Originally posted by Dan Rentea Try comparing an orange called Nikon D7200 with an orange called Nikon D750. This discussion is for children. Sure we can compare it, other have done it to, but in the end all of them say the same thing: different sensor format, different image quality. So it's like comparing oranges to apples, not oranges to oranges.
I want to save the honor of the 6D? You make my day with this statement. Who are you, a five year old child?
Pixel shift function is like wireless control. Canon 6D have it built in, Pentax K-3 II doesn't, but it does have a wireless memory card. It takes a little longer to wirelessly transfer images from K-3 II via wireless memory card, but in the end it does pretty much the same thing. Same thing with pixel shift vs stacking images.
Have you touched a 6D, or you just read the reviews online about it? I actually said that I loved the image quality from K-5 II and K-3 II (I owned both cameras), but there were other reasons than image quality that made me leave Pentax. Forget for a second this debate that you seems to have with me and read from the beginning all I wrote.
You came with this theory that if I shoot at ISO 1600 and f4 on full frame I will get the same image quality if I use ISO 800 and f2.8 on APS-C. But no, actually I can not get the same image quality. Why? Let me put you this way. Let's say we have an APS-C with 24mp and a full frame with 24mp (Nikon D7200 and Nikon D750). If I take 240 people and put them in a handbal court they will probably fit, but they will not have verry much space to move. But if I take those 240 people and put them in a fotball court, they will have more space to move. It's the same thing with megapixels. A larger pixels crowd per square centimeter mean high image noise at high ISO values, it means a weaker final resolution. And this is one of the reasons why D750 is way better in low light than D7200.
And so where do you put the limit of your therory? the D750 is better at 12800 isos than the D7200 at 100 isos? And what if I take a very old FF and quite new APSC body?
Let take a look of what DxO says of high iso performance of 6D vs K3:
iso 800 K3: 32 db of signal vs noise ratio, 10.69 EV of dynamic range, 7.49 bits of tonal range, 18.75 bit of color sensitivity
iso 1600 K3: 29 db of signal vs noise ration, 9.85EV of dynamic range, 7 bits of tonal range, 17.7 bit of color sensitivity
iso 1600 6D: 32 db of signal vs noise ratio, 10.7 EV of dynamic range, 7.5 bit of tonal range, 19.2 bit of color sensitivity.
iso 1600 D750: 32.5db of signa vs noise ratio, 10.8EV of dynamic range, 7.5 bit of tonal range, 19.5 of color sensitivity.
So sure 6D at iso 1600 is significantly better than 800 iso on K3, but when we compare iso 800 of K3 and iso 1600 of 6D, we get the same performance.
This is basically because an FF has approximately double the surface of sensitivite area, in this precise cases, each photosite surface is twice as big on the 6D. At the same exposure both camera get same light per surface area and so the whole 6D sensor and each individual pixel get the double of light.
Now if you move your apperture by one EV on the APSC, the light density double, and the whole sensor and also each photosite get rougly the same total amount of light on the K3 at f/2.8 as on the 6D at f/4.
So you can stretch the stadium analogy all you want, the key question for the stadium is the difference in size of both stadium and how much you get.
In APSC vs FF to be precise and exact there 2.33 the surface area on the FF than on APSC (a bit more difference on Canon APSC sensors as they are slightly smaller). This is 1.1 EV. So in theory you gain really 1.1EV of light... Basically 1.1EV or 1EV is the same so in most cases you can round it.
But sure, the Canon sensor is only getting 1EV difference and getting exaclty the performance of K3 at iso 800. It miss the 0.1EV because the Sony sensor is slightly better.
No the an FF at 12800 iso isn't looking better than an APSC at iso 100. There actually some correspondance, there mathetical formula for that... and funily the practical measurements match it.
Canon 6D at 1600 iso isn't doing any better than that K3 at 800 isos.
Another way to see it, is to compare the pictures for example at imaging resource.
On the left is the 6D at iso 1600 on the right is the K3 at iso 800... To me 6D picture look like a slightly blured and less sharp version of the K3 and I would have difficulties to say that the iso 1600 picture of the 6D look better... So yes I really think that an iso 800 f/2.8 shoot of K3 can give you as much quality as an iso1600 f/4 shoot of a 6D. No issue at all.