Bellows extension factors

[Mark_Se]

Do I have to take care of the bellows extension factors to get the right exposure when shooting architecture (interior and exterior)? I mostly shoot with 65mm and 90mm. Or is this just an issue when shooting stuff like portraits?

[Joanna Carter]

The only time bellows factor comes into play is, roughly, when the distance to the subject is less than 10 times the focal length. Thus, for a 90mm lens, when the lens to subject distance is less than 900mm (3ft).

e.g.

90mm lens with a bellows length of 127mm

127^2 (16,129) / 90^2 (8,100) = 1.99 (1 stop extra required)

90mm lens with a bellows length of 180mm

180^2 (32,400) / 90 ^2 (8,100) = 4 (2 stops extra required)

[Mark_Se]

thank you Joanna!

[darr]

Or another way is simply measure your bellows. For example, if you have 90mm or less of bellows extended with a 90mm lens -- no need for exposure compensation. If you have more than 90mm with a 90mm lens, then exposure compensation is needed. An easy way to determine how much is for each 25% of increased bellows extension, add 1/2 stop of exposure. For a 50% increase I add one stop, etc.

Steve Simmons of View Camera magazine has published this method and I have been using it ever since. Just carry a cloth tape measure (used in sewing) in your bag, and your good to go. :)

Darr

[Ron Marshall]

This is useful:

http://www.calumetphoto.com/item/CC9201/

[drew.saunders]

Or another way is simply measure your bellows. For example, if you have 90mm or less of bellows extended with a 90mm lens -- no need for exposure compensation. If you have more than 90mm with a 90mm lens, then exposure compensation is needed. An easy way to determine how much is for each 25% of increased bellows extension, add 1/2 stop of exposure. For a 50% increase I add one stop, etc.

Steve Simmons of View Camera magazine has published this method and I have been using it ever since. Just carry a cloth tape measure (used in sewing) in your bag, and your good to go. :)

Darr

I use a variation on this method, but, rather than trying to measure where the film plane is, I measure based on the front and rear standards. For example, when I focus my 165mm lens at infinity, for my Ebony 45SU, the distance from the front of the metal vertical part of the front standard to the rear of the metal vertical part of the rear standard is 130mm. Then, using Steve Simmons' method, I know that adding 1/6 of the fl is 1/3 of a stop, +1/4 fl is 1/2 stop, etc., so I'd make a chart and attach it to the lensboard, something like this:
158mm = 1/3 (that's 165/6 + 130. The film plane to nodal point is 165/6 + 165, but that's harder to measure)
171mm = 1/2
185mm = 2/3

etc. up to about 340mm, which is as far as the camera extends. (365mm of extension, but I'm not measuring from the film plane to the lensboard, remember.)

So, for the OP, for a 90mm lens, let's say on your camera that when focused at infinity, you get 110mm between two easily found landmarks on your front and rear standards (just use the same landmarks). Then, 90/6 + 110 = 125mm for these landmarks to be 1/3 of a stop compensation (which you may not bother with), 90/4 + 110 = 133mm (unless you can really measure 132.5mm on your tape measure) which needs 1/2 of a stop, etc.

Drew

[Leonard Evens]

Or another way is simply measure your bellows. For example, if you have 90mm or less of bellows extended with a 90mm lens -- no need for exposure compensation. If you have more than 90mm with a 90mm lens, then exposure compensation is needed. An easy way to determine how much is for each 25% of increased bellows extension, add 1/2 stop of exposure. For a 50% increase I add one stop, etc.

Steve Simmons of View Camera magazine has published this method and I have been using it ever since. Just carry a cloth tape measure (used in sewing) in your bag, and your good to go. :)

Darr


It might be noted that the rear flange focal length for short focal length lenses is often less than the actual focal length. For example, when my 90 mm lens is focused at infinity,. the standards are about 87 mm apart. As in this case, the difference is usually small enough that it doesn't invalidate the method suggested above.

[kev curry]

Just carry a cloth tape measure (used in sewing) in your bag, and your good to go. :)

Darr

Or another great idea picked up here is... sew the cloth tape along one edge of the dark cloth and you wont even have to go into your bag;-)

[aduncanson]

Or another great idea picked up here is... sew the cloth tape along one edge of the dark cloth and you wont even have to go into your bag;-)

I have been thinking about this kind of solution and it occurred to me that rather than a standard tape one could use a logarithmic rule marked in stops; where say 50mm was marked "0" , 71mm > "1", 100mm > "2", 141mm >"3"...

Do the math to fill in the 1/3 stops (or maybe finer) marks. Then to use the rule you measure the bellows in stops and subtract the stop value for the particular lens when focused at infinity. That difference is the necessary bellows factor correction.

A more subtle correction is needed for telephoto and retrofocus lenses. (This is true whether you measure in inches, cm or stops as I suggest.) Each of those may require its own "origin" to measure from. It could be found by focusing at infinity, placing the stop (or inch or cm) value of the focal length on the front standard and note where the film plane falls.

[Jim Fitzgerald]

Or another way is simply measure your bellows. For example, if you have 90mm or less of bellows extended with a 90mm lens -- no need for exposure compensation. If you have more than 90mm with a 90mm lens, then exposure compensation is needed. An easy way to determine how much is for each 25% of increased bellows extension, add 1/2 stop of exposure. For a 50% increase I add one stop, etc.

Steve Simmons of View Camera magazine has published this method and I have been using it ever since. Just carry a cloth tape measure (used in sewing) in your bag, and your good to go. :)

Darr

I've been doing this for years and it works fine for all of my formats. 4x5,8x10,11x14 and 8x20. Good luck.

Jim

[Michael Gordon]

I don't like to mix mathematics with my photography, so I go the very simplified route and use the FREE QuickDisk (http://www.salzgeber.at/disc/). No brain necessary.

If you're uncertain if you need to compensate, stick the QuickDisk in the scene, and measure it on the GG to see if the exposure needs compensation. Nice and easy!