Busting the FF vs Crop DoF Bokeh Myth

Started Jul 27, 2009 | Discussions
Kuivaamo Senior Member • Posts: 2,248
Re: I think I found out where the DoF confusion is...

therickman wrote:

Yes, but you wouldn't view a 20X30 print from the same distance as a 4X6. You'd stand back farther to comfortably view the whole image.

Not necessarily. People do admire large prints from close up, and if you want your prints to stand up to such scrutiny, you have to take this into consideration when you determine your acceptable CoC (for performing hyperfocal focusing, for instance). It's the same with megapixels: you'll get by with 6 mp for any print size if you assume that people always stay far enough from the print, but you'll need more if you want to maintain e.g. 300 ppi for closer inspection.

So, essentially, DoF has to do with the distance between the viewer and the picture, right?

It is one of the things that affect DoF, along with enlargement ratio, aperture, focal length and distance.

Were you to stand back from a 20X30 picture so that it is relatively the same size as you'd view a 4X6 at arm's length, then the details of the 20X30 would look exactly the same as the 4X6, therefore the actual measured DoF hasn't changed at all.

Yes, when you make the assumption that the print always occupies the same portion of the viewer's field of vision. In Dofmaster calculations the assumption is an 8x10" print viewed from 25 cm away, or any other combination of print size and viewing distance that impose the same limits on human acuity (i.e. print bigger but stand further back, or print smaller but view closer).

If you want to use hyperfocal focusing, and plan to make a large print that looks good from a foot away, you should choose a smaller CoC than suggested by Dofmaster by default. I you only plan to make 4x6" prints, you can relax your CoC criterion and get away with a larger aperture and consequently a higher shutter speed. There is no "absolute DoF" at capture.

Richard Veteran Member • Posts: 4,858
Re: In reality, you are wrong.

I shoot sports as well. If you have a 5d2 at 21 mp and I disagree with you. Sure there are places where you can't get closer, but that is not the majority of photography, street photography, portrait, landscape, even sports, all allow you to move around. There are some situations where you can't. But in those situations, you have to change lenses, this is outside the test of the same lenses same distance or different distance. That is why I said, if I don't like the perspective because when you move it can change. But lets look at your situation. You are taking a picture with your 8 or 10mp crop camera, you are using a 400 2.8, if you switch to a ff camera you either have to do one thing or another. You put on your 800 which is outside of the scope of the same lens or you keep the 400 on and move closer. But if you have a 5d2 and keep the same 400 lens, you just crop the image because it has about the same resolution as your crop camera after you have cropped it to the same FOV.

So reality is this. If you run up against a barrier, you put on a different lens, no matter which camera you have.

Cal Dawson wrote:

I agree "But not with you" It is reality. I come up against barriers and obstacles all the time which prevent my getting closer, Whether it be sidelines (Sports) Barricades (Police, Fire and of course Zoos) so of course this is in fact reality not an assumption. The OP's findings are valid for anyone who shoots anything but portrait (A completely controlled environment) I've been here before and returned the FF camera as being inadequate for the job (Too much FOV for the job) and no way to get closer.....

Richard wrote:

My conclusion:
At the same distance from subject,

This is an assumption and is not reality.

In reality, if I have a 50mm lens on a crop body and I take a picture of someones face, I will stand 8 feet way move closer or farther away to frame the persons face.

If I put that same lens on a full frame body, what will I do. I will do what every person that is not using a zoom lens does, I sneeker zoom until the persons face is framed correctly. That means I move closer. Maybe to 4 feet. This is what makes the oof even more oof and depth of field changes.

Your method of of the same distance may produce negligable differences but it is not what most people are talking about when they talk about the DOF changes when you go to FF. They mean because you have to move closer to keep framing the same.

Now if you don't like the perspective, you may change to a different lens but then it is not using the same lens.

So from my perspective, because I am going to frame the subject the same way using a particular lens (unless I don't like the perspective) DOF will always be less on the FF body.

Kjeld Olesen
Kjeld Olesen Veteran Member • Posts: 4,117
You did not apply the equivalence principle (nt)
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OP therickman Senior Member • Posts: 1,305
Re: I think I found out where the DoF confusion is...

Kuivaamo wrote:

therickman wrote:

Yes, but you wouldn't view a 20X30 print from the same distance as a 4X6. You'd stand back farther to comfortably view the whole image.

Not necessarily. People do admire large prints from close up, and if you want your prints to stand up to such scrutiny, you have to take this into consideration when you determine your acceptable CoC (for performing hyperfocal focusing, for instance). It's the same with megapixels: you'll get by with 6 mp for any print size if you assume that people always stay far enough from the print, but you'll need more if you want to maintain e.g. 300 ppi for closer inspection.

So, essentially, DoF has to do with the distance between the viewer and the picture, right?

It is one of the things that affect DoF, along with enlargement ratio, aperture, focal length and distance.

Were you to stand back from a 20X30 picture so that it is relatively the same size as you'd view a 4X6 at arm's length, then the details of the 20X30 would look exactly the same as the 4X6, therefore the actual measured DoF hasn't changed at all.

Yes, when you make the assumption that the print always occupies the same portion of the viewer's field of vision. In Dofmaster calculations the assumption is an 8x10" print viewed from 25 cm away, or any other combination of print size and viewing distance that impose the same limits on human acuity (i.e. print bigger but stand further back, or print smaller but view closer).

I understand many viewers will stand up close to look at detail, etc. But, with most photographers or artists behind a certain piece of work, the desire is to have the viewer appreciate the image in its entirety first and foremost. Then, if the intracacies of how the painting or picture was constructed are to also be appreciated by the artist (mosaics, pointilism, panoramas, etc.) then closer inspection of detail is warranted. If I take a photograph of Pittsburgh, yet all I wanted the viewer to appreciate was the PPG building, then I would have taken a picture of only the PPG building, not the entire city. When I display an image, it is to be viewed in its entirety, from a normal comfortable distance. Therefore, DoF does not change whether it's printed at 4"X6" or 20'X30'.

For instance, Had Georges Seurat only wanted you to see this...

... then he'd only have painted that and called it a day. Up close, it's a bunch of colored dots in a chaotic mixture. Stand back farther, you can see it's a man's head. However, Seurat doesn't just want you to see the mess of dots or the man's head, he wants you to appreciate the entire painting first...

... and then appreciate the detail, how it was ultimately constructed.

So, as a photographer knowing most of my images will be seen anywhere from 4X6 to 8X12, my understanding of DoF is how a viewer sees my images in their entirety from a normal viewing distance. Therefore, DoF doesn't change.

BTW - pointilism painting works in the same manner as megapixels.

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xtoph Veteran Member • Posts: 9,871
different enlargements

consider just one final print size, let's say 5x7 (which used to be a standard used by 35mm camera companies).

now, to enlarge an image from a crop sensor to 5x7 you have to enlarge more than you enlarge an image from a ff sensor.

the more you enlarge, the more more you notice blur.

so in the unusual situation where you hold perspective (distance) and fl constant but use different format sizes, your crop sensor will give the appearance of less dof. this is the source of the discrepancies you observed in dof calculators (they are not mistaken).

the reason that we usually gloss smaller sensors as having deeper dof is, as you know, because to get the same framing we change either fl or perspective. but format size alone also has an effect because we have to enlarge different formats by different amounts to obtain the same size final print (coc is only defined for a given print size).

climbng_vine Forum Member • Posts: 86
Re: You are adding to the myth

Roger Krueger wrote:

climbng_vine wrote:

Roger Krueger wrote:

How? If I'm wrong then all the DoF equations must be wrong too.

No, because they aren't saying the same thing you are.

Yes, they are.

No. No, they aren't. If you think they are, provide your evidence.

Fine, so I should have said it as "a lens-format combination which produces a given field of view". (Format and crop being indistinguishable.) I greatly doubt anyone but you was confused.

This is the point (and by the way, condescension from people who are mistaken is hilarious). I am not at all confused, but the great mass of threads on this topic are evidence that many people are, because of the mushy use of terms and concepts here. The entire issue here is about different size sensors, so yes, in fact, it is CRITICAL to distinguish between field of view and focal length, because between different sensor sizes is when the difference between the two matters.

I'm not going to reply to the rest, because you're repeating yourself and you're still wrong. And if I were to correct you again, I'd be repeating myself. Anyone who cares can just re-read the last page once more.

Cal Dawson Veteran Member • Posts: 4,810
Re: In reality, you are wrong.

I didn't say all photography. Just as there are times you cannot get closer there are times when you can. There are many times when the 500 is not long enough and I don't have another lens to change too. Many times I can only get so close to an eagle before it says enough and leaves. Sure I can use a FF 5D2 and crop and guess what I have the same DOF as a crop (Which by the way is what the OP is suggesting). Unfortunately a very Vocal group here seem to think you can cross that barrier/sideline/ Comfort zone (wildlife) and things will work but it doesn't, the animal runs, the security removes you or you are ejected from the playing field. All the OP said was if all things are the same the end result will be a similar DOF there was no mention of changing lenses/ distance etc that was brought up later by those that failed to see the intent. I don't believe the OP stated that if you change distance (FOV) the DOF stayed the same....

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OP therickman Senior Member • Posts: 1,305
Re: different enlargements

xtoph wrote:

consider just one final print size, let's say 5x7 (which used to be a standard used by 35mm camera companies).

now, to enlarge an image from a crop sensor to 5x7 you have to enlarge more than you enlarge an image from a ff sensor.

the more you enlarge, the more more you notice blur.

So, you're saying if I enlarge an image taken from an 11MP FF 1Ds to 20X30, and compare that to a 20X30 print taken from a 15MP crop 50D, the 50D's image will be blurrier?

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OP therickman Senior Member • Posts: 1,305
Re: In reality, you are wrong.

Cal Dawson wrote:

All the OP said was if all things are the same the end result will be a similar DOF there was no mention of changing lenses/ distance etc that was brought up later by those that failed to see the intent. I don't believe the OP stated that if you change distance (FOV) the DOF stayed the same....

That's exactly it. Jeesh, someone on here understood my OP.

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Cal Dawson Veteran Member • Posts: 4,810
And why would you????

that was not the point of the post, When all things are equal except the FOV the resulting DOF will be the same....
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dopravopat
dopravopat Senior Member • Posts: 1,180
Forget the print size, or whatever size

Print size has nothing to do with capturing the image, DOF and Bokeh. It is just the same as zooming a digital picture on your monitor to 25%, 50%, 100%, 200%, etc... But the image was once taken, unless you do some fancy postprocessing to affect bokeh, it remains the same image, independent on the magnification you look at it.

To your scenario:

Take the picture as described, EOS 5D, 50 mm lens stopped down to f2, a six foot tall man standing 10 feet away from the camera, just to fill the the image frame. Now, what am I interested in is, take the EOS 50D, attach a 30 mm lens, stop it down to f2, take a picture of a six foot tall man standing 10 feet away from the camera, so that he just fills the image frame. I am sure the FF frame will have a lot less DOF and also a different bokeh rendering. In order to achieve the same DOF with the EOS 50D and 30 mm lens, you would have to stop it down to f1.3. OK, the closest we have is 1.4. I would love to see the two images compared (FF, 50mm, f2 and 1.6 crop 30mm, f1.4). The actual print size is irrelevant. Just the two images should be printed the same size.

I hope you understand what I mean. DOF and bokeh is different when you have the same scene on FF and on crop and by that I mean the same compostion, ISO, shutter speed , aperture and frame filling, maintaingin relative subject sizes as you see them on FF. You can just approach the same look by stopping the wider lens on crop (when compared to FF) to a lower aperture, and setting a lower ISO or shorter shutter speed.

Bokeh and DOF is identical only if you use the same lens and setup, that you showed us in the original post (and I agree 100% withe that). What the crop camera does is just a cutout of the FF image. You could as well crop the FF image and get exactly the same result that you have from a crop camera (size in MP is irrelevant). When viewed at same size, the DOF and also bokeh, since you use the same lens, will be identical.
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Kuivaamo Senior Member • Posts: 2,248
Re: I think I found out where the DoF confusion is...

therickman wrote:

So, as a photographer knowing most of my images will be seen anywhere from 4X6 to 8X12, my understanding of DoF is how a viewer sees my images in their entirety from a normal viewing distance. Therefore, DoF doesn't change.

If you're saying that to justify the comparison in your original post, then sorry, your philosophy does not apply in this case. You presented crops with different enlargements and claimed it was evidence that the DoF is the same. Any normal person will view those crops from the same distance (especially since they're side-by-side), so your argument breaks down right away (and I'm not convinced people move away from their monitors when they're shown a larger image, either).

When it comes to photography in general, great, those are your personal criteria for quality and you can choose them as you see fit. I, and many others I'm sure, on the other hand am also concerned how my prints look when inspected more closely. Thus, I want a more stringent CoC criterion as well as more resolution when I print big.

Kuivaamo Senior Member • Posts: 2,248
Re: In reality, you are wrong.

therickman wrote:

Cal Dawson wrote:

All the OP said was if all things are the same the end result will be a similar DOF there was no mention of changing lenses/ distance etc that was brought up later by those that failed to see the intent. I don't believe the OP stated that if you change distance (FOV) the DOF stayed the same....

That's exactly it. Jeesh, someone on here understood my OP.

Problem is, the OP's assertion is still wrong.

mattr Veteran Member • Posts: 3,532
Re: Busting the FF vs Crop DoF Bokeh Myth

therickman wrote:

My conclusion:

At the same distance from subject, using the same exact lens, there is absolutely no difference in DoF and bokeh between images produced by a full frame and crop camera.

The question is how you define "images".

Of course there is no difference if your definition is the optical image produced by the lens. Full frame and crop sensors will just show more or less of this image.

Kuivaamo Senior Member • Posts: 2,248
Re: Forget the print size, or whatever size

dopravopat wrote:

Print size has nothing to do with capturing the image, DOF and Bokeh.

DoF does not exist independently as a part of your image file. Every single DoF calculation assumes a print size and viewing distance.

From Wikipedia: http://en.wikipedia.org/wiki/Circle_of_confusion

" In photography, the circle of confusion diameter limit (“CoC”) is sometimes defined as the largest blur circle that will still be perceived by the human eye as a point when viewed at a distance of 25 cm (and variations thereon).

With this definition, the CoC in the original image depends on three factors:

1. Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2000, 52), is approximately 25 cm. At this distance , a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.

2. Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. A comfortable viewing distance is also one at which the angle of view is approximately 60° (Ray 2000, 52); at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8″×10″ image. It often may be reasonable to assume that, for whole-image viewing, an image larger than 8″×10″ will be viewed at a distance greater than 25 cm, for which a larger CoC may be acceptable.

3. Enlargement from the original image (the focal plane image on the film or image sensor) to the final image (print, usually). If an 8×10 original image is contact printed, there is no enlargement, and the CoC for the original image is the same as that in the final image. However, if the long dimension of a 35 mm image is enlarged to approximately 25 cm (10 inches), the enlargement is approximately 7×, and the CoC for the original image is 0.2 mm / 7, or 0.029 mm. "

And what does CoC have to do with DoF? Well, you cannot calculate DoF without CoC.

Case closed.

climbng_vine Forum Member • Posts: 86
Re: In reality, you are wrong.

Kuivaamo wrote:

therickman wrote:

Cal Dawson wrote:

All the OP said was if all things are the same the end result will be a similar DOF there was no mention of changing lenses/ distance etc that was brought up later by those that failed to see the intent. I don't believe the OP stated that if you change distance (FOV) the DOF stayed the same....

That's exactly it. Jeesh, someone on here understood my OP.

Problem is, the OP's assertion is still wrong.

No. It simply isn't. You are bringing in a different factor (enlargement size) to label his assertion "wrong", but that was DELIBERATELY left out. It wasn't what he was addressing--what he was addressing is the view written here constantly by people who don't know what they're talking about, that FF has thinner DoF than crop sensors. A few people understand this to be implicitly qualified with... "if you alter physical variables to keep composition roughly the same between the two", but nearly everybody who spouts it, and the newbies who pick up on it, think it means that from the same DISTANCE, not with the same composition, and with the same lens parameters, that the larger sensor will have thinner DoF. This is not true, and that is exactly what the OP was trying to demonstrate, and did.

This leaves aside the issue that the enlargement size hoo-ha is overblown to begin with. For an 8x10, there is not a significant DOF difference until you get closer than a foot or further than thirteen or fifteen feet, neither of which are the usual viewing case. They are not unheard of, but are very rare, and should not be used to confuse those who don't understand the larger issue.

Kuivaamo Senior Member • Posts: 2,248
Re: In reality, you are wrong.

climbng_vine wrote:

Kuivaamo wrote:

therickman wrote:

Cal Dawson wrote:

All the OP said was if all things are the same the end result will be a similar DOF there was no mention of changing lenses/ distance etc that was brought up later by those that failed to see the intent. I don't believe the OP stated that if you change distance (FOV) the DOF stayed the same....

That's exactly it. Jeesh, someone on here understood my OP.

Problem is, the OP's assertion is still wrong.

No. It simply isn't. You are bringing in a different factor (enlargement size) to label his assertion "wrong", but that was DELIBERATELY left out. It wasn't what he was addressing--what he was addressing is the view written here constantly by people who don't know what they're talking about, that FF has thinner DoF than crop sensors. A few people understand this to be implicitly qualified with... "if you alter physical variables to keep composition roughly the same between the two", but nearly everybody who spouts it, and the newbies who pick up on it, think it means that from the same DISTANCE, not with the same composition, and with the same lens parameters, that the larger sensor will have thinner DoF. This is not true, and that is exactly what the OP was trying to demonstrate, and did.

This leaves aside the issue that the enlargement size hoo-ha is overblown to begin with. For an 8x10, there is not a significant DOF difference until you get closer than a foot or further than thirteen or fifteen feet, neither of which are the usual viewing case. They are not unheard of, but are very rare, and should not be used to confuse those who don't understand the larger issue.

This enlargement "hoo-ha" is as much an integral part in determining DoF as viewing distance, aperture, focal length and shooting distance. You need to know all of them in order to calculate DoF. You cannot ignore changing any one of them.

Doing the test as OP did in order to prove Dofmaster calculations wrong is utter fallacy. Just think about it. Dofmaster calculations assume a constant output size. If you don't keep your output size constant, how can you expect your results to agree with Dofmaster?

Cheburashka Regular Member • Posts: 297
Let's revist what the OP has said

therickman wrote:
That's exactly it. Jeesh, someone on here understood my OP.

Allow me to quote your OP. Let's begin with the title:

"Busting the FF vs Crop DoF Bokeh Myth"

So, what, exactly , is the "myth"? Let's continue to the text of your OP:

"At the same distance from subject, using the same exact lens, there is absolutely no difference in DoF and bokeh between images produced by a full frame and crop camera."

The natural conclusion, from what you wrote, is that the "myth" is that people are comparing the DOF of FF and crop using the same lens at the same distance from the subject and saying that the DOFs are different.

Do tell. I have missed all those posts where people have been saying that.

But, in fact, under those circumstances, the DOFs will be different unless you print the FF image 1.6x larger, or crop the FF image to the same framing as the 1.6x image.

On the other hand, what I do read all the time is people saying "FF has less DOF than crop". And what they mean by that, as has been explained to you by many people numerous times in this thread, is that for the same perspective, framing, and f-ratio, FF has less DOF than crop for the entire captured image displayed at the same size and viewed from the same distance with the same visual acuity .

But people don't mention all the qualifiers because for most people that is the most obvious manner in which to compare systems. With the exception of Cal Dawson, apparently, most people don't use the same lens on the their FF DSLR as they would on a 1.6x DSLR and then crop the image to the same framing as they would have gotten with a 1.6x DSLR. Do people sometimes do that? Yes. Sometimes . But it is a rare event indeed for the vast majority of people , except, perhaps, when they are shooting extreme telephoto or macro with apparent magnifications greater than 1:1.

So, do us all a favor and answer this one question: is it more natural to compare the DOF of different systems with the whole of the captured image, the same perspective, framing, display dimensions, viewing distance, and visual acuity, or is it more natural to compare the DOF of different systems is a different manner?

And even if you think the latter, you've not "busted" and "myths" -- you've merely brought attention to the fact that most people have a different idea of the conditions of what constitutes a more "natural" comparison, and that these conditions are so "obvious" to them, that they leave them out when making the statement that "FF has less DOF than crop".

Kjeld Olesen
Kjeld Olesen Veteran Member • Posts: 4,117
Bacause it is the only thing that makes any sense!

If the FOV is not equal, then all things can not be the same.

If all things are not the same, the only sensible comparison - and what the "myth" is all about - is that the use of equivalent FOV and perspective (distance) results in a more shallow DOF on FF when using the same f-stop - not apperture diameter.

This is clearly a myth busting thread that has gone totally ballony, so I'm bailing out no matter what.

Cal Dawson wrote:

that was not the point of the post, When all things are equal except the FOV the resulting DOF will be the same....
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mattr Veteran Member • Posts: 3,532
Re: Bacause it is the only thing that makes any sense!

Kjeld Olesen wrote:

This is clearly a myth busting thread that has gone totally ballony...

Well, the OP is already "ballony". Somebody actually did extensive tests to confirm that putting differently sized sensors behind a lens does not change the optical image produced by the lens - kind of funny!

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