Why Should We Care About Crop Factor?

[Judobreaker]

Oh don't worry, I understand completely what you guys are trying to say. Of course I know that it is much easier to achieve a thinner DOF with my D800 (although that is not the main reason I bought it, it can be pretty neat though).
I just simply can't agree with the statement that sensor size has an effect on how DOF works, because that is physically impossible.
I fully agree on the fact that with an FX sensor you'll usually get closer or use longer lenses and your DOF will be thinner as a result, but that is a result of the lens. That may be labelled as an indirect effect of the sensor size, sure I won't disagree on that, but theoretically speaking it is still not the sensor that has the actual effect.
I suspect we're going to have to agree to disagree on that statement, even though we probably agree on how it actually works. xD

 

[Helen B]

The sensor size has an effect on the MACC (maximum acceptable circle of confusion) at the camera's image plane for any given final image size and desired resolution (MACC at the final image size) because of the degree of magnification from the camera image to the final image.

For a given, fixed perspective (camera position), focus distance and angle of view (ie "same picture" criterion) the sensor size will affect the focal length. The focal length affects the DoF, as does the MACC. I don't think Ysarex has suggested anywhere that the sensor size, per se, has a direct effect on DoF, but it does have an effect, as he says.

 

[amolitor]

Oh, so you admit that you're just being an obnoxious pedant for the purpose of maintaining a fight about.. nothing, Judobreaker? Ok then.

 

[Ysarex]

Oh don't worry, I understand completely what you guys are trying to say. Of course I know that it is much easier to achieve a thinner DOF with my D800 (although that is not the main reason I bought it, it can be pretty neat though).
I just simply can't agree with the statement that sensor size has an effect on how DOF works, because that is physically impossible.
I fully agree on the fact that with an FX sensor you'll usually get closer or use longer lenses and your DOF will be thinner as a result, but that is a result of the lens. That may be labelled as an indirect effect of the sensor size, sure I won't disagree on that, but theoretically speaking it is still not the sensor that has the actual effect.
I suspect we're going to have to agree to disagree on that statement, even though we probably agree on how it actually works. xD

No, I don't have to agree to disagree, you are wrong. Any practical use of DOF while working with a camera includes accounting for the magnification limits enforced pragmatically by the sensor size.

I do however agree with Andrew.

Oh, and I'm not worried.

Joe

 

[Ysarex]

Oh don't worry, I understand completely what you guys are trying to say. Of course I know that it is much easier to achieve a thinner DOF with my D800 (although that is not the main reason I bought it, it can be pretty neat though).
I just simply can't agree with the statement that sensor size has an effect on how DOF works, because that is physically impossible.
I fully agree on the fact that with an FX sensor you'll usually get closer or use longer lenses and your DOF will be thinner as a result, but that is a result of the lens. That may be labelled as an indirect effect of the sensor size, sure I won't disagree on that, but theoretically speaking it is still not the sensor that has the actual effect.
I suspect we're going to have to agree to disagree on that statement, even though we probably agree on how it actually works. xD

Just one more thing. There is obviously a clear consensus here that you are wrong. Derrel has told you you're wrong. I have told you you're wrong. Andrew has told you you're obnoxious, etc. etc.

But please note: Helen has now told you you're wrong. Hopefully you've been around here long enough to know that once Helen tells you you're wrong it's over. Should you proceed in the face of that with the "agree to disagree" BS you'll be a whole lot more than just wrong and obnoxious. Just lookin' out for you here.

Joe

 

[runnah]

There was a time when it made sense, when they were building 35mm film cameras, and crop-sensor DSLRs, simultaneously. They did, at that time, need to emphasize to 35mm film shooters that while their existing lenses WOULD work on the new digital bodies, there was gonna be a difference in field of view. That was a very specific marketing tactic for a very specific interval in the industry.

It's no longer relevant, and it creates far more total confusion than clarification now.

Well I think this summed things up nicely.

 

[Judobreaker]

Oh don't worry, I understand completely what you guys are trying to say. Of course I know that it is much easier to achieve a thinner DOF with my D800 (although that is not the main reason I bought it, it can be pretty neat though).
I just simply can't agree with the statement that sensor size has an effect on how DOF works, because that is physically impossible.
I fully agree on the fact that with an FX sensor you'll usually get closer or use longer lenses and your DOF will be thinner as a result, but that is a result of the lens. That may be labelled as an indirect effect of the sensor size, sure I won't disagree on that, but theoretically speaking it is still not the sensor that has the actual effect.
I suspect we're going to have to agree to disagree on that statement, even though we probably agree on how it actually works. xD

Just one more thing. There is obviously a clear consensus here that you are wrong. Derrel has told you you're wrong. I have told you you're wrong. Andrew has told you you're obnoxious, etc. etc.

But please note: Helen has now told you you're wrong. Hopefully you've been around here long enough to know that once Helen tells you you're wrong it's over. Should you proceed in the face of that with the "agree to disagree" BS you'll be a whole lot more than just wrong and obnoxious. Just lookin' out for you here.

Joe

Everybody laughed at Columbus because he said the world was round. That didn't make him wrong did it?

I stand by my statement that sensor size itself does not affect DOF, whatever you guys say. It is simply physically impossible that sensor size affects the DOF.
Yes, you guys are correct by saying that people tend to change other factors because of the larger sensor (focal length, subject distance), however that only means it has an effect on the shooter, not on the DOF itself.

The DOF of an image coming from a camera is determined by aperture, focal length, subject distance and sensor resolution. Sensor size does not matter.

 

[Sventek]

People might be interested in this: Image sensor format - Wikipedia, the free encyclopedia

 

[Ysarex]

Oh don't worry, I understand completely what you guys are trying to say. Of course I know that it is much easier to achieve a thinner DOF with my D800 (although that is not the main reason I bought it, it can be pretty neat though).
I just simply can't agree with the statement that sensor size has an effect on how DOF works, because that is physically impossible.
I fully agree on the fact that with an FX sensor you'll usually get closer or use longer lenses and your DOF will be thinner as a result, but that is a result of the lens. That may be labelled as an indirect effect of the sensor size, sure I won't disagree on that, but theoretically speaking it is still not the sensor that has the actual effect.
I suspect we're going to have to agree to disagree on that statement, even though we probably agree on how it actually works. xD

Just one more thing. There is obviously a clear consensus here that you are wrong. Derrel has told you you're wrong. I have told you you're wrong. Andrew has told you you're obnoxious, etc. etc.

But please note: Helen has now told you you're wrong. Hopefully you've been around here long enough to know that once Helen tells you you're wrong it's over. Should you proceed in the face of that with the "agree to disagree" BS you'll be a whole lot more than just wrong and obnoxious. Just lookin' out for you here.

Joe

Everybody laughed at Columbus because he said the world was round. That didn't make him wrong did it?

I stand by my statement that sensor size itself does not affect DOF, whatever you guys say. It is simply physically impossible that sensor size affects the DOF.
Yes, you guys are correct by saying that people tend to change other factors because of the larger sensor (focal length, subject distance), however that only means it has an effect on the shooter, not on the DOF itself.

The DOF of an image coming from a camera is determined by aperture, focal length, subject distance and sensor resolution. Sensor size does not matter.

People change other factors within the limits of what is possible. You can't move mountains to take a photograph and moving yourself relative to a mountain range isn't going to count for squat. All through this thread words like practical and pragmatic have been used because the limits of what is possible are pragmatically real. DOF in use is pragmatically real as well.

Where
H = hyperfocal distance
f = lens focal length
N = f/stop
c = circle of confusion (tied to sensor size).


That is the standard formula for calculating hyperfocal distance. Please demonstrate with examples of how you can alter only the value of c without effecting the value of H and you get to be right. Otherwise you continue to stand corrected. It's math 1, you 0. And now you're lookin' like more than just wrong.

Joe

 

[Derrel]

Everybody laughed at Columbus because he said the world was round. That didn't make him wrong did it?

I stand by my statement that sensor size itself does not affect DOF, whatever you guys say. It is simply physically impossible that sensor size affects the DOF.
Yes, you guys are correct by saying that people tend to change other factors because of the larger sensor (focal length, subject distance), however that only means it has an effect on the shooter, not on the DOF itself.

The DOF of an image coming from a camera is determined by aperture, focal length, subject distance and sensor resolution. Sensor size does not matter.

Judobreaker, I think Janice said it best:

 

[sleist]

I stand by my statement that sensor size itself does not affect DOF, whatever you guys say.

[SNIP]

The DOF of an image coming from a camera is determined by aperture, focal length, subject distance and sensor resolution. Sensor size does not matter.

You are contradicting yourself within the same post.
The bolded (by me) text in your first statement can be interpreted to imply that sensor size can impact DOF.
To go on to say that sensor size does not matter is a contradiction.

You seem to be arguing both sides whenever it seem convenient to do so.

 

[amolitor]

Everybody laughed at Columbus because he said the world was round. That didn't make him wrong did it?

Interestingly, everyone knew the world was round, and about how big it was. Columbus sold a story about how, sure it's round, but it's a lot smaller than everyone says, so China is basically right there. In fact that is almost no way Columbus didn't also know how big the earth was, so he was almost certainly selling a bogus story about China in order to fund an expedition to whatever it was that was most likely right out there.

I stand by my statement that sensor size itself does not affect DOF, whatever you guys say. It is simply physically impossible that sensor size affects the DOF.

Yes, you're standing by an accurate statement that has nothing whatsoever to do with what's being talked about, because you want to keep fighting, because you're that kind of guy. Why don't you stand by the statement that some trees are pretty tall, or that some people are combative idiots? That would be exactly as relevant.

Your argument can be used to show that no other single factor affects DoF either. Aperture doesn't affect DoF because if I use some other camera and some other lens to take some different picture it has exactly the same DoF, so aperture is out. Ditto subject distance. Ditto magnification.

THEREFORE DOF IS A UNIVERSAL CONSTANT! WOOO!

 

[manaheim]

I think this discussion has run its course, and has delved well into the depths of ridiculousness.

My advice, to everyone involved, would be to weigh the amount of those arguing for or against the DOF being affected by crop sensors, and then re-evaluate your own position based upon the total mass on either end of that scale.