1. ## DOF question

I 've asked a question about the diffraction of small f-stop diameter in my last post. And, now I'd like ask about caluculating DOF for my particular shooting situation. As I mentioned before, I am shooting 6 people, who are standing very closely each other in front of black seamless, in the studio using 8x10 with a 165mm super angular lens. Because I want to make people just fit in the frame, the lens is very close to them. (about 30 in.) Then, to make everything in focu s I think I have to stop down to f64 . (Near distance 30in. Far distance 70in) T hen, I'm going to make at least 30in x 40in prints from the neg. Now, I am wondering where to focus. I know that I have to fucus 1/3 of the po int in the area where to be focused and depends on circle of confusion. Since as we know, in the large format, when we move the focusing nob, the size of imag e changes a lot, I 'd like to know the exact point to be focused to get everythi ng in focus. Is there any fomula which I can caluculate the DOF in this particular situation. Thanks Joe

2. ## DOF question

The Rodenstock DOF/Scheimpflug rotary calculator will fit in your shirt pocket and easily calculate this for you.

Many cameras let you focus the lens which does not change the film to subject distance. Some let you focus the film which does change the film to subject distance.

To keep a given extension when focusing Linhof makes some heavy duty focus rails that will let you move the camera front and back to obtain focus while keeping a lens to film distance at a constant. These will easily support an 810 camera.

We even set up the Smithsonian with one of these to move a very large and heavy IR video camera for use in restoring old paintings.

BTW, I trie to email this to you but your address bounced back.

3. ## DOF question

Joe, please read http://www.cs.berkeley.edu/~qtluong/photography/lf/how-to-focus.html and use II.3 without any movement. The formulas are much simpler on your rail (image space) than if applied in the scene (object space). Also, try to provide us with a valid email.

4. ## DOF question

I found this long and helpful article and reproduce it here. It argues that as the format increases, depth of field and diffraction decrease at an equal rate. This means that an 8x10 camera can use much smaller apertures than a 35mm before diffraction becomes a problem. When you get to the end of the article, you will see that there is a 6-stop difference between 8x10 and 35mm: f64 for an 8x10 camera is equivalent to f8 for a 35mm. You won't have a diffraction problem when using f64 with 8x10. This may even be the optimum aperture, just as f8 is about optimum for 35mm. Where else does the f64 Group get its name? I stop down to f45-f64 with 8x10 as a matter of course. I bet this article with spark some controversy.

5. ## Re: DOF question

After the above, I hesitate to add, but a simple way of calculating the maximum is that the human eye, generally can focus detail to about 8Lpm and so if you intend to enlarge your 8x10 to 32x40 or 4x you need a minimum of 32Lpm to appear sharp.

The maximum stop down for this would be about F22-32. But you need to stop down further for your group shot... With results that may not be as good as you want.

Also with 165mm S/A the curvature of the field is such that you may also have issues at the edge of the frame with distortion and sharpness as well.

6. ## Re: DOF question

You do know you are responding to an 11 year old thread, right?

7. ## Re: DOF question

Originally Posted by E. von Hoegh
You do know you are responding to an 11 year old thread, right?
But newcomers are always admonished to "Search the Archives!".

What do you expect them to find in the archives... only current stuff?

- Leigh

8. ## Re: DOF question

Originally Posted by Leigh
But newcomers are always admonished to "Search the Archives!".

What do you expect them to find in the archives... only current stuff?

- Leigh
He's been here nearly as long as the thread has, he's no "noob"

9. ## Re: DOF question

Maybe it's taken 10 years to compose the perfect response?

10. ## Re: DOF question

Ha ha.

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