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01-01-2011, 07:10 AM   #1
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Oh My...

Right I need ISO explaining in a simpleton way. I understand 100 iso is good on sunny days but what about 200,400 etc. Sorry if this is a dumb question guys.

01-01-2011, 07:20 AM   #2
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The short and pragmatic answer: since turning up ISO results in more noise you'd normally want to use as low a value as the available light permits.

A dumb question is the one not asked :-)
01-01-2011, 07:23 AM   #3
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So would it be a good idea to try and use between 100 and 400 as a rule?
01-01-2011, 07:28 AM   #4
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QuoteOriginally posted by fourfivesix Quote
So would it be a good idea to try and use between 100 and 400 as a rule?
In general, you want to keep the ISO value as low as possible to maintain the highest possible image quality (lower noise, higher dynamic range, better colors, etc). However, if there isn't enough light, keeping the ISO value too low will result in a shutter speed that might be too low (assuming you are hand-holding your camera). This will often result in a blurry photo. So it's a balancing act to try to raise the ISO levels to a point that gives you a sufficiently short shutter speed for the aperture you are shooting at.

EDIT: Which body are you shooting with?

01-01-2011, 07:35 AM   #5
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Its a k200
01-01-2011, 07:42 AM   #6
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QuoteOriginally posted by fourfivesix Quote
Its a k200
I haven't actually used a K200D, but from what I've read (and my 3 years using a K10D, which should perform similarly), you could probably shoot at 800/1600 if you are careful to exposure properly. You'll certainly get more noise at 800/1600 than 100-400, but that's usually preferable to getting a blurry shot if you don't have enough light to work with.
01-01-2011, 07:51 AM   #7
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QuoteOriginally posted by fourfivesix Quote
So would it be a good idea to try and use between 100 and 400 as a rule?
That's an old rule I think. The new generation Pentax cameras, K-x, K-r, K-7 sensors/software are much better at controlling noise at high ISO than earlier cameras. Therefore the upper limit of ISO for acceptable results has increased.

How high an ISO one can use is ultimately dependent on how the photo is displayed and what level of noise is tolerable for that display. However, it is not unusual for K-x users to push ISO to 1600-3200 with excellent results for electronic display.

It is pretty easy to determine for yourself what level ISO results in images "good enough" for your purposes. Just retake the same scene with increasing ISO & see which photos are ok.

The noise, focus, sharpness, etc requirements for acceptable electronic display are much lower than for large prints viewed close up, so there's nothing wrong with shooting for highest quality just in case you might want to enlarge or display in a more demanding medium.
01-01-2011, 08:10 AM   #8
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Four, as said, if you can get acceptable F stop for what you're shooting and shutter speed--not so much for handhold blur but for subject motion blur--use the lowest ISO you can.

But a good rule of thumb for you to up your ISO to say 800 when it's still fairly sunny is for fast moving objects. At a given F stop for various ISOs, say F8, you know that an ISO of 800 is going to result in a shutter speed 4 times faster than ISO 200.

It's not exactly a clean math equation like this, but it's the easiest way to explain it.

01-01-2011, 08:16 AM   #9
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How much noise is acceptable depends on the subject; for people snaps it usually doesn't matter too much, whereas a macro shot where the point is getting as much very fine detail as possible could be ruined at even moderately high ISO.
01-01-2011, 08:42 AM   #10
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some times it's too dark and people still want a pic they might use high ISO, a grainy picture is better than no pictures ... and normally depending on the camera, 400 is still pretty good, even 800 in these new cameras.
01-01-2011, 08:47 AM   #11
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So forgive my stupidity this is a long learning curve for me, the higher iso settings also let you use a faster shutter speed?
01-01-2011, 08:53 AM   #12
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QuoteOriginally posted by fourfivesix Quote
So forgive my stupidity this is a long learning curve for me, the higher iso settings also let you use a faster shutter speed?
it's just the amount of light enter.

for example. holding aperture constant.

shutter 1/40 ISO 100 = shutter 1/80 ISO 200

same amount of light going in, so to answer your question, yes.
01-01-2011, 08:58 AM   #13
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QuoteOriginally posted by fourfivesix Quote
So forgive my stupidity this is a long learning curve for me, the higher iso settings also let you use a faster shutter speed?
For the same exposure, yes.

To get a certain exposure, you are basically balancing three things; how large the aperture is, how long the shutter is open and the ISO (sensitivity of the sensor). So for example, if an image was properly exposures at f/4, 1/100s and an ISO setting of 200 you could increase both the shutter speed and ISO setting (by one stop) and get the same exposure at f/4, 1/200s, ISO 400. You basically have half the light hitting the sensor because the shutter was open for half the time, but you've made the sensor twice as sensitive by doubling the ISO setting.
01-01-2011, 08:59 AM - 1 Like   #14
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Here is a camera simulator that lets you see what happens when you change ISO, f-stop, and shutter speed.

Aperture, shutter and ISO value | SLR Camera Simulator

Tim
01-01-2011, 09:00 AM   #15
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Think of it this way:

F stop - how much light is let in from that available

Shutter speed - how long the light is let into the camera

ISO - how sensitive the sensor is to the light coming into the camera


Those three will control the various aspects of the image you see once you press the shutter button.

F stop will influence the depth of field (how much of the image from front to back is in focus) and sharpness to a large degree

Shutter Speed will impact how SHARP the image is - most folks can't hand hold at <1/60th without significant blurring for example -

ISO will impact how grainy the image looks. Lower ISO numbers mean more smooth images while higher ISO means more sensitivity but also more graininess to pictures (potentially but in reality almost always)

All can be varied in M mode and Auto control much of this for you. Basically, sunny day, good light, ISO 100-200 for everything outside. Inside taking shots of a kids basketball game under mediocre lights may mean using ISO 800-3200 to get shots that stop the action.

I was always taught to decrease the f-stop first to increase the shutter speed and only if that was not enough to then increase the ISO. Getting a sharp image is the first goal, if its sharp you can clean up a lot of noise (graniness) with post-processing I'm learning.

Hope that helps a bit. CNET has a video that takes a stab at ISO as well:
Please Explain: ISO - Digital Cameras
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