As you can see here http://en.wikipedia.org/wiki/Circle_of_confusion the differences in CoC are related to the magnification from the original image/sensor size to the 8" x 10" print which is used as a reference.
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d7100 crop mode
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Yes...now try it without enlarging one over the other.
More to it really
From Joseph James essay
keeping in mind that aperture diameter = focal length / f-ratio, and assuming that all images are viewed from the same distance with the same visual acuity (for non-macro situations only)
- For the same perspective, framing, f-ratio, and display size, larger sensor systems will yield a more shallow DOF than smaller sensors in proportion to the ratio of the sensor sizes.
- For the same perspective, framing, aperture diameter, and display size, all systems have the same DOF.
- If both formats use the same focal length and f-ratio (and thus also the same aperture diameter), but the larger sensor system gets closer so that the subject occupies the same area of the frame, and the images are displayed at the same dimensions, then the larger sensor system will have a more shallow DOF in proportion to ratio of the sensor sizes.
- For the same perspective and focal length, larger sensor systems will have a wider framing. If the same f-ratio is used, then both systems will also have the same aperture diameter. As a result, if the image from the larger sensor system is displayed at a larger size in proportion to ratio of the sensor sizes, or the image from the larger sensor system is cropped to the same framing as the image from the smaller sensor system and displayed at the same size, then the two images will have the same DOF.
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Another really good example of when Sensor size does not affect DoF
Note no change in DoF
Remember my contention though is really that In-Camera crop modes do not change DoF just as cropping in post does not.
Like this example
cropping Dof
For fun:
I have a room that is completely dark. No light at all and the walls are black. It has a window that exactly matches the dimensions of the D7100 1.3 crop mode frame. The scene outside the window is a simple yard with a black ball that's centered in the window, from my camera's perspective, and is 60 feet away. Camera on the tripod with my 50mm lens set f1.8 and focused on that ball. Camera is position so the widow exactly fills the D7100 1.3 crop mode frame, and everything outside that frame is black. I take two pictures. One in 1.3 crop mode we'll call "pic C" and one with crop mode turned "off" well call "Pic N". Every setting on the camera was the same except crop mode. Nothing in the scene changed. The result is that those 15.36 MP of pixels, that are common to both "pic C" and "Pic N", are absolutely identical in every way. Now looking at the yard and black ball in both pictures...is there a 1 stop of DoF difference between the crop mode pic and the non-crop one? If so, under what conditions?
Sorry for sounding goofy with this. Friday
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Alphabart
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Geee...
The actual DOF of a DX vs DX crop is actually the same. Try it and see for yourself.
It's the same as you crop in photoshop. no difference
if you print and expand the size of the image the DOF size changes physically but not the ratio of the DOF. But this is a non discussion
The actual DOF of a DX vs DX crop is actually the same. Try it and see for yourself.
It's the same as you crop in photoshop. no difference
if you print and expand the size of the image the DOF size changes physically but not the ratio of the DOF. But this is a non discussion
...that DoF has nothing to do with sensor size - if everything else is kept the same (FL, Aperture, distance to subject) the DoF will be the same.
Under what conditions. Sorry if it has already been discussed, but...Another really good example of when Sensor size does not affect DoF
Note no change in DoF
Remember my contention though is really that In-Camera crop modes do not change DoF just as cropping in post does not.
Like this example
cropping Dof
For fun:
I have a room that is completely dark. No light at all and the walls are black. It has a window that exactly matches the dimensions of the D7100 1.3 crop mode frame. The scene outside the window is a simple yard with a black ball that's centered in the window, from my camera's perspective, and is 60 feet away. Camera on the tripod with my 50mm lens set f1.8 and focused on that ball. Camera is position so the widow exactly fills the D7100 1.3 crop mode frame, and everything outside that frame is black. I take two pictures. One in 1.3 crop mode we'll call "pic C" and one with crop mode turned "off" well call "Pic N". Every setting on the camera was the same except crop mode. Nothing in the scene changed. The result is that those 15.36 MP of pixels, that are common to both "pic C" and "Pic N", are absolutely identical in every way. Now looking at the yard and black ball in both pictures...is there a 1 stop of DoF difference between the crop mode pic and the non-crop one? If so, under what conditions?
Sorry for sounding goofy with this. Friday
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My opinions are my own and not those of DPR or its administration. They carry no 'special' value (except to me and Lacie of course)
I have a camera on a tripod and shoot something.
At 50 mm lens DX I get the framing which I need and I shoot at say F8 to get the desired DOF. In Crop I need only 40 mm to get the same framing, right? Will I need F8 to get the same exposure (provided iso and shutter are the same)? Will the DOF change if I keep the aperture of F8? Can I use a more open aperture to get the desired DOF?
Yeah, provided you have the same FL. Buuuuut.... if you want to get the same framing, don't you need a different FL? And this leads to different DOF at the same Aperture? Isn't it possible that this might actually be what the OP actually meant? Crop = shorter FL (to get the same framing) = different DOF at same Aperture or Different Aperture to get the same DOF?
That's why I said FL
But the point of the D7100 crop mode isn't really to get the same frame is it? The idea is to give you more effective "reach" when something is further away and you want to fill the frame with it. Yes you could move closer to the subject or put on a longer lenses then you would have to use the crop mode, but it's there when you can't do these things.Well, I have not designed it, I don't really know why they put it there, but the real benefit of it may not actually be the tighter framing and longer reach, but as has already been mentioned, the faster fps and bigger buffer. These are the reasons I use it and I'd actually love to see a poll asking real life D7100 users why they use crop ;-)That's why I said FL
Actually, tighter framing with just a rectangle in the VF is bit harder for me, since I am used to using the whole VF for framing. Longer reach can be easily achieved by simpy PP cropping those 24 mpx as you want, even asymmetrically, especially if the subject is moving fast around the scene.
BirgerH
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If everythings kept the same, DOF depends on sensorsize. This is from Wikipedia:
Where N=apeture number, c=CoC in mm, f=focal length in mm and s= distance to subject in mm
CoC is depending of the sensorsize and is bigger the bigger sensor (everything else the same).
Or based on magnification DOF is
where m is the magnification.
So if everything is kept the same, with two different cameras (different sensorsizes), same focal length, same aperture and same distance to subject DOF will not be the same.
BirgerH.
SORRY problems with DPR showing the formulas - I'lll try Again.
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BirgerH
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If everythings kept the same, DOF depends on sensorsize. This is from Wikipedia:
Where N=apeture number, c=CoC in mm, f=focal length in mm and s= distance to subject in mm
CoC is depending of the sensorsize and is bigger the bigger sensor (everything else the same).
Or based on magnification DOF is
where m is the magnification.
had to do it this way
BirgerH.
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But you're not really keeping everything the same as your enlarging to the same print size...one resulting image over the other. CoC changes. With two different cameras (different sensor sizes), same focal length, same aperture and same distance to subject DoF will be the same (both resulting images printed at the resulting native resolution and view at the same distance by the same person)...unless you're magnifying one image to match the other. Right?If everythings kept the same, DOF depends on sensorsize. This is from Wikipedia:
Where N=apeture number, c=CoC in mm, f=focal length in mm and s= distance to subject in mm
CoC is depending of the sensorsize and is bigger the bigger sensor (everything else the same).
Or based on magnification DOF is
where m is the magnification.
So if everything is kept the same, with two different cameras (different sensorsizes), same focal length, same aperture and same distance to subject DOF will not be the same.
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BirgerH
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Correct, Mako - but that is exactly how the camera does it, when cropping in camera - in different to your cutting with a scissorBut you're not really keeping everything the same as your enlarging to the same print size...one resulting image over the other. CoC changes. With two different cameras (different sensorsizes), same focal length, same aperture and same distance to subject DoF will be the same unless you're magnifying one image to match the other. Right?If everythings kept the same, DOF depends on sensorsize. This is from Wikipedia:
Where N=apeture number, c=CoC in mm, f=focal length in mm and s= distance to subject in mm
CoC is depending of the sensorsize and is bigger the bigger sensor (everything else the same).
Or based on magnification DOF is
where m is the magnification.
So if everything is kept the same, with two different cameras (different sensorsizes), same focal length, same aperture and same distance to subject DOF will not be the same.
DOF is about magnification - a long way.
You never see the Pictures in the size of the sensor - they are only comporable on your screen or printed out in the same viewing size - which always will mean - different magnification - thats the point.
Getting the same DOF (and the same size of your subject) you should then view a 10x15cm DX Picture together with a 15x22,5cm FX.
Anyway, I think we do agree.
BirgerH.
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Not different than cutting with scissors...try it. Take the picture of the ruler in both modes and examine where the DoF boundaries are. Crop mode is cropping with Adobe...but in camera.Correct, Mako - but that is exactly how the camera does it, when cropping in camera - in different to your cutting with a scissorBut you're not really keeping everything the same as your enlarging to the same print size...one resulting image over the other. CoC changes. With two different cameras (different sensorsizes), same focal length, same aperture and same distance to subject DoF will be the same unless you're magnifying one image to match the other. Right?If everythings kept the same, DOF depends on sensorsize. This is from Wikipedia:
Where N=apeture number, c=CoC in mm, f=focal length in mm and s= distance to subject in mm
CoC is depending of the sensorsize and is bigger the bigger sensor (everything else the same).
Or based on magnification DOF is
where m is the magnification.
So if everything is kept the same, with two different cameras (different sensorsizes), same focal length, same aperture and same distance to subject DOF will not be the same.
Not always. DoF is not defined by always selecting "fit to screen".
I do understand what you mean and you are correct in that regard, I think
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My opinions are my own and not those of DPR or its administration. They carry no 'special' value (except to me and Lacie of course)
I agree the real benfit is the faster fps and the ability to take more shots before the buffer fills. I usually do any cropping I need in PP, the only time I use the crop mode is for things like taking shots of the moon, since everything around it is just black and I know I will not need to crop it differently so I might as well have a smaller file size. But I may use it in other situations if I need more fps.Well, I have not designed it, I don't really know why they put it there, but the real benefit of it may not actually be the tighter framing and longer reach, but as has already been mentioned, the faster fps and bigger buffer. These are the reasons I use it and I'd actually love to see a poll asking real life D7100 users why they use crop ;-)That's why I said FL
Actually, tighter framing with just a rectangle in the VF is bit harder for me, since I am used to using the whole VF for framing. Longer reach can be easily achieved by simpy PP cropping those 24 mpx as you want, even asymmetrically, especially if the subject is moving fast around the scene.
Let's stick with Joseph's essay. In practical terms he's talking about equivalent lenses in point two. Like using a 300 f4 on FX (75mm) and 200 f2.8 on DX (71.4mm, close enough), and then stopping down from there.
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Jim
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Jim
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