A7r RAW data file sizes & who really needs 36Mp?

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blue_skies
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A7r RAW data file sizes & who really needs 36Mp?
6 months ago

Reading the amazon statistics that the A7r is outselling the A7 and A7-kit really surprised me. Are all these pre-order placed by professionals that must have the best? Or are people putting in dual orders, just to get in the queue? Or are amateurs falling for the hype of 'bigger is better'?

I think that Sony must be surprised by now: the D800E was a 'niche' camera, and this lines up with the A7r. Per the specs, I think that Sony made the A7 the more user-friendly camera, and this should be the camera that most of us look at first, imho. Even if you review the D800/E versus D600, most recommend to go with the D600, unless you have special needs (e.g. Thom's recommendation )

Just a couple of things that caught my attention:

File Sizes:

The recent FW updates improved RAW compression from ARW2.2. to ARW2.3 on the Nex-6/7.

Nex 6 and Nex-7 use 12 bit RAW data:

  • Nex-6 uses ARW2.3 to encode 16Mp x 12 bit / 8 = 24MB and requires 16MB storage
  • Nex-7 uses ARW2.3 to encode 24Mp x 12 bit / 8 = 36MB and requires 24MB storage

A7 and A7r use 14 bit RAW data:

  • A7 uses ARW2.3 to encode 24Mp x 14 bit / 8 = 42MB but requires 24MB storage
  • A7r iuses ARW2.3 to encode 36Mp x 14 bit / 8 = 63MB but requires 36MB storage
  • Note: Nikon D800E allows non-compressed RAW files which have been reported around 70MB, with their compressed format matching that of the A7r at 36MB.

A7r JPG files vary around 6MB to 14MB, give or take.

That is, if you shoot in RAW+JPG, you capture about 50MB per image. A 16GB SDcard fills up with roughly 300 images for A7r and 450 images for A7 (Note - as reported by Sony in their brochure ). Per their brochure, pure RAW is (A7r/A7) 600/405 and 870/630 images for extra fine JPG.

True Resolution

Other than those that must have the extra detail for cropping or mural printing, I question the 36Mp usefullness: read http://www.dantestella.com/zeiss/resolution.html about resolution and DOF: he says that for a 50mm FL lens on FF: "we are talking 30 line pairs per millimeter" for sharpness resolution.

That is quite a bit below the 'max' lens-resolution, and the theoretical sensor resolution:

  • A7: 83 lp/mm
  • A7r: 102 lp/mm
  • Nex-6: 105 lp/mm
  • Nex-7: 128 lp/mm

Lenses of-course can resolve much higher than this, or can they? In the corners? Which f-stop? Which DOF? And which MTF curve?

Looking at the downloadable RAW+JPG shots from Amsterdam(?), down-load link, I hardly can see the justification for the higher Mp, as so much in the image is OOF (DOF limit). Such shots illustrate that the 36Mp is NOT needed for many shots. I mean, it bodes well for using the camera in APS-C crop-mode which is indeed a benefit of the 36Mp camera.

To really get all these pixels to become sharp, I imagine tripod based shooters, with stopped down apertures, diffraction limited, shooting still life, nature, etc. That takes time and care.

Then I also read these big debates about the true resolution benefits, and the resolution being measured at MTF8% instead of at MTF50%. A good read-up is here, I quote:

  • "How is MTF related to lines per millimeter resolution? The old resolution measurement— distinguishable lp/mm— corresponds roughly to spatial frequencies where MTF is between 5% and 2% (0.05 to 0.02). This number varies with the observer, most of whom stretch it as far as they can. An MTF of 9% is implied in the definition of the Rayleigh diffraction limit"

Perceived image sharpness (as distinguished from traditional lp/mm resolution) is closely related to the spatial frequency where MTF is 50% (0.5)— where contrast has dropped by half.

This figure represents a sine pattern (pure frequencies) with spatial frequencies from 2 to 200 cycles (line pairs) per mm on a 0.5 mm strip of film

I should add in that those skilled in post-editing can do a lot with boosting the contrast and making use of every bit of contrast difference, even at the 8%.

Also:

Some food for thought: the 24Mp A7 resolves about the same resolution as the 22Mp 5D-MIII, and then there is this outcry of the DxO report that shows that the D800, when downsampled to 5D-MIII is not the same shaprness (expectedly so, which leads to another discussion).

If you print big, at 'optimal' 250 dpi, read this:

  • "D600 native size is 6,016 × 4,016. That's about 24" x 16" optimal. D800 native size is 7,360 × 4,912. That's a little smaller than 30" x 20" optimal.Both can scale up to their largest print size, 45" x 30" and be well above their minimum"

And read this:

  • "At 30 x 40 , you’ll probably see a visible difference. As you get larger in size, the D800 images will really pull away from the D600s (or the D4′s for that matter), but you’ll have to go fairly big to start to see a real difference. So, honestly, unless you’re printing really large files, I’d have a hard time telling you to choose anything other than the D600"

Yes, bigger is better - I am not denying that at all. But 24Mp and 36Mp hardly make for a 'better' picture by themselves - it is up to the photographer to do the real work. High IQ lenses help, and the lack of AA filter does promise uncompromised details (btw - the Sony brochure shows that the AA filter is not there, but that the sensor topping is there), so I can see the buzz being about the A7r, for a while to come.

But, comparing the specs and pricing, of the two cameras, I would have expected the A7 to outsell the A7r by a landslide, which is not the case. So, is everyone really getting the proper camera for themselves?

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Cheers,
Henry

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