One of the first lessons we learn in photography is to always try to shoot at the lowest ISO possible. In theory, this produces the cleanest images with the least amount of noise and gives us the most room to work with in post-processing, provided you expose the shot correctly. However, shooting at lower ISOs can cause more harm than good, especially when lighting starts to get tricky.
As this video from nature and wildlife photographer Simon d'Entremont explains, shooting at a lower ISO can result in a poor signal-to-noise ratio, which creates more noise in the resulting image. Worse still, the visible noise will increase as you lift the raw file in post, especially when lifting the shadows or exposure of the file.
To illustrate this, Simon shows us an example of two files, one taken at ISO 12,800 and the other at ISO 1,600. When he lifts the exposure of the ISO 1,600 file to match the 12,800 shot, it produces significantly more noise than the image shot at the higher ISO. Simon goes into more detail about the impact of ISO on shooting in different environments with practical examples where higher ISOs will result in better images.
As someone who primarily shoots at night, I was afraid to let my ISO creep above 6,400 for the longest time. Yet, now, I’m happy to shoot in auto ISO and allow it to go as high as it needs to for the scene, as long as I don’t let it blow out the highlights. This way, I rarely need to push the shadows in post and can even make the final image look cleaner by pulling the shadows back a bit while still having plenty of information to work with.
I shoot live theatre and very rarely drop below ISO 4500. I usually operate between 8000 to 18000. There's just no other way to do it but fortunately the nature of the lighting and images themselves let me get away with it. I shoot manual with auto ISO maxed at 25,500 because I'm constantly negotiating with aperture and shutter speed depending on the speed and depth of action on the stage. I also usually under expose by about 2/3rds of a stop.
There is no real way around increasing the ISO to get the lightness you need in a photo, as it is virtually impossible to get a ADC that had the bit depth and input voltage range to natively cover the entire output range of the analog path.
The current solution with very few exceptions, are to use fixed gain on-sensor amplifiers to just cover the signal path losses leading to the variable gain amplifier. If the exposure will be very low, then cranking up the gain will lead to more of that otherwise low gain aspect of the analog signal being amplified into the range of the ADC. The only down side is that the gain effects everything in the frame, thus some highlights or specular will be more likely to clip.
Some cinema cameras will use super high end ADCs that can effectively cover the full output range of the sensor, thus no need for actual ISO adjustments, and instead they will simulate the effect of ISO settings in post, (e.g., some of the RED cameras). Though they get insanely expensive.
With playing with raw files on sites like DPreview, I have yet to see a ILC camera that is anywhere near being ISO invariant, thus it is best to use the proper ISO for the scene you are photographing. With that in mind, there are exceptions. For example, since the VGA applies gain to the entire analog signal, you may encounter situations where you may accept extra noise in order to preserve certain highlights or brighter parts of a scene. In which case, when you have a good feel for how far you can push things in post for each ISO, you may end up doing things like using a slightly lower ISO in order to preserve certain brighter parts of the image, while leaning more on your denoiser for darker areas.
Say What? If I had to remember all that (Naruto Uzumaki) I would never enjoy taking another shot the rest of my life!
In practice is is simpler than it is to explain. Basically, you will get a feel for things with experience, such as if there is a venue you occasionally go to, as well as the limits of your camera. For example, imagine a scenario such as you regularly go to a specific venue, and you notice that some of the lights in a chandelier clip at ISO 1600, but can be recovered at ISO 800 on your specific camera. Then in that case, you may choose to use a lower ISO for the location, and recover things in post, as even for cameras that some have touted as being very ISO invariant, the sample raw files will show difference when you start pushing the recovery 4-5 stops in ACR, but such a difference can be compensated for with a slightly higher noise reduction setting in one of the more modern noise reduction plugins, thus in that scenario, a user may opt to just turn the ISO down slightly in that spot and fix things in post in order to preserve the highlights.
With many ILC cameras, you either see a single wide range VGA that will cover an entire range, or for more expensive cameras,you may see 2 or even 3 smaller range VGAs with lower noise floors (while it is hard to get much info for cameras, for RF and lab equipment where the data needs to be known, it is easier to see how variable gain amplifiers are handled. There are some with small gain ranges but lower self noise, and others with wider ranges but more noise, and highly specialized devices where there if a fixed gain and a $15,000+ ADC that can sample the entire range of the analog front end, where hardly anyone will purchase the equipment because the final device becomes prohibitively expensive. In the case of the cameras, you may choose choose to go to be beginning of a second VGA rather than staying near the end of the first, e.g. if a camera switched to the 2nd amp at ISO 800, then often you will see lower noise levels and better dynamic range at ISO 800 than at ISO 640.
Most mirrorless cameras are iso invariant. Like my Sony A7m3. Either under around 500 or over 500 iso. So you can expose so that highlights are preserved and lift the shadows in post. That’s something I care about. Still I have yet to see any tests where increased iso do not cater for more noice. Anyways I think a good photo is not a perfectly clean and ultra sharp image. But after fighting grain in the old days I kind of enjoy a modern digital camera. Anyways good advices from a expert. I don’t have much to back up what I am saying. Obviously correct exposed images and frozen action photos are the way to go. Still a little bit underexposed is not a a bad thing.
That would only work fully if a camera was purely using 2 separate fixed gain LNAs, If they are using variable gain amplifiers then limiting things to 2 gain settings only, would cause compromises on SNR. For example, Thy playing around with a bunch of the newer mirrorless cameras in this chart. https://www.dpreview.com/reviews/image-comparison/fullscreen?attr134_0=s...
and https://www.dpreview.com/reviews/image-comparison?attr18=lowlight&attr13...
Their test charts have long links, but the best you will find with current consumer camera tech are cameras where above a certain ISO, the noise stops changing because the camera has exhausted the analog gain, and is purely using "digital" gain which is essentially telling the ADC to just add multipliers to the values it is reading. which basically brings out no additional shadow detail, but sacrifices highlight detail when a multiplied value gets clipped to the max value the bit depth of the ADC supports (can be seen with some of the newer Hasselblad where after ISO6400, they stop applying additional analog gain.
ISO invariance isn't that high tech those days. My old a7 III does it in two ranges, one from ISO 100 and another from ISO 640. So if there are bright objects in the frame I just use those two ISOs. I wish there is an auto ISO mode that uses only those two.
The premise of the video is based on a straw man because no one limits themselves to 100 ISO. At least I have never heard of anyone doing so, and I talk with many photographers on an everyday basis and watch and read photography content dozens of times every week. I have never even seen it suggested that one should use base ISO - never not once in the digital age have I seen any such thing even suggested!
I hate to be "that guy," but I disagree. The lowest native ISO should always be the default ISO unless a special circumstance requires a change. Even in low light, using a low ISO with a longer exposure time will give better results than cranking up the ISO with a shorter exposure time. Especially in regards to ISO noise. The exception being that a higher ISO and wider aperture being needed to freeze motion, or the photographer desperately needs to quickly capture the moment and has no time to spare. A lower ISO will also give you more latitude for shadow/highlight recovery in post production. This is especially powerful when combined with exposure compensation. Even on cameras with dual native ISO, the base ISO will still give less noise than the secondary native ISO. There are certainly times when a higher ISO is necessary. You should use whatever ISO gets the job done, but the base ISO should always be the default.