Exposure compensation with bellows question.

[Mark Sawyer]

Or...

You can measure the bellows extension and aperture and divide to find your actual f/stop.

It's in the name "f/stop".

"f" means "focal length"

"/" means "divided by", (or in fractions, "over").

"stop" means "the diameter of the aperture stopping the light".

It's not that hard, people...

[Doremus Scudder]

Or...

You can measure the bellows extension and aperture and divide to find your actual f/stop.

It's in the name "f/stop".

"f" means "focal length"

"/" means "divided by", (or in fractions, "over").

"stop" means "the diameter of the aperture stopping the light".

It's not that hard, people...

Well, getting situated in front of my camera lens to measure the apparent aperture usually is either impossible or puts me in mortal danger And, I have similar problems placing a target in the scene; either it won't stay put or the delicate subject may get damaged. So...

Using the method:

Ext² / Fl² = Exposure Factor
Where Ext = Bellows extension measured from film plane to lens nodal point (middle of the lens for most designs)
and Fl = The focal length of the lens.

I made a small chart for all the lenses I normally use (75mm 90mm 135mm 210mm 240mm 300mm) working backward from the exposure factor series; 1.5, 2, 3, 4, 5, 8, 12, 16, 20. (that's exposure changes in stops of 2/3, 1, 1 2/3, 2, 2 2/3, 3, 3 2/2, 4, and 4 2/3 respectively). I simply carry the chart with me in the field (in my exposure record notebook)along with a small tape measure. If I think I need to add exposure to compensate for bellows extension, I just measure film plane to lens board and look up the factor for the lens I'm using on the chart. That seems to work well for me in the field with my wooden folders.

If I were doing lots of studio work with a monorail camera, I might be sure I have a scale mounted on the camera rail to save a bit of time.

Here's my chart for your extending pleasure
BellowsExtension.pdf

Best,

Doremus

[Mark Sawyer]

Well, getting situated in front of my camera lens to measure the apparent aperture usually is either impossible or puts me in mortal danger ...

I made a small chart for all the lenses I normally use...

If measuring the aperture is difficult in your usual situation, just make a chart of the aperture sizes at the standard f/stops. Say you have a 210mm lens; at f/5.6, divide 210mm by 5.6, your actual aperture size is 37.5mm. At f/8, 210mm divided by 8 is 26.25mm, etc. Now just measure your bellows extension and divide by your aperture size and you'll have your actual, real, working f/stop value.

Or you can divide the square of this by the square of that and get another number to multiply your exposure by...

[Doremus Scudder]

If measuring the aperture is difficult in your usual situation, just make a chart of the aperture sizes at the standard f/stops. Say you have a 210mm lens; at f/5.6, divide 210mm by 5.6, your actual aperture size is 37.5mm. At f/8, 210mm divided by 8 is 26.25mm, etc. Now just measure your bellows extension and divide by your aperture size and you'll have your actual, real, working f/stop value.

Or you can divide the square of this by the square of that and get another number to multiply your exposure by...

Well, I've made the chart and have it with me, but it's just the exposure compensation. That said, all I have to do is measure and apply the appropriate compensation; zero calculating anything. If I were doing lots of macro work (like you do), having a real, working f-stop value would likely be valuable. Still, I get around the whole depth-of-field calculation thing by using a focus-spread method of finding the optimum f-stop, which works regardless of bellows extension.

More than one way to peel the onion

Doremus