Crop vs Full Frame - DoF

[Helen B]

This is from Bob Atkin's website Jake posted.:
• 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

Well, yes. You are using the full-frame sensor as if it was a crop sensor. Of course the results will be identical in terms of DoF. The difference comes when you use the full area of the larger sensor.

Best,
Helen

 

[djd3mo]

There are four main factors that determine depth of field: distance to the object that is focused on, relative aperture (f-number), focal length of lens and maximum acceptable diameter of the circle of confusion (how much blur can be tolerated in the image on the film/sensor before it appears to be out of focus in the final, viewed, image - with the same CoC criterion being applied to both of the viewed images).

The latter comes into play when comparing different sensor sizes (and even sensors of the same size but different photosite sizes)...

Actually it doesn't care about sensor size. You are right, it's the Circle of Confusion the fourth element (but I didn't want to add more confusion ). But the CoC is also a lens parameter and it's independent of the sensor size or pixel density. Those being said, for FX lenses we have a CoC of ~0.03mm and for DX lenses we have a CoC of ~0.02mm. Indeed these values were chosen when the lenses were built considering the final print, but they aren't related to the sensor size.

 

[Helen B]

Sorry, but I have the impression that you don't understand this issue.



Best,
Helen

 

[Robin Usagani]

Then to fill the sensor with the subject for the full frame, you have to come closer. That means the distance is not the same. But this is limited to macro world because you are already at the minimum focus distance usually.

 

[djd3mo]

Sorry, but i have the impression that you don't understand this issue.

Best,
helen

And why would you have this impression ?

 

[frisii]

Is there a significant difference in the DoF on a Full Frame vs a Crop?

Yes

 

[Helen B]

Sorry, but i have the impression that you don't understand this issue.

Best,
helen

And why would you have this impression ?

"But the CoC is also a lens parameter and it's independent of the sensor size or pixel density. Those being said, for FX lenses we have a CoC of ~0.03mm and for DX lenses we have a CoC of ~0.02mm."

No. Those CoCs have nothing to do with the lens itself. They are chosen for the sensor size.

"If the FoV is bigger but the focal length is the same then what changed ? Well, the size of the optical elements grew. The lens is thicker and another "side" effect of this growth is a shallower DoF."

No. If that was true an FX lens on a DX body would produce a different DoF than a DX lens on a DX body. It doesn't.

Best,
Helen

 

[djd3mo]

No. If that was true an FX lens on a DX body would produce a different DoF than a DX lens on a DX body. It doesn't.

Well, it does !

 

[Helen B]

Well, it does !

That confirms my suspicion.

Sorry,
Helen

 

[Robin Usagani]

I go with full frame so I look cooler mr derrel.

Sigh.. This topic again. Basically if you shoot with with a full frame, using cropped sensor would give you the same thing except you crop some of the picture around it. As simple as that.

Yes, this topic again; you might note that the OP has 12 posts to his name...the queartioin comes up quite often...I've tried to give some real information about the FF vs APS-C DIFFERENCES without sighing over a repetitive post topic.

Your thought process in this post isn't clear to me Schwetty. Not sure what you mean "using cropped sensor would give you the same thing except you crop some of the picture around it. A simple as that." Uh, no, it's not as simple as that, and the images made with a crop-body and a FF body are often vastly different, and are nowhere near the same thing.

Try using a 135mm lens on a 1.6x Canon body indoors; then, actually ENJOY being able TO use the same 135mm lens, indoors. Sorry, but the much larger sensor area of 24x36, either film or digital, is quite a bit different than capturing on APS-C or 4/3 or other tiny sensors. Schwetty, I see you're shooting with full-frame digital; why not APS-C digital? How did you arrive at your current format of choice? Were you after the superior High-ISO performance of the full-frame cameras?

 

[Mike_E]

Try reading this, it may help..Understanding Depth of Field in Photography

 

[djd3mo]

This is from Bob Atkin's website Jake posted.:
• 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

Well, yes. You are using the full-frame sensor as if it was a crop sensor. Of course the results will be identical in terms of DoF. The difference comes when you use the full area of the larger sensor.

You're saying that the original full frame photo has a different DoF than the APS-C photo but after I crop the FF photo to the APS-C size, the DoF is identical ? Wow ! Are the photosites getting closer ?

OK! Enough is enough.

Besides the distance, focal length and aperture, which you already know how they work, we have the circle of confusion. Indeed - confusion.

Once and for all, the Circle of Confusion is a LENS parameter. When a lens is built, it's built for a specific camera format. It's calculated so for a fixed size photo it produces the same clarity. So, if it's built for a FF camera the CoF is ~0.03 and if it's built for a APS-C camera the CoF is ~0.02. The FX CoF is bigger because it's intended to be used on FF camera bodies, therefore bigger sensors, so it can get away with a smaller magnification when printed on the same size paper. But if you look at two pictures taken with two different format lenses, DX and FX, (while camera body, distance, focal length and aperture stay the same) on your desktop at 100% magnification, then the difference is obvious. While if you change the bodies but the lens used is the same then there is no difference at all at 100% magnification.
I cannot give an example for the first situation yet, but I can give you an example for the second one:

Same lens 70-180 mm Zoom-Micro-Nikkor, same aperture f/8, same focal length 180mm, same distance 0.72m, same angle 45 degrees, same crop at 100% magnification.
Different cameras:
D3

And D300

Focused on 15 bar. Credits - Nikon D3 Reviewed. FX vs DX formats
May the light be with you !

 

[Helen B]

You are still misunderstanding this. Please carefully read what I wrote. The example you show demonstrates one of the statements I made, and contradicts nothing I have written. Please note that at the outset I stated that the DoF comparisons I was giving were for when the final image is presented at the same size (using the full size of the initial image). The example you show is for the same final magnification (subject to 'print') - this is a different case. It may sound complicated, but once you understand how and why the maximum CoC criterion is arrived at it becomes clear.

I'll reiterate the fact that the CoC is chosen for the format. Lenses are indeed designed for optimum performance and coverage for a particular format, but this has more effect on their maximum resolution and may have no effect on DoF, simply because DoF is all about objects that are not in perfect focus.

Even within a format it is often advisable to use different CoC criteria for different situations. There's little point in setting the maximum CoC to a value significantly smaller than the size of a photosite, for example. The more the format is magnified to the final image, or the higher the resolution of the recording medium the more likely it is that a smaller maximum CoC criterion will be justifiable. This is also noticeable in film - I shoot large format for both magazine covers and for very large prints, and I can use different CoC criteria for each application. Same with 16 mm film - we had to decrease our CoCs for the same lenses as film improved.

Best,
Helen

Best,
Helen

 

[djd3mo]

You perfectly understand the sensor to print process and how a CoC is determined, but you don't get the optics ! After the CoC is established, the lens is built to reach that value. CoC is a characteristic of the lens. It represents the maximum spot diameter of the projected image of a focused point onto the surface of the film/sensor. It's actually the diameter of the spot of light. And it DOES affect the DoF !!! I will give the examples at the end of this post.

You are talking about DoF from the perspective of the final print but take into consideration that a lot of cropping can be done in between taking the photo and printing. You cannot say that for every different crop you may have a different DoF. If I print the two photos from the previous post at a 4x6 format they will look the same. They will have the same depth of field.

Let me give you another example. The DX crop of a D3x 24.5MP photo is a 10.5MP photo and a D80 photo has 10.1MP. The D3x DX cropped photo and D80 photo would have the same size and roughly the same pixel density, therefore you can print them at the same paper size. Where is the difference now ?

Now let's get back to the last part of your statement: "Lenses are indeed designed for optimum performance and coverage for a particular format, but this has more effect on their maximum resolution and may have no effect on DoF, simply because DoF is all about objects that are not in perfect focus."

Now let me show a couple of pictures and then you tell me if the different DoF has anything to do with the different lenses:
Same camera Nikon D80, same distance (not measured but I didn't move the tripod nor changed camera angle or elevation), same focal length 135mm, same aperture f/8, same photographer ( ).
Different lenses:
Nikon AF-S 55-200mm f/4-5.6 G ED DX VR:

And Sigma 70-300mm f/4-5.6 DG APO Macro - Nikon AF-D FX:

You may safely say that the DoF increases with the CoC, while the CoC is a characteristic of the lens. I admit I mistook the direction of the change, but there is definitely a difference, you may easily see it !

 

[Dao]

From Wikipedia: " the circle of confusion diameter limit (“CoC”) for the final image is often defined as the largest blur spot that will still be perceived by the human eye as a point."


From Bob Atkin: "It's important to note that DOF isn't a lens characteristic like focal length or aperture. It takes into account some subjective factors like print size and viewing distance. That's the reason different values for the CoC are used for different formats. Larger formats need to be enlarged less than smaller formats, and so a larger CoC can be used."


From NikonUSA "In photography, the circle of confusion (CoC) is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image format, but the most apprpriate value depends on visual acuity, viewing conditions and the amount of enlargement."


I strongly believe CoC is not a physical property of a lens.

My Canon APS-C camera CoC is 0.018mm or 18 microns, it is 18 microns when I use my 50mm lens. It is 18 microns when I use my 85mm lens. And it is going to be 18 microns when I use my 14mm lens. However, when I mount those lens to my EOS film body, the CoC becomes 29 microns (or 0.029mm).