Digital Photography ISO

Discussion in 'Articles of Interest' started by VidThreeNorth, Aug 8, 2018.

  1. VidThreeNorth

    VidThreeNorth No longer a newbie, moving up!

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    This is something I have been struggling with, and after reading this article, I'm still struggling. I "grew up" in film and I understand film ISO. I also understand the basics of electronic sensors. So I should see a digital ISO and know what it is telling me, right? Well, I really don't. I just use it like I was using a film camera as best as I can.

    "You probably don't know what ISO means – and that's a problem" Published Aug 6, 2018 | Richard Butler


     
  2. jcdeboever

    jcdeboever TPF Supporters Supporting Member

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    Digital ISO is similar to film. It is gain.

    When you need to gain shutter speed to meet your requirement. If your subject is stationary and your ISO is 200, your lens focal length is 50mm, happy with aperture setting for depth of field, and your proper exposure calls for 1/125s shutter speed, then your good. Same scenario but your subject is moving and you want to freeze the movement and you know you need at least 1/500s to do so, you will need to increase your ISO 2 stops, 800 ISO in order to gain up to 1/500s for proper exposure.

    That's how I look at it. I use it to gain shutter speed for double the focal length of lens when hand holding or when a subject is moving and I want to isolate the subject and movement.
     
  3. Ysarex

    Ysarex Been spending a lot of time on here!

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    Richard Butler can be obtuse at times and hard to understand, but he tends to be accurate.

    What camera are you shooting? That will help a lot.

    Joe
     
  4. snowbear

    snowbear fuzzy-wuzzy Supporting Member

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    or an amplifier - basically the same thing.

    Oh, and for the record, ISO refers to the "International Organization for Standards," the acronym actually derived from isos (Greek for "equal").
     
  5. VidThreeNorth

    VidThreeNorth No longer a newbie, moving up!

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    Uh, actually, this is what the article is getting at. No it is NOT necessarily "gain". It might be gain, but that is not specified. The only thing specified is that the JPEG output corresponds to certain expectations regarding the camera settings used when taking the picture. For example, if you look at a "RAW" file, it might simply be parameters set in a file header with no difference at all between the real recorded data from this group of settings and another.
    [2018-08-15 reformatted and clarified -- a bit.]

    . . .

    Yup. That's how I look at it too -- because that is all that I know about what is actually happening.

    Hmm. Good questions. I guess for the last year I have mainly used the Yi-M1 for stills, though I used a Sony a5000 quite a bit as well, and my Panasonic GF-3, and occasionally, other stuff. For the coming year, I think I will use the Yi-M1, Sony a5000 and the Olympus OM-D EM10. Oddly, after suffering through all the early firmware versions of the Yi-M1, the last version 3.1 is actually quite good for my needs. I think it is one of the best setup for use with adapted manual lenses around. And they probably released that firmware after the last of the bodies was already sold to an end user. I think I respect that much of their effort.
     
    Last edited: Aug 15, 2018
  6. Designer

    Designer Been spending a lot of time on here!

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    No.

    Understandable.

    Nope.

    ISO in film is related to the sensitivity of the film, however; ISO in digital is actually applied gain. Sort of like turning up the volume control on a stereo. Notice; it is applied to the data AFTER the data has already been captured.

    This implies that it has absolutely nothing to do with exposure, which it doesn't. The purpose of ISO in your firmware is for the camera's display to enable it to produce a viewable image for you to evaluate composition, histogram, and focus.

    Therefore; ignore the "exposure triangle" meme, and consider your exposure to be regulated by your aperture and shutter speed. You can let the camera select the ISO by setting it to "auto", which should give you a viewable image.

    Variables that affect exposure
     
    Last edited: Aug 14, 2018
  7. Ysarex

    Ysarex Been spending a lot of time on here!

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    Shadow Improvement versus ISO setting.

    The Sony and Olympus you noted are included in Bill's data base -- no Y1-M1. I added the Canon for comparison so you could see a situation where there's a big difference. Apart from the Olympus jump from base to ISO 400 both the Olympus and Sony tend toward ISO invariance. I believe I read that the Y1-M1 was built on a Sony sensor and so it would likewise tend toward ISO invariance.

    Raising ISO reduces dynamic range. Here's that chart: PDR versus ISO for the Sony and Olympus. The Olympus again show a bump between base ISO and ISO 400 that suggests the sensor may have dual impedance channels.

    DR dropping with increasing ISO is the opposite of film behavior and so the film analogy is weak. Film DR drops when it is pushed and that's a better analogy to digital ISO. Contrary to popular misunderstanding ISO does not increase the light sensitivity of the sensor. When circumstances require, raising the ISO reduces exposure to the sensor and we're simply left with less recorded data due to less exposure. ISO takes that less data and by one or another or combination of methods brightens it to the level required for a normal brightness photo.

    As Richard Butler explains the colloquial understanding of ISO's relationship with noise is fundamentally a misunderstanding. Noise in a photo can result from multiple sources some pretty esoteric like heat build up due to very long exposure. For most of us doing normal photography there are two noise sources in our photos; shot noise and read noise. The dominant noise source in modern cameras is shot noise and that is a function of exposure. Note for example the noise level in this photo taken at ISO 12,800: socks -- I exposed for minimal noise. The noise level is a function of the exposure and not the ISO 12,800 setting on the camera. Shot noise is in the light itself and the better the SNR (more exposure) the less noise and the worse the SNR (less exposure) the more noise.

    Read noise comes from the electronics in the camera and in the case of ISO the electronics that boost, gain, amplify, brighten, the sensor signal to the ADC. With each generation of new cameras we reduce or remove read noise from our systems (better engineering). That's what ISO invariance is all about. With todays modern cameras read noise is rapidly becoming a non-issue. Note that in the graph above I referenced an old Canon 5dIII to get a result that wasn't basically pretty flat. With read noise eliminated from our systems ISO can be thought of as only useful to the process of generating a camera JPEG of the required brightness (can't live without chimping!).

    Joe
     
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  8. VidThreeNorth

    VidThreeNorth No longer a newbie, moving up!

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    @Ysarex: Thanks for those links! I've had a lot of fun playing with the graphing functions. The Yi-M1 has the same sensor as the Panasonic GH5, and it looks like the same sensor is in the GX9, so I am using them to represent the Yi-M1.

    I get the distinct impression that Sony deliberately bypassed an upgrade to their Micro 4:3 sensor lineup. There has not been a true "back illuminated" Micro 4:3 sensor. That should have been the natural development step before the APS-C and Full Frame sensors. Yet magically, Sony was able to come up with APC-C and Full Frame back illuminated sensors (a6500 and the a7iii). Hmm...
     
  9. Ysarex

    Ysarex Been spending a lot of time on here!

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    The cost differential for BSI is leveling out but has to date remained a factor of consequence in determining the camera model price point where it is introduced.

    Joe
     
  10. vin88

    vin88 TPF Noob!

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    I know what ASA does for film. never knew what ISO did. now in the digital age, its point and shoot, dam the consequences.
     
  11. Designer

    Designer Been spending a lot of time on here!

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    Actually, when some of us try to create a certain image, we will use some or all the tools that were used in film technology PLUS any digital tools we need.

    Digital is not "better" in terms of image quality, but it certainly opens up many more possibilities than with film alone.

    The "point and shoot" folks haven't tried to learn photography, and assume (erroneously) that among the many images they capture, they will get one or two "keepers". This is like fishing with a net and hoping to catch a trophy. I think you can safely ignore the "spray and pray" crowd and their limited view of art and the world.
     
  12. Ysarex

    Ysarex Been spending a lot of time on here!

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    ASA? ....dam the consequences? WTF?!

    I started in photography when ASA was the film sensitivity standard here in the US. I've followed along and kept up through the transition to digital and continue to enjoy taking photographs as I did 40 years ago.

    Whatever it is that you're trying to say or comment on I suspect is predominantly your problem.

    Joe
     

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