[ElJamoquio]

I'll state this again, this was a comparison showing a 7.5 year old 8 mp APS-C vs a 21 mp FF. Even though the APS-C test is already severely handicapped with 1.62x less linear resolution, it still manages to show higher absolute resolution.

I read you the first time. Both cameras have the same pixel density. Both show a lens that, at f/1.2, is limited by the lens' ability to resolve rather than the density of the pixels.

Repeat the test with any modern 16/18/24 mp APS-C sensor, and the APS-C border will have higher absolute resolution at any aperture, not just <f/2.0.

I disagree. Even in this extreme case (an f/1.2 lens at f1.2) it's not like the border performance of the APS-C is spectacular. At f/2.8, any equivalent-pixel-density FF will beat the APS-C, and at f/5.6 the FF will trounce the APS-C.

On top of that, I'm not even sure I care that an f/1.2 lens at f/1.2 has poor border performance. If I'm running the lens at f/1.2 it's so less things are in focus, and 90+% of the time the focus is going to be at the center.

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Last edited by ElJamoquio; 11-01-2012 at 10:57 PM.

[Cannikin]

I read you the first time. Both cameras have the same pixel density. Both show a lens that, at f/1.2, is limited by the lens' ability to resolve rather than the density of the pixels.

I disagree. Even in this extreme case (an f/1.2 lens at f1.2) it's not like the border performance of the APS-C is spectacular. At f/2.8, any equivalent-pixel-density FF will beat the APS-C, and at f/5.6 the FF will trounce the APS-C.

When did this become a discussion of equal pixel density? That's not how LW/PH works.

If you want to compare absolute LW/PH numbers across systems (a really bad idea in the first place), you need to know that the numbers scale by total linear pixels, not by physical pixel density. The denominator "PH" stands for "picture height", meaning the numbers are normalized with regard to sensor size. In practice this means the test chart is shot such that it has the same extent viewed at the same image size. The APS-C test is not a crop of the FF test. This means a 24mp APS-C sensor and 24mp FF will have the same theoretical LW/PH limit. Notice Photozone has the NEX-7 and D3X graphs/numbers scaled very similarly (the difference being the weaker AA filter on the D3X).

Now, because of the nature of using contrast, by way of MTF, to measure resolution, you can get higher resolution with more pixels even when the MTF50 frequency with the larger pixels does not reach the theoretical limit of the sensor ("lens limited resolution"). Lens blur is not a hard limit, but continuously variable, and the "limit" is determined by how you sample and measure it. Pixels can only assume discrete values, and smaller pixels can sample and distinguish finer gradients of contrast than large ones. This can easily increase the frequency at which the contrast level falls below the MTF50 contrast threshold without increasing lens resolution.

Take a look at these two tests of the same lens with the same size APS-C sensors, the only difference being one is 10mp the other 16mp:
Nikkor AF-S DX 35mm f/1.8 G - Review / Test Report - Analysis
Nikkor AF-S DX 35mm f/1.8 G - Review / Test Report - Analysis

Notice the curves are almost exactly identical, and at f/1.8 are well under the resolution potential of both sensors. Notice how moving from 10mp to 16mp the LW/PH figures of both the "border" and "extreme" are scaled very closely to sqrt(16/10), leaving the overall curve, and ratio of resolution to theoretical maximum, relatively unchanged (note, though, that this scaling is not linear on larger scales as it is limited by diffraction and particular characteristics of the lens' PSF of course).

Now back to the Canon 50 f/1.2. Here is Lenstip's test, shot with both the 50D (15mp) and 1ds Mk III (21mp): Canon EF 50 mm f/1.2L USM review - Image resolution - Lenstip.com

Lenstip quantifies resolution in lp/mm (line pairs per millimeter), which really contains the same information as LW/PH (as long as you know sensor size), only it is resolution density rather than total lines. The 50D's border numbers exceed the 1Ds3's at all apertures, even when factoring in the different "decency levels" Lenstip assigns to each sensor. And what's really interesting is the comparison between the 50D and the "APS-C edge" on the 1Ds3's graph. Notice that the 50D's curve has the same shape, but the numbers exceed the APS-C edge on the 1Ds3's at all apertures, demonstrating my point that increasing sensor resolution does matter even when "lens resolution limited".

Anyway the real moral of this story is that pictures shot on APS-C and FF with the same lens are not comparable! Comparisons of LW/PH or resolution "sweet spots" are meaningless, because the images are totally different! And then there's the fact that lens resolution can only be measured as part of total system performance (including RAW/JPEG image development), and not in isolation. There's a reason why Photozone has a disclaimer that results are not comparable across systems.

[Fl_Gulfer]

It's taken them over 5 years to produce a T/C,,, so I would say the world is going to end the 21st of next month is a more reliable statement than a FF is in the works......

[Kunzite]

If their owner back then decided a TC is not profitable enough or whatever, it doesn't mean Pentax is unable to make one in less than 5 years.

[hypervel]

It is getting better, but the problem with mirrorless (except for Nikon's 1 cameras) is that it has lousy continuous auto focus. Sticking PDAF on the sensor does make a big difference in that regard and maybe that will be the answer, but till that is figured out, I think full frame and mirrorless are not going to go well together.

About what I was thinking. I have a V1 and love the outright performance of it. Really, I could care less about the jump to FF- I see FF becoming the Medium Format standard of what's to come. I feel APS-C is the "35mm" of the Digital sensors. Smaller sensors are pulling forward, giving us smaller kits with very nice performance parameters. Were Pentax to meld a V1 with a k5...... On-chip PDAF sans mirror with a heeeeeeeeuge EVF (upsized from what is considered acceptable), K5 build and feel. I'd be on it. As it stands, the new K5ii isn't enough for me to really be interested in. Grow a set, Pentax. Your next camera needs to be a leap over Canikon. Innovate, and quickly.
Nikon could build one today if they weren't so chicken about cannibalizing sales. Narrow, narrow thinking.

[falconeye]

Anyway the real moral of this story is that pictures shot on APS-C and FF with the same lens are not comparable! Comparisons of LW/PH or resolution "sweet spots" are meaningless

That's true.

But you can compare equivalent lenses and care about proper normalization and calibration of resolution figures.

E.g., cf. LumoLabs -- Camera Equivalence -- Whitepaper §4.2.2.

The result then is that -- contrary to common wisdom -- FF camera/lenses have MUCH better corner performance than crop camera/lenses.

Crop does NOT crop the sweet spot out of FF lenses. It is just an urban legend grown from improper comparisons.

[filorp]

Crop does NOT crop the sweet spot out of FF lenses

it does when you compare 12MP FF camera to 5MP crop APSC or 36MP camera to 15MP APSC crop.... or other cases of the same pixel density....

[Clavius]

Crop does NOT crop the sweet spot out of FF lenses. It is just an urban legend grown from improper comparisons.

Very interesting, because I've recently discovered that my "FF" lenses, turn out to be not THAT compatible with FF after all.

One example: mounted on my 5D, my 50 1.4 suddenly has corner and border softness, including some fignetting. This never showed on my crop camera though. I've noticed this with 4 others of my "FF lenses" also. How else can this be explained then that the crop camera crops off those ill-performing corners and borders?

[digital029art]

Makes sense that the REAL lens is revealed on FF, just as it would on film.
Personally I'd just like to be able to use these FF lenses as intended!

[thibs]

Very interesting, because I've recently discovered that my "FF" lenses, turn out to be not THAT compatible with FF after all.

One example: mounted on my 5D, my 50 1.4 suddenly has corner and border softness, including some fignetting. This never showed on my crop camera though. I've noticed this with 4 others of my "FF lenses" also. How else can this be explained then that the crop camera crops off those ill-performing corners and borders?

Because it is only a part of the whole story?
What about resolution (among other things) and softness compared to what exactly (if comparable at all....)

[Clavius]

Because it is only a part of the whole story?
What about resolution (among other things) and softness compared to what exactly (if comparable at all....)

The border and corner softness compared to the center sharpness of course.

[ElJamoquio]

The thing is, the center of (good) FF lenses has about 1.5x better linear resolving power in lw/ph (at the same pixel density) just because the ph is so much bigger.

The borders are then only 1.3-1.4x as good as APS-c borders. Is this really a problem?

[Class A]

The border and corner softness compared to the center sharpness of course.

Why "of course"?

Say you have FF corners that resolve as much as APS-C centres. Why then care that your FF centres are even better?

Centres will always perform better than corners; the interesting question is how what you've cropping away with a smaller sensor performs with a bigger sensor in comparison to equivalent image areas captured by the smaller sensor.

Sometimes one has to compare apples with oranges in order to have a fair/relevant comparison. Just like IQ comparisons between sensors with Bayer-AA-filters and those without require capture-sharpening for the former and no sharpening for the latter.

[Fontan]

What if pictures you take don't have a whole lot in the corners otter than skies and dirt and some background? It seems like pics I see around here are like that. Is a Corner sharpness a bit overrated perhaps?

[vonBaloney]

Why "of course"?

"Of course" because it was obvious what he was referring to.

Say you have FF corners that resolve as much as APS-C centres. Why then care that your FF centres are even better?

Centres will always perform better than corners; the interesting question is how what you've cropping away with a smaller sensor performs with a bigger sensor in comparison to equivalent image areas captured by the smaller sensor.

Sometimes one has to compare apples with oranges in order to have a fair/relevant comparison. Just like IQ comparisons between sensors with Bayer-AA-filters and those without require capture-sharpening for the former and no sharpening for the latter.

Equivalent systems are a totally different question. The question is how the same lens performs on different formats. You equivalence guys seem to think that "equivalent" photos are the only valid comparison one can ever make when different-sized sensors are involved. But I don't have two equivalent systems (why would I?) and don't care about that. But I might want to know how a particular lens that I actually have performs on each type of sensor. If I have a lens that is a good performer on APS-C, I might be curious to know that I would not like it so much on an FF because of too soft edges -- edges I never see on APS-C. Or vice-versa, maybe APS-C is "stressing" the lens too much and FF is more suitable. Those are the interesting questions I am interested in -- I don't give a crap about equivalence (which often involves fantasy lenses that don't even exist) and it is annoying to have all discussions twisted to fit into that box...