DOF

D.S.

D.S.

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Using my 50mm f1.4 as an extreme example, say I am shooting at f1.4 and I focus on a flower 1m in front of me the DOF is very very shallow, a few mm. If I then look up and focus on a tree 100m away is the DOF still going to be a few mm, or does the DOF increase as the distance to subject increases?

Is there a handy scale anywhere I can print out and keep in my camera bag?
 
I'm certain that the DOF is affected by the working distance between the lens and the subject

have a look here.
 
Yes and yes. DoF changes a lot with distance, and also with f/number, focal length and format size.

All the answers are here: www.dofmaster.com You can also print out handy DoF scales to stick to your lens caps :thumbs:
 
HoppyUK said:
Yes and yes. DoF changes a lot with distance, and also with f/number, focal length and format size.

All the answers are here: www.dofmaster.com You can also print out handy DoF scales to stick to your lens caps :thumbs:
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Please explain to me how the DOF is changed by format size. What you didn`t include was the the "Circle of confusion." This will change the Hyperfocal distance, therefore altering the near and far calculations.
 
classcams said:
Please explain to me how the DOF is changed by format size. What you didn`t include was the the "Circle of confusion." This will change the Hyperfocal distance, therefore altering the near and far calculations.
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the larger the format size the smaller the depth of field will be given all other factors being the same.. roughly speaking

An example being your 50mm lens at aperture f1.4 on a full frame will give a narrower depth of field than on a crop sensor. methinks...
 
onform said:
the larger the format size the smaller the depth of field will be given all other factors being the same.. roughly speaking

An example being your 50mm lens at aperture f1.4 on a full frame will give a narrower depth of field than on a crop sensor. methinks...
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Methinks you are incorrect. You just make a statement without any explanation, this just will not do.
 
classcams said:
Please explain to me how the DOF is changed by format size. What you didn`t include was the the "Circle of confusion." This will change the Hyperfocal distance, therefore altering the near and far calculations.
Click to expand...

onform said:
the larger the format size the smaller the depth of field will be given all other factors being the same.. roughly speaking

An example being your 50mm lens at aperture f1.4 on a full frame will give a narrower depth of field than on a crop sensor. methinks...
Click to expand...

Format size is central to everything. When that changes, so must everything else for any comparisons to be meaningful. If you go into www.dofmaster.com format is the first thing you input for calculations. Circle of confusion is set by international standards, so I left that out.

Onform, you need a bit more to make what you're saying true. 50mm lens on full frame should be properly compared to a 30mm lens on crop format (Canon 1.6x actually 31mm) to mainatin the same field of view. When you do that, depth of field is increased on the smaller format by about 1.3 stops. The difference is the f/number x crop factor, so if you have f/4 on full frame, you will get the same depth of field at f/2.5 on crop.

If the crop factor was 1.4x, the DoF difference would be one stop exactly. Likwise, with the 2x crop factor of 4/3rds format, DoF is increased by two stops over full frame. By the same token, compacts have a tiny sensor with a crop factor around 5x, which explains their great depth of field.

Having said all that, DoF is not such an exact science in practise. It is subject to a lot of variables which change as you move and zoom. Even if you agree with those international standards in the first place ;)
 
What you are saying is, a 50 mm lens has less DOF full frame than on a crop frame providing I change the lens for a 30mm. It`s like saying my younger son is taller than your son providing I swap my younger son for my older son.
 
classcams said:
What you are saying is, a 50 mm lens has less DOF full frame than on a crop frame providing I change the lens for a 30mm. It`s like saying my younger son is taller than your son providing I swap my younger son for my older son.
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My head hurts.............
 
classcams said:
What you are saying is, a 50 mm lens has less DOF full frame than on a crop frame providing I change the lens for a 30mm. It`s like saying my younger son is taller than your son providing I swap my younger son for my older son.
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That would be for the same framing from the same camera position. If one used the same lens on a smaller-format camera, one would have to move further away from the subject to achieve the same framing, thereby increasing DOF, all other things being equal.
 
classcams said:
What you are saying is, a 50 mm lens has less DOF full frame than on a crop frame providing I change the lens for a 30mm. It`s like saying my younger son is taller than your son providing I swap my younger son for my older son.
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What I'm saying is, it is image size (magnification) which is fundamental to depth of field. That is at the heart of it and is defined by both the format and the lens. In practise this often gets shortened to just the lens because you normally don't change format, it is fixed within the camera, but with the new development of full frame and crop format digital running side by side, we have a new situation where the two need to be understood as separate factors, but used together.

If you are taking a picture of your son (it doesn't matter which one :) ) with both a full frame camera and a crop, and you want the same framing with both, what is going to happen is that you will use a 50mm lens on the full frame and a 31mm lens on the crop. So the crop's image will be smaller and, despite the greater degree of enlargement needed for final output, you will get greater depth of field from it. If you want depth of field to be the same in both pictures (and for them also to be identical in framing and perspective) then you must use a lower f/number with the crop, 1.3 stops lower if you're using Canon (1.28 stops, since you're being picky ;) ).
 
This is my last attempt. I have a full frame camera (5D) and a crop camera (10D) and one lens 50mm. DOF on both cameras will be exactly the same within reason BUT with the crop camera the shot will have to be enlarged more to equal the 5D shot on the PC because it is a smaller sensor. Therefore the C of C will be enlarged more on this shot giving a less than perfect shot. Concerning the full frame shot a full 36 * 24 shot will have used the periphery of the lens and its less than perfect edges. I say no more on this subject.
 
Blapto said:
Depth of field is affected by magnification of the subject in the format in which it is displayed and the circle of confusion at the time the image was taken.

Read:
http://photo.net/learn/optics/dofdigital/
and
http://www.luminous-landscape.com/tutorials/dof2.shtml

And then come back to discuss it properly, rather than making things up as you go along.
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Amen. Please DO NOT protest something as false/true/whatever if you have no proof or understanding to discuss it properly. DoF DOES change with format size.
 
onform said:
the larger the format size the smaller the depth of field will be given all other factors being the same.. roughly speaking

An example being your 50mm lens at aperture f1.4 on a full frame will give a narrower depth of field than on a crop sensor. methinks...
Click to expand...

This is only true when you reframe so the framing in both your formats is the same. But this means the distance to the subject is changing (so not all the factors are being the same).

If all the factors are left the same then DOF is the same simply because you can think of smaller format as being a crop of the larger one.

Having said all that, there is a difference though because pixels/grain sizes (and hence circle of confusion) is different for small and large formats.
 
Woodsy said:
Amen. Please DO NOT protest something as false/true/whatever if you have no proof or understanding to discuss it properly. DoF DOES change with format size.
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If everybody did that, this would be a dull place indeed. I seem to explain something about depth of field three times a week, and that's fine by me if it helps people's understanding. Nothing to get upset about and easy enough when you consider all the factors.

dalex_257 said:
This is only true when you reframe so the framing in both your formats is the same. But this means the distance to the subject is changing (so not all the factors are being the same).

If all the factors are left the same then DOF is the same simply because you can think of smaller format as being a crop of the larger one.

Having said all that, there is a difference though because pixels/grain sizes (and hence circle of confusion) is different for small and large formats.
Click to expand...

In the context of depth of field, if you think of crop format simply as a larger format but cropped, you get confused. You have to change lenses or distance also to get like for like, not to mention CoF and viewing distance etc and all the other stuff that goes into the formulae.

Crop format is a different format in its own right. Everything changes. So you have to consdier everything differently. It stands alone. If you want to compare different formats and lenses, then you have to be very clear and specify the parameters. It's all in www.dofmaster.com and if you tap in the variables, out comes the answer.
 
Woodsy said:
Amen. Please DO NOT protest something as false/true/whatever if you have no proof or understanding to discuss it properly. DoF DOES change with format size.
Click to expand...

........which is why large format film photographers regularly use f32 (and even f64).....

But it doesn't matter if you don't understand why, just that it does is good enough ...
 
HoppyUK said:
In the context of depth of field, if you think of crop format simply as a larger format but cropped, you get confused. You have to change lenses or distance also to get like for like, not to mention CoF and viewing distance etc and all the other stuff that goes into the formulae.
Click to expand...

You misread me - I was replying to the statement that said "given all factors being the same ...". If you forget about formats and how one forces you to work differently from the other for the moment and just concentrate on that from the point of view where in both cases all factors (lens, distance to subject, aperture, pixel dimensions/CoC and distance to the focal plane) remain the same for both formats then from optical perspective a simple math will tell you that it is nothing but a crop. On practice though only difference you would have say on FX and DX Nikon bodies with the same lens, focused on the same subject that is at the same distance from the camera with the same lens aperture will be sensor pixel size (and that affects CoC) and that is what affecting DOF.

I think people tend to get easily confused when they start talking about DOF and cropped sensor versus full frame, medium format etc etc just because of this. But it is simple really - photographer aesthetics and principles aside, all factors being the same do not change DOF. Different formats themselves force you to work at different distances with different framing and approaches - but that is the whole other story.

There is a good "down to earth" explanation for all DOF and sensor sizes issues by Bob Atkins here and important comment about CoC from Bob on this Photo.net forum (scroll down to the last comment). Citing Bob here as it is exactly the point I was trying to make:
If you use the same lens on a Canon APS-C crop sensor camera and a 35mm full frame body and crop the full frame 35mm image to give the same view as the APS-C crop image, the depth of field is IDENTICAL.
Click to expand...
 
dalex_257 said:
You misread me - I was replying to the statement that said "given all factors being the same ...". If you forget about formats and how one forces you to work differently from the other for the moment and just concentrate on that from the point of view where in both cases all factors (lens, distance to subject, aperture, pixel dimensions/CoF and distance to the focal plane) remain the same for both formats then from optical perspective a simple math will tell you that it is nothing but a crop. On practice though only difference you would have say on FX and DX Nikon bodies with the same lens, focused on the same subject that is at the same distance from the camera with the same lens aperture will be sensor pixel size (and that affects CoF) and that is what affecting DOF.

I think people tend to get easily confused when they start talking about DOF and cropped sensor versus full frame, medium format etc etc just because of this. But it is simple really - photographer aesthetics and principles aside, all factors being the same do not change DoF. Different formats themselves force you to work at different distances with different framing and approaches - but that is the whole other story.
Click to expand...

But all factors are not the same. Format has changed, and that is fundamental.

What that forces you to do is not "to work at different distances with different framing" it forces you, first and foremost, to change lenses or you will get a completely different image. But you can make them the same by changing focal length for framing, and modifying the f/number to adjust for depth of field.

The only difference then is one of potential image quality, which has far more to do with resolution, pixels and noise and dynamic range etc etc than it has to do with circles of confusion. That is the whole other story, but it's not relevant to depth of field.

Edit: crossed post on your late edit, but if you want to be ultra-correct about it, what Bob Atkins is saying is also strictly wrong. I think we both understand the point that is being made, but I think it's not relevant. When you change format, everything else changes with it. You cannot say "IDENTICAL" as you have said there, because at the vey least either the degree of output magnification is changed, or the viewing distance of a smaller print, so that is your circles of confusion screwed. And Bob's too.

(Double Edit in here: Having now seen the links to Bob Atkins, and read what he says in context, I understand what he is saying and he is correct. I am also correct in what I am saying, but I had interpreted it differently. So both are correct, but neither particularly relevant to what matters in practise, because you never actually work that way.)

I think what this debate boils down to, if there is anybody else left with the will to read on, is that what I am saying is that format is at the heart of everything. It dictates what lenses you use and the image framing you get, and everything else has to change along with that. That strikes me as being plain common sense, and is how it works in practise. Saying everything remains the same or IDENTICAL (as you do) is an unhelpful distraction.
 
HoppyUK said:
But all factors are not the same. Format has changed, and that is fundamental.
Click to expand...

Boom, done. End of argument tbh.

DOF does indeed change when comparing full frame to a crop. For example, getting an equivalent 'look' of a 200mm f/2 wide open on a FF camera for a crop sensor would (in real world terms) require a 135mm f/1.4 wide open.

If the focal length has changed, then the DOF that's the result of a specific f/stop has also changed to suit that crop.
 
2Thumbs said:
Boom, done. End of argument tbh.

DOF does indeed change when comparing full frame to a crop. For example, getting an equivalent 'look' of a 200mm f/2 wide open on a FF camera for a crop sensor would (in real world terms) require a 135mm f/1.4 wide open.

If the focal length has changed, then the DOF that's the result of a specific f/stop has also changed to suit that crop.
Click to expand...

Phew! :) And I like your real world example, that's what matters :thumbs:
 
This is a very silly argument on two counts. :lol:

Firstly, there is actually no such thing as DoF. There is a plane of focus in any shot and that's it. An object is either on this plane of focus or it's not. What we actually use DoF to describe is a "zone of acceptable sharpness". So, as we all know even with everything cast in stone when it comes to making the shot in the camera, a 4 inch print will have a totally different look in terms of DoF to an 4 foot print.... and even that changes depending on where you view them both from.

The other point is that all of you are really correct in what your saying.

Format on it's own has no effect on DoF at all. None...zip.... nada....zilch.

It does of course force some major changes if you want to take two matching shots on two different formats and this changes the DoF.

So, that sorted... pint anyone? :D
 
lol....excuse me for not reading all of the discussion about the technicalities above but here's my 2 cents...

Distance from lens to subject will actually have a bigger difference than aperture. This is demonstrated by macro lenses, where users often struggle to achieve a large enough DoF, even when using small apertures like f/16.
 
Blue Eagle said:
lol....excuse me for not reading all of the discussion about the technicalities above but here's my 2 cents...

Distance from lens to subject will actually have a bigger difference than aperture. This is demonstrated by macro lenses, where users often struggle to achieve a large enough DoF, even when using small apertures like f/16.
Click to expand...

Sure it varies a lot with distance, and you need to know that at close range it gets very narrow, as the subject gets larger, and that at longer range it is much greater and you can't do much by way of movement to change that.

I think the important consideration is control of depth of field. You need to know and understand the key factors but most of the time a lot of them are fixed, and f/number is the only thing left that you can change to control it.

In a real situation, subject distance and focal length are fixed in order to give the perspective and framing that you want. You can mess about with both of those things but, if the main subject remains the same size, so does depth of field, so you're still stuck with it. Camera format is obviously fixed, so the only variable you have to control DoF is f/number.
 
dazzajl said:
This is a very silly argument on two counts. :lol:

Firstly, there is actually no such thing as DoF. There is a plane of focus in any shot and that's it. An object is either on this plane of focus or it's not. What we actually use DoF to describe is a "zone of acceptable sharpness". So, as we all know even with everything cast in stone when it comes to making the shot in the camera, a 4 inch print will have a totally different look in terms of DoF to an 4 foot print.... and even that changes depending on where you view them both from.

The other point is that all of you are really correct in what your saying.

Format on it's own has no effect on DoF at all. None...zip.... nada....zilch.

It does of course force some major changes if you want to take two matching shots on two different formats and this changes the DoF.

So, that sorted... pint anyone? :D
Click to expand...

Absolutely correct and I could not have put it better.

Now, how about that pint :thumbs: (I think I'll have it tonight)
 
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