Best low light FF Canon DSLR

Started 3 months ago | Discussions thread
Dr_Jon Veteran Member • Posts: 6,079
Re: Best low light FF Canon DSLR
1

steks wrote:

Thanks for all the reactions, to keep things short, is it fair to say that there is difference in low lIght IQ, but it’s wrong te expect a high improvement when using an comparable aperture.

Lets compare a 30mm f/1.4 on my 77D cropsenor with a 50mm stopped down to f/2.2 on a 6D (30x1.6=48 and 1.4x1.6=2.2) am I correct when saying, that because of the double in size photosites on the 6D (24,2/20,2x1.6=1.9), you can expect one stop extra sensitivity? Furthermore you have the abiltity to use faster primes, lets say a 50mm f/1.4 which also gives you an extra stop?

About an TTL flash, Thanks for the advice, i have one and used it quite a lot on my 400D when I only had a kit lens. I will experiment with it again, but there are a lot of situations where a flash won’t be the best or easiest solution.

It's complicated as the older Canon's performance varies quite a bit with ISO. The newer ones are better for that, but the DPAF ones lose a little to sensors with one pixel per pixel (if you see what I mean). The big thing to help at higher ISOs is to have a dual-gain sensor, which Canon haven't done yet. A BSI sensor helps a teeny bit, but Canon don't have them either (but doesn't really matter at APS/FF sizes).

Generally what you need to consider:

* The f-stop is light per unit area. So at the same f-stop bigger sensors receive more light in the same time period. (Or conversely the smaller sensors' data is spread more widely at the final viewing size, which is usually sensor size independent.) Pixel size doesn't matter much as you get more pixels for the same area of the final image (it does if you pixel-peep, but that means zooming into the image more and is meaningless).

* Note faster lenses only help at a particular sensor size if:
(i) They enable you to reduce the ISO (otherwise the camera just alters the shutter speed to keep the light gathered the same).
(ii) You can live with the depth of field you end up with.

* Image noise is mostly noise in the incoming light, if you capture twice the light the percentage of that which is noise goes down by 1.4x.

* The camera noise tends to even out at ISO 800 and above, so not a factor unless you have a dual-gain sensor. It causes the step in the Sony graph here:
http://www.photonstophotos.net/Charts/PDR.htm#Canon%20EOS%206D,Nikon%20D850,Sony%20ILCE-7M3
(BTW the bouncing of the 6D graph is because it only does whole ISO stops in hardware, if you want +/- 1/3 stops it shoots at a whole ISO - i.e. 100, 200, 400, 800... - and pushes or pulls the digital image 1/3 of a stop.)

* Other really minor factors are how permissive the colour filters over the pixels are (mostly they capture a bit either side of the nominal light, so let maybe 40% of the incoming light through, not the 33% you might expect) plus the Quantum Efficiency (QE), namely what percentage of incoming photons get converted to electrons, this varies with colour and most ways of calculating it from DXO (or similar) data have so many error sources I'd ignore them and assume it's about 50% and so you don't care when comparing cameras. Oh and how well the microlenses and light pipes aim the light into the pixel, which again like the previous two I wouldn't worry about.

So in summary at higher ISOs you mostly care about about sensor size or if a dual gain sensor is available (not for Canon). At lower ISOs you want one of the newer Canons with the analogue to digital converters on the sensor, as that reduces the camera's low ISO noise significantly, so for FF 5D4 or R, but not RP as that's the 6D2's sensor.

Oh and don't forget whether it can AF well at low light levels...

I think the 5D4 is probably numerically the best Canon DSLR for low light overall, although the 6D's noise can look more pleasing (very subjective). But a Sony A7rIII is better.

Or just ignore all that and use either Neat Image 8 or DXO Photolab's Prime noise reduction....

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