DOF and Sensor Size

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Archive 2005 · DOF and Sensor Size

nsbca
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p.7 #1 · DOF and Sensor Size

jasin wrote:
You guys are too funny, no wonder so many of the intelligent canonites have been spending so much time over at Nikon.
It's astounding that so many know so little!
I can't believe that there are still people comparing croping in PS to straight from camera.
DOF scales also ask film format as well by the way.
Cheers,
Jasin.

You guys over there at Nikon are too funny. Why can't you all talk about something more then Canon?

Aug 15, 2005 at 07:52 AM

jasin
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p.7 #2 · DOF and Sensor Size

And what post would that have been, unless it was just appreciating fine equipment like our own!
Cheers,
Jasin.

Aug 15, 2005 at 07:55 AM

cwphoto
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p.7 #3 · DOF and Sensor Size

OK, once and for all:

All those who believe DOF is controlled by Aperture, Subject Distance and Focal Length only, move to the left of the room<

OK.

Now all those who think that the sensor size also affects the DOF move to the right>

OK.

All those on the left of the room are correct. All those on the right of the room, are well, incorrect.

That's just the way it is, you can't change the laws of Physics - if you are on the right and still think you are correct - sorry!

Aug 15, 2005 at 07:59 AM

nsbca
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p.7 #4 · DOF and Sensor Size

This one.

Keith Wong wrote:
I think I need to refocus the debate.

The fact is - larger sensors are better. I'm sure that all of you believe this to some extent. This is one of the reasons why our DSLR's outperform P&S cameras, and why digital MF backs outperform DSLR's.

The point of contention here (I think) is whether a FF sensor has enough of a performance advantage over a 1.5 crop sensor. The two are not dramatically different in terms of size - not to the same magnitude as say, comparing a DSLR sensor to a P&S sensor. What's more, there are other ways in which to improve the performance of smaller photosites - better microlens and electronics design. I can see where the disagreement is, and I don't think it's going to be resolved one way or another in the short term.

I personally want a FF sensor, except that I can not get over the cost hurdle just yet. If the 5D turns out to be all that has been rumoured, it will definitely be on my shopping list.

jasin wrote:
Huh! hey Keith I see the LARGER sensor really works for you!
Oh thats right you don't have one so what gives you the right to comment.
Stick to reading buddy!
Oh and Alan, right on Tiger!
Cheers,
Jasin.

Seems the 5D is all the talk in Nikon land as well.

Aug 15, 2005 at 08:00 AM

steve_t
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p.7 #5 · DOF and Sensor Size

cwphoto wrote:
OK, once and for all:

All those who believe DOF is controlled by Aperture, Subject Distance and Focal Length only, move to the left of the room<

OK.

Now all those who think that the sensor size also affects the DOF move to the right>

OK.

All those on the left of the room are correct. All those on the right of the room, are well, incorrect.

That's just the way it is, you can't change the laws of Physics - if you are on the right and still think you are correct - sorry!

The bit you seem to be stubbornly missing is that the size of the final print is a factor. DOF calculations all assume a standard print size and viewing from a standard distance. If you shoot with a cropped sensor (and for this purpose it doesn't matter if you use a DSLR or an APS-C camera and digitize the negative) then you need to enlarge more to get your standard print size. This extra enlargement reduces DOF.

Aug 15, 2005 at 08:28 AM

jasin
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p.7 #6 · DOF and Sensor Size

CW did you get your FACTS from the back of a pack of honey smacks or what?
I think I will leave it to you guys to work out , oh and nsbca don't you mean F5?
Cheers,
Jasin.
Oh and CW sorry I lean to the right but try this on for size!
Why smaller image sensors have greater DOF
1. For a given field of view (picture angle), the lens focal length must be proportional to the diagonal of the image sensor. For example, the diagonal of 35 mm film is 43 mm. A lens with focal of 43 mm, mounted in a 35 mm film camera, will provide a field of view of 53º. To obtain the same field of view (53º) in a sensor witch diagonal is half that of 35 mm film, we must use a lens witch focal length is 43/2 mm. (By the way, a lens with focal length that is equal to the diagonal of the sensor is called a “normal lens”, as it provides a field of view that is approximately the same as the human eye).

2. In the formula of the hyperfocal distance, the diameter of COC must be proportional to the size of the image sensor. The reason for this is obvious: the image from a smaller sensor must be more enlarged than an image from a larger sensor. So, in order to obtain the same COC in the printed image, the COC (in the sensor image) must be smaller for the smaller sensor.

From what was told in the previous paragraphs, it can be demonstrated that, for a given lens aperture and a given field of view, the hyperfocal distance is directly proportional to the sensor size (that is, a smaller sensor has smaller hyperfocal distance and, as a consequence, larger DOF). I leave the demonstration of this statement as an exercise to the reader.

Aug 15, 2005 at 08:58 AM

AJSJones
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p.7 #7 · DOF and Sensor Size

cwphoto wrote:

That's just the way it is, you can't change the laws of Physics - if you are on the right and still think you are correct - sorry!

With a Horseman kit in your sig, I'd expect you to get it right

The whole point of this thread has been that DoF is NOT a law of physics. It is a result of the properties of the human eye to perceive what is acceptablysharp and its limitations.

It is NOT an intrinsic property of the captured (on the film or on the hard disk) image, it is a combination of the captured image and how it is presented and seen. If I were to print a 4x6 image of a receding fence taken with shallow DoF (aka some in focus and some out of focus) on a 16 MP FF camera for example and ask you which fence posts were acceptably sharp, you would give a different answer than someone looking at a 100% view on screen or on a 16 x 24 print.

Here we go

If you don't look at an image it has no DoF.
OK
In order to determine DoF you have to look at the image.
OK
How you look at it will determine what you see as sharp.
OK?
Or not?

Aug 15, 2005 at 04:12 PM

Imagemaster
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p.7 #8 · DOF and Sensor Size

AJSJones wrote:

The whole point of this thread has been that DoF is NOT a law of physics. It is a result of the properties of the human eye to perceive what is acceptablysharp and its limitations.

Does that then mean that your 8x10 print will only have half as much DOF when viewed by a half-blind person

Seems to me like thousands upon thousands of photographers have been producing beautiful photographs for the last 100 years without having to worry the least bit about all this technical jargon over DOF.

Sure, you can teach students all this technical stuff about sensor size, lenses, COC, etc., but so what? A 747 pilot does not need to know how everything on a 747 works to be a good pilot or to operate that model plane efficiently. I am sure many photographers have been using DOF very efficiently without having to know a single fact about COC.

Whether or not sensor size changes DOF is really quite insignificant in the larger picture.

The photographer has far more control over DOF through the use of other factors.

Aug 15, 2005 at 05:20 PM

jdaily
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p.7 #9 · DOF and Sensor Size

"I don't like the answer, so let's change the model, and the model is meaningless anyhow."

Aug 15, 2005 at 05:27 PM

steve_t
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p.7 #10 · DOF and Sensor Size

Imagemaster wrote:
Perhaps the definition of DOF is just too narrow and there should be more than one definition. You are taking DOF from a three-dimensional world and putting it onto a two dimensional piece of paper. Sounds to me like you just lost all your DOF. Unless you are using three-dimensional paper.

DOF would still apply in this case, but you'd need a whole bunch of new formulae.

Seems to me like thousands upon thousands of photographers have been producing beautiful photographs for the last 100 years without having to worry the least bit about all this technical jargon over DOF.

Many of these same photographers came up with the math and/or were deeply interested in the amount of DOF they wanted in their prints.

Sure, you can teach students all this technical stuff about sensor size, lenses, COC, etc., but so what? A 747 pilot does not need to know how everything on a 747 works to be a good pilot or to operate that model plane efficiently. I am sure many photographers have been using DOF very efficiently without having to know a single fact about COC.

You would be utterly amazed by the amount of technical detail a 747 pilot needs to know about his aircraft before he's allowed to fly it. The theory of how it flies and the circumsances in which it will not are definitely on the list.

Whether or not sensor size changes DOF is really quite insignificant in the larger picture.

The photographer has far more control over DOF through the use of other factors.

The photographer has no control over sensor size (except by cropping the completed image to give an effective reduction) but the bigest factors are always focal length, aperture and distance. The OP wanted to know if these were the only factors though and the answer is no.

Aug 15, 2005 at 05:58 PM

ishmaiel
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p.7 #11 · DOF and Sensor Size

C'mon guys - take it outside.

The sensor size, DOF, crop factor, and effective focal length undergarments have been hanging out there too long. This issue has been discussed to death. Let's get onto something different.

Aug 15, 2005 at 06:02 PM

Jeff Donald
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p.7 #12 · DOF and Sensor Size

Perhaps the definition of DOF is just too narrow and there should be more than one definition. You are taking DOF from a three-dimensional world and putting it onto a two dimensional piece of paper. Sounds to me like you just lost all your DOF. Unless you are using three-dimensional paper.

DOF didn't really exist until there was photography (capturing a 3 dimensional world on a 2 dimensional medium). Try to find a 16th Century painting that displays DOF. DOF is an optical phenomenon that can be described mathematically, but it is hardly a "law of physics" as some have claimed.

Why try to teach the whole story of DOF or just tell part of the story? Students have an inquiring mind and want to know the intimate details of how things work. It also saves many of the students time in the studio. They conceptualize the shot and with a complete understanding of DOF they can choose the lens, frame the shot, set the aperture and take the shot in much less time. That sure is impressive to an AD, as opposed to photographers that move the camera stand back and forth and switch lenses etc. trying to get the shot right. A through understanding of the techniques and processes goes a long way to solving complex compositional issues.

Aug 15, 2005 at 06:09 PM

nsbca
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p.7 #13 · DOF and Sensor Size

I just got of the phone with Canon Tech Support and asked about DOF and the calculations. The Tech, Jeff, stated that there would be NO difference in DOF between the 1Ds Mark II and the 1D Mark II when using the same lens at the same settings.

These are the guys that make the things.

He stated that because the rear element of the lens (and here is where the whole medium format argument gets thrown out the window) remains the same distance from the focal plane (sensor) the phyical attributes of the lens do not change and therefore the DOF scales remain a constant while mounted on either body.

The whole print size argument is moot because if you are printing an image taken with a 1Ds Mark II you are much more likly to print larger (I am) then if you had taken the same image with the 1D Mark II. Because you can!

Hear is the number (US) for anyone who wants to confirm this: 800-828-4040.

For all of you who keep quoting all of your varied internet sources, I will say that I just read on the internet this morning that Mars on the 27th of this month will appear as large as the moon. And as for quoting recognized sources, I beleive I could argue that slavery and genocide are the will of God by quoting a sentence here and a sentence there directly from the Bible. It's been done before.

Believe what you like.

Aug 15, 2005 at 06:40 PM

Jeff Donald
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p.7 #14 · DOF and Sensor Size

Aug 15, 2005 at 06:48 PM

EnCapture
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p.7 #15 · DOF and Sensor Size

some folks cant admit when they are WRONG.

Aug 15, 2005 at 06:51 PM

Monito
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p.7 #16 · DOF and Sensor Size

nsbca wrote: He stated that because the rear element of the lens (and here is where the whole medium format argument gets thrown out the window) remains the same distance from the focal plane (sensor) the phyical attributes of the lens do not change and therefore the DOF scales remain a constant while mounted on either body.

And you believed him?

nsbca wrote: I could argue that slavery and genocide are the will of God by quoting a sentence here and a sentence there directly from the Bible.

Please don't.

Aug 15, 2005 at 06:56 PM

steve_t
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p.7 #17 · DOF and Sensor Size

Just go and play with this handy web page. Try changing the parameters (including camera body) and see what happens as you change each.

http://www.dofmaster.com/dofjs.html

Aug 15, 2005 at 07:06 PM

nsbca
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p.7 #18 · DOF and Sensor Size

Jeff Donald wrote:
I just got of the phone with Canon Tech Support and asked about DOF and the calculations. The Tech, Jeff, stated that there would be NO difference in DOF between the 1Ds Mark II and the 1D Mark II when using the same lens at the same settings.

These are the guys that make the things.

The Tech Support guy is just that. He does not have Ph.D. after his name is ignorant about the factors of DOF.

And your doctorate was in what? Optical engineering? I'll take the word of someone trained by Canon on the characteristics of a Canon lens over some link to a self proclaimed photography guru's web page.

This what I've kown all along, and the Canon Tech just confirmed that for me.

Aug 15, 2005 at 07:12 PM

steve_t
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p.7 #19 · DOF and Sensor Size

nsbca wrote:
Jeff Donald wrote:
I just got of the phone with Canon Tech Support and asked about DOF and the calculations. The Tech, Jeff, stated that there would be NO difference in DOF between the 1Ds Mark II and the 1D Mark II when using the same lens at the same settings.

These are the guys that make the things.

The Tech Support guy is just that. He does not have Ph.D. after his name is ignorant about the factors of DOF.

And your doctorate was in what? Optical engineering? I'll take the word of someone trained by Canon on the characteristics of a Canon lens over some link to a self proclaimed photography guru's web page.

This what I've kown all along, and the Canon Tech just confirmed that for me.

Hmm, option (a) trust a photographer and lecturer in the subject when he tells you something about how cameras work or (b) believe what some low paid drone on a tech support line thinks is true but isn't in his database of answers.

Tricky one that.

Aug 15, 2005 at 07:16 PM

bouch
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p.7 #20 · DOF and Sensor Size

Jeff,

There are just some people who, if they don't know, you can't tell them

I do wish, though, that we could get nsbca to shoot a view camera at f/4 or f/8 without tilt and then we'll see what he thinks about DOF and format size.

Aug 15, 2005 at 07:21 PM

nsbca
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p.7 #21 · DOF and Sensor Size

bouch wrote:
Jeff,

There are just some people who, if they don't know, you can't tell them

I do wish, though, that we could get nsbca to shoot a view camera at f/4 or f/8 without tilt and then we'll see what he thinks about DOF and format size.

How far is the focal plane from the rear element of the lens of the large format camera as opposed to that of a 35mm? Are we using the same (85mm) lens or ar the charateristics different? There is more to the equation you just put forth then merely the size of the sensor or film.

If I were to take my 1Ds sensor and put it directly in the middle of the same large format camera, all other things being the same, I would have the same exact DOF with an extremely cropped image.

Aug 15, 2005 at 07:40 PM

AJSJones
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p.7 #22 · DOF and Sensor Size

I guess those that do not understand the concept of "circle of confusion" are doomed to be trapped within it (whether they work for Canon or Nikon or whomever).

I'm totally OK if someone wants to redefine how 1) to define and then 2) calculate DoF in a world of variable pixel pitch and variable format and variable screen resolutions and prints of different sizes from different formats at different ppi.

So far no-one who does not like/believe/understand the current (60+ year old) concept/definiton and calculation of DoF has proposed anything sensible as an alternative in this thread. Heck, they haven't even defined what they mean by DoF.

Until then, I'm outta here

Aug 15, 2005 at 08:00 PM

Monito
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p.7 #23 · DOF and Sensor Size

nsbca wrote: If I were to take my 1Ds sensor and put it directly in the middle of the same large format camera, all other things being the same, I would have the same exact DOF with an extremely cropped image.

Yes, the same DoF at the sensor plane. But not the same DoF in an 8x10 print made from the sensor image and an 8x10 print made from the large format negative (say 8x10). I think you would prefer to look at an 8x10 print from 15 inches away than to look at a 22.5 x 15mm (7/8 x 5/8 inch sensor size) print from the same 15 inch distance.

You wrote "all other things being the same". That is not enough. You have to be precise. You might mean that the print size is the same (8x10) or you might mean the magnification to print size is the same (1:1) yielding 8x10 and 7/8 x 5/8, respectively.

As has been said, you have to account for all of the variables: 1) lens focal length 2) sensor or negative size, 3) print size, 4) viewing distance, 5) accepted size of circle of confusion in the print for that viewing distance.

N.B.: The distance to the rear element is not a factor and doesn't appear in DoF formulae or interactive calculators. A standard design 21mm lens for a rangefinder has a different distance to the rear element than a retrofocus 21mm such as an SLR might use, to make room for the mirror. But both lenses will have the same depth of field on 35mm film.

Distance to rear element

Aug 15, 2005 at 08:03 PM

slin100
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p.7 #24 · DOF and Sensor Size

A picture, or in this case two, will be worth the thousands of words thrown around so far. Can someone with two different format cameras do this? I can simulate this with my single DSLR, but I suspect someone will cry foul.

Aug 15, 2005 at 08:38 PM

mudlake
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p.7 #25 · DOF and Sensor Size

Sam Bennett wrote:
The reason the DoF ends up being different is because you have to use different focal lengths to accomplish the same goal. So, say you want to take a headshot of someone, and you want the FoV of an 85mm lens. With a FF camera, you'd use an 85mm lens, with a 1.6 cropper you'd most likely use a 50mm lens. If you look at the math (I'm going to use a mythical 53mm lens for the 1.6 cropper, just to prevent hair splitting), you'll see that from the same distance you get:

85mm from 10ft @ f/2.8: 8.36 inches DoF
53mm from 10ft @ f/2.8: 13.8 inches DoF

So for all practical purposes (the ones that matter), then yes - FF cameras will produce narrower DoF. If you look at the difference between the two cameras, you'll see that 8.36 * 1.6 = 13.376, so the DoF difference calculation is pretty easy. Use the crop factor as a multiplier to get the DoF equivalent as well.

This also illustrates why most Medium Format lenses don't open up past f/3.5 in general. The DoF at f/3.5 is very narrow already, an 1.4 lens on a Medium Format body would be practically useless.

This also illustrates why FF cameras will in general have a sharpness advantage for certain types of photography. If you're shooting at f/1.8 on a 1.6 crop camera to achieve a certain Depth of Field effect, the same image can be obtained at f/3.6 on a FF camera, which with most lenses is much closer to the "sweet spot" in terms of sharpness.

Sam said it the best on the very first page. Read it again above. It's the simplist and the most practical explanation for 99% of us here. Getting bogged down in the science isn't helping the vast majority. Understanding what Sam wrote above is.

Aug 15, 2005 at 09:04 PM


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