. But then I found an even easier method, applicable to any lens :

Since long bellows extensions are mainly in relation to close-up subjects, I now use the little Calumet visual calculator. You put a square little target temporarily on the subject, then simply compare its size on the ground glass using a special little ruler marked in f-stop correction increments. Although these are no longer made, I believe there are still equivalent products available, or you might find a used Calumet one.

No math needed, nothing electronic or battery dependent needed.

Click to expand...

Here's a device that you can printout and use to make the determinations. I've only used it for a dry run which seems to work.