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How To's

Photography Fundamentals – How ISO Changes Your Photos

Published August 28, 2020

In recent weeks, I’ve started posting some fundamental articles on how to use your camera if you’re starting out. In the past couple weeks, we’ve discussed both how aperture affects your images, and how shutter speed changes your images, so today, we’re going to cover the final piece to that equation, with ISO.

But as a recap, lets first discuss what we’ve already talked about in previous articles. While all three of these settings will adjust your exposure, each one has a different additional change to your images. In the aperture article, we discussed how aperture would change your depth of field or focus on the focal plane. A larger aperture (or smaller number such as f/1.8, f/2.2 or f/4) will result in a smaller focal plane in focus, whereas a smaller aperture (f/11, f/14, f/18) will have a larger focal plane in focus. Shutter speed is going to cover the sharpness of moving objects. If you shoot at fast shutter speeds, such as 1/200th or 1/500th of a second, your moving object will likely have little to no motion blur, whereas slower shutter speeds (1/10th, 1/25th) will show more movement.

How ISO Alters Your Images

Your lens controls aperture, and its parameters will be dependent on the design of the optics in your lens. Your camera body controls your shutter speed, and those parameters are dependent on the specific camera. And traditionally, ISO was controlled by the film you were choosing for your camera. In that traditional sense, different film stocks would have different sensitivities to light – but in the modern era, it is now controlled by your camera.

And ISO is just that – your light sensitivity rating. Higher ISOs, such as ISO 6,400 or ISO 12,800 will have a very high sensitivity, allowing you to shoot in darker environments. Where low ISOs (ISO 100, ISO 200, etc) will have a lower level of sensitivity, and will typically be used in brighter environments. So why wouldn’t you just shoot using higher ISOs?

To put it simply, when you increase the sensitivity to light your camera has, you also increase the amount of grain and/or noise your images have. Higher ISOs generally mean a less clear image, with more noise (particularly in your shadows) and less contrast in your images overall.

ISO Examples

Here are some examples of different ISOs and how they affect the image’s colors and detail. These images were shot using the Canon 5d Mark IV.

The History of ISO

As mentioned above, ISO started in the era of film photography, and where the common phrase sensitivity got its start. In the film era, you would need to load your camera up with film to capture images. This strip of transparent film would be sensitive to light through the use of small silver halide crystals. The larger the crystals, the more sensitive to light the film would be, but larger crystals also means noiser images. These differences in silver halide crystal sizes would eventually be identified using the term ISO. ISO 100 would have very small crystal sizes, allowing you to capture a cleaner image overall, but need more light to capture that image. Whereas ISO 1600 would have a larger crystal size, and need less light – but would give you a noiser image.

Over the years, photography transitioned into digital photography, and film was no longer required to capture images – but the ISO moniker stayed. Now, ISO is dictated by your sensor’s sensitivity to light, not through the use of silver halide crystals, but by voltage. Though the general practice remains the same, the higher the ISO, the more sensitive your sensor is to light, but at the cost of more noise.

ISO Standards within Photography

Fortunately, because ISO is always evolving through digital camera technology, there is no standard in the level it can alter your images. Where shutter speed and aperture have been standardized for nearly two hundred years, ISO evolves with each new camera system. Theoretical limits have been passed, and some of the new cameras available now offer ISO up to 102,400 and beyond.

With each new generation of cameras, the cleanliness of the files at higher ISOs has gotten better, and what was once considered unusable, now is pretty clean images. Though the principle remains the same – if you can shoot at a lower ISO, you should.

As mentioned, this is just a fundamentals article on ISO. Certainly, there are a number of additional settings, such as Native ISO that will alter your images even further, but that goes beyond the scope of a basics article. 

 

And that pretty much covered the fundamentals of ISO. Do you have any questions or comments? Feel free to post them in the comment section below. And if you missed the first two parts of this series, be sure to read ‘The Fundamentals of Aperture‘ and ‘The Fundamentals of Shutter Speed‘ for more information.

Author: Zach Sutton

I’m Zach and I’m the editor and a frequent writer here at Lensrentals.com. I’m also an editorial and portrait photographer in Los Angeles, CA, and offer educational workshops on photography and lighting all over North America.

Posted in How To's
  • Thom Hogan

    Two problems with that idea. First, it just prolongs the myth that a sensor can be made more sensitive to light than it is, because people won’t understand that nuance. Second, by bumping gain to get higher DNs, you actually make the final data more prone to errors. That, too, is a nuance that people aren’t understanding, particularly when the “gain” switches from amplification to multiplication.

  • tmcgill

    So I do think there’s another consideration here if we want to be semantically correct. The word “sensitivity” essentially means, in typical human usage, something like “how much the output changes from a given change in input.” If we are talking about only the physical hardware of the sensor, sure, the sensitivity is fixed. But if we are talking about the entire sensor system, the whole block made up of hardware sensor plus gain/ADC/other circuitry, then the word “sensitivity” is entirely appropriate. For one setting, a small number of additional photons creates a small change in the output. For another setting, the same number of additional photons creates a large change in the output. it is not incorrect to label the latter system as more sensitive to its input than the former. I don’t think the involvement of gain, etc. should be left out of the picture, as without them the whole thing doesn’t even really make sense, but there is a reason people lean on the word “sensitivity” here and it isn’t entirely wrong.

  • George Theodore

    Isn’t it this simple? After aperture and shutter have completed their exposure role, our sensor converts photon information to electrical signals. These are then amplified according to our ISO choice before conversion to digital values.

    Why do we have noise (not grain) at higher ISO values? Noise is always present from various sources and especially from electrical signals. Because our “amplifier” doesn’t distinguish between “good and bad” parts of the signals, everything is amplified including noise.

    At lower ISO values we have high signal to noise ratios (SNR). As we get into higher ISO values the SNR drops.

  • Size of crystals, that makes sense. What about that ASA? ISO lived, ASA…no mention.

  • spider-mario

    ISO standard 12232 doesn’t say what camera settings like “ISO 102400” mean.

    Doesn’t this kind of do?

    Note 2 to entry: In DSCs employing an automatic exposure control system, the difference between the EI value used to capture an image and the sensitivity setting is called the “exposure bias”.

    —-

    A camera manufacturer who refers to “ISO 102400” is probably talking about either a Standard Output Sensitivity or a Recommended Exposure Index of 102400. Either way, they aren’t complying with ISO 12232 because ISO 12232 requires them to say which one they are referring to.

    They do, in the “SensitivityType” EXIF tag.

  • spider-mario

    ISO standard 12232 doesn’t say what camera settings like “ISO 102400” mean.

    Doesn’t this kind of do?

    Note 2 to entry: In DSCs employing an automatic exposure control system, the difference between the EI value used to capture an image and the sensitivity setting is called the “exposure bias”.

    A camera manufacturer who refers to “ISO 102400” is probably talking about either a Standard Output Sensitivity or a Recommended Exposure Index of 102400. Either way, they aren’t complying with ISO 12232 because ISO 12232 requires them to say which one they are referring to.

    They do, in the “SensitivityType” EXIF tag.

  • Kenneth_Almquist

    ISO standard 12232 doesn’t say what camera settings like “ISO 102400” mean.

    ISO 12232 defines “Standard Output Sensitivity” (abbreviation “SOS”) which is analogous to ISO speed for film. It also defines “Recommended Exposure Index” (abbreviation “REI”), although a “Recommended Exposure Index” is inherently subjective because it’s defined in terms of the exposure that makes photographs appear to be correctly exposed. It also defines a few other things which I won’t list because they aren’t used.

    A camera manufacturer who refers to “ISO 102400” is probably talking about either a Standard Output Sensitivity or a Recommended Exposure Index of 102400. Either way, they aren’t complying with ISO 12232 because ISO 12232 requires them to say which one they are referring to.

  • Leo Anthony Geis

    Please consider this another vote for retracting the article. ISO 12232 is reasonably explicit and authoritative. As previous posters have presented, teaching neophytes incorrect abstractions is counterproductive…and a consumer protection concern if one is charging for the instruction. Over the past few months I’ve witnessed self-certified “teachers” and “thought leaders” claiming that the ordinate of a photo histogram indicates dynamic range, that narrow-angle lenses “compress” distance…and that ISO is a part of exposure in digital imaging.

  • Verochka Tzimmermann

    indeed I wonder is lensrentals has a decent editorial policy to prevent certain people from “posting some fundamental articles” like the one in question…

  • Verochka Tzimmermann

    > Discussing ISO as sensitivity to light is a useful way to teach people how ISO will affect their images.

    the only useful way to teach people is to teach them how things really are

    > knowing the technical details of how a camera interprets a specific ISO setting doesn’t make you a better photographer.

    ouch, so misrepresenting things apparently does ?

    > Talking about gain or ADC doesn’t make it easier to understand

    make an effort

  • spider-mario

    It’s also kind of strange to imply that ISO hasn’t been standardized. What’s ISO 12232, then?

    Well, it’s a standard that implies that if an image has a reported ISO value of 102400, it means, more or less, that a mid-tone in the image corresponds to approximately 10???lx·s. That’s pretty much it, indeed no physical limit here.

  • Bruno

    Thank you for setting things straight, Thom. The propagation of this misconception is so annoying …

  • Or they might just ban you and delete your thread. Hope not.

  • Thom, someone downvoted you and I was wondering who the twit that does not understand simple science was. It was you?

    🙂

  • Thom Hogan

    The problem is the word “sensitivity.” Photo diodes have a fixed sensitivity, and the only variables that ultimately impact your image are: (1) amount of light; (2) aperture; (3) shutter speed; and (4) math used to convert what was captured into a pixel value.

    It’s actually important to know #4. Why? Because there are three different math points that cause different impacts. First is gain, which happens in the sensor, and is the least sensitive to producing downstream noise. It’s why you want to know where the dual gain point is on a modern sensor, because the two best results are obtained at base ISO and dual gain point. The second is ADC capability, which these days pretty much doesn’t enter the equation any more (e.g. Read noise is very low, low enough that it is no longer a prominent producer of noise). Third is post ADC math. Nikon is nice enough to tell you when they’re using post ADC math: they identify those ISO values HI and not with an ISO value. Post ADC math can be very problematic due to the math being used, and it produces visible artifacts, which we call noise.

    Proper noise management is, in the following order:
    1. Produce more exposure if you can (more light, open the aperture, lower the shutter speed).
    2. Use ISO with a native gain (base or dual gain point).
    3. Use numbered ISO values.
    4. Use HI ISO values.

  • Thom Hogan

    EXPOSURE is LIGHT filtered by APERTURE filtered by SHUTTER SPEED. That determines how many photons actually are present at the focal plane.

    ISO is not the sensor’s “sensitivity” to light. Sensors, like film, are fixed in sensitivity. X photons generates Y charge, period. (Technically, there’s another aspect involved, which is efficiency, as some sensors are more efficient at collecting the photons that are presented to them, but that’s a whole ‘nother can of worms to discuss, and not overly important to the ISO discussion.) The only thing ISO values does in a camera is change the math the camera uses on the Y charge. And that “math” is mostly comprised of two different things: gain within the sensor, and how the ADC deals with the charge.

    There is no “theoretical limit” to ISO. There IS a theoretical limit to photons (0 to the maximum charge storage the sensor’s photosites can handle).

    Most modern sensors have gotten to the point where “noise” caused by the electronic components is not the gating issue to “noise” in the final image. What you’re really seeing in low light photography is the randomness of photons.

    I agree with others, this article is misleading and should be withdrawn.

  • Franz Graphstill

    “Over the years, photography transcended into digital photography”

    I’m fairly sure that’s not the verb you intended.

  • spider-mario

    Discussing ISO as sensitivity to light is a useful way to teach people how ISO will affect their images.

    Is it? A lot of misconceptions seem to arise from it.

  • William H

    These articles are fundamentally misleading and should be retracted.

  • sir_c

    I agree on the first part, but a little less on the second. That part would fit in a more in-depth article on sensitivity though, because the story as it is suits best for basic understanding.

    For more advanced (edge) cases, it does help to know how the gain is implemented, because with the ISO-invariant sensors you can win quite some leeway. But yes, that is in-depth stuff, not for introductory blog posts.

  • Anun

    Not only ISO setting dosn’t alter sensitivity to light, there is no grain in digital. Teaching people incorrect reality does not help in the long run at all. Also, increase in ISO does not increase shadow noise – in fact the exact opposite tends to be true: at fixed exposure incresing ISO tends to reduce noise in the shadows.

    Even if the target audience is JPG-shooters, it is no good to teach them incorrect stuff as it is quaranteed to cause problems later on.

  • Josh Zytkiewicz

    Quit being so pedantic. Discussing ISO as sensitivity to light is a useful way to teach people how ISO will affect their images. Talking about gain or ADC doesn’t make it easier to understand and knowing the technical details of how a camera interprets a specific ISO setting doesn’t make you a better photographer.

  • Verochka Tzimmermann

    now that we know that “ISO” does not change any “sensitivity to light”… at best dialing a higher nominal ISO will increase a gain before ADC or switch extra sensel capacity off in dual gain sensel designs… or in some cameras at some nominal ISO ranges it will be simply digital multiplication post ADC and/or ISO-by-tag in a raw file… by “sensitivity to light” it is not… shame !

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