Why does FF yield shallower DOF?

To get the same field of view, the crop-sensor camera needs to shoot with a shorter lens. The shorter lens yield wider DOF. Is that why the crop-sensor gives more DOF?

If you shoot with the same lens on both cameras (same scene, same shooting position, same f/stop) and then crop the FF image to equal the FoV of the 1.6 crop-factor sensor will you have the same DOF?

n1as wrote in post #15595460
To get the same field of view, the crop-sensor camera needs to shoot with a shorter lens. The shorter lens yield wider DOF. Is that why the crop-sensor gives more DOF?

If you shoot with the same lens on both cameras (same scene, same shooting position, same f/stop) and then crop the FF image to equal the FoV of the 1.6 crop-factor sensor will you have the same DOF?

There are plenty of articles and threads already explaining this. Please do a search.

Such a topic will spawn an 80 page thread again...

If you want the technical answer, they don't. DOF for the same focal length framing the same subject matter is identical on FF and APS-c. Having to back off to obtain the same framing on an APS-c body give you MORE distance to target, which increases the DOF. It has nothing to do with the lens, or the sensor.

As presented, your question doesn't make much sense. Of course, if you use a shorter lens, you will get greater DOF. That is optical physics. Don't bother with the whys, just go shoot.

Be prepared for as many different answers as responses. This is like arguing the relative merits of FF vs. APS-c or Canon vs Nikon. Opinions are a lot like pennies; everyone has a drawer full of them, so they aren't worth much.

Canon_Lover: Articles that explain a phenomenon that does not exist? Or articles explaining why the entire thing is irrelevant? The only DOF that can possibly matter is the body/lens/aperture and focal distance you are working with right now. Very few of us shoot two cameras simultaneously. I would guess ZERO. What is happening to a camera/lens system you are not using will have very little impact on the photo you are currently taking.

Canon_Lover wrote in post #15595535
There are plenty of articles and threads already explaining this. Please do a search.

Such a topic will spawn an 80 page thread again...

If each question was only answered ONCE and allowed a single thread per - there wouldn't be much to a forum...

Canon_Lover wrote in post #15595535
There are plenty of articles and threads already explaining this. Please do a search.

Such a topic will spawn an 80 page thread again...

Please don't assume I didn't search. I did but found no quick answers.

Fortunately, the 80 pages will be nicely contained in this one thread where people who are uninterested in the topic can safely step around it.

TSchrief wrote in post #15595568
If you want the technical answer, they don't. DOF for the same focal length framing the same subject matter is identical on FF and APS-c. Having to back off to obtain the same framing on an APS-c body give you MORE distance to target, which increases the DOF. It has nothing to do with the lens, or the sensor.

As presented, your question doesn't make much sense. Of course, if you use a shorter lens, you will get greater DOF. That is optical physics. Don't bother with the whys, just go shoot.

Be prepared for as many different answers as responses. This is like arguing the relative merits of FF vs. APS-c or Canon vs Nikon. Opinions are a lot like pennies; everyone has a drawer full of them, so they aren't worth much.

.

Sorry, I don't completely follow this. I'm not interested in opinions, I'm looking for the technical facts. I know from experience that larger sensors give shallower DOF but I want to know why.

Help me phrase my question so it can be understood...

Depends:

When you:
- Stand in the same spot
- Using same lens at same aperture
- Take a photo of the same subject
Then the APS-C camera will give LESS DOF than a FF camera, for any given print size

^ Please note there is no typo above, the crop camera gives LESS DOF than a FF camera for the above situation

When you:
- Using same lens at same aperture
- Take a photo of the same subject
But you equalise your framing by:
- Cropping the photo OR moving foward OR zooming in
then the FF camera gives you less DOF than a crop camera

n1as wrote in post #15595460
To get the same field of view, the crop-sensor camera needs to shoot with a shorter lens. The shorter lens yield wider DOF. Is that why the crop-sensor gives more DOF?

Yes, this is the complete, total answer. And this answer isn't limted to just 1.6X and FF...it spans everything from tiny sensor P&S cameras to medium format digital. The larger the format, the longer the focal length you need to take the same picture.

This move to longer focal lengths with larger formats is entirely why larger formats give less DOF.

Yes. Cropping a larger format to be the same as a smaller format then makes the two cameras the same. The only difference you might have here is a different number of pixels (depending on what specific cameras you are talking about).

How big a thread gets is no issue for me, but you might find your answer quicker looking through a previous one.

https://photography-on-the.net …/showthread.php​?t=1148826

n1as wrote in post #15595780
Sorry, I don't completely follow this. I'm not interested in opinions, I'm looking for the technical facts. I know from experience that larger sensors give shallower DOF but I want to know why.

Help me phrase my question so it can be understood...

The fact is that sensor size has (almost) NO impact on DOF. Several things have a much larger influence.

1.) Focal length of the lens in use.
2.) The aperture setting.
3.) Distance from sensor to subject.

If you mount lens A on a full frame camera and take a photo, then mount that same lens on an APS-c camera and take a photo framed exactly like the first one you took, you will notice that DOF is EXACTLY the same, assuming the same aperture. In photographic terms, sensor size has no effect on DOF. Period.

Sensor size does play a very minimal role in the calculation of the 'circle of confusion'. If you want to put some numbers on it, you'll have to do the research. Look into "Optics" and/or "Physics of Electromagnetic Radiation". As far as photography goes, sensor size has no impact on DOF. DOF is governed completely by items 1 through 3 above.

I find it curious that you "KNOW" something that isn't true. Do you also know that tomato juice will remove skunk smell? Or that aspirin is a blood thinner? There is an interesting book out, the title of which is, I believe, 101 Things Everyone "KNOWS" That Aren't True. Lots of people believe something called 'centrifugal force' exits. No such animal in the world of Physics.

TSchrief wrote in post #15597318
The fact is that sensor size has (almost) NO impact on DOF. Several things have a much larger influence.

1.) Focal length of the lens in use.
2.) The aperture setting.
3.) Distance from sensor to subject.

If you mount lens A on a full frame camera and take a photo, then mount that same lens on an APS-c camera and take a photo framed exactly like the first one you took, you will notice that DOF is EXACTLY the same, assuming the same aperture. In photographic terms, sensor size has no effect on DOF. Period.

Sensor size does play a very minimal role in the calculation of the 'circle of confusion'. If you want to put some numbers on it, you'll have to do the research. Look into "Optics" and/or "Physics of Electromagnetic Radiation". As far as photography goes, sensor size has no impact on DOF. DOF is governed completely by items 1 through 3 above.

I find it curious that you "KNOW" something that isn't true. Do you also know that tomato juice will remove skunk smell? Or that aspirin is a blood thinner? There is an interesting book out, the title of which is, I believe, 101 Things Everyone "KNOWS" That Aren't True. Lots of people believe something called 'centrifugal force' exits. No such animal in the world of Physics.

Sensor size WILL determine your shooting distance, or focal length used, so to say it has no effect on DOF just adds confusion to this already confusing subject.

msowsun wrote in post #15597368
Sensor size WILL determine your shooting distance, or focal length used, so to say it has no effect on DOF just adds confusion to this already confusing subject.

Please explain how, when I take my 400mm (the longest lens I own) to shoot birds or football, the choice of a 1.3 crop body (1D Mark IV) vs full frame body (1D X) will determine my shooting distance or my focal length. Either way, I'm stuck at 400mm and the birds or players are not getting any closer because of which body I choose.

Zivnuska wrote in post #15597417
Please explain how, when I take my 400mm (the longest lens I own) to shoot birds or football, the choice of a 1.3 crop body (1D Mark IV) vs full frame body (1D X) will determine my shooting distance or my focal length. Either way, I'm stuck at 400mm and the birds or players are not getting any closer because of which body I choose.

Using an example where you are focal length limited and cropping to the same physical sensor size regardless of format is deliberately confusing the issue.

If you take the OP's question for normal, everyday shooting without being focal length limited, then people will use longer focal lengths with larger formats, which yields shallower DOF.

It's people who insist on interjecting more esoteric situations where one is focal length limited who needlessly confuse people with these discussions. You are taking what should be a small exception to what we are discussing and using it to negate the rule. This is not helpful to the OP.

With a bit of thought you will realize that if you shoot two different formats but crop them both down to the same physical size, then for all intents and purposes you are not really using two different formats anymore. That's why a focal length limited example is not germaine to a comparison of DOF on two different formats.

Zivnuska wrote in post #15597417
Please explain how, when I take my 400mm (the longest lens I own) to shoot birds or football, the choice of a 1.3 crop body (1D Mark IV) vs full frame body (1D X) will determine my shooting distance or my focal length. Either way, I'm stuck at 400mm and the birds or players are not getting any closer because of which body I choose.

It needs to be noted though that for a given output size, when you can't change your FL or position, the APS-C camera gives LESS DOF. By definition it would be a more magnified view = less DOF at any given output size

JeffreyG wrote in post #15597429
Using an example where you are focal length limited and cropping to the same physical sensor size regardless of format is deliberately confusing the issue.

If you take the OP's question for normal, everyday shooting without being focal length limited, then people will use longer focal lengths with larger formats, which yields shallower DOF.

It's people who insist on interjecting more esoteric situations where one is focal length limited who needlessly confuse people with these discussions. You are taking what should be a small exception to what we are discussing and using it to negate the rule. This is not helpful to the OP.

With a bit of thought you will realize that if you shoot two different formats but crop them both down to the same physical size, then for all intents and purposes you are not really using two different formats anymore. That's why a focal length limited example is not germaine to a comparison of DOF on two different formats.

But Jeffrey the issue is being able to equalise framing is a theoretical fantasy. The reality is, we are always focal length limited, or always position limited. Who here can foot zoom to whereever they want unless they are Superman? Who here can use any focal length from 8mm to 1200mm? Who here actually will equalise their framing when they change lenses or camera? The reality is they can't or don't.

Therefore Zivnuska's example, whilst only showing one side of the story (and yours showing the other), is no more or less valid than your scenario