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Thread: Something about ISO I dont understand?

  1. #1

    Default Something about ISO I dont understand?

    Does higher ISO give you clearer pictures than lower ISO pictures or do they just give you the option to take photos at a quicker speed and reduce the quality of the photo. Please explain? Thanks

  2. #2
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    Default Re: Something about ISO I dont understand?

    ISO actually determines how sensitive your camera's sensor is to the amount of lighting present. Raising the ISO means you can take pictures in low light situations.

    For Example, you take a picture in a room using the same aperture and shutter settings, but one picture you use an ISO rating of 100 and the other you use an ISO rating of 1600, the 1600 will turn out brighter compared to the other picture.

    High ISO ratings are useful in other cases as well, for example, in order to correctly expose a picture, you need a shutter speed for 1/40, but you find that it is not fast enough for you as your hand shakes alot, you can actually raise the ISO rating and thus increase your shuuter speeds to maybe 1/60 and leaving the exposure level correct at the same time.

    But high ISO ratings are not all good, as you raise the ISO ratings, noise is introduced into your pictures. Higher ISO, more noise. If you do not know what noise is, just try taking a picture in your room with a ISO rating os 1600, and magnify the picture on your computer. You will see that the picture is somewhat grainy, that is noise.

    So to your question, yes ISO enables you to take pictures at a greater speed but at the same time, it sort of degrades the quality of the picture. It's not all bad though, sometimes in certain pictures, noise seems to actually look good. It all about your own imagination!

    I hope that I got all these correct, I'm just a newbie as well. Hope that I dont give you any wrong information =)

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    Default Re: Something about ISO I dont understand?

    If you've shot on film before you'll know what ISO is.

    ISO = ASA = Film Speed.
    As the name suggests, film speed is how 'fast' the film is. I guess you should have your basic theory down that the more light is that is taken in, the faster shutter speed you will be able to get, right?

    So, translating this to ISO, it means, with a higher ISO film (now simulated by boosting ISO levels on your camera), what you are doing is making the image plane more sensitive to light.

    The skinny: Higher ISO when there's less light, lower ISO when there's plenty of available light. On a bright, sunny day expect to use no higher than ISO200 (unless you want the grain/noise). On a cloudy day, ISO200 may still be used, but sometimes I go up to ISO400. I use the 30D which has 1/3-stop selection for ISO/shutter speed/aperture, which is really flexible. Indoors, depending on available light, the ISO speed usually fluctuates. I generally look for shutter speeds no slower than 1/25, because of motion blur (if you're shooting an event with people). In fact, 1/25 is very generous, normally motion is frozen at 1/40 or above (if it's an indoor event, not talking about sports or anything).

    So, on to some actual numbers. For example, I take a photo with 1/60, f/2.8, ISO100. By increasing the ISO speed by two stops, I can get the same photo with the same exposure at 1/250 (two stops faster), f/2.8, ISO400, or 1/60, f/5.6 (two stops) ISO400.

    However, because you are increasing the sensitivity of the sensor to light, your sensor will be more prone to producing noise, just like how if you raise the gain (mic's sensitivity to sound) too high on a microphone, there will be buzzing.

    Generally, Canon's later generation of DIGIC II processors and sensors handle noise very well. There is little noticable noise up to ISO800 most of the time. If you (or your client) like(s) the noise, then by all means shoot at high ISO speeds (but only if you want the noise or have no choice).

  4. #4

    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by Jiaqing View Post
    For Example, you take a picture in a room using the same aperture and shutter settings, but one picture you use an ISO rating of 100 and the other you use an ISO rating of 1600, the 1600 will turn out brighter compared to the other picture.
    Am afraid this is not very accurate because using 1600 vs 100 will not give you a "brighter" picture.

    For example, if shooting at 1/250 using ISO 200 is the correct exposure, you will find that you have to shoot at 1/125 using ISO 100. There is a physical relation but you will get the correct exposure, not brighter.

    A higher ISO is most commonly used to give you a faster shutter speed to enable good hand held shots. Even in bright daylight sometimes high ISO is used because the subject may be moving like shooting sports for instance.

    On film, higher ISO gives you less saturation and slightly more contrast. Digital is slightly different as these settings can be customised.

    Noise is also not quite the same as grain on film but commonly used as a comparison to explain the effect.


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    Default Re: Something about ISO I dont understand?

    For Canon's 5D ISO 50, not as good as ISO 100 in terms of IQ and you lose about a stop of DR for the whites. So in short, in general, higher ISO = higher noise, but there are some exceptions.

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    Default Re: Something about ISO I dont understand?

    think of this in the audio way:

    higher ISO = higher gain = more noise
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  7. #7

    Default Re: Something about ISO I dont understand?

    So Higer ISO gives you higher shutter speeds to avoid taking blur pictures for example in the dark am i right? But in exchange for noise. So lower ISO doesn't mean better quality pictures. One more question, does 400 ISO good for taking photos on film or is 200 better or do you decide which one according to the lighting conditions. Thanks for explaining

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    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by Anti-Social View Post
    So Higer ISO gives you higher shutter speeds to avoid taking blur pictures for example in the dark am i right? But in exchange for noise. So lower ISO doesn't mean better quality pictures. One more question, does 400 ISO good for taking photos on film or is 200 better or do you decide which one according to the lighting conditions. Thanks for explaining
    Hi Anti-Social,

    err....low ISO also means less noise/grain, and that means better quality (resolution) pictures, right? It's always better to take pictures in low ISO when possible. You can degrade (introduce noise) a high resolution picture but can't improve on a low resolution one.

    Same applies to film (unless you want the grainy effect). Better to use low ISO number films if possible. Yes, lighting considerations play a part in determining what sort of film you load into your camera. Once loaded, you're committed. There is a way of rolling up the film, changing film, and reloading it again, but you REALLY don't want to try that.


    Bernard

  9. #9

    Default Re: Something about ISO I dont understand?

    So I dont think i will be changing flims just for the sake of the iso . Thanks for the reply. By the way, why does the shop sell the high ISO films more expensive than the low ISO flims?

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    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by Anti-Social View Post
    So I dont think i will be changing flims just for the sake of the iso . Thanks for the reply. By the way, why does the shop sell the high ISO films more expensive than the low ISO flims?
    Why not? How do you think people covered events during the film days? It's not possible to use a single iso for both day and night most of the time. High iso films are more expensive probably due to less of them being made since most people (normal consumers) seldom use fast speed film.
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    Default Re: Something about ISO I dont understand?

    Yeah maybe. Even if I do change films, I would hardly change it to a higher ISO most likely a lower ISO flim. 200 seems very well balanced between 100 and 400. Unless its a 1. Important event 2. I have a tripod. By the way how do you tell to camera to wind to the spot where you left off? If some "error" occurs will the pictures be destoryed? Thanks again

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    Default Re: Something about ISO I dont understand?

    I believe you can't 'resume' a roll of film. You have to

    1. finish shooting it.
    2. rewind at the point where you want to stop, and not reuse it anymore.

    I may be wrong(?)

  13. #13

    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by Anti-Social View Post
    Yeah maybe. Even if I do change films, I would hardly change it to a higher ISO most likely a lower ISO flim. 200 seems very well balanced between 100 and 400. Unless its a 1. Important event 2. I have a tripod. By the way how do you tell to camera to wind to the spot where you left off? If some "error" occurs will the pictures be destoryed? Thanks again
    Quote Originally Posted by calebk View Post
    I believe you can't 'resume' a roll of film. You have to

    1. finish shooting it.
    2. rewind at the point where you want to stop, and not reuse it anymore.

    I may be wrong(?)
    I used to switch films between cameras during the film era. Here's how I did it:

    1. note the shots taken as shown in film counter. Manually unwind and stop when u "feel" the film leader had dislodged from the receiving sprocket.

    For PnS with auto rewind, u will "hear" a soft click when the film leader dislodge from the receiving sprocket and u must then instantously open the backcover or battery cover to stop the rewinding. If u missed it, the film leader will be totally wound into the canister and there's no way to take it out to continue the re-use of the unused portion again.

    2. to re-use the roll again, load it into any camera like how u would normally load a fresh roll. Put lens cap on and for better security, put camera into a bag and fast forward click to the last number of shots taken plus 2 extra blank shots for added assurance to avoid double exposure.

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    Default Re: Something about ISO I dont understand?

    Woah, clever man. Risk involved, though, so again, do at your own risk.

  15. #15

    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by calebk View Post
    I believe you can't 'resume' a roll of film. You have to

    1. finish shooting it.
    2. rewind at the point where you want to stop, and not reuse it anymore.

    I may be wrong(?)
    You can resume the film. Most cameras sllow you to rewind leaving the film leader out so you can pull it back out again. Just remmeber where you shot till then leaving the lens cap on shoot till you are the next blank frame to resume
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    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by calebk View Post
    I believe you can't 'resume' a roll of film. You have to

    1. finish shooting it.
    2. rewind at the point where you want to stop, and not reuse it anymore.

    I may be wrong(?)
    Hi calebk,

    in the old days (I sound old already.....hehe ), this is how it's done...

    Note the number of exposures used on your camera. Rewind the film. Use a special instrument to retrieve the film leader from the cassette, load the cassette as per normal and shoot with the lens cap on until you're about 2-3 frames ahead from where you left off. The extraction instrument can be purchased or manufactured at home (I have not tried this), buying is OK as it's very cheap.

    Told you guys you didn't wanna know......


    Bernard

  17. #17

    Default Re: Something about ISO I dont understand?

    Ouch that seem quite of a pain . Now I know how to change flims . Thanks again for explainin

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    Default Re: Something about ISO I dont understand?

    ISO = Image Stabilizer On?

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    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by wazzup View Post
    ISO = Image Stabilizer On?
    waa sweeeee... i got 1600 stabiliser on my cam

  20. #20

    Default Re: Something about ISO I dont understand?

    Quote Originally Posted by wazzup View Post
    ISO = Image Stabilizer On?
    not OFF meh ?

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