Photoforum Photography Challenge 2011-12 - Long depth of field & hyper-focal distance

[TCampbell]

While a shallow depth of field of a nearby subject can create a beautifully de-focused background (often called "bokeh" -- but that's another challenge) sometimes we want a very broad depth of field.

Situations where this is useful are when you have both a near and far subject and want both subjects in sharp focus, or situations where you have a long subject (e.g. imagine shooting a photo looking down the side of a long train, road, etc.)

Depth of field is increased by reducing the aperture diameter (use a focal ratio with higher number... e.g. f/16 is much higher than f/2). This decreases the size of "circles of confusion" (more on that when we get to a narrow depth-of-field / "bokeh" challenge). Technically there is one precise point where focus is "perfect." Every other point is not technically "perfect" -- but the amount of blur is so tiny that it simply isn't noticeable. Circles of confusion are based on the circular opening created by the lens aperture. So when this starts out very tiny (small aperture / high focal-ratio value), the circles of confusion are also so tiny that "blur" is very hard to see. The result is a shot that seems to be focused throughout the entire photo.

From Wikipedia:

In optics and photography, hyperfocal distance is a distance beyond which all objects can be brought into an "acceptable" focus. There are two commonly used definitions of hyperfocal distance, leading to values that differ only slightly:
Definition 1: The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.

If you have a camera that you can manually control such as a DSLR and a lens that has depth-of-field indicator marks adjacent to the focus ring:

1. put your camera on manual mode and put your lens on manual focus mode.
2. set the camera aperture to the highest focal ratio your lens can achieve (e.g. f/22)
3. turn the focus ring until the "infinity" mark is aligned with the depth-of-field mark on the far side of focus.

If you do not have depth-of-field marks on your lens you can look up the hyper-focal distance using a chart. DOFmaster.com has an online look-up tool (tell it what type of camera you have, the focal length of your lens (or the focal length you'll be using if it's a zoom lens), and the aperture you'll be using (which should be the smallest diameter / largest focal-ratio you can achieve.) They will calculate the hyper-focal distance for your particular focal length and focal ratio. Manually turn you focus ring to this distance.

If you have a point & shoot camera and can't manually focus your lens or manually control your aperture, turn your camera's mode dial to the "landscape" setting (usually this is an icon with mountains.) This will bias the camera's exposure settings to use high focal ratios (small aperture) and maximum depth of field possible.

In this first example, I have a long fence and want the entire fence in sharp focus along with the windmill. I was shooting at 70mm. I set my aperture to f/22. The hyper-focal distance for my camera (full-frame sensor) with a 70mm lens at f/22 is 24 feet and this achieves acceptable focus on all objects from 12 feet to infinity. I now just need to make sure that the closest object I want in focus is at least 12 feet away, compose the shot and shoot.



Here are a few more examples... although these use lower focal ratios, the depth of field still achieves the effect I want. Check the focus on the leaf and chapel (yes... I did plant the leaf in that spot for the shot.)





This is a very useful technique for landscape and/or architecture photography (which is why the "landscape" icon on a point & shoot camera will generally achieve the same effect.)

And now for the rules:

1. Only photos taken during the challenge period should be posted.
2. Limit of 2 pictures per post for this topic.
3. Discussion of technique and/or inspiration is encouraged!
4. Remember - this is NOT a contest - no voting, no prizes - other than better photos!

And the most important rule: Have fun!

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[KevinH]

Hello:I went to DOFmaster and Wiki to study a little. There is no mention of smaller size sensors having anything to do with hyperfocal distance. Formula only includes f and a. So, there is no need to use a multiplication factor when printing a hyperfocal chart, correct?

Kevin

[TCampbell]

Great question!

There is some subjectivity in circles of confusion. Depth of field is based on some notion of "acceptable focus". As you crop in on the center of an image and enlarge it, you enlarge "everything" including any softness. The more you crop and enlarge, the more you reduce the depth of field.

The first time I learned this, someone told me that a crop-frame camera has lower DoF than a full-frame (and me knowing that the lens doesn't change) -- it didn't make sense. That was, until they told me that it wasn't really the lens... but the enlargement process that makes a difference. The enlargement process is universal -- meaning it even applies AFTER you take the image. E.g. take any image you've ever made... zoom way in and crop it, then enlarge the cropped section to the same dimensions as the original. Re-inspect the image and you'll notice that the DoF was reduced (even though it's the SAME image... you didn't even take different photograph.) You'd have to crop and zoom a few different areas... something in the near foreground vs. something at the intended focus point. But you should be able to notice that in the near foreground that used to seem acceptably sharp will no longer look as good once you've zoomed in, cropped the section, and enlarged to original size again. You've magnified the softness. Basically you've "enlarged" the circle of confusion.

Here's where we tread carefully because there are two or three different ways to explain the differences and they seem contradictory unless you check the wording carefully.

1. If you compare a full-frame and crop-frame camera but compose the shots using the same lens so that the "field of view" is the the SAME then the crop-frame camera will have more depth of field than the full-frame camera. That's because in order to see the same field of view in a crop-frame camera which was visible in the full-frame camera you'd have to stand back much farther to get everything in the frame. Standing back farther increases the depth of field. (Did I really just say the crop-frame camera has greater depth of field than the full-frame camera? Yes... I did. But wait... there's more!)
2. If you ignore the field-of-view and simply use the same lens on both the crop-frame and full-frame body cameras, you'll notice the full-frame camera has more depth of field (because you're not moving the camera like we were in example #1 above). Waitaminute! I just said in #1 that the crop-frame has more depth-of-field than the full-frame body and here I am in #2 explaining that the full-frame camera has more depth-of-field than the crop-frame camera. I appear to be contradicting myself. This is why I said you have to read carefully... note that in example #1 the lens was the same, but we changed the body AND we changed the lens-to-subject distance to maintain the same framing. But in #2 we change ONLY the body and leave the lens-to-subject distance identical (at which point the framing is no longer identical.) So the contradiction is explained in that the shooting circumstances weren't really the same. This is while you'll sometimes see contradictory statements on the Internet about crop vs. full-frame DoF.
3. If you do a repeat of #2... except this time we crop in on the image we took with the full frame camera so that it's the identical field of view as was captured by the crop frame camera, then the depth of field will be... identical.

Since a crop frame camera is enlarging the image more as compared to a full frame camera, the circle of confusion factor assigned is different. You'll notice if you use the DOFmaster online tools to calculate the hyper-focal distance and leave everything the same except for the camera body, the hyper-focal distance will change when you change the body.

For example, if I plug in a 50mm lens at f/22 but tell DOFmaster the body is a 7D (APS-C) it gives me a circle of confusion size of 0.019mm and a hyper-focal distance of 19.2 feet. If I only change the body to a 5D mk II (full-frame body) the circle of confusion size increases to 0.03mm and the hyper-focal distance drops to 12.2 feet. For Nikon if I plug in a D7000 it gives me a CoF of 0.02mm and a hyper focal distance of 18.3, but a Nikon D700 (full-frame) is 0.03mm and 12.2 (same as the Canon full-frames).

The image circle being projected into the sensor body doesn't change whether it's full vs. crop frame. What changes is that a crop-frame sensor has to enlarge the image a bit more to create the same size output and that enlargement slightly reduces the DoF.

The opposite of this challenge is to deliberately maximize the circles of confusion to create a nice pleasing background blur. If you really want to see the circles of confusion in a very obvious way with a shallow depth of field, shoot a photo where the out-of-focus background contains holiday lights (which may be a hint regarding when I plan to spring the opposite challenge.)

In the end, this challenge is really just about dialing in settings to maximize your depth of field and, as an aside, the notion that focusing the lens to something a less than "infinity" actually provides slightly more depth of field that focusing to exactly "infinity". If you also pick up how circles of confusion work then that's a bonus -- but the goal of the challenge wasn't to get quite that complicated (I didn't intend for anyone to have to do math in order to participate.)

[Dazzaone]

Don't understand all the blah blah blah jargon, but going on a shoot today so will have this theme in mind

[Dazzaone]

Managed at last to get something for this thread Tim, sorry it has taken so long but it's the wrong time of year for this type of subject, the weather is hit and miss and near impossible to get out never mind trying to use this depth of field, but just had to get something...

[TCampbell]

Dazz! That is REALLY amazing... it's a perfect example of foreground/background subject selection. I can see the rusty age of the leading edge of the gate in sharp focus while still being able to count the stones in the tower in the background. It's also a fantastic use of B&W with all the texture, structure, and contrast.

[Grandpa]

The mountains of northwest Virginia this past weekend...

[ChicagoJohn]

DAMN! This is one of the most interesting challenge topics I've encountered in the past year, Tim. GREAT job in presenting it !!!! Folks vary in their interest in the technology, I just happen to be on the same page you are. I'm going to give it a shot as I think I understand the physics involved... we'll see.

Dazzaone... I'm at a loss for words, man, but that's never stopped me before You have now racked up two of my favoritist images ever. I'm not going to say any more than that; to conserve words, as Dane thinks to be a good idea; and also not to skew others' experience, but suffice it to day I would give this five "likes" if there were a way to do so. And in lieu of that capability, I shall use the tools available. This image is, in my opinion, worthy of serious study.

Grandpa, I also really love your image, not only for how it illustrates the concept Tim has asked for, but more importantly the "life force and beauty" criterion of Alexander Pope. And more importantly to me, the contrasts; initially between the impermanence of the contrails and the tree, the colors, the geometry, and then there is the "life and force" element of how nature creates a dimunitive, almost bonsai, tree to survive in this environments. One of my very favorite places is the Canadian Rockies, and you hike out there and see these very small, but very old pine trees. There is a haiku in there somewhere. Found it....

Virginia: Autumn.
Mountains and a clear blue sky;
Lens transcends the eye.

or...

An evergreen tree,
jet trails fading in the sky;
What will come next? (note the missing syllable in the last line of the haiku)

I may have something in my portfolio to start with, but I'll definitely give this one some thought and try to come up with something this coming week, Tim.

[ChicagoJohn]

After the intro and the subsequent images, I thought I could best contribute by lowering the bar.
So here is an image I took a while back as part of a "concrete abstract" shoot; one that I think, to a limited extent, includes the extended DoF concept, but which also transcends the subject-background dichotomy. And I may yet have one more before getting up off my butt and doing something new, like Dazzaone did.


CA pillars by ChicagoJohn, on Flickr

Now come what come may;
time runs through the roughest day:
Tomorrow!... and tomorrow....

[Denim]

My attempt at long/short range focus. Weak, but I'm trying.