Crop sensor effect on apertures

[smi]

Dear All,

I want you opinions in a rather technical matter that has been troubling me.

I have read in a number of threads, that in equal apertures, full frame cameras produce smaller depth of field than the cropped ones. s

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

 

[PhillipA]

Dear All,

I want you opinions in a rather technical matter that has been troubling me.

I have read in a number of threads, that in equal apertures, full frame cameras produce smaller depth of field than the cropped ones. s

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

I believe that if the focal length, aperture and the distance stay the same, then the DOF will be the same as well.

However if you change either the focal length or the subject distance to keep the framing of the image the same, then the FF combination will give a shallower DOF at the same aperture.

This is because either the closer distance or the longer focal length lens required to maintain the same framing on the FF camera will produce the shallower DOF - not the sensor size.
--

Judge: ' This image may be better in black and white - perhaps even just black! '

 

[CalBoy87]

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

Not exactly. You have to include FL in this equation as well. You can say that 50mm lens with aperture at f/2.8 on APS-C Canon camera will give you same DOF as 80mm lens with aperture at f/4.5 on FF Canon. More interesting reading is here:
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

 

[Majoren]

Dear All,

I want you opinions in a rather technical matter that has been troubling me.

I have read in a number of threads, that in equal apertures, full frame cameras produce smaller depth of field than the cropped ones. s

Wrong

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

Given the same lens, then the only change is the Field of View. FOV.
But that impacts the percieved DOF of the total image.

a 50mm on FF vs 50mm on CROP is still a 50mm lens, hence it will give you the same DOF.
-- It is a piece og dumb glass, doesnt change a bit. Unless you smash it!!

take a picture from same distance with same lens. crop the FF to match the FOW of the crop, and all you have lost are some pixels.

But on a CROP you will have lost a major part of the image, reduced FOV.

To re-gain that lost FOV , you can walk backwards until you have the same FOV as an FF would have given you.

And due to that increased distance the DOF have become deeper.

and vice versa.

Majoren

 

[akin_t]

This is asked way too often, there should be a forum sticky explaining it.

 

[jase]

Agreed! To state that the sensor size affects depth of field is to say that if you cut the middle out of a print, you have increased the depth of field of the shot.

--
jase

 

[Bogdan_M]

Dear All,

I want you opinions in a rather technical matter that has been troubling me.

I have read in a number of threads, that in equal apertures, full frame cameras produce smaller depth of field than the cropped ones. s

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

A x mm f/2.8 lens on a 7D behaves like a x/1.6mm f/4.5 lens on a 5D, more exactly.

You have a thorough essay here:
http://www.josephjamesphotography.com/equivalence/index.htm#equivalence

But in short, yes, for the same framing, using a crop sensor will result in more DOF and more noise.

--
Kind regards,

Bogdan

 

[PhillipA]

I wish I'd said that ;-)
--

Judge: ' This image may be better in black and white - perhaps even just black! '

 

[graphikal]

Dear All,

I want you opinions in a rather technical matter that has been troubling me.

I have read in a number of threads, that in equal apertures, full frame cameras produce smaller depth of field than the cropped ones. s

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

In determining equivalence, one needs to apply the crop factor to both the focal length and the aperture. It is indeed true that an f/2.8 lens on APS-C behaves like an f/4.5 lens on full frame (of 1.6x less focal length, of course).

 

[Keith Z Leonard]

Phillip A has it correct, it does not change the properties of the lens, but since to keep the same framing people move back more, that changes the apparent DOF. The physics don't change by magic, the use changes.

 

[Great Bustard]

Dear All,

I want you opinions in a rather technical matter that has been troubling me.

I have read in a number of threads, that in equal apertures, full frame cameras produce smaller depth of field than the cropped ones. s

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

For the same perspective, framing, shutter speed (adjust the ISO accordingly), and display size, yes. For the full monty, see here:

http://www.josephjamesphotography.com/equivalence/

 

[Keith Z Leonard]

Great link, my problem with this issue is that people often don't add the qualifiers, and if they do, they don't explain why they matter.

Same distance, same lens, same DOF. Save FRAMING, same lense, different DOF. Also a part of the confusion is talking about the DOF in terms of aperture, gives people the wrong idea. The aperture doesn't change, but rather distance to subject, though that's harder for people to understand, I suppose.

 

[Great Bustard]

Great link, my problem with this issue is that people often don't add the qualifiers, and if they do, they don't explain why they matter.

Same distance, same lens, same DOF. Save FRAMING, same lense, different DOF. Also a part of the confusion is talking about the DOF in terms of aperture, gives people the wrong idea. The aperture doesn't change, but rather distance to subject, though that's harder for people to understand, I suppose.

See the box here:

http://www.josephjamesphotography.com/equivalence/#dofbox

where four different scenarios are discussed.

 

[Peter 13]

According to your experience is that true? Does that mean that an f/2.8 lens on a 7D, behaves like an f/4.5 lens on a 5D?

Yes but of different FL as well. For example, the 50/1.4 becomes basically 80/2.2.

Given the same lens, then the only change is the Field of View. FOV.
But that impacts the percieved DOF of the total image.

a 50mm on FF vs 50mm on CROP is still a 50mm lens, hence it will give you the same DOF.

No, it will give you less DOF. Just use any DOF calculator, or better yet, try to understand it.

 

[carlk]

The simplest and most straightforward answer is apertures, focal length, everything is the same on aps-c or on full frame. The only thing different is the FOV. You can be very happy if you just stop here.

You can make things complicated ONLY when you want to make FOV the same. There are many good explanations here including the link by Great Bustard. Just remember fundamentally the only thing different is the FOV (cropped).

 

[tom sugnet]

200 f/2 on 1.6x crop won't give you a 320 f/2 lens, but 320 f/3.2 lens mmwise and DOFwise
People always forget the DOF part.

Were DOF unchanged, 135 f/2 would behave llike a 200 f/2 lens on 1.6x crop, and we all know it's not true, on crop it's more like a 200 f/3.2 lens.

--
Feel free to visit my photo sites:
http://tom.st , http://www.foto.tom.st

 

[Keith Z Leonard]

"200 f/2 on 1.6x crop won't give you a 320 f/2 lens, but 320 f/3.2 lens mmwise and DOFwise
People always forget the DOF part.

Were DOF unchanged, 135 f/2 would behave llike a 200 f/2 lens on 1.6x crop, and we all know it's not true, on crop it's more like a 200 f/3.2 lens."

This is the myth we are trying to dispell. 200 f2 on crop gives you.....200 f2 with a cropped image. The FOV matches a 320mm. To get the same framing as you would an uncropped image you back up, and THAT changes the DOF.

 

[Keith Z Leonard]

"Just use any DOF calculator, or better yet, try to understand it."

Argumentum ad hominem, good use of the fallacy.

Same DOF with same distance, different DOF for same framing, because you have to change distance on the crop to get the same framing.

 

[Peter 13]

"200 f/2 on 1.6x crop won't give you a 320 f/2 lens, but 320 f/3.2 lens mmwise and DOFwise
People always forget the DOF part.

Were DOF unchanged, 135 f/2 would behave llike a 200 f/2 lens on 1.6x crop, and we all know it's not true, on crop it's more like a 200 f/3.2 lens."

This is the myth we are trying to dispell. 200 f2 on crop gives you.....200 f2 with a cropped image. The FOV matches a 320mm. To get the same framing as you would an uncropped image you back up, and THAT changes the DOF.

It changes before you back up as well. It is a hard myth to dispell because it is not a myth.

You get less DOF with just cropping (and a different FOV as well), and more DOF if you back up to frame the same object.

http://www.dofmaster.com/dofjs.html

 

[carlk]

There is FOV difference but no DOF difference. DOF will be different ONLY if you try to make FOV the same by: 1) change distance or 2) change focal length. This has been repeated by so many people so many times I really don't know why there are still people who can't get it.