DOF and Sensor Size

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Archive 2005 · DOF and Sensor Size

bouch
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p.3 #1 · DOF and Sensor Size

nsbca wrote:
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.

Yeah, but the point is, when you change sensor size you do change focal length. I don't shoot 1.6x tighter when I shoot my 20D compared to my 1Ds. I don't shoot 5x tighter when I use my SD400. Do you?

Aug 13, 2005 at 02:38 AM

Jeff Donald
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p.3 #2 · DOF and Sensor Size

The “Circle of Confusion” is an arbitrary factor, used as an aid in selecting an appropriate depth of field to provide subjectively “acceptable” sharpness for a desired enlargement size. It is a term that has been adopted as an attempt to describe the amount of subjective “unsharpness” that is acceptable to the human eye in a photographic print. It has ABSOLUTELY NO BEARING WHATSOEVER on the physical depth of field properties of a lens or camera format. As someone rightly pointed out, you can't change physics, even if you pretend you can by posting contrary notions on your web site.

Depth of Field is result of the eyes ability to tell when images are sharp. Take a page with hundreds of different size dots on it. Use a magnifying glass and determine that no two dots are the same size. Now view the page from a comfortable distance of say 10 inches, about 25 cm, and the eye will interpret many of the smaller dots as the same size. The minimum size that the eye can resolve is called the limit of resolution of the eye and is a result of the diffraction limitations of the eye. An average eye can resolve about .003 inches (.08 mm). In practice a more liberal limit of .01 inches (.25 mm) is used. This is the basis for all CoC numbers used in DOF calculations. A picture can be thought of as a collection of dots and if the dots appear sharp the print will appear sharp.

The advent of digital photography has not changed the human eye, it is still analog. Nor has it changed the appearance of prints, whether produced by an inkjet printer or more traditional wet methods.

Aug 13, 2005 at 02:44 AM

AJSJones
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p.3 #3 · DOF and Sensor Size

nsbca wrote:
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.

It is true that the image falling on the sensor is the same is the same image for a given distance, FL and fstop. However, the DoF is not "embedded" in the sensor information. There is no such item as "theoretically" in focus that can be defined without referring to the human eye's capability.
If you printed, let's say a hypothetical FF 24x26mm sensor image of a landscape at 24x36mm and looked at it from 18 inches, it would likely look small but supersharp in its entirety, and appear to be all in focus. Same would likely be true for a 4x6 print. Print it at say 8x12 inches and the pebbles in the foreground would seem a little fuzzy, while the branches of the tree in the distance still looked sharp. Blow it up bigger and you will see that the flowers at the focus point in the mid ground are still sharp but both the pebbles and the branches seem less sharp. The degree to which you magnify the image has a demonstrable effect on what is perceived (only your eye/brain can do the perceiving) to be in focus.

Aug 13, 2005 at 02:55 AM

nsbca
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p.3 #4 · DOF and Sensor Size

bouch wrote:
nsbca wrote:
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.

Yeah, but the point is, when you change sensor size you do change focal length. I don't shoot 1.6x tighter when I shoot my 20D compared to my 1Ds. I don't shoot 5x tighter when I use my SD400. Do you?

The focal length of a lens is a mathamatial equation that has nothing to do with the fact that you shaved a few MM of the sides of your sensor. You are talking about adding other varialbles to the equation such as perspective and changing lenses to accommodate FoV. Yes, then things change, but you haven't changed the actual DOF of a given lens/body combination.

Aug 13, 2005 at 03:32 AM

Mark Sisco
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p.3 #5 · DOF and Sensor Size

Wow, this thread makes my non-physics minded head spin.

OK, here's my question (probably a stupid one) and the bottom line for me. Let's say you have a basic DOF chart or tool. One that does not claim to account for crop factors or anything. And let's say you are using a 50mm lens on a 1.3 crop sensor like a 1D, and you want to determine hyperfocal distance and the min/max distances that will be in focus at a specified aperture.

Should you select 50mm from the chart to get your answers, or should you choose 65mm (50 x 1.3)?

Don't wack me too hard if this is a really stupid question.

Mark

Aug 13, 2005 at 03:36 AM

nsbca
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p.3 #6 · DOF and Sensor Size

AJSJones wrote:
nsbca wrote:
At any given distance, any given focal length and any given aperture setting the area in focus, or Depth of Field will not change by merely changing the size of the sensor.

It is true that the image falling on the sensor is the same is the same image for a given distance, FL and fstop. However, the DoF is not "embedded" in the sensor information. There is no such item as "theoretically" in focus that can be defined without referring to the human eye's capability.
If you printed, let's say a hypothetical FF 24x26mm sensor image of a landscape at 24x36mm and looked at it from 18 inches, it would likely look small but supersharp in its entirety, and appear to be all in focus. Same would likely be true for a 4x6 print. Print it at say 8x12 inches and the pebbles in the foreground would seem a little fuzzy, while the branches of the tree in the distance still looked sharp. Blow it up bigger and you will see that the flowers at the focus point in the mid ground are still sharp but both the pebbles and the branches seem less sharp. The degree to which you magnify the image has a demonstrable effect on what is perceived (only your eye/brain can do the perceiving) to be in focus.

Then by this logic I can change the DOF characteristics of my 1Ds w/85mm lens combination by simply changing the prints size of an image form 16x20 to 40x60.

That would only be the percieved characteristics, not the mathematical ones, which, by the way, do not bend just because someone needs glasses or stands 20' from the image instead of 2'.

I understand what you are saying about one subject appearing to have a different DOF because it was blown up to a larger size, but actual DOF( the area in focus) is a mathematical equation that has nothing to do with print size.

Aug 13, 2005 at 03:47 AM

bouch
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p.3 #7 · DOF and Sensor Size

nsbca wrote:
You are talking about adding other varialbles to the equation such as perspective and changing lenses to accommodate FoV. Yes, then things change, but you haven't changed the actual DOF of a given lens/body combination.

Other variables to accomadate FoV? Field of view is everything here. I see you have a 1DMkII. Tell me, do you frame everything 1.3x tighter than when you used to shoot 35mm film, or do you frame everything the same but use shorter focal lengths? Can you just answer that question?

BTW, if you do frame everything the same except with shorter lenses, you'll have more DOF than full-frame.

Finally, perspective isn't part of this at all - it's only related to distance to subject - has nothing to do with focal length, field of view, format size, DOF, etc.

Aug 13, 2005 at 03:48 AM

Jeff Donald
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p.3 #8 · DOF and Sensor Size

A mm is always a mm and you must use the actual focal length in DOF calculations.

Aug 13, 2005 at 03:49 AM

nsbca
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p.3 #9 · DOF and Sensor Size

Mark Sisco wrote:
Wow, this thread makes my non-physics minded head spin.

Mark

Stay with the original chart. Nothing on the lens has changed just because you have changed bodies. The same area will be in focus.

Aug 13, 2005 at 03:50 AM

EnCapture
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p.3 #10 · DOF and Sensor Size

FOCAL LENGTH DOES NOT CHANGE!!!! ONLY FIELD OF VIEW!!!! ou dont get closer to the subject, just a smaller crop of the full framed version. DOF is determined by physics. not the human eye, and not anything else. going by the explanation in here, FOV is also determined by the strength of one's prescription for their glasses since what may seem in focus to one will be blurry to another (i know its a silly and extreme example but it is also very applicable)

Edited by EnCapture on Aug 12, 2005 at 11:10 PM GMT

Edited by EnCapture on Aug 16, 2005 at 06:15 AM GMT

Aug 13, 2005 at 03:53 AM

Jeff Donald
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p.3 #11 · DOF and Sensor Size

I understand what you are saying about one subject appearing to have a different DOF because it was blown up to a larger size, but actual DOF( the area in focus) is a mathematical equation that has nothing to do with print size.

I quoted the mathematical equation in my first post. The equation needs a number for CoC, which is based on the limit of resolution of the human eye. The limit of resolution of the human eye will change as the distance to the viewed print changes.

Aug 13, 2005 at 03:54 AM

bouch
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p.3 #12 · DOF and Sensor Size

EnCapture wrote:
FOCAL LENGTH DOES NOT CHANGE!!!! ONLY FIELD OF VIEW!!!! ou dont get closer to the subject, just a smaller crop of the full framed version

Edited by EnCapture on Aug 12, 2005 at 10:55 PM GMT

But, EnCapture, this simply isn't the way people use cameras. No one tends to shoot tighter the smaller their format. They shoot the same field of view but use shorter focal lenghts. Is this point lost on you, or do you simply disagree?

Aug 13, 2005 at 04:06 AM

EnCapture
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p.3 #13 · DOF and Sensor Size

bouch wrote:
EnCapture wrote:
FOCAL LENGTH DOES NOT CHANGE!!!! ONLY FIELD OF VIEW!!!! ou dont get closer to the subject, just a smaller crop of the full framed version

Edited by EnCapture on Aug 12, 2005 at 10:55 PM GMT

But, EnCapture, this simply isn't the way people use cameras. No one tends to shoot tighter the smaller their format. They shoot the same field of view but use shorter focal lenghts. Is this point lost on you, or do you simply disagree?

we arent talking about how people use a camera. the original question asked was whether frame size alters DOF (actual physical portion of the image that is in focus that is measurable). since nothing else was mentioned (such as changing lenses, circles of mass destruction or anything else) you have to assume that the original poster was asking that if under controlled conditions and only sensor size being the variable, would the DOF change. and the answer is no. just as focal length is determined only by the lens and not by crop factor etc.

Edited by EnCapture on Aug 12, 2005 at 11:15 PM GMT

Edited by EnCapture on Aug 16, 2005 at 06:15 AM GMT

Aug 13, 2005 at 04:13 AM

nsbca
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p.3 #14 · DOF and Sensor Size

bouch wrote:
nsbca wrote:
You are talking about adding other varialbles to the equation such as perspective and changing lenses to accommodate FoV. Yes, then things change, but you haven't changed the actual DOF of a given lens/body combination.

Other variables to accomadate FoV? Field of view is everything here. I see you have a 1DMkII. Tell me, do you frame everything 1.3x tighter than when you used to shoot 35mm film, or do you frame everything the same but use shorter focal lengths? Can you just answer that question?

BTW, if you do frame everything the same except with shorter lenses, you'll have more DOF than full-frame.

Finally, perspective isn't part of this at all - it's only related to distance to subject - has nothing to do with focal length, field of view, format size, DOF, etc.

What has anything you have just said have to do with Depth of Field? If I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?

DOF, I will repeat, is the area in front of and behind the focus point that is in focus.

Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.

Aug 13, 2005 at 04:15 AM

EnCapture
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p.3 #15 · DOF and Sensor Size

nsbca for presicdent and encapture for vice president!!

Aug 13, 2005 at 04:17 AM

bouch
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p.3 #16 · DOF and Sensor Size

Hrow wrote:
What a fire storm to a simple question. I am well aware that distance and lens impact DOF but that wasn't the question. Nor was the impact of distance, lens or aperture even a consideration when the question was framed because the question was not will the need to change focal lengths to accomadate different sensor sizes to produce the same picture result in different DOF? The answer to that is obviously yes. But that wasn't the question.
The question arose from the assertion that the sensor size itself impacts DOF. To me that made no sense but I often miss things so I thought I would ask.

To the poster who asked who suggested that view camera users use F64 and swings and tilts to get acceptable DOF... there is a difference between acceptable DOF and great DOF. Why do view camera users use F64 and S/T? Because they can! When done properly and for good purpose the DOF on a view camera far exceeds anything available on a 35mm or medium format but it is not because the film size is bigger, it is because the film and/or lens plane is altered to match the subject.

I am well aware how swings and tilts work - I've been shooting Canon T/S lenses for 30 years. I would certainly consdier the Canon T/S lenses something "available in the 35mm format". I stand by my claim that view cameras would hardly be useable if they could only be stopped down to f/22 and didn't have movements.

I can't hardly believe that you can't see how format size from a practical point of view affects DOF. Camera users don't shoot the same focal length regardless of format, they shoot the same field view regardless of format.

Aug 13, 2005 at 04:17 AM

bouch
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p.3 #17 · DOF and Sensor Size

nsbca wrote:

Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.

The intened print size is built into the equation. They don't ask you for it because it's assumed. The assumption is normally an 8x10 print, I believe.

Here's what Norman Koren has to say:

An object at a distance s in front of the lens is focused at a distance d behind it, according to the lens equation: 1/d = 1/f - 1/s, where f is the focal length of the lens. If the lens were perfect (no aberrations; no diffraction) a point at s would focus to an infinitesimally tiny point at d. An object at sf , in front of s, focuses at df , behind d. At the film plane d, the object would be out of focus; it would be imaged as a circle whose diameter Cf is called its circle of confusion. Likewise, an object at sr, behind s, focuses at dr, in front of d. Its circle of confusion at d has diameter Cr.

The depth of field (DOF) is the range of distances between sf and sr, (Dr + Df ), where the circles of confusion, Cf and Cr, are small enough so the image appears to be "in focus." The standard criterion for choosing C (the largest allowable value of Cf and Cr) is that on an 8x10 inch print viewed at a distance of 10 inches, the smallest distinguishable feature is (allegedly) 0.01 inch.

Aug 13, 2005 at 04:21 AM

bouch
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p.3 #18 · DOF and Sensor Size

nsbca wrote: If I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?

No, the DOF doesn't change, the FOV does. Is that how you normally shoot?

Aug 13, 2005 at 04:26 AM

Clayphish
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p.3 #19 · DOF and Sensor Size

And this would be why the Sigma 30mm 1.4 + 1.6x camera wouldn't really simulate the a 50mm 1.4 + ff camera when it comes to DOF and FOV.

Aug 13, 2005 at 04:27 AM

Jeff Donald
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p.3 #20 · DOF and Sensor Size

Lastly, how come DOF scales ask for focal length, f/stop setting and distance from subject to arrive at an acurate DOF. Never once in my life did I ever see a DOF scale the asked how large the intended print size is.

The CoC is already factored in to the equation based on the size of a standard print and standard viewing distance. Canon list the size they use on their site. Most DOF calculators allow you to pick a CoC or pick a format (which changes the CoC value).

Here is the best treatment on the web of DOF and CoC to the best of my knowledge. Van Walree covers CoC, confusion over background blur etc. His text is concise and to the point, but not brief. Anyone who really wants to argue beyond this point should start quoting scholarly text, as Van Walree does. Linking to a site is not a scholarly text. Everything I have posted in this thread I can quote numerous college texts confirming what I've written.

Aug 13, 2005 at 04:34 AM

nsbca
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p.3 #21 · DOF and Sensor Size

bouch wrote:
nsbca wrote: If I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?

No, the DOF doesn't change, the FOV does.

Exactly.

bouch wrote:
Is that how you normally shoot?

That is irrelevant. DOF is a mathematical equation. The way I normally shoot cannot change that.

Aug 13, 2005 at 04:37 AM

bouch
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p.3 #22 · DOF and Sensor Size

nsbca wrote:
bouch wrote:
Is that how you normally shoot?

That is irrelevant. DOF is a mathematical equation. The way I normally shoot cannot change that.

Why irrelevant? If you wanted to shoot something with a 180 on a 1Ds, you'd change to a 140 or something on your 1D, right? You wouldn't shoot tighter, would you? So if you switched to 140 you'd end up with more DOF, right? And what forced you to switch to 140? The format size.

Bob Atkins doesn't seem to think DOF can be pinned so precisely. From the before referenced photo.net article:

First, DOF relates to a print or other reproduction of an image. It's NOT an intrinsic property of a lens. If you put a lens on an optical bench you can measure focal length, you can measure aperture, but you can't measure depth of field. Depth of field depends on some subjective factors which I'll discuss later.

Edited by bouch on Aug 12, 2005 at 09:49 PM GMT

Aug 13, 2005 at 04:45 AM

Jeff Donald
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p.3 #23 · DOF and Sensor Size

f I am standing 20' from a 50' high white plaster wall with my 180mm 3.5 mounted on a tripod set at f/3.5 and I first attach my 1Ds to the lens and take an image. Then, leaving the lens set the way it is and the tripod in the same position, I take another image with my 1D Mark II has the DOF changed?

How can the DOF change? The image has no foreground and no background. Your example is irrelevant to a discussion of DOF.

Aug 13, 2005 at 04:47 AM

Phil Bonner
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p.3 #24 · DOF and Sensor Size

The way folks stated it, the FF would provide more shallow depth of field - period. All I know is that the DOF/Bokeh/background blur of images shot with my 20D and 85L at f/1.2 appear just as shallow and dreamy as those that I see here shot by others with FF cameras at f/1.2.

Now if we were shooting the same subject and I had to move in closer to the subject to get the same framed shot with the FF that I had taken with the 1.6 crop 20D, then of course I would expect that the closer distance tothe subject would cause the image to have shallower DOF. Anyone who has shot macro knows about hyper shallow DOF due to close proximity.

Edited by Phil Bonner on Aug 12, 2005 at 08:59 PM GMT

Aug 13, 2005 at 04:56 AM

bouch
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p.3 #25 · DOF and Sensor Size

Jeff Donald wrote:Here is the best treatment on the web of DOF and CoC to the best of my knowledge.

Good link, Jeff. The example Grommit photos at f/22 are interesting - really shows how DOF is an inexact science. The background car at f/22 & 28mm is as blurry as in the 100mm photo but is part of the DOF because it's small enough that it looks acceptably sharp.

Aug 13, 2005 at 04:59 AM


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