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View Full Version : Why do you have limited DOF in 8x10?



franklphoto
13-Jun-2008, 20:06
Please explain...

Matt Miller
13-Jun-2008, 20:16
To simplify, it's the long focal lengths.

franklphoto
13-Jun-2008, 20:21
To simplify, it's the long focal lengths.

even in a 240mm or 210mm?

Jeff Conrad
13-Jun-2008, 20:45
To a first approximation, with the same image framing from the same camera position using the same f-number, the DoF is inversely proportional to magnification. Consequently, with 8x10 you get roughly half the DoF you'd get with 4x5 for the same image. Equivalently, to get the same DoF with 8x10 as with 4x5 you need twice the f-number (e.g., f/45 vs. f/22).

Eric Leppanen
13-Jun-2008, 20:45
A 110 to 150mm lens is the longest focal length that can hold sharpness in a near-to-far composition (i.e., foreground is a few feet away, background is infinity, both are in sharp focus) by stopping down to f/45. This rule holds regardless of the camera format used. Longer focal lengths require front or back tilt to keep the foreground and background simultaneously sharp.

110mm and 150mm lenses on 4x5 provide moderately wide to normal angles of view, respectively. On 8x10, these same focal lengths provide ultra wide to wide angles of view. To provide the same angle of view as a 4x5 camera, an 8x10 camera must use double the focal length, at a cost of reduced depth of field.

A 210 or 240mm lens cannot keep foreground or background simulteneously sharp without resort to tilt, regardless of the camera format being used.

Daniel_Buck
13-Jun-2008, 20:50
even in a 240mm or 210mm?
from the way I look at it (if you are coming from 35mm SLR or range finders) is that with a 210 lens on a 35mm camera, you'll usually have something out of focus, anyone who's used a long lens on a 35mm knows that. 210mm lens is a wide lens on 8x10, however it's still a 210mm lens, so it still has the same DOF that the 210mm lens would have on a 35mm camera. It's just different looking on an 8x10, because that 210 doesn't give you a thin view angle that it did on the 35mm, it gives you a much wider view angle, but with the same DOF.

I might be wrong, but that's how I've always thought of it.

Greg Lockrey
13-Jun-2008, 21:28
Basically with wider f numbers you have less depth of field. As lens sizes increase so does the actual width of an aperture at any given f/stop hence the DOF will decrease. It is a function of the size of the circle of confusion.

Peter K
14-Jun-2008, 02:23
At the LF-info page http://www.largeformatphotography.info/
also this question will be answered. "Introduction to Depth of Field (PDF)"

ljsegil
14-Jun-2008, 03:43
It is a function of the size of the circle of confusion.
I couldn't agree more, and worse is the that the size of the circle increases with the confusion, and vice versa, ad infinitum. Thus was born photography, confusedly?
LJS

Greg Lockrey
14-Jun-2008, 03:59
I couldn't agree more, and worse is the that the size of the circle increases with the confusion, and vice versa, ad infinitum. Thus was born photography, confusedly?
LJS

Yeah, that circle too. :p :D :D

Jeff Conrad
14-Jun-2008, 05:16
In my previous post, I somewhat misspoke in attempting to oversimplify things. Actually, the DoF of different formats arises from both the magnification and the circle of confusion. To a first approximation (we make a lot of them in photography ...), the DoF is inversely proportional to the square of the magnification. For the same picture, the magnification with 8x10 is twice that with 4x5. On a given format, doubling the magnification increases the f-number by a factor of four (e.g., f/90 vs. f/22). This dreadful situation is partially offset when obtaining the greater magnification on a larger format; the larger negative needs less enlargement for the same size final image, so the circle of confusion for the larger format is greater. For 8x10, the common value for CoC is 0.2 mm vs. 0.1 mm for 4x5. So with twice the magnification but also twice the CoC, the net effect is that, with the same f-number, the DoF for 8x10 is approximately half that for 4x5.

For those who must know, the gory details are covered in Depth of Field in Depth (http://www.largeformatphotography.info/articles/DoFinDepth.pdf) (PDF), in the section Depth of Field and Camera Format.

Walter Calahan
14-Jun-2008, 05:20
Let's circle our wagons. HA!

Explaining circles of confusion to my students usually only enhance their confusion. Grin.

Brian Ellis
14-Jun-2008, 07:28
The simplest and more or less accurate answer is that to make the same photograph with an 8x10 camera as you make using a smaller format camera a lens on an 8x10 camera has to be longer than the lens on the smaller format camera. Since focal length is one of the three factors that affects depth of field (aperture and distance from subject are the other two), all other things being equal a lens on an 8x10 camera will produce half the depth of field (or circles of confusion twice as large) as a lens on say a 4x5 camera when making the same photograph with both cameras (all other things remaining equal) because the lens on the 8x10 camera will have to be twice as long as the lens on the 4x5 camera in order to do that.

If you then ask why lens focal length affects depth of field, you get into a more complex question. You'll stay saner longer and know all you need to know for photography purposes by just accepting the fact that longer focal length lenses produce shallower depth of field (all other things being equal) than shorter focal length lenses and you have to use longer lenses on an 8x10 camera than you do on smaller format cameras to make equivalent photographs.

Gene McCluney
14-Jun-2008, 07:31
You have "exactly" the same DOF in 8x10 as in 35mm, if you use the same focal length. For example..a 300mm lens on a 35mm and a 300mm lens on an 8x10 camera will have exactly the same depth of field at f22. The visual difference is that a 300mm lens used on a 35mm camera is an extreme telephoto, and a 300mm lens designed for and used on an 8x10 is considered a normal focal length (not wide or telephoto). But the depth-of-field is the same for any given f-stop.

Greg Lockrey
14-Jun-2008, 07:36
You have "exactly" the same DOF in 8x10 as in 35mm, if you use the same focal length. For example..a 300mm lens on a 35mm and a 300mm lens on an 8x10 camera will have exactly the same depth of field at f22. The visual difference is that a 300mm lens used on a 35mm camera is an extreme telephoto, and a 300mm lens designed for and used on an 8x10 is considered a normal focal length (not wide or telephoto). But the depth-of-field is the same for any given f-stop.

Of any given f/stop of a similar focal length focused similarly.

Ralph Barker
14-Jun-2008, 08:44
Also, don't forget that DOF is ultimately a function of the perception of sharpness in a print of a given size. As such, the "acceptable" CoC on smaller formats is smaller due to the greater magnification needed to reach the given print size.

Most DOF calculators assume a print size of 8x10, viewed at a standard distance, and vary the CoCs for the various film formats accordingly.

Jim Galli
14-Jun-2008, 11:52
The depth of field with a 300mm f4 lens is the same on a 35mm camera as it is on an 8X10 camera. What has changed is the angle of view of the area that you see with a 300. On an 8X10 you see an image with an angle of view that is normal to slightly wide. On the Nikon you see a slice out of that which is 1.5 X 1. Think about it. On the Nikon the great empty depth of focus is pronounce, often what the picture is about. On the 8X10 it's just part of the scene and you stop down until everything is sharp just like the Nikon with a 35mm.

Some of us use this phenomenon to our advantage. We'll do a portrait with a 460mm lens focused in close on the 8X10 where the depth of field is a scant .75 - 1 inch. We'll focus on the bridge of the nose and have just enough to fool you into thinking the eyes are in sharp focus. Sometimes you have to let the nose go in order to get the eyes. The result when done well can be an image that seems to have surfaced partially in water. Add the lovely bokeh of an antique lens and you can achieve something non-achievable with computers and photo shop.


http://tonopahpictures.0catch.com/TailgatePortraits/JasonS.jpg
Jason

E. von Hoegh
14-Jun-2008, 16:50
Depth of field = the scene you are photographing; the field between the nearest and farthest objects you want in acceptably sharp focus.

Depth of focus is (all other things being equal) dependant upon the reproduction ratio.
Meaning it is a function of format and focal length; The 300 on 35mm will have the same depth of focus as a 300 on 8x10. but a much narrower field of view.

Jeff Conrad
14-Jun-2008, 19:03
The DoF for 35 mm and 8x10 images taken from the same camera position with lenses of the same focal length using the same f-number is the same only if the images are given the same enlargement. This usually isn't the case, though. If the 8x10 image is contact printed and the 35 mm image enlarged 8x, the 35 mm image will have less DoF than the 8x10 image. This shouldn't really come as a shock; as Jim mentioned, the 300 is a moderate wide angle on an 8x10, but is a moderately long telephoto on 35 mm.

Either situation would seem an unusual comparison of the two formats, and doesn't seem what the original poster had in mind. With a more normal comparison (i.e., taking essentially the same picture), a 35 mm image taken with a 40 mm lens from the same spot using the same f-number and given 8x enlargement would have 8x the DoF of the 8x10 contact print.

Indeed, large format has a big advantage in obtaining shallow DoF. But it's a result of greater magnification with the larger format.

Depth of focus is the distance the image plane can move while keeping acceptable sharpness for an object at a fixed distance from the camera. It's closely related to, but not quite the same as the depth of field (the two are approximately, but not exactly, conjugate). The distinction is probably small enough to ignore for government work.

David Finch
14-Jun-2008, 19:12
So, class . . . which of the following statements is (or are) correct?

(1) Strictly speaking, lens length, f-stop, and film size are all irrelevant to DOF. Only metric aperture at the pupil opening counts. An 80mm lens at f16 has a pupil opening of 5mm, which gives you good DOF without tilts. It's the 5mm opening that gives you the DOF. Nothing else counts. The longer the lens, the smaller the f-stop needed to keep the opening to 5mm, but that's only because of f-stops aren't designated proportionately.

(2) Film size does make a difference. DOF is inversely proportional to magnification, i.e., to the size of the image captured by the film. An 8x10 image identical to that of a 4x5 image is twice as large, and therefore provides only half the DOF.

(3) Forget film size or metric aperture. A lens of a given focal length projects the same image on the film plane no matter what film size, aperture, or f-stop. The smaller the film size, the smaller the piece of that image that is captured on film. DOF gets deeper as the film gets smaller, but only because the field of view gets bigger.

(4) At Sunny-16, you never have to worry about DOF. There's no such thing as Sunny-45 or Sunny-64, because LF photographers use light meters all the time.

Bill_1856
14-Jun-2008, 21:45
A standard 300mm lens, stopped down to f:64, and focused at 16' will have a depth of field from 8' to infinity. No too shabby, since you'll be working on a tripod, anyhow.

Alan Davenport
15-Jun-2008, 08:12
Please explain...

If you're more confused now than when this started, get a copy of The Camera by Ansel Adams.

audioexcels
16-Jun-2008, 12:04
A 210 or 240mm lens cannot keep foreground or background simulteneously sharp without resort to tilt, regardless of the camera format being used.

You mean keeping foreground "and" background simultaneously sharp while the center or other sections are blurred out?

http://flickr.com/photos/21314968@N02/2230246353/

This looks extraordinarily sharp on the foreground and background using the Caltar/Rodenstock 240 which barely covers the format's IC.

Here's another that's not too shabby using a 300mm lens:

http://flickr.com/photos/pierrehebert/2457461245/

Eric Leppanen
16-Jun-2008, 14:43
You mean keeping foreground "and" background simultaneously sharp while the center or other sections are blurred out?

http://flickr.com/photos/21314968@N02/2230246353/

This looks extraordinarily sharp on the foreground and background using the Caltar/Rodenstock 240 which barely covers the format's IC.

Here's another that's not too shabby using a 300mm lens:

http://flickr.com/photos/pierrehebert/2457461245/I was referring to the foreground being a point a few feet in front of the camera, the background being infinity, and everything in between being sharp.

In your first photograph, I can't tell how far away the foreground is, but the waterfall in the background is not at infinity. You will have some more DOF here than would otherwise be the case.

In your second photograph, this is a more distant shot; there is no near foreground. I can see how a 300mm lens would have sufficient DOF to do a good job here.

Leonard Evens
18-Jun-2008, 10:37
I must say I am always mystified by the false things photographers believe about depth of field. There were many examples of this in the responses to the question. I admire Jeff Conrad's attempt to set the record straight, but it sometimes seems like herding cats. You get control of one misconception and another pops up.

The fact of the matter is that depth of field depends on fairly simple principles from geomtric optics, and the formulas governing it are not hard to derive and are well known. It takes a bit more skill to interpret the formulas to answer questions such as what happens when you compare formats, because the answer depends a lot on just what question you ask. If you really want to understand it, read Jeff's article. If the mathematics (which just needs high school algebra and some geometry) puts you off, then just take his word for it. DON"T TRY TO INVENT SIMPLIFLICATIONS BASED ON PARTIAL RULES OF THUMB. Such rules work in special circumstances but none of them work in general. If you haven't actually done the work necessary to find out what the answer is, ask someone, like Jeff, who has.

Let's take the rule quoted above. "DOF depends on the actual diamter of the aperture". That it true only if the coc and focal length. are fixed. To see this, just look at the formula for the hyperfocal distance which may be expressed as the focal length times the ratio of the diameter of the aperture to the coc. But looking at things this way is not too helpful, in any case, since you are unlikely to know the diameter of the aperture, unless you go to the trouble to calculate it from the focal length and the f-number. (I suppose you could try to measure it, but that would be even harder.) It is better to express the hyperfocal distance as the square of the focal length divided by the product of the f-number and the coc. The effect of the square makes applying this more complicated, and that is the source of a lot of confusion.

For distant objects, a useful approximation tells you the DOF depends only on the hyperfocal distance and the distance at which you focus, so if you know the former, you have pretty much everything you need. But this is not the case for closer subjects, such as portraits. In that case, it is best to use an approximation which expresses the answer in terms of the f-number, the coc and the magnification for the plane of exact focus. You see that, expressed this way, it doesn't depends on the focal length, but it does depend on the magnification, the coc. and the f-number. However, this can also be misleading, because the magnification depends on the focal length and subject distance. The reason the rule is useful, is that you can judge magnification visually, without knowing those quantities by looking at the gg.

This aversion to thinking in terms of formulas often leads people to carry things to ridiculous extremes. I remember looking at a web site in which someone is trying to convince you that the DOF depends only on the magnfication, not on the focal length. Even for a fixed format, this is nonsense because it is clearly not the case if much of the scene is distant from the camera. The author of this assertion then goes further by showing you examples of what he claims is true, but, in the examples, it is clearly false. He believes so strongly in his assertion that he ignores what is plainly before his eyes,