Crop + F2.8 v Full Frame + F4

akr

akr

Messages
2,770
Name
Al
Edit My Images
Yes
This is a it of a thinking aloud thread so please excuse me!

I have the 70-200 f4.

Now lots of people recommend the 70-200 f2.8 (or 2.8) in general for the increased OOF areas amongst other things.

I've recently got a 5D and for the same Field of View, I believe the DOF of the 70-200 f4 @f4 and the 5d is shallower than the 40d and 70-200 f2.8 @f2.8. ( did a couple of DoF master online tests - this could be wrong but I think we are good on this point :thinking:)

So, my question is, or really something to think about for people wanting f2.8 and have f4 lenses could it be cheaper to get a second hand full frame camera for that extra effect? I guess my 85 f1.8 in terms of DoF becomes 50mm f something lower than f1.8 in terms of DOF.

Clearly f4 is f4 and in terms of shutter speed that won't change, AF may not be as fast and you would have to move forwards \ backwards to get the same FoV but am I missing something in terms of DOF?

And that's my slight random thought over! :)
 
akr said:
This is a it of a thinking aloud thread so please excuse me!

I have the 70-200 f4.

Now lots of people recommend the 70-200 f2.8 (or 2.8) in general for the increased OOF areas amongst other things.

I've recently got a 5D and for the same Field of View, I believe the DOF of the 70-200 f4 @f4 and the 5d is shallower than the 40d and 70-200 f2.8 @f2.8. ( did a couple of DoF master online tests - this could be wrong but I think we are good on this point :thinking:)

So, my question is, or really something to think about for people wanting f2.8 and have f4 lenses could it be cheaper to get a second hand full frame camera for that extra effect? I guess my 85 f1.8 in terms of DoF becomes 50mm f something lower than f1.8 in terms of DOF.

Clearly f4 is f4 and in terms of shutter speed that won't change, AF may not be as fast and you would have to move forwards \ backwards to get the same FoV but am I missing something in terms of DOF?

And that's my slight random thought over! :)
Click to expand...

What are you smoking? :LOL: That makes absolutely no sense.
 
That sort of makes sense to me actually. (except the "85mm f/1.8 becomes 50mm and something lower than f/1.8 in DOF terms, that doesn't make sense)

As I understand it (feel free to correct me, any experts on here, there's a fair chance I've got stuff wrong).
The 40D is 1.6 crop, so for DoF terms you multiply the f/stop by 1.6 to get the equivalent of the aperture in FF DoF terms, when you shoot at shorter focal lengths to compensate for the crop factor.
Since 1.6x is slighty more than a stop (which is ~1.4x), it makes sense that if you shoot with the 40D one stop faster and maintain the same framing, the DoF will still be slightly larger than the FF at 1 stop slower.
In FoV and DoF terms, the 70-200 f/2.8 on a 40D is equivalent to a 112-320mm f/4.5 on a 5D


I really hope this doesn't end up as another "sensor size does/does not affect DOF" argument.
 
Last edited:
Its not always about dof. An f/2.8 lens will always be faster than an f/4 lens no matter what body it's on, and that's the main reason why people buy f/2.8 telephotos.
 
EdBray said:
What are you smoking? :LOL: That makes absolutely no sense.
Click to expand...

Having an 8 month old is doing strange things to by brain. On the plus side, red bull sales are up 500% in my neighbourhood!

I did say I was thinking aloud :puke: I think I mean an 85mm f1.8 on a FF might give you roughly the same DOF as a 50mm f.14 on a crop (I've not worked it out hence my slightly loose assertion!)

I feel this post may prove my undoing! :help:
 
odd jim said:
Its not always about dof. An f/2.8 lens will always be faster than an f/4 lens no matter what body it's on, and that's the main reason why people buy f/2.8 telephotos.
Click to expand...

Absolutely, purely talking about DOF. The F4s are lighter as well of course....

I guess what I was wondering is let's say you had a 24-105 f5, a 70-200f4 and a 17-40 f4 and you decided you wanted f2.8 for the DOF you could go 24-70 2.28 \ 17-55 f2.8, 70-200 f2.8 or keep your kit and get a FF body which might get you the same effect for less money?

Or I could be lacking in sleep!:)
 
akr said:
Thanks, and so do I. :nono:
Click to expand...

Sorry, I've been slowly editing my post for the last 5 minutes :LOL:

I think I understand relationships between sensor size, aperture, focal length and DoF, so I post with confidence, then I start having doubts about my understanding, so I have to edit bits :wacky: :bonk:
 
akr said:
Absolutely, purely talking about DOF. The F4s are lighter as well of course....

I guess what I was wondering is let's say you had a 24-105 f5, a 70-200f4 and a 17-40 f4 and you decided you wanted f2.8 for the DOF you could go 24-70 2.28 \ 17-55 f2.8, 70-200 f2.8 or keep your kit and get a FF body which might get you the same effect for less money?

Or I could be lacking in sleep!:)
Click to expand...

...in fact I'd go as far to say the reduced dof of f/2.8 telephotos is sometimes an unwanted side effect of shooting sports when you have to open up. For candids and street shooting it's quite nice on the other hand.

I think purely for dof, people generally go for fast primes, though, and for the zooms and telephotos, it's more for the speed of the lens, but what you say holds truth. Though you'd have to sell the 17-55 f/2.8 if it's the Canon as it's EFS!
 
squishy said:
That sort of makes sense to me actually. (except the "85mm f/1.8 becomes 50mm and something lower than f/1.8 in DOF terms, that doesn't make sense)
Click to expand...

It makes perfect sense if you perception is from using a crop body.

i.e. If you used to using a 40D, then the 85mm lens you used to use on the 40D will now be like a 50mm lens on a 5D in terms of FOV, but the DOF would be like shooting an 85mm F1.1 on his 40D.
 
Groan.... :LOL:

Beyond the aperture size what makes the difference with the same lens is the camera to subject distance and if you were to shoot with APS-C and full frame from the same position with the same lens at the same aperture the DoF would be the same. The reason it looks different between formats of different sizes is because the FoV is different and you choose different focal lengths or camera to subject distances to get the FoV you want and thus the DoF looks different.
 
While that is true woof woof, it's pretty meaningless for actual photography, because you're going to take the same picture no matter what size the sensor is.
And when your taking the same framed picture, not keeping all the settings the same for arguments sake, what size your sensor is will affect dof.
 
woof woof said:
Groan.... :LOL:

Beyond the aperture size what makes the difference with the same lens is the camera to subject distance and if you were to shoot with APS-C and full frame from the same position with the same lens at the same aperture the DoF would be the same. The reason it looks different between formats of different sizes is because the FoV is different and you choose different focal lengths or camera to subject distances to get the FoV you want and thus the DoF looks different.
Click to expand...

Lol, looks like someone is trying to be too clever... :LOL:

squishy said:
While that is true woof woof, it's pretty meaningless for actual photography, because you're going to take the same picture no matter what size the sensor is.
And when your taking the same framed picture, not keeping all the settings the same for arguments sake, what size your sensor is will affect dof.
Click to expand...

+1

FF has approx. 1.3 Fstop's advantage.
 
Last edited:
Neither the sensor nor the DOF alters the focal length of a lens.

I think what you mean is that to get the same FOV on a crop camera as opposed to a FF you have to change the viewpoint by getting further back and THAT will increase the DOF at the same stop.

.
 
Can we just have a sticky explaining this once and for all? It's such a tired debate.
 
The23rdman said:
Can we just have a sticky explaining this once and for all? It's such a tired debate.
Click to expand...
I just thought the same thing. :LOL:
 
petersmart said:
Neither the sensor nor the DOF alters the focal length of a lens.

I think what you mean is that to get the same FOV on a crop camera as opposed to a FF you have to change the viewpoint by getting further back and THAT will increase the DOF at the same stop.

.
Click to expand...

:|

MomentCapture said:
It makes perfect sense if you perception is from using a crop body.

i.e. If you used to using a 40D, then the 85mm lens you used to use on the 40D will now be like a 50mm lens on a 5D in terms of FOV, but the DOF would be like shooting an 85mm F1.1 on his 40D.
Click to expand...
 
In conclusion I think the answer is yes.

Thanks all.
 
squishy said:
While that is true woof woof, it's pretty meaningless for actual photography, because you're going to take the same picture no matter what size the sensor is.
And when your taking the same framed picture, not keeping all the settings the same for arguments sake, what size your sensor is will affect dof.
Click to expand...

Of course it isn't meaningless. What an odd thing to say :wacky: You'll be telling me that I can't get shallower DoF with a 25mm on MFT than 85mm on FF next :LOL: I can, BTW, because my 25mm will focus a lot closer than my 85mm :LOL:
 
I'm a bit puzzled as to why people are arguing with Alan on this. He has it exactly right.
 
paulcamcas said:
I'm a bit puzzled as to why people are arguing with Alan on this. He has it exactly right.
Click to expand...
Because:

  • Generally you wouldn't shoot with the same lens on at the same point if you were using FF and crop. You'd either use a different lens or change position which would give you a different photo. The reason you would do either of those two things is only due to the sensor size.
  • If you did take the photo with the same lens at the same position and then cropped the image so it was the same FoV, you would have effectively changed the sensor size of the FF camera to be to crop format.
  • All DoF calculations are related back to the sensor size through the Circle of Confusion which is directly related to the sensor size.
  • DoF is only relevant when you render the image on a screen or print. The consequence of that is that DoF will vary from the same picture depending on how much it is cropped, how big the image you render is and how far away you view it from. Render it small and look at it a long way away, it'll look sharp, render it large and look at it closely, the more critical the DoF becomes. In printing an image to a certain size, you are worried about magnification of the actual image (i.e. the 24x36mm or 22.2x14.8mm of the sensor). The more you magnify the image to a certain size, the less DoF it has (i.e. the smaller format will have less DoF than the larger).

You can also see it rehashed here: http://en.wikipedia.org/wiki/Depth_of_field#DOF_vs._format_size

All of these things are affected by sensor size directly. So in the real world, DoF is affected by sensor size (and subsequent print size)....
 
Last edited:
paulcamcas said:
I'm a bit puzzled as to why people are arguing with Alan on this. He has it exactly right.
Click to expand...
if you stand in the same place with a 50mm lens on a d300 and d700 and focus on the same thing using the same settings the depth of field will be greater on the full frame,
but if you stick a 75mm lens on the d700 to give the same field of view as the d300 with the 50mm (75mm in 35mm terms) the depth of field will be shallower on the d700.
so hes not right.
 
arad85 said:
Because:

  • Generally you wouldn't shoot with the same lens on at the same point if you were using FF and crop. You'd either use a different lens or change position which would give you a different photo. The reason you would do either of those two things is only due to the sensor size.
  • If you did take the photo with the same lens at the same position and then cropped the image so it was the same FoV, you would have effectively changed the sensor size of the FF camera to be to crop format.
  • All DoF calculations are related back to the sensor size through the Circle of Confusion which is directly related to the sensor size.
  • DoF is only relevant when you render the image on a screen or print. The consequence of that is that DoF will vary from the same picture depending on how much it is cropped, how big the image you render is and how far away you view it from. Render it small and look at it a long way away, it'll look sharp, render it large and look at it closely, the more critical the DoF becomes. In printing an image to a certain size, you are worried about magnification of the actual image (i.e. the 24x36mm or 22.2x14.8mm of the sensor). The more you magnify the image to a certain size, the less DoF it has (i.e. the smaller format will have less DoF than the larger).

You can also see it rehashed here: http://en.wikipedia.org/wiki/Depth_of_field#DOF_vs._format_size

All of these things are affected by sensor size directly. So in the real world, DoF is affected by sensor size (and subsequent print size)....
Click to expand...

scottthehat said:
if you stand in the same place with a 50mm lens on a d300 and d700 and focus on the same thing using the same settings the depth of field will be greater on the full frame,
but if you stick a 75mm lens on the d700 to give the same field of view as the d300 with the 50mm (75mm in 35mm terms) the depth of field will be shallower on the d700.
so hes not right.
Click to expand...


:clap: :clap:
 
scottthehat said:
but if you stick a 75mm lens on the d700 to give the same field of view as the d300 with the 50mm (75mm in 35mm terms) the depth of field will be shallower on the d700.
so hes not right.
Click to expand...
Actually, the depth of field will be identical, if the same aperture was used, but the composition will look differently.

edit: it seems that some literature believes that DoF is identical regardless of focal length (given distance and aperture are the same), unless one reaches wide-angle territory. Others think that DoF changes between different focal lengths. If the latter is true, then above statement would be of course wrong.
 
Last edited:
Cistron said:
Actually, the depth of field will be identical, if the same aperture was used, but the composition will look differently.
Click to expand...

Ah, but it won't.
As arad explained, DoF is relative to the size and distance from the viewer the image is being rendered at, so while you could crop the FF image to the same FoV as the crop sensor and then have identical DoF, as a whole image the DoF will be larger on the FF camera under that circumstance.

It took me a while to understand that myself!
 
Last edited:
"if you were to shoot with APS-C and full frame from the same position with the same lens at the same aperture the DoF would be the same"

This is what Alan said and it is correct. Of course the composition would be different but the depth of field would be identical. If you want a similar composition, you would move closer with the FF camera and the depth of field would reduce.

Ignore the above, it was wrong. I think.
 
Last edited:
For arguments sake lets pretend we have 2x 135mm F/2 primes, one Canon 7D (crop) and one 5D (FF). Fit one lens to each camera and aim at the same focus point from exactly the same position. Lets say that the focus point is a pretty woman within a croud 50 feet away.

On both bodies the woman would like identical with exactly the same depth of field against the immediate central background. The difference will be that the FF body will show much more of the surrounding croud, more people, closer objects, further objects etc.

The depth of field will be identical for both photos but the FF body will simply show more around the edges, giving the "perception" of more depth, but really just blurring the borders:). Of course, if you crop the final output of the FF down to crop size, both images will be identical from a DOF perspective. So, F/2 on a crop is the same as F/2 on FF. Both offer exactly the same DOF, but the FF will simple give a wider FOV.
 
Last edited:
paulcamcas said:
"if you were to shoot with APS-C and full frame from the same position with the same lens at the same aperture the DoF would be the same"

This is what Alan said and it is correct. Of course the composition would be different but the depth of field would be identical. If you want a similar composition, you would move closer with the FF camera and the depth of field would reduce.
Click to expand...
wrong.


if you have an (set at f2.8)
50mm on a 1.5x crop it will give you 75mm in 35mm temrs, so if you focus on something 10 foot away the dof will be = 42.195cm

and full frame
50mm on a full frame is 50mm, same again focus on something 10 foot away
the dof will be = 63.636cm so more dof then then the crop.

But to get the same field of view as the crop camera on the full frame use a 75mm lens and focus again at 10 foot away and the dof will be = 28.056cm which is 12cm less dof then the crop camera with the same field of view.
 
akr said:
Having an 8 month old is doing strange things to by brain. On the plus side, red bull sales are up 500% in my neighbourhood!

I did say I was thinking aloud :puke: I think I mean an 85mm f1.8 on a FF might give you roughly the same DOF as a 50mm f.14 on a crop (I've not worked it out hence my slightly loose assertion!)

I feel this post may prove my undoing! :help:
Click to expand...

AKR - keep at it... I like the idea of 'cheating' to get a specific look, very resourceful*

(*if you have a spare FF body to hand :LOL:)
 
I stand corrected - I wasn't thinking 50mm = 75mm and hence doing it wrong.
 
Orville said:
For arguments sake lets pretend we have 2x 135mm F/2 primes, one Canon 7D (crop) and one 5D (FF). Fit one lens to each camera and aim at the same focus point from exactly the same position. Lets say that the focus point is a pretty woman within a croud 50 feet away.

On both bodies the woman would like identical with exactly the same depth of field against the immediate central background. The difference will be that the FF body will show much more of the surrounding croud, more people, closer objects, further objects etc.

The depth of field will be identical for both photos but the FF body will simply show more around the edges, giving the "perception" of more depth, but really just blurring the borders:). Of course, if you crop the final output of the FF down to crop size, both images will be identical from a DOF perspective. So, F/2 on a crop is the same as F/2 on FF. Both offer exactly the same DOF, but the FF will simple give a wider FOV.
Click to expand...

Now I'm really confused, because this is what I thought in the first place.
 
What everyone who is confused here is forgetting is that DoF is ONLY relevant when you render the image. Using a FF and APS-C with the same lens at the same distance and printing to a fixed image size (say 12x8) will render the DoF differently. This is because you have magnified things differently, so area for area, you are magnifying the captured image more with the APS-C sensor to get the same area on the print. If you crop the FF so it has the same FoV as the crop and print it at 12x8, the DoF will be identical. You haven't changed the captured image, you've changed the size it is rendered at. People have the misconception that DoF is done at image capture. It isn't, it's defined when you render the image (and view it).

If you have difficulty thinking about this, just take a simple example. Take any image you have from any camera. View it at 100% (i.e. pixel peep). Now view from exactly the same point and view it so it is an image that is 800 pixels along its longest axis. Which is sharper? Which has more DoF? Simple - the one at 800 pixels. Same image, same data, you're just viewing it with different rendering parameters....
 
Orville said:
For arguments sake lets pretend we have 2x 135mm F/2 primes, one Canon 7D (crop) and one 5D (FF). Fit one lens to each camera and aim at the same focus point from exactly the same position. Lets say that the focus point is a pretty woman within a croud 50 feet away.

On both bodies the woman would like identical with exactly the same depth of field against the immediate central background. The difference will be that the FF body will show much more of the surrounding croud, more people, closer objects, further objects etc.

The depth of field will be identical for both photos but the FF body will simply show more around the edges, giving the "perception" of more depth, but really just blurring the borders:). Of course, if you crop the final output of the FF down to crop size, both images will be identical from a DOF perspective. So, F/2 on a crop is the same as F/2 on FF. Both offer exactly the same DOF, but the FF will simple give a wider FOV.
Click to expand...

No. You've forgotten the output, how the image is rendered as a print or screen image.

arad85 said:
What everyone who is confused here is forgetting is that DoF is ONLY relevant when you render the image. Using a FF and APS-C with the same lens at the same distance and printing to a fixed image size (say 12x8) will render the DoF differently. This is because you have magnified things differently, so area for area, you are magnifying the captured image more with the APS-C sensor to get the same area on the print. If you crop the FF so it has the same FoV as the crop and print it at 12x8, the DoF will be identical. You haven't changed the captured image, you've changed the size it is rendered at. People have the misconception that DoF is done at image capture. It isn't, it's defined when you render the image (and view it).

If you have difficulty thinking about this, just take a simple example. Take any image you have from any camera. View it at 100% (i.e. pixel peep). Now view from exactly the same point and view it so it is an image that is 800 pixels along its longest axis. Which is sharper? Which has more DoF? Simple - the one at 800 pixels. Same image, same data, you're just viewing it with different rendering parameters....
Click to expand...

Yes.

The factors affecting DoF are sensor size, focal length, shooting distance and f/number. If you change any one of those things, DoF changes.

And at all times, DoF calcs assume a standard size print, viewed from a standard distance (eg, A4 viewed from 15in, which is the length of the diagonal).

As Andy says, this is the bit that many people seem to overlook, but it is actually at the heart of the whole thing. The starting point is the final printed image, and how much detail the human eye can resolve under the standard viewing conditions. All the other calculations are worked back from that.
 
arad85 said:
What everyone who is confused here is forgetting is that DoF is ONLY relevant when you render the image. Using a FF and APS-C with the same lens at the same distance and printing to a fixed image size (say 12x8) will render the DoF differently. This is because you have magnified things differently, so area for area, you are magnifying the captured image more with the APS-C sensor to get the same area on the print. If you crop the FF so it has the same FoV as the crop and print it at 12x8, the DoF will be identical. You haven't changed the captured image, you've changed the size it is rendered at. People have the misconception that DoF is done at image capture. It isn't, it's defined when you render the image (and view it).

If you have difficulty thinking about this, just take a simple example. Take any image you have from any camera. View it at 100% (i.e. pixel peep). Now view from exactly the same point and view it so it is an image that is 800 pixels along its longest axis. Which is sharper? Which has more DoF? Simple - the one at 800 pixels. Same image, same data, you're just viewing it with different rendering parameters....
Click to expand...

Um. You've lost me. So I shoot a portrait at f1.4. DoF is so shallow that only the tip of the nose is in focus. I shoot at 12mp, so 4200 pixels on the long edge. Are you saying that if I crop to 800 pixels the DoF changes? Or are you saying if I resize the image to 800 pixels that the DoF changes?
 
I can't believe how many people are struggling with this concept, and have got the wrong end of the stick...
 
chrisgeary said:
Um. You've lost me. So I shoot a portrait at f1.4. DoF is so shallow that only the tip of the nose is in focus. I shoot at 12mp, so 4200 pixels on the long edge. Are you saying that if I crop to 800 pixels the DoF changes? Or are you saying if I resize the image to 800 pixels that the DoF changes?
Click to expand...
Both. If you crop to 800 and print at the same size as you printed at 4200 and view from the same distance then DoF will be shallower as you are looking more closely at the image (assuming you don't start to see the pixelation in the image). If instead you resize the image to 800 pixels and display it so it is ~20% the size (i.e. you just shrink the image) DoF will be deeper.

It's all about visual perception. In reality, everything that is in front of or behind the plane of focus is out of focus. It's just whether you notice it when you look at the print (rendered image).

It's simple to try. Take any of your images - the one that you think looks the sharpest. View the image so it is displayed at 20% and look at the DoF. Now zoom it to 100%. Does the apparent DoF (i.e. the bits you think are and aren't in focus) change? Certainly does here. Same image, no processing, just displayed at a different size...
 
MomentCapture said:
I can't believe how many people are struggling with this concept
Click to expand...
It's because people are thinking as DoF as a characteristic of the lens and the DoF is "captured" by the sensor and is therefore a static thing.
 
You must log in or register to reply here.
Back
Top