Advantages of full frame?

[adam]

I'm curious about the advantages of shooting full-frame versus shooting crop. I've read various assertations that switching from a 40D to a 5D is like upgrading all of your glass, that a crop body gives you extra "reach" when using telephoto lenses, that you'd get similar quality shooting with a crop body as you would shooting full-frame and croping in post, and that the real image quality difference in full-frame comes when you shoot at high ISOs. So which, if any, is it?


I'm pondering what I'm saving my money up for...not in the immediate future, but probably a few months down the road. Among other things, I do a lot of airplane photography...say I took a picture of a plane with a 300mm lens and the plane filled the frame on my 40D. Now, say I took a picture of the same plane with the same lens at the same distance with a 5D and cropped it in Camera Raw such that the plane filled the frame. Which picture would be sharper?


(I don't shoot at high ISOs, but I do quite a bit of landscape/cityscape shooting where the more detail the better, so I'm already fairly certain a full-frame body would make that look nicer.)

[Colin]

With a full frame, you can use the entire full size lens, collect more light, and any errors in the optics will be relatively smaller in proportion to your image. You also get a more shallow depth of field with a given lens aperture, because the wider angle of view means that you can get closer.


A crop body focuses your pixels in a smaller area. it effectively crops the image for you, so you don't waste your pixels if you would have cropped anyway.


A crop body has an advantage if you arelikely to crop anyway (telephoto/macro), and you can then use the EF-S line of lenses as well.


However, if you have the glass for it (and don't mind carrying it) I'd lean towards a full frame.


If you can get a full frame body with pixel density the same as the crop body, the only advantage of the crop body would be smaller file sizes. Technically, ignoring a host of other parameters, the crop body and the cropped full frame body would have identical resolution with the same lens.

[Daniel Browning]

I've read various assertations that switching from a 40D to a 5D is like upgrading all of your glass,

Correct. All EF lenses have MTF curves optimized for full frame, so there is higher contrast and sharpness for a given print size.

That a crop body gives you extra "reach" when using telephoto lenses

True.

that you'd get similar quality shooting with a crop body as you would shooting full-frame and croping in post

That's only true if the FF body has the same pixel size. For example it's true when comparing the 5D2 and 20D: both have the same reach because they have the same pixel size. But the 50D is far superior to the 5D2 for reach.

and that the real image quality difference in full-frame comes when you shoot at high ISOs.

High ISO is one of the biggest, most important reasons to shoot full frame (and is one of the principle reasons that I do), but it's certainly not the only reason. Even at low ISO there are differences, such as higher dynamic range and better contrast.

say I took a picture of a plane with a 300mm lens and the plane filled the frame on my 40D. Now, say I took a picture of the same plane with the same lens at the same distance with a 5D and cropped it in Camera Raw such that the plane filled the frame. Which picture would be sharper?

The 40D would be sharper by far. The 50D would be better still.

(I don't shoot at high ISOs, but I do quite a bit of landscape/cityscape shooting where the more detail the better, so I'm already fairly certain a full-frame body would make that look nicer.)

Yes it would.

I'm curious about the advantages of shooting full-frame versus shooting crop.

There is a huge price premium to pay for a full frame sensor.

In new cameras, the 50D and 5D2 are similar enough to compare for this purpose (although the 50D has better autofocus, gapless microlenses, and an all new sensor with gapless microlenses instead of a copy of an older sensor with a few CFA changes).

The build and features of the 5D1 are similar to the old 20D.

20D used: ~$300
50D: $1200
5D1 refurb: $1400
5D2: $2700

$2700 - 1200 = 1500. There is a $1,500 price premium just for the sensor size alone. If you compare the 5D1 to the 20D, the premium is closer to $900. In other words, if you didn't really need the sensor size, you could save $900 and just buy a 20D.

Is sensor size really worth that much to you?

The answer depends on your need for the benefits that go along with full frame:

The big three, IMHO, are:

* Lens availability.
* Control over depth of field.
* Increased light gathering power.

For example, there are no wide angle primes for APS-C (EF-S), but there are dozens available on full frame. The 14mm f/2.8 on full frame would be most similar to a 9mm f/1.8 on APS-C, but there is no such lens for APS-C. The 24mm f/1.4 would be similar to a 15mm f/0.9 on APS-C, but again no such lens exists. The widest prime built for APS-C is the Sigma 30mm f/1.4, which is equivalent to a 50mm f/2.2 on full frame.

By "equivalent", I mean they would have the same field of view, same depth of field, same diffraction, and same light gathering power (light intensity times total area).

To me, those are the main benefits, but there are more:

• Larger viewfinder.
• Using EF lenses as designed (e.g. 17-40 becomes a "super wide angle" instead of a "normal")
• Higher contrast from EF lenses.
• Higher resolution from EF lenses.
• Higher dynamic range.
• Lower noise, especially shadow noise.
• Better low light capability.

If you upgrade to full frame, but you can't afford a lens that is long enough, and you have to crop the sensor down to APS-C size anyway, then you've effectively thrown away all that sensor you paid for.


For example, 200mm f/2.8 on APS-C is similar to 300mm f/4.5 on FF.The 55-250mm f/4-5.6 IS is equivalent to a 100-400 f/6.4-9.0 on FF, but the 100-400 we do have has much wider aperture than that.


So if there is a longer, slower lens available for full frame, with similar autofocus capability, then you can upgrade and still get similar photos. But Canon often does not make a longer, slower version of the lens we're using on APS-C, and if they did, it wouldn't autofocus.


The only time you will get a benifit from full frame is if you actually *use* the full frame, which rules out cropping. For that reason, the 50D is the best choice for airplane photography on a limited budget.

[Colin]

Err... I meant what Daniel said... []

[Tom Alicoate]

That was a lot of great advice. One other benefit to Full frame is that of diffraction. It is a little complicated and I am not the person to explain it, but diffraction for landscapes where you want to get a large amount of the photo in focus can be difficult with an APS-C sensor without also getting some of the blur associated with diffraction.


I have thought about this long and hard too. I have almost decided that instead of the 5DMKII, I will go with the 60D whenever that comes out. I want thelower noiseof the Full frame, but I can't loose the higher pixel density provided by the XXD series. I can't afforda lens longer than 400mm, and a high quality photograph with a littlewolf is not nearly as desireable to me as a larger wolf with a little bit of noise.


Of course in a perfect world I would have the funds for a 5DMKII for portraits and Landscapes, and an XXD for nature and aviation photos. []


Tom

[Daniel Browning]

Thanks for the post, Tom. I too would prefer a detailed, but noisy wolf. I have a comment about one thing, though:

One other benefit to Full frame is that of diffraction. It is a little complicated and I am not the person to explain it, but diffraction for landscapes where you want to get a large amount of the photo in focus can be difficult with an APS-C sensor without also getting some of the blur associated with diffraction.

That idea is believed by many respected photographers and is a widely held position on many forums, web sites, and magazines. You are in good company. However, it's actually a misconception.

The reality is that diffraction is the same for all cameras, no matter the sensor size, because it scales in perfect proportion with depth of field.

For example, let's assume a 30x20 print size viewed at a close distance with a high acuity. If made from a full frame camera at f/22, it will have reduced contrast caused by diffraction. To get the same depth of field on APS-C, one needs to only stop down to f/14. Stopping down to f/22 would cause the APS-C to have *deeper* depth of field than the full frame camera, and that is not necessary, desirable, nor comparable. Instead, it should have the same iris diameter (focal length divided by f-number) in order to have the same angle of view, perspective, and depth of field.

The same 30x20 print made from an APS-C camera at f/22 will have *much* worse diffraction softening. So on the face of it, one might draw the incorrect conclusion that full frame has an advantage with regards to diffraction. But it doesn't, because the APS-C doesn't *need* to stop down to f/22 in order to get the same depth of field.

The diffraction is the exact same on both. It scales to all sensor sizes. On an 6x9 medium format camera (84x54mm), f/22 causes much less diffraction bluring, but the depth of field is much thinner than on 35mm. To get the same depth of field, one must stop down the 6x9 lens to f/51, but then the diffraction is back to being the same.

It goes in the other direction, too. A digicam (9x6mm) only requires f/5.6 to get the same deep depth of field as f/22 on full frame. And diffraction, too, is the same on a digicam at f/5.6 as it is at f/22 on FF35.

Essentially, diffraction and depth of field are the same on all cameras of all sensor sizes. The only difference is that larger sensors may have the *option* of using thinner DOF (and the reduced diffraction that goes with thinner DOF). If the large formats are used at the same DOF, then diffraction too is the same. Other things scale with DOF as well, including low light capability.

In short: diffraction scales with DOF, no matter the sensor size.

[Tom Alicoate]

Daniel,
Yep, thats why I didn't pretend to know anything about diffraction. It looks like I need to get my photo books out again. I was confused by some of the talk when the 50D came out, around seeing diffraction when stopping down.This was not due to the sensor size it was due to the decreased pixel size and I forgot about that. It is in fact good news that an APS-C camera can get the same DOF as a FFwithout stopping down as much. In fact one of the things I have noticed with my lenses is that there is anoticeable increase in sharpness closer to the sweet spot of the lens.For landscapes I am actually better off trading in some of that DOF for increased sharpness by opening things up a little, say to f8, orf11, rather than f22 or higher. I have not completely thought through this idea yet so I will pose it as a question. Does this mean that if DOF is a goal, and keeping a lens close to its sweetspot is a goal, than a APS-C sensor actually has some advantage here?


Thanks for an interesting thread!


Tom

[Jon Ruyle]

Does this mean that if DOF is a goal, and keeping a lens close to its sweetspot is a goal, than a APS-C sensor actually has some advantage here?

I'm sure Daniel will have a more authoratitative answer, but my guess is the reason for the percieved "sweet spot" is that diffraction has not yet set in in. If this is true, then the answer would be no.

[Daniel Browning]

It's also true if something other than pixel density is the limiting factor in image quality.

You're right; thanks for the correction.

I was confused by some of the talk when the 50D came out, around seeing diffraction when stopping down. This was not due to the sensor size it was due to the decreased pixel size and I forgot about that.

Yeah, pixel size is a whole new (and big) topic. Under ideal circumstances (no diffraction, perfect focus, no motion blur, etc.), the 50D will have 21% higher resolution than the 40D. Under no circumstances will the 50D ever have *less* resolution; however, in the very worst circumstances (f/45 diffraction, focus way off, severe motion blur, etc.) the increase in resolution will be vanishingly small (0.1%). Every photograph will be between 0.1% better and 21% better. For most people, I think it will be much closer to 21%.

It is in fact good news that an APS-C camera can get the same DOF as a FF without stopping down as much.

I don't subscribe to that idea, personally. The way I see it, there is no advantage to either; they are just equal.

In fact one of the things I have noticed with my lenses is that there is a noticeable increase in sharpness closer to the sweet spot of the lens. For landscapes I am actually better off trading in some of that DOF for increased sharpness by opening things up a little, say to f8, or f11, rather than f22 or higher.

Yes, that is because the effect of diffraction is reduced.

I have not completely thought through this idea yet so I will pose it as a question. Does this mean that if DOF is a goal, and keeping a lens close to its sweetspot is a goal, than a APS-C sensor actually has some advantage here?

I think it's actually a disadvantage. Generally speaking, I think it could be said that the sweet spot varies by format size. One example might be:

• 4/3rds: f/4
• APS-C: f/5
• FF35: f/8
• 6x9: f/18

So if an FF35 lens has aberrations at f/5, but becomes diffraction limited at f/8, that's great for FF35 cameras. But when you put that lens on an APS-C camera, you get aberrations at f/5 or too much diffraction at f/8.

This is a natural consequence of the fact that we have so many decades of lens development for FF35, but only a few lenses built specifically for APS-C only. In cases where there is a lens built specifically for APS-C, it usually tromps the equivalent EF lens (e.g. EF-S 17-55 vs. EF 17-40; EF-S 60mm f/2.8 macro vs EF 50mm f/2.5 macro).

The lenses we do have for APS-C (EF-S) must have aberrations corrected at a higher spatial frequency and a wider f-number than equivalent EF lenses in order to have the same image quality.

One way to think of it is like this: the crop factor must apply to the *MTF chart* as well as focal length and f-number; otherwise the image quality will not be as good as FF35.

Thanks for an interesting thread!

You're very welcome.

I would think...

Thanks for the response, Johan.

For example, assuming we use the 5D1 and 50D as examples; the 50D would have to have the aperture stopped down much farther than the 5D1 would for the same depth-of-field*,

[* At least at the pixel level; maybe it would be different at equal print/output sizes?]

I kindly think you are mistaken, pixel level or not. To get the same angle of view, the focal length must be different between the 50D and 5D1. With a longer focal length and the same f-number, the 5D1 would have a wider iris diameter, which changes the geometry between subject and focal plane to change, which changes depth of field. However, if the f-number is 1.6X narrower, then the iris diameter returns to the same size as the 50D, and the geometric relationship between the subject, iris, and focal plane are again the same, so depth of field is the same. I think you'll find that DOF calculators and other resources will reinforce what I'm saying.

You do bring up an important factor, though, which is the effect of resolution. The 5D1 and 50D only differ in resolution by 2.2 megapixels, which is not enough to have a big effect on depth of field; however, there are times when total resolution can, indeed, affect depth of field.

If the 5D2 at f/9 is compared with the 40D at 5.6, for example, both will have the same depth of field at normal print sizes. However, at very large print sizes, where the 5D2's immense resolution can be utilized, it's possible that the DOF will be thinner. This would require the resolution to be preserved from the lens (aberrations, motion blur, etc.) through processing and display (e.g. 30x20 print size). Of course, if the thinner DOF is not desirable, it's always possible to just blur the 5D2 image so that it only has 10 MP of resolution, and then the DOF will be the same as the 40D again.

Basically, DOF will be affected by anything that affects total resolution; not in absolute terms, but relative to the viewer's acceptibly sharp CoC.

While I'm on a tangent, I might as well discuss reproduction magnification. To make a 12x18 print, the full frame sensor is enlarged by a factor of 12.7x. To make the same size print, an APS-C sensor must be enlarged by 20.3x. It is magnified much more because it is smaller. Notice that the difference between the two is the same as the crop factor (1.6X). It is that reproduction magnification that causes f-number to scale with sensor size for depth of field, diffraction, and a variety of other things.

Daniel Browning said: Instead, it should have the same iris diameter
(focal length divided by f-number) in order to have the same angle of
view, perspective, and depth of field.


I understand all those terms, but not that statement; would you mind explaining what you mean a little more simply?

It's my pleasure.

For other readers, let me prefix the explanation by saying that iris diameter means the same thing as pupil opening, physical aperture, absolute opening, "hole in space", and other similar synonyms. It does not mean f-number (which is "relative" aperture). The iris diameter is the focal length divided by f-number. For example, 50mm f/1.2 has an iris diameter of 41.7mm (50/1.2=41.7).

Let me try phrasing it in two additional ways:

• For a given field of view, focus distance, and bellows factor, the lens with the widest iris diameter will project the thinnest DOF, no matter what the focal length, f-number, or sensor size.
• Similarly, if any two lenses have the same iris diameter, the DOF will be the same, no matter what the focal length, f-number, or sensor size. Given the same field of view, focus distance, and bellows factor.

The iris diameter of 50mm f/2.8 is 18mm. The iris diameter of 80mm f/4.5 is 18mm. When 50mm f/2.8 on APS-C is compared with 80mm f/4.5 on FF35, one finds that they have the exact same perspective, angle of view, depth of field, and diffraction.

In short: Apply the crop factor to f-number and everything evens out.

This article is why I purchased a used 5D even though I have a 40D. http://www.kenrockwell.com/tech/full...-advantage.htm

He addresses quite a few assumptions.

Ken's site has some good content, but it's mixed in with a lot of misinformation, myths, and misconceptions. I did a quick review of that article; please oblige a brief response to a few of his points:

Bigger pixels collect more light (photons). More photons means more clean image compared to the relatively constant amount of electrons making noise. (Yes, I'm simplifying, but it's why bigger sensors are quieter and cleaner.)

Fatter pixels catch more light, so the larger camera doesn't have to amplify them so much for the same ISO sensitivity. This means that even though we wind up with the same exposure, noise and crud aren't amplified as much, leaving us with a much cleaner images without having to cheat with wimpy noise reduction filtration. There is simply less noise.

This is a myth that I busted on April 25th:

Myth busted: smaller pixels have more noise, less dynamic range

...all cameras smooth over the noise in flat areas to varying amounts where it's most visible...

That's only true for JPEG images, not raw.

the larger format camera sees the subtle difference between the white window frames and the light tan house

This is due to the difference in the spectral response of the color filter array and the JPEG processing, not anything caused by the format size difference.

Aside from those three myths, the information appears to be correct.

Thanks for the discussion, everyone.

[ShutterbugJohan]

If made from a full frame camera at f/22, it will have reduced contrast caused by diffraction. To get the same depth of field on APS-C, one needs to only stop down to f/14. Stopping down to f/22 would cause the APS-C to have *deeper* depth of field than the full frame camera, and that is not necessary, desirable, nor comparable.

What? I would think that it would be the opposite.


For example, assuming we use the 5D1 and 50D as examples; the 50D would have to have the aperture stopped down much farther than the 5D1 would for the same depth-of-field*, because the circle of confusion changes, and the 5D1 would render as sharp somthing that the 50D, with it's higher pixel density would render out-of-focus. Right?

Instead, it should have the same iris diameter (focal length divided by f-number) in order to have the same angle of view, perspective, and depth of field.

I understand all those terms, but not that statement; would you mind explaining what you mean a little more simply?


Thanks!


--Johan


* At least at the pixel level; maybe it would be different at equal print/output sizes?