Technique for increasing depth of field

[Doremus Scudder]

"1) Camera movements. First thing I would do is place the plane of exact focus where I wanted it to be. The art in this is defining the concept "where I wanted it to be" for your own work..."

I agree that placing the plane of sharp focus optimally is essential to optimizing depth of field. Really, though, camera movements don't do a thing to increase depth of field. What they can do is better position the plane of sharp focus so that you don't need so much depth of field to get everything acceptably sharp in the print, which means you don't have to stop down as much.

Practice helps to get a sense of where the plane of sharp focus is best placed. I try to visualize where that plane goes in the scene so that it's closest to all the various elements that I want in sharp focus. I then choose three focus points that lie on my visualized plane and use these to apply the movements. Sometimes this is easy; just look at what's closest or farthest from the camera position. Often, especially if lots of tilt/swing have been applied, it's not so intuitive what is "in front of" and "behind" the plane of sharp focus. It the plane of sharp focus is closer to horizontal than vertical in the scene, then "in front of" becomes "above," and "behind" becomes "below" the plane of sharp focus.

In cases like this, it helps to find several candidates for the near-far focus points, focus on them, and note the distances on the scale on the camera bed to find which really use the most/least bellows draw to get into sharp focus.

This is also a good way to check if the movements you've applied are optimum. Check the focus spread with no movements applied. Then apply the movements and see if the focus spread is smaller. Remember, the smaller the focus spread, the larger the optimum aperture for the desired depth of field will by. Try several positions of the tilt/swing to see which one gives you the smallest focus spread and choose the one that gives you the best optimum aperture.

Best,

Doremus

[Ulophot]

[QUOTE= If the plane of sharp focus is closer to horizontal than vertical in the scene, then "in front of" becomes "above," and "behind" becomes "below" the plane of sharp focus.
[/QUOTE]

How does that happen? Is there a flip in relative positions at 45 degrees? I'm trying to visualize why that would be the case.

[lassethomas]

Well, as already stated I think, all the movements in the world won't increase depth of field.
And visualizing what happens when you apply either tilt or swing takes some training. When depth of field becomes a cone and eventually front and back becomes above and below or right and left.
And when you apply both tilts and swings complexity multiplies and at least my mind directly has severe problems visualizing and controlling the result.

So don't overdo it. Learn to early identify scenes and compositions where movements are non productive or at the very least of very limited value. They are perhaps more common than we think. And then just stop down to get what you want i focus.

That said, I love the near-far method. It really works, movements or no movements. Thanks Doremus for pointing that out and convincing me.

[Michael R]

Depth of field boundaries tilt with the plane of focus.

How does that happen? Is there a flip in relative positions at 45 degrees? I'm trying to visualize why that would be the case.

[Bruce Watson]

“4) Lens choice. For a given camera position and subject position, shorter lenses give you more DOF than longer lenses. That said, I hardly ever did this -- I always wanted to keep cropping to a minimum.”

Bruce, it’s easy to take for granted that a wider Angie lens gives more DOF, but in reality, at the same aperture and the same magnification, all lenses have the SAME DOF.

Learn to read. I didn't say a thing about magnification being equal. I said "for a given camera position and subject position". If camera position is the same, and subject position is the same, different focal length lenses will render different magnifications. Duh.

[Doremus Scudder]

How does that happen? Is there a flip in relative positions at 45 degrees? I'm trying to visualize why that would be the case.

Philip,

It's simply that the plane of sharp focus has been moved to an almost horizontal position. The graphic Michael posted show the principle very well, but let's put that into practice.

Imagine a scene with a long, flat foreground that has on little rock close to the camera along with some small bushes/trees. Then there's a range of low mountains in the distance. One might want that little foreground rock in sharp focus and the distant mountains as well.

So, one would pick focus points for applying movements that lie at about the middle of the foreground rock for near and halfway up the mountain range for far. Then front/back tilts would be used to position the plane of sharp focus so that it intersects those two points. (Note: this set of focus points is for working with the camera movements; we aren't focusing the camera yet.)

After this, you can see that the plane of sharp focus is now much closer to horizontal than vertical. Maybe even more horizontal than Michael's graphic. So the next question is, where are the near-far focus points for determining focus spread and optimum depth of field? Since the plane of sharp focus is almost flat, there is no longer a real "in front of" or "behind," rather things that stick up above the plane of sharp focus are now the nearer, and things that are under it are farther, in terms of the geometry of the optics.

An object that is the highest above the plane of sharp focus is going to be the near focus point. This could be a foreground tree or the top of a foreground boulder, but it could also be a more distant, very tall tree. Conversely, an object that is lowest underneath the plane of sharp focus is going to be the far focus point. This is likely the base of the distant mountain range, but there may even be a valley of some sort that's even lower somewhere in the scene.

At any rate, identifying those near-far points is important for making sure you get the right focus spread and the right aperture.

Hope that's clear,

Doremus

[Doremus Scudder]

Learn to read. I didn't say a thing about magnification being equal. I said "for a given camera position and subject position". If camera position is the same, and subject position is the same, different focal length lenses will render different magnifications. Duh.

Bruce,

Don't be too harsh... I think many of us assume that we want a particular framing, so when using a shorter focal length lens from a particular camera position, would end up cropping the final image, thereby magnifying it, in order to get the original framing we had in mind. In such a case, the magnification introduced by the cropping cancels out the improved depth of field achieved by choosing a shorter focal length lens exactly and we end up with, essentially, the same image with the same depth of field.

Only if we can live with the wider view and the different composition in the uncropped image do we have an advantage, and that's only because the final image is smaller, i.e., not magnified as much.

Best,

Doremus

[pdmoylan]

Learn to read. I didn't say a thing about magnification being equal. I said "for a given camera position and subject position". If camera position is the same, and subject position is the same, different focal length lenses will render different magnifications. Duh.

My comment was intended to help the op, and since you did not mention magnification, I thought it helpful to buttress your comment. Not sure how one can get emotionally bruised when I was not criticizing, nor countering your comment. Getting out an photographing may relieve the injudicious antagonism. The OP is here to learn, we understand you probably know all of this.

For years this was a relatively safe and civil forum. Let’s try and buck the contrary trend.

[Eric Woodbury]

Is there a telecentric lens available for large format? These change the rules on depth-of-field. DOF is no longer an issue, but everything is a trade. Only one magnification.

Therefore, use what you have, focus on what's most important, stop down, keep the contrast up. Add a sharpening mask if you must.

[Michael Kadillak]

I am not 'back and forth' focusing. I am just slowly closing the aperture while studying the GG. I pick my near point and far focus points and watch both as I close down. If that mountain in the back and the bush close in front of me both come into focus at the same time, I know I've placed my plane of focus in the 'right' spot. If the mountain comes into focus while the bush is not yet become sharp, then I need to move my focus plane closer to the camera.

Vaughn nailed it. Put your focal plane in the correct orientation and watch the GG. If you have to high intensity LED flashlights are cheap these days to check yourself as you stop down. I put macro correction wafers and even bandaids from my backpack at various points in the scene to check it on the GG. I would shoot this with my 210 mm Computar/Kowa and an 8x10 all day long. The scene is not that complicated as long as you properly put your plane of focus in the correct place.