DOF calculator

I was juts playing with this DOF calculator and noticed something strange (or may be not).
My understanding is the APS-C sensor will have larger DOF compared to FF (with everything else being same i.e. lens focal length, f stop and subject distance).
However this calculator shows it reverse. i.e DOF larger for FF.
E.g. 7D, 400mm f/5.6 @ 60 feet DOF = 1.44 ft
5D3, 400mm f/5.6 @ 60 feet DOF = 2.28 ft

So, is my understanding wrong or this calculator has a bug?

That's correct. (The Website)

However; To get the same framing with 35mm sensor, one must get closer to the subject, hence making the depth of field less.

http://www.cambridgein​colour.com …al-camera-sensor-size.htm

rndman wrote in post #15843310
My understanding is the APS-C sensor will have larger DOF compared to FF (with everything else being same i.e. lens focal length, f stop and subject distance).

That is incorrect, having the same values a crop and a FF sensor will have the same depth of field.

Crops appear to have more because you have to stand further away usually to get your subject into frame. But if it's at the same distance, it will be the same whether you're on a FF or a crop.

With larger format (FF compare to cropped):
Near distance is: Shorter
Far distance is: Longer
DOF is: More
Hyperfocal Distance is: Less

Calculator is fine.

maverick75 wrote in post #15843327
That is incorrect, having the same values a crop and a FF sensor will have the same depth of field.

Crops appear to have more because you have to stand further away usually to get your subject into frame. But if it's at the same distance, it will be the same whether you're on a FF or a crop.

No, that is wrong. If everything else is the same (distance, aperture, focal length) the crop body will have less DOF because you have to enlarge the image more. Of course, the image framing will be very different. To frame the subject the same, you will get more DOF with the crop body due to standing further back or using a shorter lens.

sandpiper wrote in post #15843395
No, that is wrong. If everything else is the same (distance, aperture, focal length) the crop body will have less DOF because you have to enlarge the image more. Of course, the image framing will be very different.

Didn't quite understand this, but I'm guessing you're in the multiply the focal length by 1.6 camp.

sandpiper wrote in post #15843395
To frame the subject the same, you will get more DOF with the crop body due to standing further back

That's exactly what I said.

I said it as simple as possible.
See above.

Suppose you take a photo using a 1.6X format camera at 50mm, f/4, 1/200 and ISO 100.

If you want to take the exact same photo with a FF camera then you will need to adjust those settings.
First, you have to change the focal lenght from 50mm to 80mm to get the same framing.
Second, you have to change the aperture from f/4 to f/6.3 to get the same DOF. This is the point that is confusing you, and it is related to the change in focal length.
Finally, you have to change the ISO to 250 to offset the aperture change.

The biggest mistake you made in using the DOF calculator was to compare 1.6X to FF with the same focal length, subject distance and aperture. When you do this, the resulting photo is not the same at all because the FF camera will have a much larger angle of view. The FF camera will in fact have a bit more DOF however as indicated by the DOF calculator. This is because the FF camera requires less magnification from sensor to print, which is important in DOF calculation. But overall the focal length difference to get the same shot (described as the 50mm vs. 80mm lengths above) swamps this magnification effect, so FF has less DOF in practical use.

In short - FF cameras have less DOF than 1.6X cameras (at any one aperture) because you have to use a longer focal length on the FF camera to take the same photo.

maverick75 wrote in post #15843402
Didn't quite understand this, but I'm guessing you're in the multiply the focal length by 1.6 camp.


.

The DoF tables are based on a specific size of print, to get the same size print from a smaller sensor, you have to enlarge it to a greater degree. When you make the print, the area of the smaller sensor has to be enlarged more to fill the same area of print, that extra enlargement naturally increases the size of the circles of confusion, and it is the size of the COC that defines DOF.

Therefore, the print from the crop sensor has larger COC, which means shallower DOF.

DOF is dependent on distance, focal length, aperture and enlargement. The DOF in a 10x8 print is greater than in a 20x16 print from the same digital file, because you can more easily see the out of focus areas. It amounts to the same thing.

That is why DOF tables are such a fuzzy concept, the stated figures only apply when a print of a specific size is viewed at a specific distance (Something like a 12x8" print at arms length, but I am not sure exactly - and how far is "an arms length" anyway) and viewed by somebody with a specific degree of visual acuity (and we all differ there).

So, the 4.67 inches in the table will go out of the window if you make a bigger print, or the viewer has very keen eyesight or examines the image up close. That is also why pixel peeping is a bad thing, as you are looking at a huge image from a short distance away, which is why so many people complain about soft images when doing that. They are perfectly fine looked at normally as an actual print.

maverick75 wrote in post #15843402
That's exactly what I said.

Yeah, I know. That isn't the part I was saying was wrong (that is why I bolded the part I was saying was incorrect).

Wow.. And I thought I know everything about DOF.
Good I opened this thread. I learned something really interesting...

DOF has nothing to do with sensor size. It depends on distance, aperture, and focal length.

The reason many people associate a FF with having a shallower depth of field is because with a FF you have to get closer. So a crop at 200mm you might have to stand back 20ft, while with a full frame at 200mm you would stand closer (maybe 10-15ft) which means a shallower depth of field. So in the calculator adjust the distance and you will see

"There seems to be a common belief that the EOS 5D (full frame sensor) will provide the photographer with more or less, (depending on which techno-wiz camera geek you talk to) depth of field than a cropped sensor camera such as the EOS 30D, which can be viewed either as an advantage or a drawback (depending on which techno-wiz camera geek you talk to.) On some internet forums you'll find never ending debates over this camera vs. that camera and the difference in depth of field one format sensor will provide you over another. Forget about all that. If you're like me, I don't need nor do I want to take a ruler and a calculator with me when I'm strolling around with my camera, so I can calculate a miniscule depth of field change between camera bodies. What ever your need as a photographer may be, I am here to show you that the different camera bodies will provide roughly the same depth of field when using identical focal lengths and the same exposure. The more depth of field that the 5D supposedly gives you is a myth. Functionally, from a photographic standpoint there is no difference.

"Below are two photographs, taken one right after the other, using the EOS 30D and EOS 5D with a Sigma 105mm Macro lens, pointing at a yardstick from the same exact distance using a tripod. I'm manually focusing on the 20 inch mark of the yardstick. The only obvious difference between the shots is the field of view (not to be confused with the depth of field.) The EOS 5D will give a wider field of view than the 30D using the same focal length lens. If you examine the depth of field provided in both shots by tracing the yardstick from the 20 inch mark, you'll see that the focus field is roughly identical."

http://www.have-camera-will-travel.com …ame_vs_crop_sen​sor_-.html

Ratjack wrote in post #15843756
DOF has nothing to do with sensor size. It depends on distance, aperture, and focal length.

The reason many people associate a FF with having a shallower depth of field is because with a FF you have to get closer. So a crop at 200mm you might have to stand back 20ft, while with a full frame at 200mm you would stand closer (maybe 10-15ft) which means a shallower depth of field. So in the calculator adjust the distance and you will see

I think, the better and definitive test is to keep everything same, but change the focal length when changing the camera. Multiply the focal length by 1.6x while using FF (to maintain framing of the APS-C)...
That represent (perceived) shallower DOF that one sees.

rndman wrote in post #15843773
I think, the better and definitive test is to keep everything same, but change the focal length when changing the camera. Multiply the focal length by 1.6x while using FF (to maintain framing of the APS-C)...
That represent (perceived) shallower DOF that one sees.

If you change focal length you will be changing the DOF.

kjonnnn wrote in post #15843770
"There seems to be a common belief that the EOS 5D (full frame sensor) will provide the photographer with more or less, (depending on which techno-wiz camera geek you talk to) depth of field than a cropped sensor camera such as the EOS 30D, which can be viewed either as an advantage or a drawback (depending on which techno-wiz camera geek you talk to.) On some internet forums you'll find never ending debates over this camera vs. that camera and the difference in depth of field one format sensor will provide you over another. Forget about all that. If you're like me, I don't need nor do I want to take a ruler and a calculator with me when I'm strolling around with my camera, so I can calculate a miniscule depth of field change between camera bodies. What ever your need as a photographer may be, I am here to show you that the different camera bodies will provide roughly the same depth of field when using identical focal lengths and the same exposure. The more depth of field that the 5D supposedly gives you is a myth. Functionally, from a photographic standpoint there is no difference.

"Below are two photographs, taken one right after the other, using the EOS 30D and EOS 5D with a Sigma 105mm Macro lens, pointing at a yardstick from the same exact distance using a tripod. I'm manually focusing on the 20 inch mark of the yardstick. The only obvious difference between the shots is the field of view (not to be confused with the depth of field.) The EOS 5D will give a wider field of view than the 30D using the same focal length lens. If you examine the depth of field provided in both shots by tracing the yardstick from the 20 inch mark, you'll see that the focus field is roughly identical."

http://www.have-camera-will-travel.com …ame_vs_crop_sen​sor_-.html

Well, actually, functionally from a photographic standpoint there is a difference, a bl**dy big one. You have taken two totally different photographs.

What you have said is true, stand in the same place, with the same aperture and focal length and the difference in DOF is minimal between crop and FF (there is some as the smaller sensor requires more enlargement). Nobody disputes that, it is basic photography.

However, that is only relevant when shooting a laboratory test to prove that the DOF is the same. Those of us who live in the real world don't shoot like that, we don't randomly pick a position, and a focal length, we choose the position that gives us the best perspective for the image we want to take and the focal length that gives the framing that we want compositionally. That focal length WILL be different according to whether you are using a crop or FF body. I have never yet set up a shot, got my perspective and framing correct and then decided to switch my lens for one that would suit another format instead, thus either introducing a lot of unwanted elements in the scene, or cutting off part of what I want to see in the image, in order to keep my DOF as it would be on the other format.

No, instead, I use the correct focal length for what I am shooting. So, if I stand in the same place and shoot to obtain the same composition and framing on both formats, I will get different DOF (if I keep the same aperture) as I need to use two different focal lengths.

So, the difference is not a "myth", it is very real in the real world, where you take the shot with the framing you want.

This is an argument that goes round in circles because both sides are right, but only one side is thinking about capturing a specific image.