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  1. #1
    Senior Member

    "Automagic" ISO setting on a DSLR

    In the old film days I would select my film based on ISO. Perhaps 100 or 200 when I wanted detail - low graininess, 400 for general snapshot sort of pictures and a 800 or higher if I needed to shoot in low light or fast moving subjects. I set the film's ISO on the camera and usually shot in aperture priority mode. With my new D3400 I also tend towards aperture priority and allow the meter to set the shutter speed.

    However, on the DSLR I observe that the ISO fluctuates wildly. 100 to 26,500! With film, the ISO represented the sensitivity of the film to light. Higher ISO, more sensitive but larger grains. This was a physical characteristic of the emulsion on the film. I am trying to understand what the ISO means on a DSLR? Obviously I am not changing the number of pixels on the sensor (I don't think). I am looking to learn and get my head around this.

    And should I lock down the ISO rather than let it run wild?

    TIA,

    Ken


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  2. #2
    Senior Member
    Texas's Avatar

    Re: "Automagic" ISO setting on a DSLR

    You are on "iso auto". Turn it off, then pretend you are back in the film days.

    Pick and lock in an iso value that you want.
    D750, D90, D100, Nikon 1 J5
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  3. #3
    RIP :(
    Don Kuykendall's Avatar

    Re: "Automagic" ISO setting on a DSLR

    Quote Originally Posted by taylorkh View Post

    And should I lock down the ISO rather than let it run wild?

    TIA,

    Ken
    Auto ISO can be a great tool. You do not say which camera you are shooting since it is not in your profile. You can limit the range of your ISO in Auto. Depending on what I am shooting I set mine to a max of 1200. With my D750 that is still a good look.

    ================================================== ============================
    D750***D7100***24-120 f/4 ***70-300***Tamron 150-600***Tokina 16-28 f2.8***50mm f/1.8***Photoshop/Lightroom CC

  4. #4
    Senior Member

    Re: "Automagic" ISO setting on a DSLR

    Thanks folks,

    The camera is a D3400 - and I was a little dyslexic when typing the max - should have been 25,600 not 26,500 - not that it really matters.

    I have been doing some digging in the manual and poking around the menus. I found this statement
    (choose lower values to prevent noise (randomly-spaced bright pixels, fog, or lines)
    OK but I still cannot relate that to film characteristics.

    I also learned a bit about how the auto ISO will vary the ISO if the value I chose (currently 400) will not provide the optimal exposure. I also learned that I can set a maximum auto ISO - just set this to 1600.

    With these settings and auto ISO turned on I THINK that the ISO can vary from 100 to 1600 in P, S, or A mode. The manual says M mode as well. I thought that M meant MANUAL EVERYTHING but I guess not.

    However, I have not figured out if setting the default ISO value serves any purpose when the camera is in auto ISO mode and will vary the ISO to its liking.

    This section of the manual is not very clear.

    Thanks again,

    Ken

  5. #5
    RIP :(
    Don Kuykendall's Avatar

    Re: "Automagic" ISO setting on a DSLR

    The M mode is one of the great things about Auto ISO. I use that when I am shooting birds in flight. I want f8 @ 1/1600 sec so I set that and let Auto ISO give me the correct exposure.


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    ================================================== ============================
    D750***D7100***24-120 f/4 ***70-300***Tamron 150-600***Tokina 16-28 f2.8***50mm f/1.8***Photoshop/Lightroom CC

  6. #6
    Senior Member
    Needa's Avatar

    Re: "Automagic" ISO setting on a DSLR

    Quote Originally Posted by taylorkh View Post

    I have been doing some digging in the manual and poking around the menus. I found this statement OK but I still cannot relate that to film characteristics.

    Ken
    It isn't the same as film. ISO in a digital camera is an amplification circuit. The sensitivity of the chip does not change. The signal coming from the chip gets get increased. When this happens the noise is also increased. It is similar to film in that by increasing the setting it will allow you to increase the exposure or keep a higher shutter speed or a smaller aperture opening (higher F number) while maintaining the same exposure
    Last edited by Needa; 07-22-2018 at 05:12 AM.
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  7. #7
    Senior Member

    Re: "Automagic" ISO setting on a DSLR

    Quote Originally Posted by Don Kuykendall View Post
    The M mode is one of the great things about Auto ISO. I use that when I am shooting birds in flight. I want f8 @ 1/1600 sec so I set that and let Auto ISO give me the correct exposure.


    Sent from my iPhone using Tapatalk
    This exactly. Though I use Auto ISO in Aperture Priority all the time as well.

    ISO in the digital realm is a measure of amplification of light information after the sensor processes it. All current Nikon models have a "Native ISO" of 100, meaning that what you get at ISO 100 is pure from the sensor with no amplification. If you think about amplification in musical terms native ISO is where a guitar amplifier is delivering full, pure tone from the instrument with no distortion (i.e. "noise") of the signal. As you increase the volume (i.e. go to higher ISO values) from that point the signal will begin to distort (i.e. get noisier). How much depends on the amp/camera. Some begin to distort quickly, others may take some time, but at some point they'll all get noisy. I've found most current sensors to be really good through about 6400 depending on the amount of detail in the frame. My first Nikon, a D7000, couldn't go past 1600. My D750 can do 6400 easy. My D500 can get there as well, but for birds I don't like anything above 4000 and prefer to keep it at 3200. I should add that many cameras allow you to go below 100 which is attenuation instead of amplification. Again as with an amplifier you will lose something when you do it, the question is whether you even notice it and whether it can be dealt with in post.

    Speaking of which, all this assumes you're shooting RAW, which you should. All the time.

    With each camera I have I decide what the maximum acceptable ISO setting is for whatever situation I'm in and then I program the Auto ISO settings so that they do not exceed that while also capping the shutter speed in a way that guarantees I don't accidentally blur the photo by moving while shooting in Aperture. That leaves me to concentrate on the shot instead of the camera.

    Does that make me less of a photographer? Don't know, don't care. Are Formula One drivers today lesser drivers than those who pioneered the sport with lesser cars and manual everything? Are golfers today less talented than Jack and Arnie because they have more forgiving equipment? Honestly, who cares.

    I think anything that allows an artist of any type to concentrate on the result instead of the tools used to create it is a good thing. Sure using a DSLR is easier, but so is just about anything these days. For film photographers I can see how features like this can make you think less of the skill of the photographers using it, but for me it's all about a tradesman with a tool thing - when you're given a tool you learn how to use it to its fullest.
    Last edited by BackdoorHippie; 07-22-2018 at 01:15 PM.
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    Jake

    The imitator is a poor kind of creature. If the man who paints only the tree, or flower, or other surface he sees before him were an artist, the king of artists would be the photographer. James McNeill Whistler

  8. #8
    Staff
    Super Mod
    hark's Avatar

    Re: "Automagic" ISO setting on a DSLR

    Quote Originally Posted by BackdoorHippie View Post
    Though I use Auto ISO in Aperture Priority all the time as well.
    I rarely use Auto ISO only because I was a staunch 35mm film lover. In fact, I can't even wrap my head around how Auto ISO would work in Aperture Priority since the body changes the shutter value to compensate for a correct exposure. I know what I'm gonna look up online. Thanks for your detailed explanation.
    Cindy
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    and My 2019 Thread

    Where the Spirit does not work with the hand, there is no art
    -- Leonardo da Vinci



  9. #9
    Senior Member
    pforsell's Avatar

    Re: "Automagic" ISO setting on a DSLR

    Quote Originally Posted by taylorkh View Post
    With film, the ISO represented the sensitivity of the film to light. Higher ISO, more sensitive but larger grains. This was a physical characteristic of the emulsion on the film.
    To be more exact, the ISO of films represent the combination of the emulsion + the developing. Some companies sell/sold the exactly same film emulsion with different speed ratings (Ilford, for one), where the only difference was the recommended developing. (I'm not talking about push/pull processing, but the actual ratings printed on the film box.) One might think the camera ISO as being part of the developing - just like it is with films - and in this sense the digital and analog ISO speeds differ very little.

    Quote Originally Posted by taylorkh View Post
    And should I lock down the ISO rather than let it run wild?
    There's situations where one scenario is better than the other. In a wildly changing lighting Auto ISO might be useful. In constant lighting perhaps manual setting is better - I trust my own judgement better than the camera's.

    In any case, I think that ISO last is the preferred approach. First determine your DOF requirements and action stopping requirements, and set aperture and shutter speed accordingly. If this leads to low exposure, then adjust ISO upwards as much as you can while taking care to not clip any important highlights in the image. This approach goes by the name ETTR, expose to the right, where the "right" refers to the histogram display of your camera.
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  10. #10
    Senior Member

    Re: "Automagic" ISO setting on a DSLR

    Thank you all for the great information! This is starting to make sense.

    As to Jake's comment about Formula 1... F1 is something which does NOT make sense. Given a clean sheet of paper and the rules that the car must have 4 wheels and a driver... any competent F1 designer could easily produce a car which a human being could not drive on the track. Too fast for human reflexes and generating so much G force in braking and cornering that the driver would loose consciousness. To alleviate this the sport has incredibly complex rules which result in very overpriced cars which the lower tier constructors cannot afford and which cannot get close enough to the car they are chasing for any real racing. The results are by and large boring!

    So, even though active aerodynamics are banned, DRS was added back. Ground effect skirts are banned so we have wings which are so complex (and ugly) they only work in clean air. The "steering wheel" is a computer console and the driver has to worry about conserving tires. Rubbish. Refueling was banned (for politically correct reasons I guess) but it was a great source of entertainment. The last year of refueling (2010 I thnk?) Ferrari had a remote control "lollipop" to release the driver from the pits. It was controlled by someone in Marinallo I guess. But the remote person really did not have a good handle on things in pit lane. They would routinely send out the car with the fuel can attached, the fuel man attached, run over another team's fuel man etc. Exciting!

    Off my soapbox now And thanks again for the great information on DSLR ISO.

    Ken





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