Is Full Frame sharper than APS-C? My answer here

[NormanBates]

I have to decide between APS-C and full frame, and one of the things to look at is sharpness.

With APS-C, as opposed to full frame, you're only using the central portion of the image circle, the sweet spot: you're not using those blurry corners, and this should lead to sharper pictures. On the other hand, because the sensor is smaller but final image resolution is the same, you're blowing up the analog image that the lens projects on the sensor; this is bad, because every defect will be magnified. Which force is bigger?

I ran some tests trying to find out, shooting stills with a 5D2.

My conclusion: as a general rule, a lens will always be sharper on full frame than on APS-C, both in the center and in the corners.

You can see the tests and read a bit more about them here:
http://www.similaar.com/foto/lenstestsff/lenstestsff.html

[Sporgon]

Errr..... you're not "blowing up the analogue image bigger" if the APS or FF or any other sensor size for that matter have the same number of digital info capture points - pixels. MP is MP of digital info - the computer program enlarges the image.

The issue on smaller sensor regarding "enlarging" is can the smaller pixels capture the info accurately. In that respect they are certainly improving.

[NormanBates]

What I mean is that you've got an image circle, a bunch of photons that are projected back by the lens. This is anlogue. You put the same ~20 million photosites behind that in both cases, but on APS-C each of them is smaller.

If you want to think it like this, it's as if, instead of a ~20 Mpix full frame sensor, you had a ~50 Mpix full frame sensor, and then you used only the central portion, and enlarged it so that it is now the full image (and this is where my "magnyfy issues" argument comes in: you are enlarging the image, and this magnifies any defects in the lens).

So, yes, as you say, the thing is that the pixels are smaller, and this reduces quality.

In any case, the proof is in the pudding: fullframe gives a lot more detail.

[neuroanatomist]

No surprise there.  But just want to point out, this is a DxO-like conclusion.  You used a 5DII for the test, I can say from experience that in many situations, the APS-C sensor in my 7D delivered sharper pictures than my 5DII, by virtue of its better AF system.

[East Wind Photography]

I don't disagree with your conclusion.  The only reason I might upgrade to an aps-c from my 5d3 would be if it was also around 22mp.  However your test results would be more compelling if the target distance was also compared when at the same distance.  Effective comparison of sensor sharpness should keep all other factors the same.  Distance plays an important factor in a lenses resolving ability.

Still I do agree with your results when applied to the field.  I shoot primarily wildlife now with my 5d3 and resolving ability isn't even comparible  to my 7d.

[tortilla]

Nice work, but have a look at center crop APS-C 24 mm, how come that f9 is sharper than f5.6?

You already mentioned DoF on your site:

Add to that the fact that for a given depth of field you're closing down the iris further on your full frame lens (and this helps sharpness too) and I think the result will be pretty much general.

When you want large DoF than we're talking about f/8 (APS-C) and f/11 (FF) or so. IMO closing down even further makes the image actually softer, due to diffraction and lens design.

[Sporgon]

I don't disagree with your conclusion.  The only reason I might upgrade to an aps-c from my 5d3 would be if it was also around 22mp.  However your test results would be more compelling if the target distance was also compared when at the same distance.  Effective comparison of sensor sharpness should keep all other factors the same.  Distance plays an important factor in a lenses resolving ability.

Still I do agree with your results when applied to the field.  I shoot primarily wildlife now with my 5d3 and resolving ability isn't even comparible  to my 7d.

+1 to that in practical application.

[aznable]

No surprise there.  But just want to point out, this is a DxO-like conclusion.  You used a 5DII for the test, I can say from experience that in many situations, the APS-C sensor in my 7D delivered sharper pictures than my 5DII, by virtue of its better AF system.

a lot of people forgot that a camera it's not just a sensor

[NormanBates]

No surprise there.  But just want to point out, this is a DxO-like conclusion.  You used a 5DII for the test, I can say from experience that in many situations, the APS-C sensor in my 7D delivered sharper pictures than my 5DII, by virtue of its better AF system.

Indeed. You may also notice that I listed my best 3 lenses there, and none of them has AF.

Nearly everything on that site was created because I needed it, including these tests. They're made for me, and designed for my very special needs.
Everybody should test their equipment to see how well it fits their needs, what can be done and what's not a good idea, and where there's room for improvement. I'm just sharing my results. They shouldn't stop anybody else from running their own tests.

[dilbert]

I wonder how much of what you've observed is due to the influence of the AA filter.

[TrumpetPower!]

All else being equal, especially including the final print size (a factor which often gets ignored and confused with respect to pixel peeping), the larger the format, the better the image quality in every aspect. That includes sharpness as well as noise / grain as well as dynamic range as well as anything else you care to mention.

Of course, all else is never actually equal, which is why it's important to compare complete systems. Neoruanatomist made that point; better theoretical maximum image quality is useless if you can't properly operate (in the specific case, focus) the equipment.

There's another factor to consider. Image quality with even entry-level DSLRs and kit lenses is superlative. Anything going to the Web, 4x6 prints, and even 8x10 prints...there's no practical real-world image quality difference between a Rebel and medium format (with the exception that you can more easily get a greater amount of background separation with the larger format).

Once you're printing on a machine that won't sit on your desktop, though, the difference between the different formats starts to become apparent. You can make a great roadside billboard with a Rebel and a kit lens, but walk up to a pair of door-sized fine art prints, one made with said Rebel and the other with an 8x10 view camera, and even your half-blind great uncle will be able to tell the difference.

Cheers,

b&

[tortilla]

There are certain situations where a crop delivers higher resolution than a FF with the same lens (even disregarding DoF, AF and the corners). Roger M. Clark has nice shots of the moon with the 5D2 and the 7D that show this:

www.clarkvision.com/articles/digital.sensor.performance.summary

[NormanBates]

Indeed, if you keep lens and distance constant, APS-C will give you lots more detail. Because it's just as if you had a 50 Mpix full frame body and cropped the center of the image.

But that's not my usual scenario. For me, the right comparison is "Elmarit-R 35mm f/2.8 on APS-C set at f/2.8" vs "Summilux-R 50mm f/1.4 on full frame set at f/4.5". Similar FoV, similar DoF --> full frame is clearly sharper.

As I said, if this is not the way you shoot, run your own tests designed for your usual scenario (actually, you should run them anyway!).

[neuroanatomist]

Indeed, if you keep lens and distance constant, APS-C will give you lots more detail....

Yes, at low ISO.  But once you raise the ISO a bit, the FF delivers more detail in focal length-limited situations.

[AlanF]

My conclusion: as a general rule, a lens will always be sharper on full frame than on APS-C, both in the center and in the corners.

There is no general rule. Whether FF beats APS-C depends upon distance, size of the detail on the subject and whether it will span the length of two pixels, how good the light is etc as well as on sensor and and lens. It is remarkable how often in these forums someone does a restricted series of experiments and then claims a general rule.