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I was taking some test shots today indoors (decent amount of light) set the iso manually to 800 looked through the viewfinder and I was at 1/20 (I was using Av mode) bumped the iso to like 1000 and my shutter speed was like 1/80 i took the shot and I had a decent picture.

Question is does manually setting the iso vs auto iso (with a minimum and maximum iso) produce low noise?

Example: if i manually set my iso in AV mode will i get low noise instead of auto iso with a capped iso will I also get low noise? or are they totally different?

I asked this question here

Using Auto ISO when shooting

Looked at the answers but they didn't specifically ask or talk about settings the iso manually will lead to less noise or no noise at all

Answer that kinda talks about it

https://photo.stackexchange.com/a/126077/101502

There is only one issue with auto ISO and people who don't know how to use it. When setting the ISO manually you can limit the amount of noise in a photograph, but when your camera automatically sets the ISO, what it picks can be too high resulting in your camera producing more noise. To prevent that, cameras let you choose the maximum ISO it can automatically set.

So is setting the iso manually the way to less or no noise for photos?

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  • Peter Badida's answer contains potentially useful content that is missing from many other answers and comments. Whther it applies in the OP's situation is unknown to me. Sep 12 at 23:09
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TL;DR: In low light conditions, selecting manual or auto ISO is a decision about risks: having lower or higher noise vs. the probability of blurred pictures vs. time.


ISO, aperture, exposure time - these are the in-camera values that determine our photo. (Using a flash adds another one.)

It does not matter how the camera arrives at these values. E.g. ISO 400 is ISO 400, same noise level for the same conditions, no matter if you set it manually or automatically.

The question whether any given set of values (e.g. ISO 400, f/2, 1/60s) is optimal is highly subjective, because we can optimize for different things.

In fully automatic modes, the camera usually optimizes for a high probability of getting a usable photo. That is what we want for snapshots. We can't repeat the shot, we have to get it right the first time. We use "safe" values, or risk having no photo at all.

If we have a little more time, we can set some guidelines for the camera, we can set a fixed aperture or exposure time, a fixed ISO or a range of acceptable ISO values. That way, the camera can select values closer to what we see as the optimum. E.g. we can either set higher ISO, or risk getting more blurred images for a few good ones with less noise.

If we have a lot of time, we can select more or all values manually. We can do a lot of shots with the same values until we get one shot right. We can do a lot of shots with different values to find the best ones. And we know a few things the camera doesn't. E.g. that the camera sits on a wall or on a tripod and we can get away with lower ISO and much longer exposure times.

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No, there is no difference between Auto ISO choosing ISO 800 versus manually selecting ISO 800. The end result is the same: the photo is taken with an ISO value of 800.

Consider this scenario: You take a photo with your camera's fully automatic setting, and it selects an aperture of f/16. You then switch to Aperture Priority mode, manually select f/16, then take a photo of the same scene. Will the depth-of-field be different between the two? No, because f/16 is f/16, regardless of "who" selected it.

As a side note, this answer has a good discussion on ISO values between the standard full-stop (100, 200, 400...) values if you have a Canon. In this case, manually setting the ISO may be helpful to reduce noise by avoiding the noisier ISO values. (But note that even here, a photo at the same settings will have the same noise. By taking manual control, you're simply avoiding Auto ISO choosing a "bad" or noisier ISO.)

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First there is no such thing as "no noise". Even on base ISO you have noise in the photos.

And set ISO manual do not reduce noise. If you have two photos, one with auto ISO 100 and one with manual ISO 100 both with have (relatively) the same amount of noise. Manual setting of ISO will help you when the camera "decided" to set higher ISO to keep the rule: shutter speed = 1/focal length (this is to avoid motion blur when handheld the camera)

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You are muddling two things:

  • The particular ISO value chosen (100, 200, 1200, etc)
  • The way of choosing that value

It is the value chosen which affects the amount of noise: a high value is more likely to have visible noise, because it is trying to amplify small differences in light to make them visible. A similar kind of noise would appear if you under-exposed the image and then boosted the brightness in post-processing. Essentially, the noise is always there, but by amplifying it you make it more visible.

The flip side is that a low ISO value requires more light for the same exposure, which means you need to use a larger aperture (with the corresponding loss of depth of field) and/or a longer exposure (with the corresponding risk of motion blur). So a decision has to be made for each photo which balances these properties.

All "auto ISO" means is that rather than you making this decision, an algorithm in the camera's software makes the decision. Some cameras give you some input to that algorithm (e.g. a maximum ISO), or have multiple algorithms (e.g. some Panasonic cameras have both "Auto ISO" and "intelligent ISO"), but none have the artistic and situational awareness of a human to know which ISO works best in a particular situation.

The advice to "avoid auto ISO" is really saying "there is a good chance you will disagree with the choice the auto ISO algorithm makes". Alongside that is a separate piece of advice to avoid "very high" ISO settings, as the higher you push the gain, the more risk of noise spoiling your photo.

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  • Higher ISO settings do not cause noise. Less light allowed into the camera that makes high ISO necessary for desired image brightness is what causes noise.
    – Michael C
    Sep 10 at 7:52
  • @MichaelC My understanding is that noise is caused by attempting to recover picture information from very small differences in light, which are more likely to be random than larger differences. Letting the same amount of light onto the sensor and not pushing up the ISO wouldn't result in noise, it would result in a black image - the random differences would be ignored, but so would the differences caused by the scene in front of the lens.
    – IMSoP
    Sep 10 at 8:05
  • Which is pretty much what "for desired image brightness" directly addresses rather succinctly, wouldn't you agree? The advice to "... avoid very high ISO settings..." only applies if you have the ability to otherwise add more light to the exposure. Absent that ability, high ISO settings will often result in less noise than shooting with a low ISO and then pushing everything, including the noise, several stops brighter in post (which is what I see time & time again from those who think the ISO setting, rather than not enough light, is what causes noise).
    – Michael C
    Sep 10 at 8:12
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    @MichaelC Ah, I see what you mean. I've edited a bit more explanation into the first paragraph; do you think that's clearer?
    – IMSoP
    Sep 10 at 9:06
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    To be even more to the point, all photons are always noisy. We usually don't notice because we're usually sampling enough of them for things to average out, but when you're trying to extract an image from fewer photons, that randomness becomes more apparent. Lower ISO is not that unlike using an ND filter to smooth out running water.
    – Matthew
    Sep 10 at 15:09
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In short, manual vs automatic ISO setting has nothing to do with noise.


I'll try to give a short summary about how noise works, which you help you understand how much noise you will get in different situations.

How is ISO related to noise?

The ISO value that was used is a good indicator of how noisy the image is assuming that the photo was correctly exposed. This is why you hear that "high ISO = high noise" and "low ISO = low noise". But it is important to keep in mind that this applies only when the photo was correctly exposed (i.e. not too dark, not too bright).

Where does the noise come from?

From the above, you might conclude that you can control noise by setting a specific ISO. But stating it this way is misleading at best. Noise is not a consequence of the ISO setting. It is not even coming from the camera. Noise is inherently present in the light.* The relationship is as simple as this: "more light = less noise", "less light = more noise".

You control the amount of light reaching the sensor through the exposure time ("shutter speed") and aperture. For any given amount of light that was collected by the sensor, there is an ISO setting that will result in correct exposure (i.e. desired image brightness). If there was too little light (which also means high noise), you can compensate by setting a higher ISO. Therefore, both the amount of noise in the image, and the correct ISO value for proper exposure, are a consequence of how much light reached the image sensor.

In short: if you want less noise, find a way to let more light reach the sensor (bigger aperture, longer exposure time, or use a light source).

What happens if you set the ISO manually?

If you set the ISO to a low value manually, and let the camera determine the exposure time and aperture automatically, then one of two things may happen:

  • The camera compensates by increasing exposure time and aperture. Depending on the available light, you may be risking getting a blurred image due to camera shake. However, you will indeed have less noise.
  • The camera refuses to increase exposure time beyond a limit, and you get an underexposed photo. There is not enough light, so there is no way to avoid noise.

* This type of noise is called shot noise and it is the dominant noise source when working with modern cameras. Yes, there are other noise sources too, related to the workings of the camera, but as a first approximation you can ignore them.

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    Since you're getting into the fundamentals here, it would be interesting to add an explanation of what varying the ISO actually does do. My understanding is that it increases the gain of the sensor - effectively, measuring smaller differences in light levels; and that's why it is more susceptible to noise - the noise which was already present is amplified by the increased gain.
    – IMSoP
    Sep 10 at 12:00
  • @IMSoP: A simple way of thinking about ISO is that it increases the amount by which each photon detected in a pixel will boost the brightness thereof. If one is doing X-ray photography of a live subject and needs to minimize the number of photons to which the subject is exposed, and one wants the plate to be 10% exposed when 1,000 photons hit each square centimeter, then each square centimeter of a 10%-exposed plate will have about 1,000 small dark spots in it. If one pushed the developing so that 1,000 photons/cm2 would yield 50% exposure, there would be 1,000 bigger dots.
    – supercat
    Sep 10 at 18:01
  • "Noise is present directly in the light." I think this needs better explanation. From this one it looks like it's a part of the light as in the particles that reach the sensor which I doubt is the case. Rather particles in the environment (in & out of the lens) coliding with them, sensor not being able to capture every photon, the rest of the electronics corrupting the data, etc. Feel free to correct me or elaborate more. +1 though Sep 13 at 15:55
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    @PeterBadida I thought it would have taken too much space to go into the explanation. This is why I just put a footnote with a link to the Wikipedia page for shot noise. The idea is that light is not flowing in continuously as water would, but in discrete units (photons), as grains of sand would. If you are pouring sand at the average rate of 3 grains per second, that does not mean that every 1-second long interval will have exactly 3 grains. Some will have none, some 1, 2, 3, 4, 5, 6, etc. While the average is 3, there is a lot of variation. This variation is the noise.
    – Szabolcs
    Sep 13 at 16:21
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With some older Olympus point-n-shoot and older Canons I've seen a difference between auto-ISO (or even full auto mode) using non-standard values such as 1600 vs 1643 in the EXIF.

I haven't seen the software that's responsible for it and it might be just some bug, but that's pretty much the thing that comes to my mind. In that case using manual to fit into the standard values might be "better" matching the rest with shutter and F.

It might be that the function responsible for the calculation of ISO:

  • calculated on more granular level - which may introduce less/more light (therefore noise) thus manual mode might use a slightly worse/better exposure,
  • or used the standard value internally, but wrote the granular result to EXIF - a bug

Other than that, I can't see any difference between auto-ISO vs manual ISO if all other factors are kept constant. In you change the rest, well, it's not auto-ISO vs ISO question anymore.

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  • This answer contains potentially useful content that is missing from many other answers and comments. Whther it applies in the OP's situation is unknown to me. Sep 12 at 23:08
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No. An ISO sensitivity produces the same amount of noise whether it is set automatically or manually.

Manually controlling ISO allows you to choose a better ISO for the same scene as the camera. Most cameras respond to low-light conditions by raising the ISO to prevent motion blur from subjects, the photographer or both, and some cameras allow their exact behavior to be customized.

When you are in control of the ISO, you can deliberately select a lower shutter-speed than the camera would. This lets you use a lower ISO and therefore capture an image with lower noise. If you are operating a camera with image-stabilization or with a stabilized lens attached, then you can get sharp images at much lower shutter-speeds as long as you are capturing a still subject. Even then, you can decide to tolerate or purposefully select a shutter-speed than shows motion blur for artistic reasons.

Another less known point is that most Auto ISO systems select sensitivity in 1/3 stops while camera sensors do not have a completely linear correspondence between ISO and noise. This depends on the particular sensor and whether all gain is applied before Digital-to-Analog conversion or not. Modern sensors with Dual-ISO design also have a level at which noise reduces despite ISO sensitivity being higher. By knowing your camera, you can make better choices when selecting the ISO sensitivity.

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  • You said when I manually choose the iso i can change the shutter speed. Are you talking about manual mode? I know I can change all three ss, iso and aperture. But what about AV mode where the camera chooses the shutter no matter what your iso is at? Just wondering
    – JcbJoe
    Sep 14 at 4:33
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    All 3 exposure-parameters related for a given exposure. So, when you lower ISO, shutter-speed lowers automatically to compensate if you are in Aperture-Priority mode. If you are in Shutter-Priority mode, then you can select a lower shutter-speed yourself and the aperture will open wider (until the maximum of the lens and further you will get under-exposure). In Manual mode you control all 3, so you have to compensate yourself to maintain exposure. Most cameras have a Program-Shift mode that allows you to change the balance of aperture and shutter-speed in Program mode too.
    – Itai
    Sep 14 at 5:04

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