Focusing at the Correct Distance to Maximize the Depth of Field

[Salmo22]

The title of this thread came from a comment made by Bob Salomon (http://www.largeformatphotography.info/forum/showthread.php?137549-Schneider-210-Apo-Symmar-Sweet-Spot&p=1379537&viewfull=1#post1379537) in another thread titled "Schneider 210 Apo Symmar Sweet Spot". For all practical purposes, I'm a newbie to 4x5. Accordingly, I was intrigued by Bob's comment and want to know how I can ensure I am "...focusing at the correct distance to maximize the depth of field available at F22 before resorting to stopping down further into diffraction territory"? What technique and/or practice should I follow to achieve this goal? Hopefully Mr. Salomon will find this thread and join in the discussion.

If I've started this thread in the wrong forum, please forgive my newbie mistake and relocate to the appropriate location.

Thanks all;

Jeff

[Bob Salomon]

It is not for 45 or just large format. It applies to any format.
At normal shooting distances the depth of field runs from a point 1/3rd of the way into a scene towards the lens and ⅔rd of the way towards infinity so you want to focus 1/3rd of the way into the scene that you want.
At close distances the focus point changes to half way into the subject.

[Dan Fromm]

http://www.trenholm.org/hmmerk/download.html

[photog_ed]

https://en.m.wikipedia.org/wiki/Hyperfocal_distance

[Sal Santamaura]

It pays to visit the home page. Here are two useful pages from this forum's founder:


http://www.largeformatphotography.info/how-to-focus.html


http://www.largeformatphotography.info/fstop.html

[David Karp]

I second Sal's recommendation. Those articles are hugely useful.

Also, Linhof published a table you can use to help select the point of focus and f/stop using the process described in the second of the two articles Sal linked above. You should be able to find it on the Internet.

[Vaughn]

The 'trick' I have come to use is to estimate about 1/3 of the way between the near and far points I wish to have in focus. I watch these two points on the GG as I slowly close the aperture down. If my far and distance points come into focus at the same aperture, then I know I am focused properly. If the near point comes into focus before the far point, for example, then I know I am focused too close in the scene, and I will change the focus point a little and check again.

[Dan Fromm]

Hmm. Why use inaccurate rules of thumb when DoF given focused distance, focal length and how much the negative is to be enlarged isn't that hard to calculate?

[Vaughn]

Hmm. Why use inaccurate rules of thumb when DoF given focused distance, focal length and how much the negative is to be enlarged isn't that hard to calculate?
Largely because I do not enlarge and what I see is what I get (not exactly a rule of thumb in this case). Heck of lot easier than measuring distances and calculating measurements I don't need, or may not be able to use in the field. But it fits the way I work, and I like being able to stay under the darkcloth until everything is composed and focused. YMMD. It also helps that I am very near-sighted and can fine-focus nicely without a loupe.

Not that I get it right every time, either!

[Doremus Scudder]

A couple of comments for the OP:

First, as you can see, there's a bit of complexity involved to focusing, especially when it's a view camera capable of movements. Merklinger's books are practically a university-level course; the articles on the LF home page (which I also wholeheartedly recommend) also take a bit of time to digest and apply. So: Don't get discouraged! It's a lot, but it's not all that difficult.

That said, the general principles are not all that many nor all that hard for a beginner to wrap his/her head around. In that spirit then:

First: Yes, most LF lenses are optimized for f/22, which means that f/22 is the best compromise between loss of sharpness due to lens imperfections (larger apertures) and diffraction (smaller apertures). So, it makes sense to try and use f/22 when possible. However, if you need more depth-of-field than f/22 allows, then don't hesitate to stop down more. The amount of extra diffraction at f/32 is negligible. FWIW, f/32 is likely my most-used stop. Don't get too hung up on the so-called "sweet spot."

When you focus on something in a scene, you place it in the plane of sharp focus. There is really only one two-dimensional plane where everything is sharpest. As you stop down, objects on either side of the plane of sharp focus become less blurry. They never get as sharp as possible, but if they get sharp enough that our eye can't tell the difference, then, for viewing, they appear equally sharp. What you see on your ground glass is what you get, for a 4x5 contact print (or larger if your camera's larger like Vaughan's :) ). If you plan on enlarging your images, then sharp enough on the ground glass may not be sharp enough for a print. Viewing the extremes of the image with a magnifier helps here. Many also build in a safety factor such as stopping down even more after all is sharp, etc.

There are other ways to ensure enough depth-of-field that don't require you to stop down and view the image.
My preferred method is simple: After applying whatever movements I need to manage the image, I focus on the nearest object I want to be in sharp focus and note the position of the standards (i.e., distance between the back and front) on the rail or camera bed. I then focus on the farthest object I want in focus and note the position of the standards. I then position the standards exactly halfway between the extremes (note: I don't have to look at the ground glass to do this last step). This is the best spot for optimum depth-of-field. The aperture is determined by how large the focus spread (the distance between the extremes of near and far focus) is. It helps to have some way to measure the focus spread. My field cameras all have millimeter scales added. You can find millimeter rulers on the web and simply print them on an adhesive backed label and stick them on your camera. Heck, you could even make pencil marks on tape and stick that on your camera; whatever works for your set-up.

Determining the best aperture for a particular focus spread requires some parameters: how much you want to enlarge, etc. This is all explained in the articles on the LF home page. However, if you want to get started, you can simply use the table given there and see if it works for you.

Here's an excerpt from the article plus the table for quick reference:

"Make your movements first. Then focus on far, focus on near, read the distance "D" in millimiters between the two positions on your rail, refocus so as to split the distance on the rail, and use the following table that I recommend you carry with you all the time. "F" is given in decimal f-stops, as on a hand-held meter, for example 16.6 is 16 and 0.6 (aka between 1/2 and 1/3) of a f-stop...

D(mm) -- F
1 ---- 16.6
2 ---- 22.6
3 ---- 32.2
4 ---- 32.6
5 ---- 32.9
6 ---- 45.2
7 ---- 45.4
8 ---- 45.6
9 ---- 45.8
10 --- 64 "

The table doesn't retain formatting well here, but you can figure it out. Example: focus spread is 3mm, you'd stop down to f/32 and a bit more.

It's pretty easy to see that for about any subject that has both near and far objects you want in focus that you're going to have to stop down past the "sweet spot" of f/22. Don't worry about this, since the table above represents the optimal compromise already. Like I said, I shoot mostly at f/32. At f/45 I can't see any diffraction at all in an 11x14 inch print; maybe a bit at 16x20. In any case, the lack of depth-of-field if you don't stop down will ruin the image anyway; you have nothing to lose.

Hope this helps a bit to get you started. Do, however, take the time when you have it to read the literature on the topic; It'll make you a better photographer.

Best,

Doremus

[Salmo22]

WOW - What an amazing response. Lots to digest; however, I'm patient and committed to learning the proper technique. With study and practice, I'll get this.

Many thanks to all who offered comments and suggestions.

Regards;

Jeff

[Jim Jones]

As I recall from calculations I made long ago, a scale like that which Doremus posted is a universal scale for any lens but for just one particular image size. For critical work with 35mm cameras, the once prevalent DOF scales were suitable for fairly small prints, perhaps up to 8x10. A similar scale giving the DOF for a range of apertures can be added to the metric scale Doremus suggests. It will be tiny on such a linear scale.. Incorporating a magnifier helps. Consider that optimum DOF varies widely, dependent on the medium, the subject, the observer, the image size, and the viewing distance. It should be art, not science.

[aduncanson]

Great answer Doremus. It reminded me that Sinar cameras have a mechanical calculator built into the rear standard to do this for you. I was expecting to find a constant ratio between focus spread and optimal f-stop indicating a constant circle of confusion, but that is not what I found. In creating that table, the authors considered the effects of diffraction limiting resolution as you stop down and actually point out that as you stop down, you must limit your enlargement to maintain a sharp print. Note that even at f/64 you can still make an acceptable 11x14 from a 4x5 negative (at least in theory.)

The 1/3 - 2/3 rule of thumb cited at the beginning of the thread is probably undeserving of even being called a rule of thumb. As cited, at extreme close ups the depth of field is split equally in front and behind the subject. When you get to the hyperfocal distance, the range of acceptable focus behind is infinite while it is clearly not infinite in front. So the 1/3 - 2/3 ratio is obviously nothing more than an intermediate value chosen to convey the idea that, apart from extreme close-ups, there is considerably more depth of field behind the plane of focus than ahead. That is a good lesson to absorb.

[tgtaylor]

There are other ways to ensure enough depth-of-field that don't require you to stop down and view the image.
My preferred method is simple: After applying whatever movements I need to manage the image, I focus on the nearest object I want to be in sharp focus and note the position of the standards (i.e., distance between the back and front) on the rail or camera bed. I then focus on the farthest object I want in focus and note the position of the standards. I then position the standards exactly halfway between the extremes (note: I don't have to look at the ground glass to do this last step). This is the best spot for optimum depth-of-field. The aperture is determined by how large the focus spread (the distance between the extremes of near and far focus) is. It helps to have some way to measure the focus spread. My field cameras all have millimeter scales added. You can find millimeter rulers on the web and simply print them on an adhesive backed label and stick them on your camera. Heck, you could even make pencil marks on tape and stick that on your camera; whatever works for your set-up.

This is essentially the method I use to focus 35mm and my medium format Pentax cameras and learned of it from a Galen Rowell book. Once you have determined where those two focus points fall on the lens you simply position the lens exactly half-way between them and choose the f-stop marked on the barrel that encompasses both points and add a little extra for insurance.

However for LF you don't have to do all that. Depending on the type of camera you have (base or axial tilt) simply choose one point, say the furthest - even infinity - and focus on that point. When it snaps into sharp focus (check it with the loupe) tilt the lens until the nearest point snaps into focus (this could be a swing depending on where your points are located). Then refocus on the first point and then back on the second point. A couple of reiterations should do it. Then stop down for anything that's soft between those two points. You can see the effect of stopping down on the GG. I think Fred Newman (?) of the View Camera Store describes this method in a video on his website.

Thomas

[Doremus Scudder]

... However for LF you don't have to do all that. Depending on the type of camera you have (base or axial tilt) simply choose one point, say the furthest - even infinity - and focus on that point. When it snaps into sharp focus (check it with the loupe) tilt the lens until the nearest point snaps into focus (this could be a swing depending on where your points are located). Then refocus on the first point and then back on the second point. A couple of reiterations should do it. Then stop down for anything that's soft between those two points. You can see the effect of stopping down on the GG. I think Fred Newman (?) of the View Camera Store describes this method in a video on his website.

Thomas

Thomas,

What you describe works for some situations, but not for others. Tilting to get near/far is impossible if the near and far objects are in the same line (e.g., a near branch and a distant horizon). I cases like these, you just have to rack back and forth. Also, if there are tall near objects in your scene, tilting will increase the focus spread, requiring a smaller aperture to get everything in sharp focus. It's better to apply whatever movements before the final determining of optimum aperture. During this process, one can see what amount of tilt is best. Often, you can reduce the focus spread with a judicious tilt/swing, but not always.

Best,

Doremus

[Vaughn]

I did have a lot of fun with front tilt out in Death Valley this month. In the redwoods, tilt is used sparingly...dang those tall trees! For the two weeks in the desert I did find myself always having to reduce the tilt after my initial adjustment...too gung-ho with the tilt! I am only a third of the way thru developing my negs. (a wind storm kept me from developing last night -- too much chance of losing power). So far so good. An obvious focus/tilt error in the Alabama Hills on one 8x10 (getting use to a 360mm!) The foreground was not equally distanced from the camera -- missed that (double/triple check those corners!)