How do you/did you learn to work with DOF?

[sully75]

Any tips on how to be more competent with knowing how much DOF you have in a scene? I'm shooting a bit more landscapes with the 5x7 and so far have been just going by feel ("I think this needs F22 and I think the focus should be here"). I'd like to be more sure of myself and be able to maximize my DOF when I need it.

Any thoughts or techniques for being more scientific about it?

[Bill_4606]

There are charts and tables that will tell you what "should" be in focus based upon the lens focal length, aperture, bellows extension, subject distance and the phase of the moon. But the best way for you determine what is in focus is to just look at your ground glass.
Think about what you want to have in focus then look for it in your image. Learn your camera's movements so you don't have to stop down to get all of your subject in focus - f:64 is not always your friend.

You mentioned that you are shooting more landscapes. Think about it... Aren't big scenes mostly at infinity? If you want to have the mountain and the grass at your feet in focus, force yourself to shoot at 5.6 and use your tilt. If you want the fence at the side to be in focus from foreground to dstant, use your swing at full open aperture.

Finally, don't listen to me... Listen to your own eyes and have fun...
Bill

[E. von Hoegh]

Any tips on how to be more competent with knowing how much DOF you have in a scene? I'm shooting a bit more landscapes with the 5x7 and so far have been just going by feel ("I think this needs F22 and I think the focus should be here"). I'd like to be more sure of myself and be able to maximize my DOF when I need it.

Any thoughts or techniques for being more scientific about it?

Set the lens to the working aperture and look at the groundglass. Not enough DOF? Use a smaller aperture. A proper (meaning dark) darkcloth helps quite a bit when looking at the GG at f 45.

[Frank Petronio]

You could shoot something wide open, half way stopped down, and all the way stopped down and see which you like best. Why not "bracket" the aperture next shoot?

[Bruce Watson]

Any tips on how to be more competent with knowing how much DOF you have in a scene?

Yup: Practice, practice, practice. It's how we learn.

To do it right, you'll have to make prints. You need to see your own personal end-to-end workflow and how your capture choices effect the final print. With that kind of feedback, you'll learn pretty quickly I think.

[E. von Hoegh]

Yup: Practice, practice, practice. It's how we learn.

To do it right, you'll have to make prints. You need to see your own personal end-to-end workflow and how your capture choices effect the final print. With that kind of feedback, you'll learn pretty quickly I think.

What Bruce said.

Keeping a log of every exposure is perhaps the single best learning aid you could use.

[sully75]

Thanks...this was the (frustrating) picture.



I was hoping to get almost everything in the picture sharp. But after reviewing this:
http://www.dofmaster.com/dofjs.html

I didn't totally get how narrow DOF on a 240mm lens is. (I didn't write down the exposure, lesson learned) but I think I did F22, focusing on the first rock on the right side that is not in shadow. But the calculator shows only 5 feet of DOF for F22 @ 10 ft.

I can't say I've had great luck figuring out what's in focus via the groundglass once the lens is stopped down.

Lesson learned. Haven't figured out a good record keeping system for my way of working but what I'm doing is obviously not cutting it.

Thanks for the thoughts.

[Leonard Evens]

I use the near/far approach.

I select a point marking the furthest distance I want in focus, focus on that (wide open), and note the position on the rail. Then I select a point marking the nearest point I want in focus and also note the position on the rail. I then measure the distance, called the focus spread, on the rail between those positions. I focus by placing the standard halfway between the near point and the far point. Finally, I choose the f-stop to use when taking the position using the focus spread.

There are a variety of ways to do that. The method I generally use is to multiply the focus spread by ten and divide the result by two. This method is based on optical thoery and assume a maximum circle of confusion of 0.1 mm. It gives a reasonable estimate of the needed f-stop, but it ignores diffraction. I often stop down an extra half stop or full stop to be sure. But if you want to choose a stop which balances defocus and diffraction, you can use the method described at
http://www.largeformatphotography.info/fstop.html.
That website also explains the rationale for different methods.

[sully75]

Leonard,

That page is helpful but I was under the impression that most lenses are made so that if you pick a point of focus, your DOF will be 1/3 in front of that point and 2/3 behind it (supported by that DOF calculator site). So if you are splitting your focus halfway between the two points, seems to me that you are going to have to use a smaller aperture to get your foreground in focus.

[Bill_4606]

I really like like the scene you selected....

For that image I would have focused wide open on the tree on the right center side of the path.
Use front tilt to get the perspective that I liked.
Double checked the focus on that tree.
Use the rear tilt at wide open aperture looking for the top and bottom to focus.
Then stop down to my len's sharpest aperture ( not it's smallest). With the film plane aligned for the scene, you effectively extend your DOF out into the scene - not straight up and down the film plane.

I'm not sure you would have ever gotten the down river tree bank sharp due to haze or water vapor but for this image you might not want it sharp.
Again, I like what you have going in that image. The lighting is focusing the viewer's attention to the path. Not the sharpness.
Bill