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This video explains how ISO is very different to what most people imagine, and how you can use this knowledge to take less noisy photos!
REFERENCES
- Sensor Analysis Primer: https://www.photonstophotos.net/GeneralTopics/Sensors_&_Raw/Sensor_Analysis_Primer/Photographic_Dynamic_Range_Shadow_Improvement.htm
- Image sensors explained: https://www.canon-europe.com/pro/infobank/image-sensors-explained/
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
Produced by Joshua Chawner
Chapters
0:00 Misunderstanding ISO
1:54 ISO Explained
3:20 Why Even Have ISO?
4:52 What Actually Creates Noise
7:12 ISO Step-by-Step Guide!
8:36 Sponsor Message from FarmKind
9:43 ISO Caveats
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how i learned to stop worrying and leave ISO on Auto
Man I thought this was going to be an expose on standards organizations! ... And then I saw the thumbnail.
Man, as an audio guy, if someone had just explained ISO as gain staging it could have made so much more sense so long ago. Thank you for finally putting it in terms I get!
I still think of it as "film speed", my back also hurts.
"I finally understand ISO!" Astrophotography: "Allow me."
10:03 I just want you all to appreciate that he used a posterized time effect on that digital noise, so that we can see it in spite of YouTube's compression. Just knowing about this requires even deeper fundamental knowledge of the nature of digital noise and video compression that he never mentions directly in the video itself.
This is why I appreciate how broadcast video cameras just call this setting "gain", and measure it in decibels!
8:30 - so you set your photo in the order the photons move from the object to the final image saved. Light from outside -> lens -> sensor -> ADC -> saved image. Makes sense.
Telling someone not to use high ISO and finding out they're "following" that advice by shooting at low ISO and brightening in post is akin to telling someone not to stick a fork in an outlet and finding out they've followed your advice by sticking car keys in an outlet instead.
Caveat number 5: Some (higher-end) cameras have a "dual native ISO" (which is basically a separate amplifier circuit)... So when you go over a certain ISO, noise _plummets_ again because it swaps over to the secondary amplifier. This is why, on my Blackmagic camera, ISO3200 often looks less noisy than ISO2800 (as it now uses said second amplifier).
The balloon analogy was just brilliant!
It would probably be helpful to explain ISO in film and that digital cameras attempt to simulate that setting using something that photographers were already familiar with.
Filmmaker and camera operator/gaffer from the German film industry here. First of all: absolute banger of a video. One of the clearest explanations of ISO I’ve seen. One small addition that might be interesting is the relationship between ISO, native ISO, and dynamic range. Most cameras have a native (or base) ISO, which is the point where the sensor delivers its maximum dynamic range. Dynamic range refers to the range between the darkest and brightest details a camera can capture at the same time. In other words, how much highlight and shadow information the sensor can record before clipping occurs. This can be checked on Photons to Photos under the Photographic Dynamic Range vs ISO setting. As you increase ISO, the noise floor rises and the total dynamic range typically decreases. Interestingly, charts like the “Shadow Improvement” graphs from Photons to Photos show that increasing ISO can sometimes make shadows appear cleaner because the signal is amplified relative to read noise. But that improvement comes at the cost of reduced highlight headroom and overall dynamic range and therefor colorinformation. So the best signal-to-noise ratio in the shadows doesn’t necessarily mean the best overall image quality. For many cinematographers and photographers, dynamic range is the more valuable resource, because it determines how much highlight and shadow information the camera can actually capture. If you have control over lighting, that’s why it’s often best to shoot around the camera’s native ISO, where you get the widest highlight-to-shadow range. Also, caveat: some cinema camera workflows (for example certain RED pipelines) behave a bit differently. In those systems, changing ISO can effectively shift the distribution of dynamic range between highlights and shadows, which is why cinematographers sometimes shoot higher ISO in very bright scenes and lower ISO in darker scenes. On most DSLRs and mirrorless cameras, however, ISO mainly affects noise and overall dynamic range, not how it’s distributed. And honestly, I’d love to see a separate @MinutePhysics video about dynamic range. It’s a fascinating rabbit hole and incredibly useful for understanding how to get the most out of a camera sensor. For anyone who wants to dive deeper into the topic, I can highly recommend the YouTube channel “Tomy’s Cinematography Courses”, which has an excellent series explaining dynamic range in detail, even though it’s still extremely unknown.
This is mentioned but not a lot of discussion: Most cameras can only do 2-3 analog gain levels(so called “Native ISO”). The rest is digital. This is very subtle, many cameras have dozens of ISO levels but just a few if them are real. Even more, there are camera can do only one gain(the amp is not configurable) and not rare to find. So check the “Native ISO” before you use it!
8:05 As a bird photographer, I love these photos! First photo is Hairy Woodpecker with Northern Flicker in the background, second photo is a female Red-winged Blackbird :)
To be fair to the advice to use low ISO, it's often not so much "take a darker photo and then brighten it later", it's more "if you can brighten the image by gathering more light (open the aperture or lengthen the shutter speed) you'll get less noise than by boosting the ISO". Another quirk is that Sony makes dual gain sensors now so there's a threshold iirc somewhere around ISO640 where the noise goes *down* slightly when you step the ISO *up* by one level. I'm not sure if they sell sensors to a lot of other manufacturers or if it's a quirk of Sony hardware only or if it applies to other brands as well
Wait, this is not a video about the International Standards Organization?
Astrophotography taught me this. We use Dark frames to subtract the average thermal noise for a given exposure length and Bias frames to subtract out the average Shot or Read noise from the ADC. I set the sensor gain to the setting that allows it to absorb the most photons without clipping, sometimes refed to as full well depth. Then I dial in the exposure length to the point where the brightest stars just about start clipping. Kinda the same idea, but a little backwards. Of course, then I take tons of pictures of the same thing and "average" them out to improve the signal/noise ratio.
Modern cameras from the last 10 years have a feature called ISO Invariance. Those sensors have such a clean analog conversion that you could just brighten up in post, and it wouldn't look much different from jacking up your ISO. Those cameras also have dual gain ISO most of the time, so those two ISOs are the only ones you theoretically ever need.