DOF and Sensor Size

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Archive 2005 · DOF and Sensor Size

nsbca
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p.4 #1 · DOF and Sensor Size

Jeff Donald wrote:
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.

Who said the wall was flat?

Aug 13, 2005 at 05:02 AM

Jeff Donald
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p.4 #2 · DOF and Sensor Size

DOF is not Bokeh and it is not background blur. This is covered at Van Walree's site. Please take a few moments and read the link I've provided so that you may contribute to this thread in a meaningful way.

Van Walree has several notable quote that you would do well to learn.

"Neither the absolute nor the relative background blur should be used as a criterion to judge the depth of field. It is a common mistake to associate telephoto lenses with a shallow DOF because of the large absolute blur."

"However, in a more general comparison of two different photographs one needs to be very careful not to base a DOF judgement on the observed background blur."

Aug 13, 2005 at 05:04 AM

slin100
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p.4 #3 · DOF and Sensor Size

EnCapture wrote:
DOF is determined by physics. not the human eye, and not anything else.

It is determined by physics, but I suggest you take a closer look at the mathematical equation. You'll find that the equation has a CoC component, the value of which is determined by the human eye!

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?

If you print both images at the same size, yes, the DOF will have changed, although with a flat wall, it's not likely you'll notice any difference.

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 DOF scales are set according to the CoC chosen by the manufacturer. There are an infinite combination of print size and viewing distance combinations that correspond to this CoC. Canon uses a CoC of .035mm for full-frame 35mm and .020 mm for 1.6x crop factor cameras.

Aug 13, 2005 at 05:04 AM

EnCapture
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p.4 #4 · DOF and Sensor Size

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

Aug 13, 2005 at 05:04 AM

Jeff Donald
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p.4 #5 · DOF and Sensor Size

Who said the wall was flat?

I assumed you were a better craftsman. The DOF at that distance etc. is about 12 inches.

Aug 13, 2005 at 05:05 AM

bouch
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p.4 #6 · DOF and Sensor Size

Phil Bonner wrote:
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.

Phil, you can achieve very shallow DOF with the 85/1.2 on a 1.6x crop camera. It may be hard to distinguish from full-frame. Here are some numbers:

85mm @ f/1.4, full-frame, focused at 100cm, DOF = 1.07cm
85mm @ f/1.4, 1.6x, focused at 100cm, DOF = .68cm

85mm @ f/1.4, 1.6x, focused at 160cm, DOF = 1.8cm (equivalent field of view as full-frame example)

Aug 13, 2005 at 05:09 AM

bouch
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p.4 #7 · DOF and Sensor Size

EnCapture wrote:

even a wall has 3 dimensions to it. it isnt completely flat. whether u can see it or not.

Oh, forget it I'm tired _peace_

Aug 13, 2005 at 05:10 AM

nsbca
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p.4 #8 · DOF and Sensor Size

Jeff Donald wrote:
Who said the wall was flat?

I assumed you were a better craftsman. The DOF at that distance etc. is about 12 inches.

With both cameras.

Aug 13, 2005 at 05:11 AM

nsbca
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p.4 #9 · DOF and Sensor Size

slin100 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?

If you print both images at the same size, yes, the DOF will have changed, although with a flat wall, it's not likely you'll notice any difference.

Why do I have to print them both the same size? If I have a 1Ds, knowing I have a higher Mp sensor wouldn't I naturally print the image larger then the image I took with the 1D Mark II? I mean I would. That was a rhetorical question.

Aug 13, 2005 at 05:15 AM

Jeff Donald
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p.4 #10 · DOF and Sensor Size

Why do I have to print them both the same size? If I have a 1Ds, knowing I have a higher Mp sensor wouldn't I naturally print the image larger then the image I took with the 1D Mark II? I mean I would. That was a rhetorical question.

This makes no sense. What are you trying to say?

Aug 13, 2005 at 05:20 AM

Phil Bonner
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p.4 #11 · DOF and Sensor Size

OT: Yes at at f/1.2 and close range for a head shot, the DOF gets ridicuously shallow - a couple hundreths of an inch. It takes both a very steady subject and camera to hit it right. Once I got the 85L and learned just how paper thin the plane of focus becomes at f/1.2, my admiration of the skill of the great 85L shooters here on FM has increased five fold.

Aug 13, 2005 at 05:25 AM

slin100
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p.4 #12 · DOF and Sensor Size

nsbca wrote:
Why do I have to print them both the same size? If I have a 1Ds, knowing I have a higher Mp sensor wouldn't I naturally print the image larger then the image I took with the 1D Mark II? I mean I would. That was a rhetorical question.

You would? If you printed an 8x12 from the 1D Mark II, you would print a nonstandard 10.4x15.6 from the 1Ds?

Aug 13, 2005 at 05:58 AM

nsbca
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p.4 #13 · DOF and Sensor Size

slin100 wrote:
nsbca wrote:
Why do I have to print them both the same size? If I have a 1Ds, knowing I have a higher Mp sensor wouldn't I naturally print the image larger then the image I took with the 1D Mark II? I mean I would. That was a rhetorical question.

You would? If you printed an 8x12 from the 1D Mark II, you would print a nonstandard 10.4x15.6 from the 1Ds?

First off I wouldn't print an 8x10 on my printer. That is the reason I have 1 series bodies and a wide format printer. I can print any size I like and I don't ever have to second guess or recalculate the DOF scales on my lenses. I KNOW IF I AM GOING TO PRINT LARGER THE IMAGE WILL HAVE TO BE SHARPER TO LOOK AS GOOD AS A SMALLER PRINT, but my lens remains a constant.

Aug 13, 2005 at 06:09 AM

Volleybob
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p.4 #14 · DOF and Sensor Size

Do this experiment.

1. Print photo
2. Observe DOF in photo (take notes if it will help you learn)
3. Take scissors and crop printed photo
4. Observe DOF in photo (compare notes)

Did DOF change? This is EXACTLY what happens with a crop frame sensor.

Aug 13, 2005 at 06:43 AM

Monito
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p.4 #15 · DOF and Sensor Size

To do the experiment you have to account for viewing distance. It is natural to bring the smaller photograph closer after the surgery.

Aug 13, 2005 at 06:55 AM

stevei
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p.4 #16 · DOF and Sensor Size

EnCapture wrote:we arent talking about how people use a camera. the original question asked was whether frame size alters DOF

I would argue that we are talking about how people use a camera, because this is the only thing that matters in this discussion. To discuss how DOF is affected by sensor size when using a camera in a way that nobody actually uses it is a meaningless discussion.

When you use different formats, whether a P&S with tiny sensor, 1.6 crop SLR, FF SLR, medium format, large format or whatever, the principle is the same, you stand in the same place with each camera, and select a focal length that gives you the field of view you need for your shot. The required focal length will be longer as the format gets larger. The DOF will decrease as the format gets larger.

The only reason someone would ask this question in the first place is if they are interested in the practical effects of sensor size on DOF, rather than the effects in some meaningless theoretical experiment.

Aug 13, 2005 at 08:13 AM

steve_t
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p.4 #17 · DOF and Sensor Size

nsbca wrote:
... I can print any size I like and I don't ever have to second guess or recalculate the DOF scales on my lenses. I KNOW IF I AM GOING TO PRINT LARGER THE IMAGE WILL HAVE TO BE SHARPER TO LOOK AS GOOD AS A SMALLER PRINT, but my lens remains a constant.

And with this statement you've just shot your whole argument down. Larger prints need sharper original images. DOF is about the SUBJECTIVE point at which an object or point in a scene becomes out of focus. The more you enlarge your image when you print it the more obvious it becomes that a point isn't sharp to within a pixel of your image so, for a constant viewing distance, DOF reduces as your prints get larger.

Having concluded that print size effects DOF take a shot with a full frame camera. Print it at 12.8x16". Crop this print to 8x10". In no way is this different to shooting with a 1.6 cropped sensor and printing at 8x10"

Aug 13, 2005 at 09:12 AM

steve_t
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p.4 #18 · DOF and Sensor Size

Volleybob wrote:
Do this experiment.

1. Print photo
2. Observe DOF in photo (take notes if it will help you learn)
3. Take scissors and crop printed photo
4. Observe DOF in photo (compare notes)

Did DOF change? This is EXACTLY what happens with a crop frame sensor.

BUT that assumes that you will always print your images from a 1.6 crop body 1.6 times smaller, which is just plain wrong. You enlarge your image 1.6 times more when you print from the cropped camera to get the same sized print and the result is a reduction in DOF. Changing lenses to get the same field of view masks this effect.

Aug 13, 2005 at 09:16 AM

aekurth
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p.4 #19 · DOF and Sensor Size

Take a few pictures folks. If you try to stand in exactly the same place and photograph the same scene with a 35mm and a medium format camera you will find that you needed a longer focal length with medium format and that you had to stop down more to get the same depth of field.

Aug 13, 2005 at 12:31 PM

EnCapture
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p.4 #20 · DOF and Sensor Size

aekurth wrote:
Take a few pictures folks. If you try to stand in exactly the same place and photograph the same scene with a 35mm and a medium format camera you will find that you needed a longer focal length with medium format and that you had to stop down more to get the same depth of field.

and once you get that same depth of field you will have a DIFFERENT FIELD OF VIEW!! bet the lens remaining constant, distance remaining constant, the DOF will be the same even if it appears different due to the crop of the image. after i do a shoot today i will do a test comparing the 1DsII and the 1DII

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

Aug 13, 2005 at 03:24 PM

bouch
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p.4 #21 · DOF and Sensor Size

EnCapture wrote:
aekurth wrote:
Take a few pictures folks. If you try to stand in exactly the same place and photograph the same scene with a 35mm and a medium format camera you will find that you needed a longer focal length with medium format and that you had to stop down more to get the same depth of field.

and once you get that same depth of field you will have a DIFFERENT FIELD OF VIEW!! bet the lens remaining constant, distance remaining constant, the DOF will be the same even if it appears different due to the crop of the image. after i do a shoot today i will do a test comparing the 1DsII and the 1DII

You won't have a different field of view in aekurth's example. You would just stop down more in medium format than 35mm. Anyone who's shot the different formats knows this....

These pretzels are making me THIRSTY!!

Aug 13, 2005 at 03:32 PM

jmcfadden
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p.4 #22 · DOF and Sensor Size

steve_t wrote:
Volleybob wrote:
Do this experiment.

1. Print photo
2. Observe DOF in photo (take notes if it will help you learn)
3. Take scissors and crop printed photo
4. Observe DOF in photo (compare notes)

Did DOF change? This is EXACTLY what happens with a crop frame sensor.

BUT that assumes that you will always print your images from a 1.6 crop body 1.6 times smaller, which is just plain wrong. You enlarge your image 1.6 times more when you print from the cropped camera to get the same sized print and the result is a reduction in DOF. Changing lenses to get the same field of view masks this effect.

Steve

you talk of being frustrated , sheesh , please re-read your reply here and Think about what you wrote , sheesh if I have achieved the framing I wanted in the VF , (forget about the FL for a moment ) WHY in the heck would I enlarge it at 1.6 or 10x or any other number you can pull out of a hat?
Digital sensors have no real physical size , this is why you FF fanatics have to let the fact that the reasons for spending 8K on a camera are ones you have to justify all the time

But in this case the argument holds no water at all, there May be reasons for FF , this isn't one of them.

Aug 13, 2005 at 03:56 PM

AJSJones
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p.4 #23 · DOF and Sensor Size

jmcfadden wrote
WHY in the heck would I enlarge it at 1.6 or 10x or any other number you can pull out of a hat?

The original assumptions for the CALCULATION of DoF for the 35mm format camera system were pulled out of a hat - they are reasonable but still "made up", "arbitrary" and "not based on a law of physics". i.e. taking a 24x36 mm negative, ENLARGING it to ~8x10 or 8x12 and viewing it from around a foot. (These numbers vary a bit because not all manufacturers of lenses pulled them out of the same hat). Now, if someone chooses 1) to use a different size negative, or sensor area etc, to print to the same size or, 2) the same sensor but different print size or 3) look at the print from closer or further away, the fixed ability of the human eye to discern detail means they should use a different CoC and therefore a different DoF.

Digital sensors have no real physical size , this is why you FF fanatics have to let the fact that the reasons for spending 8K on a camera are ones you have to justify all the time

So, by this logic, if I scan a 35mm slide, then once it's digital, the slide's dimensions become virtual and irrelevant

Of course the sensor has physical dimensions; the fact that the information is digitized has no effect on the magnification ratio of the size of the original image falling on it to the final print size. This magnification ratio is a key parameter in determining DoF. The circle of confusion will still be in the image data with the dimensions of pixels instead of mm.

encapture and nsbca:
Is it some kind of religious belief for you guys that DoF is an intrinsic property of the lens (like FL, aperture ) and all you need to calculate it is FL, aperture and subject distance??
For example
"DOF is a mathematical equation."[sic]

There is no *completely abstract* scientific equation that tells you what is in focus - it is the eye that judges whether something is in focus. The equation you refer to includes a factor (the CoC) which is determined by the biology/neurology of the human eye/brain combo, the ratio of print size to capture area and the viewing distance. If you don't accept this fact, and its consequences for this discussion, then we (or at least I) can't help you any more.

You can lead a horse to water....

Aug 13, 2005 at 05:54 PM

Imagemaster
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p.4 #24 · DOF and Sensor Size

bouch wrote:
Imagemaster wrote:
Neither sensor size nor film size affects DOF. Cameras and lenses do, but that was not the question.

Isn't format size sort of tied to the camera?

Well Mr. Know-it-all, I guess you have not heard of multi-format cameras.

Why don't you just stay out of these discussions if you don't have clue?

I beg your pardon, I did not know that you had a monopoly on voicing opinions, or are you just a self-appointed moderator

Take a Mamiya 645 camera and take a photo. Now, without changing the lens, aperture, or lens-to-subject distance, put on a 35mm roll-film holder and take a second photo. Now take your loupe and see if you can find greater or less DOF on the 645 film. Surprise, it is the same regardless of the change in film size.

The DOF was determined by the focal length of the lens, the aperture, and the lens-to-subject distance. I could put a piece of lettuce on the film plane and it would not change the DOF just ahead of that plane.

The original question: I have read a couple of posts here that indicate that DOF increases when sensor size decreases. If this is true, can someone please explain why?

"sensor size decreases" - PERIOD It is very convenient for all the vaiables others brought into this discussion, such as camera model, lens, printing, etc.

Try Mike Lepp's explanation: http://www.photozone.de/3Technology/depth2.htm

I have read a couple of posts here that indicate that DOF increases when sensor size decreases. If this is true, can someone please explain why?

I’ll explain what I call the physics by use of an example. Let’s say we take a picture of a point with a 4x5inch camera and crop out a 6x7cm, 6x4.5cm, and a 35mm frame sizes. (If you like, consider all these formats with the same focal length lens, at the same aperture, and the same distance to the point). According to the applets that take into account format size, the DOF changes for each crop. Does this make sense? Of course not! It is the same point on the same piece of film. As such, it can’t be magnified any more for each format and still look like a point and not a disk. Thus, we can conclude that COC is not a function of format. This leaves DOF as a property of the lens and focusing distance(review the above equations). Also note that the sharper the lens, the smaller the point is that can be produced on the film, the shallower the DOF (I’ll let you think about this), and the
larger a print can be made and still have the point look like a point.

Aug 13, 2005 at 06:47 PM

stevei
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p.4 #25 · DOF and Sensor Size

Imagemaster wrote:Take a Mamiya 645 camera and take a photo. Now, without changing the lens, aperture, or lens-to-subject distance, put on a 35mm roll-film holder and take a second photo.

But why would anybody do this? The two photos are different compositions, so any comparison between them is meaningless.

Aug 13, 2005 at 07:04 PM


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