But full frames have more DOF with same lens?

[coastalconn]

Just out of curiosity and Not that it matters. I guess everyone thinks about it in the sense of portraits and stuff since you need a different focal length to get the same field of view. But my thought is this, If I'm shooting my D300 with my Tamron 200-500 at 500mm and say F8, and my friend is shooting his 5dm3 with his 500mm F4 at f8 and a bird flies by at say 150 feet, a simple DOF calculator shows I have 8'9" DOF and he has 12' 7" DOF. So he would have to shoot at f5.6 to get the same depth of field and could actually pick up 1 stop of shutter speed. Obviously he would have to crop alot more to get the same image. This seems backwards of everything I have ever read?

 

[Light Guru]

Yes sensor size does effect DOF. If you really want to play with DOF try using a large format view camera where your film is say 4x5 inches or 8x10 inches. Plus you have tilt and shift movements to further effect your focal plane.

 

[o hey tyler]

If you have the same subject framing, aperture, and focal length... The full frame camera will have a shallower depth of field because you'd be closer to the minimum focus distance.

 

[coastalconn]

I get it from the practical sense, like I said portraits etc. You would need 50mm on a crop to match 75mm on a full frame. But from a pure technical standpoint, If you take a FF vs crop with the same lens at the same distance you would technically have more DOF on the FF because of the FOV... right?

 

[Helen B]

Just out of curiosity and Not that it matters. I guess everyone thinks about it in the sense of portraits and stuff since you need a different focal length to get the same field of view. But my thought is this, If I'm shooting my D300 with my Tamron 200-500 at 500mm and say F8, and my friend is shooting his 5dm3 with his 500mm F4 at f8 and a bird flies by at say 150 feet, a simple DOF calculator shows I have 8'9" DOF and he has 12' 7" DOF. So he would have to shoot at f5.6 to get the same depth of field and could actually pick up 1 stop of shutter speed. Obviously he would have to crop alot more to get the same image. This seems backwards of everything I have ever read?

As you say, to get the same image he would have to crop, so he is effectively using a crop sensor, so the DoF then becomes the same at the same focal length, focus distance and f-number.

If he doesn't crop, then at the same focal length, focus distance and f-number the larger format will have greater DoF, if the two images are viewed at the same physical size (ie 12x18 or whatever). The subject will be smaller in the image from the full frame camera, and the magnification from the camera-size image to the viewed-size image will be less for the FF - therefore the amount of blur (circle of confusion) in the FF camera image can be greater, to produce the same blur in the final image (the blur is magnified less).

When you make DoF comparisons across formats you have to be very careful about exactly what you are comparing.

 

[o hey tyler]

I get it from the practical sense, like I said portraits etc. You would need 50mm on a crop to match 75mm on a full frame. But from a pure technical standpoint, If you take a FF vs crop with the same lens at the same distance you would technically have more DOF on the FF because of the FOV... right?

Yes, however you wouldn't have the same shot. If the subject was the same size in the frame, the FF camera would have a shallower DoF.

 

[coastalconn]

I just find it interesting that us strange bird people never really talk about it. I understand if the framing was the same. But in my case we are both shooting at 500mm. So if he cropped his picture to the same size he would have more DOF, hence the entire eagle wingspan would be in focus in his shot, but not necessarily in mine... Well providing the eagle had a 10 ft wing span from my DOF calculator in the first post

 

[Helen B]

I just find it interesting that us strange bird people never really talk about it. I understand if the framing was the same. But in my case we are both shooting at 500mm. So if he cropped his picture to the same size he would have more DOF, hence the entire eagle wingspan would be in focus in his shot, but not necessarily in mine... Well providing the eagle had a 10 ft wing span from my DOF calculator in the first post

No! If he crops he will effectively be using a crop camera, and the DoF will be the same. See my previous post. Think about it: What is the difference between using a cropped section from a full frame camera and simply using a crop sensor? Think about this: what would happen if you used the 500 mm lens on an 8x10 camera and then cropped? Your theory suggests that there would be even more DoF. Do you see how absurd that is? When you crop the frame from a larger format camera it is the same as if you had used a smaller format in the first place.

 

[greybeard37 9]

I just find it interesting that us strange bird people never really talk about it. I understand if the framing was the same. But in my case we are both shooting at 500mm. So if he cropped his picture to the same size he would have more DOF, hence the entire eagle wingspan would be in focus in his shot, but not necessarily in mine... Well providing the eagle had a 10 ft wing span from my DOF calculator in the first post

No! If he crops he will effectively be using a crop camera, and the DoF will be the same. See my previous post. Think about it: What is the difference between using a cropped section from a full frame camera and simply using a crop sensor? Think about this: what would happen if you used the 500 mm lens on an 8x10 camera and then cropped? Your theory suggests that there would be even more DoF. Do you see how absurd that is? When you crop the frame from a larger format camera it is the same as if you had used a smaller format in the first place.

^^^^ What Helen B said!!!

 

[coastalconn]

I'm not talking about shooting in crop mode. So after you take the picture, and crop it on a computer you change physics? Or are DOF calculators simply wrong for different sensor sizes?

 

[Helen B]

I'm not talking about shooting in crop mode. So after you take the picture, and crop it on a computer you change physics? Or are DOF calculators simply wrong for different sensor sizes?

No, you keep physics the same. What do you think is the difference between cropping a full frame and using a crop sensor in the first place? Do you understand why and how DoF calculators take format into account? You seem to be plugging numbers into a calculator without understanding the physics. Dangerous.

There is a concept known as maximum acceptable circle of confusion (MACC). It represents how large a blur circle can be at the sensor level before it becomes visible as blur at the viewed image size. The size of it depends on how much the camera image has to be magnified. The more it has to be magnified, the smaller the MACC must be. If you crop an image, it has to be enlarged more to get to the same size, therefore the MACC needs to be smaller.

Google DoF and read more about the subject. It's all been covered countless times and there is loads of information on the web that will help you to understand the subject instead of simply crunching numbers.

 

[480sparky43 42]

......Google DoF and read more about the subject.......

Google Circle of Confusion instead..... that will lead to a quicker understanding.

 

[Village Idiot]

No! If he crops he will effectively be using a crop camera, and the DoF will be the same. See my previous post. Think about it: What is the difference between using a cropped section from a full frame camera and simply using a crop sensor? Think about this: what would happen if you used the 500 mm lens on an 8x10 camera and then cropped? Your theory suggests that there would be even more DoF. Do you see how absurd that is? When you crop the frame from a larger format camera it is the same as if you had used a smaller format in the first place.

I don't see how that's correct? Cropping an image after it's been taken will not affect the DOF of the image that has already been recorded. The crop camera will have the longer equivalent FOV if both cameras are using a 500mm lens and will have a shallower DOF. With the FF camera using an 800mm lens to have a FOV equal to a Canon 500mm lens, then it would have a shallower DOF.

If you have a photo where the crop camera takes a photo of a subject with one eye in focus and the other eye out while a FF camera has one eye in focus and the other half way in focus using the same physical focal length lens, cropping the FF photo will not magically completely blur the 2nd eye that's blurred in the photo of the crop camera.

 

[Mike_E]

No! If he crops he will effectively be using a crop camera, and the DoF will be the same. See my previous post. Think about it: What is the difference between using a cropped section from a full frame camera and simply using a crop sensor? Think about this: what would happen if you used the 500 mm lens on an 8x10 camera and then cropped? Your theory suggests that there would be even more DoF. Do you see how absurd that is? When you crop the frame from a larger format camera it is the same as if you had used a smaller format in the first place.

I don't see how that's correct? Cropping an image after it's been taken will not affect the DOF of the image that has already been recorded. The crop camera will have the longer equivalent FOV if both cameras are using a 500mm lens and will have a shallower DOF. With the FF camera using an 800mm lens to have a FOV equal to a Canon 500mm lens, then it would have a shallower DOF.

If you have a photo where the crop camera takes a photo of a subject with one eye in focus and the other eye out while a FF camera has one eye in focus and the other half way in focus using the same physical focal length lens, cropping the FF photo will not magically completely blur the 2nd eye that's blurred in the photo of the crop camera.

Apples and eggs. An 800mm lens has different characteristics than a 500mm lens.

Enlarging a crop also enlarges the blur (as Helen stated) so with the same size image each would be the same. The lens doesn't care what it's attached to, it's going to behave the same.

Circle of Confusion is likely the most aptly named term there is.

 

[Dao]

I don't see how that's correct? Cropping an image after it's been taken will not affect the DOF of the image that has already been recorded. The crop camera will have the longer equivalent FOV if both cameras are using a 500mm lens and will have a shallower DOF. With the FF camera using an 800mm lens to have a FOV equal to a Canon 500mm lens, then it would have a shallower DOF.

Basically if we keep everything else constant, just cropping the image will result the change in DoF.

When we define the DoF for a particular format , we make few assumptions. When an image is cropped and printed on the same final format/output and view at the same defined distance, the image itself is enlarged (when compared with the non-cropped version). So some of the points within the image which were a points before and now is a blur. So area was considered as sharp is not so sharp any more. And that is the reason of change in DoF.

So DoF is affected when CoC is affected.