Best low light FF Canon DSLR

Started 3 months ago | Discussions thread
Dr_Jon Veteran Member • Posts: 6,082
Re: Shed

Mako2011 wrote:

Dr_Jon wrote:

J A C S wrote:

.

But it (higher ISO) makes more light on the bottom of the tonal range useable.

This is also true, although I was just trying to make a simple point to help the OP with the answer to their question, and it has spiralled a teeny bit...

Here is an excellent related article that might shed some light and clear up a misconception or two

Mystic exposure triangle

Worth a link, it says some good things, and the odd (very) few I'd disagree with (oh and I'm still completely happy with everything I've said here, I think it's all correct).

For example:
"Scaling the raw value in the camera carries no useful function in and of itself. We could, with the same result, increase the lightness in the raw conversion process."

This is not strictly true, for three reasons.

Firstly when you digitise a signal you limit its resolution to the steps in the ADC. For example if you have a 6D with a maximum saturation of about 74,000 electrons and sample at 14 bits then you get about 5 electrons per ADC step (aka DN). If you didn't use the ISO amplifier you always get that, so as the peak number of electrons in your image reduces you get less and less steps (1,000 electrons -> 200 steps). If you amplify it you are getting more steps as you can amplify the fractions of steps in the analogue realm. Setting the ISO amplifier to 4x with our 1,000 electrons would turn them into 4,000 electrons and 800 steps from darkest to brightest. Now against that the noise can be a big problem at lower electron counts so you don't win as much as you'd like.

Example (using 5 electrons per DN at ISO 100) - 3,4,5,6,7 electrons would read as 1,1,1,1,1 with no amplification; they are 24,32,40,48,56 electrons after 8x amplification and read as 5,6,8,9,11.

Also the ISO amplifier reduces the effect of noise between it and the digitiser, so shooting at higher ISO will give you a little lower noise (e.g. in the previous example adding another electron of noise to either 1,000 or 4,000 electrons, it's 1/4 the effect in the amplified signal). This actually really matters if the ADC is not built into the sensor, as you could be getting 25 electrons extra noise (which is about right for a 6D). Hence shooting at ISO 100 and amplifying in post the camera added on average 26.4 electrons of noise. Shooting at ISO 6400 it added 2.0 electrons of noise. (Strictly it still added about 26, but the signal was boosted before that so it appears as a much smaller part of it when you turn it into an image.)

Finally if you up the ISO you'll get a JPEG where you can see the image and work out if you got the shot

Note I'm not saying you should always crank the ISO for lower light levels. The problem is every ISO increase makes the upper half of the previous ISO's data unavailable, so if you have a dark scene with a few bright highlights they will get ever more lost with increasing ISO. Shooting at low ISO and amplifying digitally in post can keep them. On a 6D shooting at ISO 800 gives about 5 electrons of camera noise and a usable pixel capacity of just over 10,000 electrons, so anything making below 10,000 electrons in a pixel can be used in the image. If your scene was mostly below 2,000 electrons you could shoot at ISO 3200, but any bright bits over 2,400 electrons would disappear, hence ISO 800 gave you the stuff between 2,400-10,000 electrons to see. The down side is you can't see much of the image you shot when you shot it and camera noise went from 2 to 5 electrons (which should be fine at these light levels). (Why not ISO 100 - too much noise.)

Not trying to argue, just pointing out it's good but not perfect.

 Dr_Jon's gear list:Dr_Jon's gear list
Nikon Coolpix 950 Fujifilm FinePix Real 3D W3 Sony RX100 V Canon EOS 5DS R Panasonic GH5 +29 more
Post (hide subjects) Posted by
BAK
MAC
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
MOD Mako2011
BAK
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow