Lens vs Camera: The FF APS-C Dilemma

Started Aug 3, 2014 | Discussions thread
pixelpushing Veteran Member • Posts: 3,229
Re: Lens vs Camera: The FF APS-C Dilemma

ProfHankD wrote:

pixelpushing wrote:

ProfHankD wrote:

BTW, my A7 averages only a tad better IQ than my NEX-7.

No offense intended, but wouldn't it be more accurate to say it's You+A7 that yields only a tad better IQ than You+NEX-7? Everything else being equal, A7 IQ should be better.

Things aren't equal because lens coverage and resolution requirements differ greatly for APS-C and FF. Having now tested a significant fraction of my lenses...

Yes, I have a big pile of old lenses, too. Not as big a selection as yours, but I've done a fair bit of shooting. What exactly have you tested, and how many?

on both the NEX-7 and A7, I can say it's a much closer IQ race than I expected. Apparently, it's also much closer than you expect.

I don't think we agree on exactly what constitutes IQ. I don't feel corner correction should be considered imagewide to alter the inherent DR, SnR, Tonal, Microcontrast and detail advantage of a larger sensor. This goes for compact to 1" to M43 to APS to FF to MF.

Perhaps for your lenses the A7 does much better, but that's not generally true over the many lenses I've tried.

Much better at what? Than what? I'm sorry, I find these to be broad generalizations without lens and image-specific data and have a hard time seeing the relevance of citing very specific corner noise after vignetting correction as general DR loss.

When one is much better than the other, it's because of lens issues. When APS-C wins, it's usually due to dark FF corners (I'm talking about old lenses designed for full frame)

I'd say this 'win' for crop would be dependent on lens(es) used, how dark is dark, and whether simple corner correction results in visible loss or if corner shading is undesirable for the subject in question. I personally prefer at least some vignetting for a variety of my shots. Not every subject is landscape or architecture requiring perfect even clarity and brightness from edge to edge.

You burn more DR fixing many FF corners than the A7 offers beyond the NEX-7. See my article:

Again, you're applying corner correction artifacts to an entire image, and I don't agree that edges = image performance, nor do they defeat all other aspects of IQ.


Lenses that are stopped down enough, or inherently very even (more common for telephotos), do tend to do a touch better on the A7 than the NEX-7.

What is 'a touch better'..? And what criteria and variables are you referencing?

Of course, it varies... and some people like vignetting (not me). Some lenses have center resolution enough for 24MP APS-C but show blurry corners on 24MP FF; others are fine on 24MP FF but yield a generally blurry 24MP APS-C crop. Oddly, APS-C + focal reducer provides a slight crop (1.1X) that seems lots less challenging for many designed-for-FF lenses than either FF or APS-C... remember a lot of folks saying good things about the 1.3X crop Canons?

Focal reducers can also cause loss of detail for crop sensors in the corners. I have to say, it seems to me your results are presented in a way to favor APS-C and therefore arrive at the counter-intuitive (sensational) conclusion that FF isn't any better with a $100 adapter. I apologize if I'm wrong, but that's the impression I get.

Not when you have to burn 1+ stops fixing dark FF corners. Of course, the A7 does win over the NEX-7 DR by a visible 0.8 stop margin when the lens is good enough. Then again, a NEX-7 beats a Canon 5D III by 1.7 stops (all using DxO's numbers). Of course, the 5D III is a FF that many consider to have fairly good DR.

Which lenses? How do you apply the loss of DR for a whole image by grading corners only?

Basically, you do get a higher base sensitivity with larger sensels, but you also get poorer QE (quantum efficiency)

Quantum Efficiency is relative, though. It doesn't mean a larger sensor 'A' with a lower QE than smaller sensor 'B' will have any lesser IQ performance. A larger car may not have the same power to weight ratio as a smaller one, but can still outperform it in every way. Too many facets to what we deem IQ to make any assumptions based on Quantum Efficiency.

and have other problems because you can't really be as aggressive about the fab technology and still get a viable yield making the larger sensors.

How do you arrive at that conclusion?

Sensor size isn't everything.

Nor is light dropoff in corners. Nor is Quantum Efficiency. Nor is 'fab technology'.

In fact, the 1" sensors perform much closer to APS-C than they should because fab techs like backside illumination are still economically viable at that size and not on APS-C.

But the back illumination gives the explanation as to why they 'should' perform as well as they do. There's no magic or bending of reality going on.

You've gotten used to having some great APS-C crop lenses, so I think you'd be seriously hurting to move to an A7 without lenses that give comparable performance on it.

When I first got my A7 kit, I was using my 55-210 and 20mm all the time. Got some great, better-than-10MP crops.

In side-by-side A7 APS-C crop vs. my circa-2006 A100, the A100 IQ is very competitive.

Again, we're dealing with vagaries and highly subjective descriptions, Prof. To some, a D100 might be competitive with an M9.

The A100 does have poorer sensitivity and DR, but the CCD gives better colors and almost no PF. Anyway, I sometimes use APS-C crop on my A7, but the NEX-7 clearly outclasses it for APS-C.

I really don't see where you're getting this, or what you're basing 'it' on. What does 'outclasses' mean, here? How exactly does the A100 have better colors than the A7, other than an individual interpretation?

The A7R looks much more competitive for APS-C crop, but I don't have one to compare for myself.

You mean the auto crop function is 15MP vs. 10MP on the A7? The latter is not constrained to that, there are several lenses on the E-Mount lineup that can be used at much larger crop (or none at all, depending on FL).

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