alt Hacker NewsGood grief, that video suffers the YouTube-ism of "ramble on about how you don't understand X" for way too long.
Video alleges people think ISO makes the sensor "more sensitive or less sensitive". (I … don't think this is common? But IDK, maybe this is my feldspar.)
(The video also quibbles that it is "ISO setting" not "ISO" … while showing shots of cameras which call it "ISO", seemingly believing that some of us believe ISO is film speed, in a digital camera?)
Anyways, the video wants you to know that it is sensor gain. And, importantly, according to the video, analog gain, not digital gain.¹ I don't know that the video does a great job of saying it, but basically, I think their argument is that you want to maximize usage of the bits once the signal is digitized. Simplistically, if the image is dark & all values are [0, 127], you're just wasting a bit.
You would want to avoid clipping the signal, so not too bright, either. Turn your zebras on. (I don't think the video ever mentions zebras, and clipping only indirectly.)
The video does say "do ISO last" which I think is a good guideline. Easier said than done while shooting, though.
… also while fact checking this comment, I stumbled across Canon's KB stating to use as low an ISO as possible, which the video rails against. They should talk to Canon, I guess?
¹with the caveat that sometimes there is digital gain too; the video notes this a bit towards the end.
Replies
i think we need to differentiate between raw or derivative format. canon KB might cater to wider audience thus the latter
Sounds like you'll be spending your day making a better video! :-)
ISO changes the analog gain and in a way yes, it does make it more sensitive to a certain range of brightness.
This is because the ADC (analog to digital converter) right after can only handle so many bits of data (like 12-16ish in consumer cameras). You want to “center” the data “spread” so when the “ends” get cut off, it’s not so bad. Adjusting the ISO moves this spread around. In addition, even if you had an infinite bitrate ADC, noise gets added between the gain circuit and the ADC so you want to raise the base signal above the “noise floor” before it gets to the ADC.
Gain is not great — it amplifies noise too. You want as low ISO as possible (lowest gain), but the goal is not actually to lower gain; your goal is to change the environment so you can use a lower gain. If you have the choice between keeping the lights off and using higher ISO versus turning on the lights and using a lower ISO, the latter will always have less noise.
Most photo cameras have one gain circuit that has to cover both dark and light scenes. Some cameras like a Sony FX line actually have two gain circuits connected to each photosite and you can choose, with one gain circuit optimized for darker scenes and the other optimized for brighter scenes. ARRI digital cinema line cameras have both and both are actually running at the same time (!).