Bellows extension and exposure

[Jon Shiu]

Robert,

Bought Simmon's book and read a little on this last night. I thought the extension was 50% for 1/2 stop. Have to reread that part. One of the best things about the view camera and movements is the whole composition thing under the cloth. Exposure though, especially with the much higher film costs at 8x10, is something I'd like to have nailed down before releasing the shutter.

Thanks

Hi, the rule of thumb would be 1 stop for bellows measuring 150% of focal length and 2 stops for 200% of focal length.

Jon

[darr]

Has anyone ever noticed Steve Diehl's simple math mistake on his RIT.edu page:

http://www.rit.edu/~swdpph/bef.html

He either meant a BF of 1.23 or a lens of 120mm. I tried to e-mail him about, but cannot find his link. Anyone know him?

[Alan Davenport]

I am wondering about significant movements affecting exposure through contorted belows distances.

While you're correct, that bellows contortions can create exposure differences across the film, I doubt if you'll need to worry. If you do manage to create a scene that goes from 1/2 lifesize all the way to infinity (for example) you could use a soft-edged 1-stop ND grad to fix it. It would be pretty difficult to get that much movement, or to find a situation where you'd need it.

FWIW, the worst I've managed to do is the following image. Movements, both tilt and swing, were sufficient to exceed the image circle of the lens if done only on the front, so I had to use rear tilt and swing as well. The trillium in the foreground was roughly 1:4 magnification, with the BG at infinity (of course!) Calculated exposure compensation was 1/2 stop more for the foreground. I took the shot when the natural light brightened a little in the near zone, and as you can see the foreground received much more exposure than the BG; I actually brought up the levels in the BG to arrive at what you see. Short answer to your question: don't worry.

[Brian Vuillemenot]

I use a Horseman light meter that slips in the back and meters through the lens and any filters I may be using. No need to worry about bellows extension- the meter takes this into account. It's dead-on at least 90% of the time (after I calibrated it for Velvia). I don't know why more people don't use these things- they make LF photography much simpler, so I can worry about more important things like composition, movements, and light rather than exposure.

[Robert Oliver]

I did the calculations at home using something similiar to Walter's formula and just copied the results to a clear plastic ruler. Whenever I rack out the bellows, I just whip out the ruler and measure from lens to film plane and expose according to the recomendation of the ruler. weighs nothing. costs nothing. I marked in full stops, and estimate half stops if I fall in between.

[steve simmons]

For every 25% add 1/2 stop of exposure. Get a cloth tape measure and keepit in your bag. It is light and takes very little space.

steve simmons

www.viewcamera.com

[squiress]

Thanks to all. One more question, relates to Telephoto lens. Does the disk and 25% equal one half stop work there as well?

Stew

[JW Dewdney]

Say you are using a 150mm lens. Drop the zero and think of it as 'f15'. Now focus on your subject and measure the extension between the standards. Say your total extension is 200mm. Again, drop the zero for 'f20'. The difference in exposure between f15 and f20 is very near or just shy of one full stop. Make the change and go. I have used this method sucessfully for years even shooting transparency emulsions and it has worked well.

That's too complicated for my liking. I just measure the extension, divide it by the nominal (infinity) extension and then square the result. That gives your exposure factor.

e.g. 150mm lens at 300mm extension (1:1)
is (300÷150)=2. 2 squared is 4. Compensation is 4x.

50mm lens at 500mm extension
is (500mm÷50mm)=10. 10 squared is 100. Compensation is 100x.

As for issues with tilts, swings, etc.. just measure from CL (centerline) of lens board (nodal pt. of course) to center of film. Or if you want to be the most anal person EVER - you could purchase graduated ND filters for each 5 degrees of swing, assuming you could find the right densities! (LOL)

[steve simmons]

Yes for telephoto lenses.

steve simmons

[Kirk Gittings]

Calumet sells a device similar to the above mentioned Quick Disk that is laminated. Put the small square in your scene and measure the compensation on the ground glass. I had a tape measure and have done the math, but find this "visual" technique is much faster and more convenient for me.

Cheers!

I downloaded the Quickdisk today for a product shoot as I could not find my Calumet. the Quickdisk worked like a charm.