Iso

Discussion in 'Digital Photography' started by Crager724, May 3, 2006.

  1. Crager724 macrumors member

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    #1
    I hate to sound like an idiot but I am wondering what the ISO setting does on my camera? I have seen this term used when comparing cameras. I have my camera's ISO setting set to Auto and it seems to work just fine. But I am curious as to what it does.
     
  2. Pistol Pete macrumors 6502a

    Pistol Pete

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    #2
    haha id also like to know...all i know is that i shoot at iso 400....
     
  3. Applespider macrumors G4

    Applespider

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    #3
    In very bright sunlight, you'd take pictures with the lowest ISO (50/80/100 on most cams) and a fast shutter speed. In overcast conditions, you're probably looking at 200 and darker than that, without flash, you may push it upwards.

    The trouble with most digital cameras (P&S at any rate) is that once you get above about ISO 200/400, they start to get very noisy so you see lots of grain in the picture. There are a few exception - Fujis seem to get a lot higher. I have an F10 that can go to ISO1600 and looks much better than my old Canon at ISO400
     
  4. tonyeck macrumors 6502

    tonyeck

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  5. Drizzt macrumors member

    Drizzt

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    #5
    Basically the ISO determines how sensitive to light the sensor (or film for our 35mm counterparts) is - the lower the number, the less sensitive it is. It is a great way to control exposurre without sacrificing the creative qualities of aperture and shutter speed.

    Quick question - do you pronounce it I-S-O or iso?
     
  6. mkrishnan Moderator emeritus

    mkrishnan

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    #6
    I think most people say "ISO" like Eye-So.

    On digital cameras, the setting essentially just adjusts the bias voltage on the sensor. :) Causes the sensor to conduct more per photon incident, and thereby show a brighter signal, but also more noise, because the pixels get activated by other garbage. :)
     
  7. Blong macrumors member

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    #7
    Hmmm - in Australia I have heard most people say I-S-O. Just like with film we used to say A-S-A.
     
  8. pdpfilms macrumors 68020

    pdpfilms

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    #8
    ok, a related question-

    I've been attempting to shoot some hour long+ exposures of stars with a digital. What would be the best setting to achieve optimal results? I attempted to shoot one at ISO 100, f/10 and the whole thing was covered with noise. For this frame I also had "long exposure NR" enabled, but it didn't seem to do anything. I'm scared that maybe dSLRs can't handle this, as leaving the sensor on for this long allows it to just generate its own noise that eventually overpowers the picture itself. I mean, you couldn't even see the stars behind this mutli-colored haze.

    Has anyone succesfully shot long-exposure star shots on a dSLR (more specifically, a Nikon D2x?)
     
  9. mkrishnan Moderator emeritus

    mkrishnan

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    #9
    Mmmm, that's a good point. People here do definitely say A-S-A. But ISO is used in a lot of engineering contexts, and at least, the engineers I know, always say Eye-So.

    As far the stars question... sites like this one:

    http://www.stargazing.net/david/astrophoto/index.html

    Might help. But what you want is going to be hard, I think. :(

    Can you explain why you need an hour-long exposure? Can you do a series of time-lapsed, overlaid images at shorter exposures? You should be able to see what you're going to see within a few seconds of exposure. After that, to be honest, that noise you're getting is probably a combination of UV and X-rays and high energy particles and just noise light in the environment. And a digital camera is not going to deal with that well. :(
     
  10. pdpfilms macrumors 68020

    pdpfilms

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    #10
    The hour long exposure was an attempt to catch as much star drift as possible. I'm not sure if overlaying images would achieve the same stripey, fluid appearance. But that's a great site... i'll have to look into that more.
     
  11. mkrishnan Moderator emeritus

    mkrishnan

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    #11
    I think since the stars move relatively slowly, if you overlay a large number of short exposure pictures, with a short inter-picture spacing, you might just get it. But I haven't honestly ever done it, so I'm not 100% sure. :(

    If you do get it, you know you're obligated to post it here, right? ;)

    EDIT: This site seems good too: http://members.ozemail.com.au/~loomberah/
     
  12. pdpfilms macrumors 68020

    pdpfilms

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    #12
    Oh, of course!
     
  13. ChrisA macrumors G4

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    #13
    ISO is a measurement of senitivity to light

    With film, ISO is a measure of the film's senitivity to light. ISO 200 film is twice as sensitive to light as ISO 100.

    With a digital camera senitivity to light is simulated by adjusting the gain setting of an ampliphier. A CCD will have a fixed true sensitivity based of how it is made.

    "Exposure" is the product of the
    (1) effectiver diameter of the lens (bigger diameter lets in more light) and
    (2) The lenght of time the shutter is open (given more time, more light gets in) and
    (3) The senitivity of the sensor or film.
     
  14. ChrisA macrumors G4

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    #14
    First off all these leters stand for the names of large organizations that worry about stuff like if the screw threads in bolts will work with the threads in nuts and how we measure hardness of sheet metal and so on.

    Some years back the ISO apopted the ASA definition of film speed.

    Before this there were two common film speed systems "ASA" and "DIN" The first American and the other German. (Hense the "A" and the "D" in the acronym) Now we all use the same ISO International standard.
     
  15. Wes Jordan macrumors regular

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    Jan 4, 2006
    #15
    More likely it is proper to say I-S-O because it is an acronym. I haven't heard it any other way.
     
  16. Crager724 thread starter macrumors member

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    #16
    Thanks for the replies I should have said in my original post that I have a digital, point and shoot Sony. Sorry for any confusion. So I'm guessing that the more ISO settings a camera has the more you can do with it, in theory.
     
  17. bousozoku Moderator emeritus

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    #17
    The more settings provided, the more you should be able to handle different levels of light but as has been said, there is a point of diminishing returns where noise overwhelms your photo at high sensitivity.
     
  18. kd5boc macrumors newbie

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    May 3, 2006
    #18
    Actually they are better for star shots as the effect called "Reciprocity Failure" is much less evident. (Google it for the definition.) As far as noise, the only real noise comes in as a purple haze in a corner or edge, and can be removed by making a lenscap on shot for about 30 minutes or so, and subtracting that "noise image" from your real one.

    I have had a few shots over 15 minutes that turned out nice and bright, but fuzzy as I'm still trying to get the focus right on these. (Focusing at night SUCKS!)

    Your multicolored haze is most likely the stars themselves. 1 hour is EXTREMELY LONG for f/10 on a DSLR, and color sensors (unlike our eyes) will actually show the color in stars.


    EDIT: Since I read and found out you have apoint and shoot Sony, if the sensor is the standard tiny one, don't bother trying to shoot start longer than about 5 minutes. But even then the small sensors are VERY suseptable to noise...that's why DSLRs are nice!
     
  19. mkrishnan Moderator emeritus

    mkrishnan

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    #19
    Actually, I'm really sorry for being so tangential, because I think there's a piece of information we haven't provided you with that is really important to your original question.

    ISO sensitivity settings are standardized, in the sense that ISO 50 or 100 should be the same from camera to camera. What is not at all the same from camera to camera, is the amount of noise that will be generated at increasing ISOs. This is very dependent on the sensor the camera uses. So it really isn't the number of ISO settings a camera has that's a feature or perk in digital cameras...it's how quickly noise becomes a problem with increasing ISO.

    If you look at DPReview.com, you will see that, in their reviews of cameras (this is the best one I know for this particular purpose) they use a loosely standardized method of testing noise as a function of ISO setting. Look at a couple of cameras, particularly comparing a dSLR to a point and shoot, or even compare a Nikon and a Canon, and then I think it'll be clearer what I mean.

    But in answer to your original question, again, ISO-Noise relationship is much more important than the raw # of ISO settings, for most users.
     

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