Photography - Optimum ISO Settings in Low Light

just answering another photography question. i just held my first photography class last weekend, which is why i am getting questions recently. again if this isnt something you are interested in, just check out this pic of aiden getting ready to party on new years eve!



so hb asks:

"I have questions regarding ISO and outdoor night shooting or low light settings (for instance low light indoors). Like what's the best ISO to achieve a clear photo. At the same time I know that too much ISO will make the photo grainy so what's a good balance? Is this even possible or do we have to have a good light source to achieve a good photo?"

quick review... ISO is the sensitivity of your cameras digital sensor to light. you can also think of it as light amplification... raising your ISO amplifies your available light. remember that raising your ISO to increase available light also increases the noise/grain in your picture.

to answer her question, the best ISO to use is the lowest setting that gives you a fast enough shutter speed to avoid blur. remember that when it starts to get darker, your camera will have to use longer shutter speeds to gather enough light for a proper exposure. as it gets darker and your camera needs longer and longer shutter speeds, you will get to a point there the shutter speeds are so slow that they will capture too much movement, which equates to blur in your picture. this is when you want to raise your ISO.

so... say your shooting outside with plenty of light. say youre at ISO100, your aperture is wide open at f1.4 aperture, and your shutter speeds are at like 1/500 second. 1/500 second is very fast shutter, fast enough to freeze motion of whatever youre shooting. now say you go inside the house, still at ISO100, f1.4 wide open, but now since its darker your camera needs 1/15 second shutter speed. thats pretty slow, and your pics will probably come out blurry because the camera will record the shake of your hand. if you remember my rule of thumb, if youre shooting with a 50mm lens, you need at least 1/50second shutter or faster to freeze the shake of your hand and avoid blur. so heres what your are looking at:

ISO 100 f1.4, shutter speed required is 1/15... too slow you need 1/50. increase your ISO

ISO 200 f1.4, your shutter speed will now be 1/30... stil too slow again you need at least 1/50. increase ISO again

ISO 400 f1.4, your shutter speed will now be 1/60... this is fast enough its faster than 1/50, so now youre good!

so ISO 400 is the lowest ISO that will give you a shutter speed of 1/50 or faster, in this case it gives you 1/60 second.

there are times when you want to have blur in your picture for artistic purposes, in which case the above information doesnt apply. say youre at a train station and want to use a longer shutter speed to make the people blurry, which implies their motion. or you may be doing long exposure photography, which requires a tripod. the fair at night is a fun place to do long exposure photography. the picture below used tripod and a 6 second exposure to capture the movement of the lights of the ferris wheel.



hope this clarifies thing a little better!