I don't agree with this.
I know you don't, and you argue my examples when I show them, that is fine, you make your cjhoices for yourself and I'll make mine for me.
But I never questioned system resolution as a concept, I know full well the interplay of the elements within that system. We just come to different conclusions when looking at the images they produce, I don't care a fig for technical theories, just understanding why I see what I see.
Well, the example I've usually seen from you is the 7D vs. the 1D III, and I think your argument usually boils down to the fact that the AA filter on the 7D is fairly strong, thus diminishing the value of the 7D. I won't deny that a strong AA filter throws another factor into the mix, and it is a factor to take into account when actually measuring different devices. Even so, the use, or not, of an AA filter isn't a reason to stop pushing megapixel count/spatial resolution. My theory always assumes "all else being equal"...in which case the AA filter would be tuned to provide similar results around nyquist for any given sensor resolution.
I don't deny that it is important to use empirical data as well, however empirical data can and is often interpreted differently. It's a subjective measure, and how the data is interpreted, according to what criteria, and by whom, are all important factors in normalizing empirical results. Personally, I see a meaningful, if not "ideal", improvement in resolution with the 7D over the 1D III in your past visual examples, you do not... That is an important discrepancy, and just because the data is yours does not inherently invalidate the observations of others. I have very good 20/10 vision with my corrective lenses, and perhaps that plays a role. If the 7D had a weaker AA filter, the difference would likely be even more pronounced. One could also perform a test with the AA filter removed from both cameras (thus eliminating the additional factor), and I think the difference in spatial resolution would be quite clear in that case.
Your argument is usually perceptual (subjective), where as I try to make mine objective. Perceptual/subjective arguments, while not invalid, are hard to use as a viable basis for comparison because of the very fact that they can be interpreted differently in the absence of normalization. You see the 7D as having no visual benefit over the 1D III...I see the 7D as indeed having a visible benefit over the 1D III, if not quite as much as theory would have predicted...all using the exact same source images that you yourself produce. That is a war neither of us will win, and one which doesn't help anyone else understand the fundamental value of having a higher resolution sensor.
A 24mp APS-C sensor would arguably demonstrate an even greater lead over the 1D III...I'd be very curious to see you perform a visual comparison of say a D7100 vs. the 1D III, or even the 5D III that was identical to your test of the 7D and 1D III. I'd wager the D7100 clearly outperforms either Canon camera in the realm of final resolving power (spatial resolution).
I'm sorry if my replies frustrate you, but you often seem to be making the (subjectively based) argument that there is no value whatsoever to increasing megapixel count beyond the point where Canon currently is (~20mp APS-C, ~24mp FF). From an objective standpoint, there most definitely is, and I think it is important that people understand that. All else being equal, you don't lose anything by moving to a higher resolution sensor, and in fact you almost always gain something.
Subjectively, images from the D800 (at least at lower ISO/in good light) are superior, often vastly superior, to anything that you can get out of any Canon camera on the market right now. As a Canon fan, I don't really like to give a bone to the competition, but in this case, both subjectively and objectively, a higher resolution sensor most definitely has something to offer...and in a clearly visible, empirical way.
No as always you completely misrepresent me, invent what you think my assertions are, even though I never actually mention them (AA filters would be a fine example) and you, yet again, refuse to even recognise the cameras I used to make my tests, there is quite a difference between a 1D MkIII and a 1Ds MkIII. But you, with your 7D and 20:30 sight have drawn your own conclusions, and bearing in mind the amount of difference between what I write and you either misrepresent, or make up, it is clear what they are.
Sorry, I know it is the 21.1mp FF 1DsIII you used...I just miss typing the s for some reason. I never intend to misrepresent the cameras you have used.
I am a photographer, that is nothing special though other than the fact that I leave and breath by images (which have never been world beaters), I don't care for theory other than an interesting diversion when I am at the computer, in my world empirical rules, I don't care for yours and AlanF's theories on why my 300 f2.8 should give me 40% more reach on a 7D as opposed to a 1Ds MkIII, I just know it doesn't, because I actually did it. And that seems to be where we differ.
AlanF used to make this wonderful theoretical argument about how the 7D vastly outperforms the FF cameras for reach, a direct test of pixel density, until he got a 5D MKIII, guess what he shoots his focal length limited birds with now?
I would use the 5D III for birds as well, but not because of pixel pitch. I'd use it because of its AF system, which is without issue vastly superior to the 7D AF system. I don't argue these points because I am a die-hard 7D fan. I'm the first to admit the 7D definitely has it's flaws, and one of the biggest is the AF system. It's better than Canon's 9-pt systems, but it has plenty of issues of it's own that reduce the keeper rate. It is easy to argue the AA filter is too strong as well, and that is often a matter of opinion...really depends on how often you shoot subjects that might produce aliasing. If I had the money to buy a 5D III right now, and use it for my bird photography I would. It's a better camera overall
That said, I wouldn't have any illusions that, assuming I could shoot the same bird with the same lens on both the 5D III and 7D, assuming both locked focus ideally, that the 7D would resolve more detail from the same distance. That isn't too much of a problem with the 5D III, though...I can always close the gap by throwing a 2x TC on my lens and using f/8 AF, and any edge the 7D may have had disappears at that point. But that isn't the point I usually debate. I am not sure about AlanF's arguments that the 7D "vastly" outperforms the 1Ds III/5D II. I would agree that, with it's archaic AF system, the 5D II was at a pretty healthy disadvantage
to the 7D. The 1Ds III? Not so much. I DO indeed believe that in your prior visual comparisons of the 1Ds III vs. 7D resolving power, the 7D detail, while not "vastly" superior (and probably not 40% superior) was better by enough of a margin to clearly see it. Maybe 25%-30% better...but as far as technology goes, a 25% improvement anywhere is usually a damn good one.
(To contrast, performance improvements in successive generations of CPUs are often only in the 10-15% range, if that. Extensive overclocking of a CPU might buy you an additional 20%, and if you are really freaking good, use expensive liquid cooling technology, etc. you might be able to extract 40% in a good overclock. If your a total wackjob with tons of disposable income, you might use liquid nitrogen and an elaborate cooling setup to double your CPU performance.)
Now, we regularly butt heads on the 1Ds III vs. 7D thing. Let's assume the 7D had pixels twice as small (i.e. you could fit 4 7Dx pixels into one 7D pixel.) Do you believe the resolution advantage of the 7Dx would be moot in comparison to the 1Ds III? The margine isn't massive between the 1Ds III and 7D. But it would be quite considerable between the 1Ds III and our hypothetical 7Dx. I may simply be misunderstanding you, but by your arguments, it always sounds to me like your trying to make the point that a camera like our hypothetical 7Dx is unnecessary, and therefor should never be made in the first place. If I'm wrong about that, please let me know. As far as I am concerned, which cameras are actually compared don't really matter...1Ds III vs. 7D, 1D X vs. 7D II, 5D III vs. 1D X...the actual cameras and their sensor's don't really matter to me. My point is that there is value to increasing sensor spatial resolution, and there will continue to be value for quite some time.
P.S. I have never said nobody would ever benefit from a high mp camera, but the number of people who are committed to Live View manual focus, tripods, and top quality lenses are few and far between, play that off against the number of times they will reproduce that image where the extra resolution would make a difference and you start to understand why the downside of high mp cameras becomes obvious, faster processors and programs and storage are not as cheap as is often put forward.
The question becomes how many is enough? For some whatever the number becomes it will never be enough, for many people crop cameras and current mp are more than capable, for most FF is overkill, truthfully overkill, I believe the ever steepening slope of diminishing returns begins in the mid 20 for ff sensors; for AF users, for hand held users, or iso's over a few hundred, for people without the very best glass even now it is moot, they are already far below their cameras potential.
Comparing photos from the D800 with photos from the 5D III, while the 5D III still tends to lock focus faster and better, when both focus properly, the D800 still has more detail. A lot more detail. So...is 23mp really enough? Is 36mp really enough? I've seen photos from some smaller form factor mirrorless and compact cameras that have even smaller pixels, and the detail levels, assuming a roughly equivalent focal length, are even higher. With some of the latest models of these cameras, which use very advanced sensor fabrication technology, not only are the detail levels high, but noise levels are still acceptable.
Assuming we don't simply divide pixels size, and also assume that pixel quality increases at a similar rate...then I think enough is a long ways away. I think we can push the envelope 3x, maybe 4x farther than were Canon is now (i.e. approaching 100mp FF), before we actually reach a point where we truly have more than enough. Why? Because then we have sufficient raw pixel information to support full 2x2 pixel downsampling to 25mp, which would greatly reduce noise, improve dynamic range, and still support printing at very large sizes. Or, it would allow cropping the middle 25% of the frame, and still having quality similar to the current 5D III. Whichever you do most often, more pixels would never be a bad thing, and quite probably a good thing, even a better thing.
Is such a capability overkill? Well, depends on who your referring to. For most entry-level DSLR users, certainly. For a range of professional, or avid enthusiast/hobbyist photographers, probably not. There is never anything wrong with better quality. Getting better quality is the reason we are all here on CR, bickering about these kinds of things. We all want, hell we all THRIVE, on better quality. If it wasn't for such a strong desire to extract ever more quality from our photos, we wouldn't have any need to upgrade our cameras at all, or spend so many hours of our lives debating the issue in forums like this. It is ok if you are personally happy with 21.1 to 22.3mp, but that does not mean continuing to push the resolution envelope offers no value to everyone else. Just because 50mp or 100mp is overkill for the average casual photographer does not mean it will never have any use or value to someone far more serious about their work. As someone who has a very good optical prescription for my eyes, I can attest to the fact that with 20/10 vision, what I get now from the 7D is not enough. The 5D III, assuming identical framing, is an improvement...but I've also seen better. Therefor, I want better. And even better. As far as I am concerned, keep improving everything, on all fronts, until you reach some unbreakable physical limitation or exponentially accelerating costs that would obliterate any value in the technological gain (and I don't think we are even remotely close to either yet.)
I'd point out that, beyond just the theoretical, I'm not arguing that every random joe with a $500 DSLR or mirrorless needs
more megapixels. I'm arguing that more resolution cannot ever be a bad thing, and if it cannot ever be a bad thing, why stop improving it? Even if we don't use every single original pixel in our final output, the more pixels you start with only ever means better results in the end (especially if you downsample the result), assuming you otherwise use the device effectively.