deeprblue wrote:
Directly, no. Indirectly, of course.

This sums up the conversation thus.

Thank you. I thought I was in some alternate reality.

DOF is determined by only two major factors:
Magnification and aperture.

Magnification is affected by three factors:
Subject distance, Focal length, and Output magnification.

Sensor size affects output magnification.

gfiksel wrote:
Mike Mahoney wrote:
From Wikipedia:

"The term circle of least confusion is often used for the smallest optical spot a lens can make"

A measurement.

Now you are making up quotes ??

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


My quote was directly from Wikipedia, verbatim. Circle of confusion is indeed a measurement. Just because you don't understand basic principles does not make the rest of us liars.

Your quote is also correct, but your interpretation of it is not.

And your understanding of it probably gained in the past few minutes through a feverish googling session. Keep it up.

Mike Mahoney wrote:

"The term circle of least confusion is often used for the smallest optical spot a lens can make"


That's brilliant, Mike. I will try to remember that

Fotofinder wrote:
DOF is determined by only two major factors:
Magnification and aperture.

Magnification is affected by three factors:
Subject distance, Focal length, and Output magnification.

Sensor size affects output magnification.

Where did I go wrong in my explanation?

Sensor size also affects FOV, which causes the human to take some sort of action. That action is either to change the subject distance or the focal length.

Why is it that the vast majority of you forget the photographer?

Is this what the term "gearhead" really means?

cogitech wrote:
Why is it that the vast majority of you forget the photographer?

Is this what the term "gearhead" really means?

The OP's question was specific to DOF and sensor size, which really is a gear specific question .. that does not make those who answer "gearheads".

You're the one who introduced photographer technique into the answer and your comments are correct. Whether or not they are relevant to the question depends on how broadly you wish to interpret the question.

"The term circle of least confusion is often used for the smallest optical spot a lens can make"

"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"


Both are correct definitions, however in the discussion of depth of field, the second is the one we are concerned with. In Canon's "Lens Work III," they call the second definition the "Permissible Circle of Confusion," which is the measurement all their lens and autofocus designs are based upon. This specific measurement is 0.035mm, according to "Lens Work III."



DOF is determined by only two major factors:
Magnification and aperture.

Magnification is affected by three factors:
Subject distance, Focal length, and Output magnification.

Sensor size affects output magnification.

This, folks, is ABSOLUTELY correct. I would add that "output magnification" is the sum of both the original image size behind the lens and the final display enlargement.

gfiksel wrote:
Mike Mahoney wrote:

"The term circle of least confusion is often used for the smallest optical spot a lens can make"


That's brilliant, Mike. I will try to remember that

Bit of a misquote there Sparky,

You have clumsily arranged this to look like those were my words, when actually I was directly quoting another source, in this case Wikipedia. Sharpen your crayons.

Mike Mahoney wrote:
cogitech wrote:
Why is it that the vast majority of you forget the photographer?

Is this what the term "gearhead" really means?

The OP's question was specific to DOF and sensor size, which really is a gear specific question .. that does not make those who answer "gearheads".

You're the one who introduced photographer technique into the answer and your comments are correct. Whether or not they are relevant to the question depends on how broadly you wish to interpret the question.

Well, considering that the very real DOF difference that is observed by so many photographers (between crop and FF) is directly due to the photographers' reaction to the difference in FOV offered by the sensor size, I'd say it would be pretty damned narrow-minded not to discuss it.

It is a hell of a lot more relevant than any CoC argument that you guys might go on about.

cogitech wrote:
Well, considering that the very real DOF difference that is observed by so many photographers (between crop and FF) is directly due to the photographers' reaction to the new FOV offered by the sensor size, I'd say it would be pretty damned narrow-minded not to discuss it.

Well considering that this type of question is asked just about weekly here, and that the threads go on for many pages and leave the OP largely as confused as when he started it may not be a bad idea to keep things simple and start with the basics.

Then you can broaden the discussion to illustrate how APPARENT visual changes in DOF are seen with different sensor sizes, and other variables.

Mike Mahoney wrote:

Well considering that this type of question is asked just about weekly here, and that the threads go on for many pages and leave the OP largely as confused as when he started it may not be a bad idea to keep things simple and start with the basics.

Then you can broaden the discussion to illustrate how APPARENT visual changes in DOF are seen with different sensor sizes, and other variables.


CoC is not the basics.

The basics of DOF are exactly what you described before; focal length, aperture, subject (focal) distance.

The bigger sensor offers a wider FOV, which requires the photographer to either increase the focal length or reduce the subject distance in order to maintain the same framing. These two things both directly affect the DOF.

This isn't a matter of a photographer changing his/her technique. It is a matter of the photographer maintaining the same framing across two different formats, and they do it without even realizing it. They just compose the shot as they normally would.

The visual differences are not apparent, they are very real. Increasing the focal length of the lens or decreasing the focal (subject) distance do not create "apparent" visual differences. On the contrary, they directly reduce the DOF in the photograph.

These effects are far more important (they influence the DOF of the photo much more) than the potential CoC differences between the formats.

Photon wrote:
But is that how you photograph? I think most of us, at least when we have the chance, choose our position to get a certain perspective and relationship of objects in the frame, and from there we choose a focal length to give the angle of view that includes only the things we want to show. I think the example is well done and 100% appropriate.

That's the way I see it.

I frame my shots with my 5D/85 1.8 the same way I would frame shots with my 40D/50 1.4; the result at equal aperatures is less DOF/more subject isolation - which by the way is both good and bad, depending on what I'm trying to shoot. For landsapes FF can be a pain in the &%$#, due the amount that one needs to stop down for decent DOF.

By the way, nice examples Paul.

cogitech wrote:
Let's look at scenario:

Photographer Joe has been using his 85mm "portrait" lens on his 1.6x crop factor camera. He likes the results, but he hears that FF cameras will give him less DOF, allowing him to isolate his subject more.

So, photographer Joe rents or buys a shiny FF camera. He wants to see how his portraits are going to look, so he goes out to the park with his kid and his 85mm "portrait" lens on his new camera.

He gets home and cannot believe his eyes. "Wow! look how shallow the DOF is!" His conclusion is that the DOF is shallower on his new camera.

We all know what really happened (don't we?).

He framed his subjects as he always did. His style has not changed, after all. In order to maintain the same shots that he did before, he moved closer.

Now, IMO, it doesn't really matter whether this DOF difference is due to the camera or due to the photographer. In fact, I think it doesn't even really matter if photographer Joe is aware that he is the cause of the reduced DOF.


Bingo. And he had to step closer because his "crop" changed.. Which came first, the chicken or the egg? Does it matter? No... So more accurately we'll say that the crop changed the equivalent focal length, or subject distance... Either way, directly or indirectly, the crop factor has affected DOF.

Chris M
www.imagineimagery.com

For landsapes FF can be a pain in the &%$#, due the amount that one needs to stop down for decent DOF.

Must be why nobody uses large format for landscapes.

RDKirk wrote:
For landsapes FF can be a pain in the &%$#, due the amount that one needs to stop down for decent DOF.

Must be why nobody uses large format for landscapes.

Stopping them down is very, very simple. Carrying them is not.