Full Frame Vs Crop Sensor

[Loswr]

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

Focal length can affect DoF - it just depends on what else you do or do not hold constant. If you change focal length without changing subject distance, you're changing DoF. If you change subject distance without changing focal length, you're changing DoF. In each case, you're changing the magnification - the size of the subject. But if you keep the size of the subject constant (e.g., move closer as the focal length gets shorter), then DoF remains constant for a given aperture - that's why the statement that DoF depends on magnification and aperture is a better way to phrase it.

Put another way, DoF is determined by magnification and aperture, and magnification is determined by focal length and subjet distance.

 

[jdramirez]

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

Focal length can affect DoF - it just depends on what else you do or do not hold constant. If you change focal length without changing subject distance, you're changing DoF. If you change subject distance without changing focal length, you're changing DoF. In each case, you're changing the magnification - the size of the subject. But if you keep the size of the subject constant (e.g., move closer as the focal length gets shorter), then DoF remains constant for a given aperture - that's why the statement that DoF depends on magnification and aperture is a better way to phrase it.

Put another way, DoF is determined by magnification and aperture, and magnification is determined by focal length and subjet distance.

I'm at work so I skimmed it... but I'll give it a real look when I'm free from my shackles.

 

[Kit.]

Yes, I've added it in the edition of my post after the one you are quoting. Still, the difference in D alone is not enough to explain the difference in acceptable DoF of wide-angle and telephoto shots.

The difference in DoF based on D alone between 17mm f/4 and 200mm f/4 is massive. 17mm f/4 with a subject 20 feet away yields a DoF extending from 14 feet in front of the subject to infinity, whereas 200mm f/4 with a subject at 20 feet yields a DoF that extends approxiamtely 4 inches on either side of the subject.

That's for the calculations based on the same circle of confusion, c (0.03mm). These setups have different magnifications, M (1/28 for 200mm, and 1/350 for 17mm), and as c = d * M, that gives us d200mm = 0.84mm and d17mm = 10.5mm. That's a huge difference in d.

If we require the 1mm d for our 17mm image, the DoF will extend 6ft, and not 14, on the front, and 18ft, and not infinity, on the back.

I also have to disagree with the idea that, "d acceptable for shooting most "17mm" subjects (sometimes up to centimeters) is unacceptable for shooting most "200mm" subjects (usually well below a millimeter, as we need to resolve hair/fabric structure)." One of the most efective uses of wide angle lenses (and particularly ultrawide lenses) is with extremely close subjects in the foreground, taking advantage of the perspective distortion that results from close subject placement to emphasize that subject within the wide FoV. In that case, I want the foreground subject to be as sharp as possible (although there's a practical limit on that with the resolution delivered by most ultrawide lenses, particularly if the subject is not at the center of the frame).

That's what we use tilt for.

However, in your calculations above it's considered OK to have a dot in the front plane of "DoF" rendered as a 1cm blob over the plane of focus.

If the aperture value is consistent crop the 17mm image to the 200mm image and you then have the same magnification, but very different dof. Change the aperture value to give yourself the same aperture area and crop and the DOF is the same.

Again, my point is that we can consider 1cm as "still sharp" on the "17mm" full image above, but we cannot afford that on a "200mm" crop from the same "17mm" image.

 

[privatebydesign]

Why must I be on lsd to understand this concept?

You don't. Look at these three images and tell me what you don't get.

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

Focal length is a function of magnification, change magnification and you change dof. So, if you shoot from the same place with different focal lengths then make same sized prints with the same aperture value the dof is different. The focal length changed the magnification so it did affect dof.

If you use a shorter focal length and move forwards to keep the subject the same size in the viewfinder and use the same aperture value, the dof will be the same because the subject magnification is the same, but the perspective will be different. As per the second LL ink above.

If you shoot different formats from the same place you need to change the focal length to get the same fov and change the aperture value to give the same actual physical aperture and the dof is the same. Did you notice in the above example that 75mm/f2.8 = 26.8mm, 100mm/f3.5=28.6mm and 150mm/f5.6=26.8mm, all three apertures are basically the same actual physical size. In this instance focal length, in and of itself, did not affect dof, as different focal lengths from the same place took images with the same dof.

You need to disassociate dof from focal length, think magnification and it gets a little simpler.

 

[Kit.]

Why must I be on lsd to understand this concept?

You don't. Look at these three images and tell me what you don't get.

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

As long as you capture
the same scene (with the same subject distance and angle of view)
through the the lens entrance pupil of the same size,
and expect the same sharpness from the image on your final medium (display or print),
it doesn't matter what focal length you are using, you will get the same DoF.

However, in order to capture the same scene, you will be required to use a particular focal length depending on the size of the sensor area you are going to use to capture the picture.

 

[ecka]

Micheal's latest musings on the subject:
The Full Frame Myth

Interesting musings. His viewpoint seems to be that current APS-C sensors can deliver IQ on par with FF sensors in many situations - and that's true. But the converse is that FF at it's worst is equivalent to APS-C, and in many situations, it's better.

Also, aside from the IQ considerations, can I get DoF from an APS-C sensor equivalent to f/1.2 on a FF sensor with the same framing and perspective? No. Likewise, a significant portion of my shots are at ISO 3200 or higher, and APS-C is significantly inferior to FF in terms of noise at those high ISO settings.

From a practical level, we buy cameras and not sensors. There is not an APS-C dSLR that can deliver 12 fps or has the most advanced AF and metering systems that Canon has to offer.

So I keep coming back to my earlier point: the primary advantage of APS-C sensors, and the cameras in which they are used, is that they cost less.

+1

Smaller pixels tend to produce more false color (noise, grain, bayer demosaicking errors, rough color gradation patterns). Therefore, APS-C requires better lighting conditions to achieve the IQ level similar to same resolution FF sensor ... and perhaps a better lens, which would make the price close to FF combo (it is sad to watch m4/3 users being robbed by Pana, Oly and Leica). In perfect lighting conditions, the difference may be negligible.

 

[Kerry B]

Ecka you are right. In the real world with good light I would not hesitate to use a crop sensor camera with a good lens. The problem is noise at high ISO when light levels drop. This is where a full frame body comes into its own. The maximum ISO I use on my 7D is 800 whereas on my 5Dmk111 I will go to 4000 ISO. I do not rely on test charts to tell me what the best images are from a camera, I rely on experience and the final image displayed on my computer.

 

[ecka]

Ecka you are right. In the real world with good light I would not hesitate to use a crop sensor camera with a good lens. The problem is noise at high ISO when light levels drop. This is where a full frame body comes into its own. The maximum ISO I use on my 7D is 800 whereas on my 5Dmk111 I will go to 4000 ISO. I do not rely on test charts to tell me what the best images are from a camera, I rely on experience and the final image displayed on my computer.

Actually, I was talking about low ISO , but yes, FF wins the high ISO battle by 2 stops.

 

[Sabaki]

So to further my question:

16-35mm f/2.8 L II on a 5D3 Vs 10-22mm on a 70D, which theoretically would give the better image?

 

[Marsu42]

16-35mm f/2.8 L II on a 5D3 Vs 10-22mm on a 70D, which theoretically would give the better image?

The often criticized "problem" of current Canon ff lenses is the lack of corner performance esp. wide open (if you care about that). Ignoring that, the ff sensor can always generate higher res yadayadayada (see posts above), this is visible in the iso crop.

Another potential fact to keep in mind is that you can buy nearly 3x 70d+10-22 for 1x 5d3+16-35 :->

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=412&Camera=453&FLI=0&API=0&LensComp=271&CameraComp=736&SampleComp=0&FLIComp=0&APIComp=0

 

[Loswr]

So to further my question:

16-35mm f/2.8 L II on a 5D3 Vs 10-22mm on a 70D, which theoretically would give the better image?

The 16-35 on FF, which is why I sold my 10-22 after getting the 16-35 II. The 10-22 will have less barrel distortion at the wide end, the FF/16-35 image would still be sharper after correction.

Of course, for the price of the 5DIII+16-35 II, you could buy two 70D bodies and four 10-22 lenses...

 

[ecka]

16-35mm f/2.8 L II on a 5D3 Vs 10-22mm on a 70D, which theoretically would give the better image?

The often criticized "problem" of current Canon ff lenses is the lack of corner performance esp. wide open (if you care about that). Ignoring that, the ff sensor can always generate higher res yadayadayada (see posts above), this is visible in the iso crop.

Another potential fact to keep in mind is that you can buy nearly 3x 70d+10-22 for 1x 5d3+16-35 :->

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=412&Camera=453&FLI=0&API=0&LensComp=271&CameraComp=736&SampleComp=0&FLIComp=0&APIComp=0

For fair comparison it should be 16-35L@16/5.6 vs 10-22@10/3.5, or at least choose the best performing aperture number from each lens. "Wide open" vs "wide open" is pointless.

 

[Marsu42]

"Wide open" vs "wide open" is pointless.

I see your point, but I beg to differ concerning the conclusion: If you want the thinnest dof (or fastest speed) with any lens/camera combination you'll use "wide open" a lot in reality, so it's perfectly valid to look at this performance no matter the synthetic equivalence.

 

[mackguyver]

"Wide open" vs "wide open" is pointless.

I see your point, but I beg to differ concerning the conclusion: If you want the thinnest dof (or fastest speed) with any lens/camera combination you'll use "wide open" a lot in reality, so it's perfectly valid to look at this performance no matter the synthetic equivalence.

+1 and another comparison that is pretty valid - the 16-35 II vs. the Tokina 11-16, both at f/2.8:
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=412&Camera=453&Sample=0&FLI=0&API=0&LensComp=718&CameraComp=0&FLIComp=0&APIComp=0

 

[Skulker]

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

Focal length can affect DoF - it just depends on what else you do or do not hold constant. If you change focal length without changing subject distance, you're changing DoF. If you change subject distance without changing focal length, you're changing DoF. In each case, you're changing the magnification - the size of the subject. But if you keep the size of the subject constant (e.g., move closer as the focal length gets shorter), then DoF remains constant for a given aperture - that's why the statement that DoF depends on magnification and aperture is a better way to phrase it.

Put another way, DoF is determined by magnification and aperture, and magnification is determined by focal length and subjet distance.

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

 

[Skulker]

So to further my question:

16-35mm f/2.8 L II on a 5D3 Vs 10-22mm on a 70D, which theoretically would give the better image?

Are you photographing apples or oranges?

 

[Sporgon]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

 

[wsheldon]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

Exactly my thought. But interesting illustration that the DOF and therefore amount of OOF blur of objects in the background is determined by aperture and magnification regardless of how large or small they are rendered by the lens perspective.

 

[Skulker]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

you are, I'm sure, entirely correct, although i can't say i bothered to check. Also i don't belive he mentioned a lot of other things, probably because they were not related to what he was talking about.

 

[Kit.]

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

Focal length can affect DoF - it just depends on what else you do or do not hold constant. If you change focal length without changing subject distance, you're changing DoF. If you change subject distance without changing focal length, you're changing DoF. In each case, you're changing the magnification - the size of the subject. But if you keep the size of the subject constant (e.g., move closer as the focal length gets shorter), then DoF remains constant for a given aperture - that's why the statement that DoF depends on magnification and aperture is a better way to phrase it.

Put another way, DoF is determined by magnification and aperture, and magnification is determined by focal length and subjet distance.

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

I don't see how the context of the article would contradict anything said in this thread.

The article studies "zooming by feet", while keeping the same sensor format.

The thread discusses changing sensor formats, while keeping the perspective intact.