1. ## Re: Missing exposure equation

Agree and before anything I try to guess exposure by Sunny 16 in my head

then meter

then decide which to use

Thank you

Originally Posted by Emmanuel BIGLER
Hello from France!

I have always found, for this kind of "photographic" calculations where a 4-digit precision is useless, that a good ol' dedicated analogue slide rule is more useful than any computer system, be it an expensive mobile phone

Can serve as an exposure meter, based on the legendary "sunny-16" rule!

2. ## Re: Missing exposure equation

Winnie-The-Poo sometimes referred to himself as " . . .a bear of very little brain . . " then made some simple or common sense evaluation of a situation. I often feel the same way about myself, or maybe I am just lazy as my mother0-in-law says.

I just can't bring myself to intellectually engage with the complexities of exposure and DOF the way some here do. I do admire and respect the pool of experience and knowledge here, it is deep and wide.

I tend to use two lenses most; a 150mm and a 210mm. To adjust exposure, I measure bellows extension from the GG to the lens board. I know there are other, more technically correct ways to make this measurement. Then I adjust the exposure for the 150mm by 1/3 stop for each inch of extension beyond 6 inches. For the 210mm, I open up by 1/4 stop for each additional inch of extension beyond 8 1/4 inches. This has worked pretty well for me in the field and in indoors. I can do this in my head with a chil wind spitting sleet. Someday I may p;ut an inch scale or infinity reference marks directly on the camera.

I may have misunderstood the op and discussion. If so, I apologize.

3. ## Re: Missing exposure equation

Jim Noel above spoke to the technique I have used for a long time.

You only need to know the focal length of your lens in inches and the extension of the bellows. So a 150mm lens is a 6 inch lens, and a say 12" extension on the bellows. Just change the unit of your numbers to Apertures: 6" becomes F6,

and 12 inches becomes F12. So the difference is F6 to F12 or 2 stops. By the way, anytime your extension is double the focal length, you are at life size, and the compensation is always 2 stops by the way. And the object you are focused on will be the same distance from the lens board as the film plane is on the back side of the lens (the extension) So with our 15mm lens at 300mm extension we are at 300mm or 12" from the subject, and at full life size.

And at 1.5 times the focal length, you are at 1/2 life size. and it is a 1 stop compensation. Also you should compensate mostly through shutter speed as otherwise you lose depth of field if you open the lens too much.

Rod

4. ## Re: Missing exposure equation

Originally Posted by Jim Noel
Use full apertures to get a very close estimate of needed aperture.
Lets say you are using an 8" lens. You measure the bellows extension and find it to be just under 11". from 8 to 11 is one stop. Open our lens one stop and forget the complicated math.
Yes, that's the way I do it.