Understanding ISO

Myky D

Myky D

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This is the bit that really gets me - I seem to have broken a tooth on it or something because the mental cog just keeps slipping.

The other day I was in Canterbury Cathedral togging, and so bumped up the ISO to the max on my Canon 450 - I think it's 1400. The pics came out noisy.

I dropped it down to 400, they came out soft to the point of blurry.

This was using the largest apeture/fastest shutter speed I could.

Is there a really easy, bear-of-very-little-brain, hard-and-fast rule that even I would be able to use and apply to my photography? I thought it was:

Dark = high number
Bright = low number.

This doesn't seem to be the case.

Unless it's just me. And Shirley it can't be that.
 
It's just you! :)

You need to up the ISO if the light is poor - but you need a camera that can handle high ISO without noise. If you use a low ISO in poor light you'll be using slow shutter speeds and/or wide apertures and may get 'blurry' pics through camera shake or poor focussing/shallow DOF - unless you use a good sturdy tripod.
 
My guess is that by dropping the ISO you ended up with a shutter speed that was too slow for hand holding?

ISO, aperture and shutter speed all inter relate to each other.

A good and reliable rule of thumbs to eliminate camera shake is to make sure that your shutter speed is at least the equal of your focal length. So if shooting at 100mm, you need a shutter speed of at least 100th sec. Always use the lowest ISO you can and start increasing the value until you achieve the shutter speed you need. Remember that an under exposed shot will have more noise than a correctly or even slightly over exposed one.

HTH :)
 
Dropping the ISO shouldn't affect the 'sharpness' of the image... merely the noise levels - high ISO= noise
low ISO = smooth

Use a higher ISO when there's not enough light to get an exposure without camera shake...

Did you mean that when on 400 ISO you had such a low shutter speed that camera-shake resulted in a soft, blurry image?
 
You're pretty much there already - the ISO setting on a DSLR is analogous to the film speed on an analogue SLR...

Low ISO like 100-400 is used when you've got plenty of light - it gives the best, low noise images your camera sensor can detect but it's slow so when you took a handheld image inside the catherdral you got blur - the camera wasn't steady enough.
Can you check the exif data to see what speed you were using? I'm guessing it was slower than 1/60 so it's likely to be blurred.

Higher ISO (anything above 800 really) essentially increases the signal-to-noise ratio of your sensor so that it can expose quicker but at the risk of adding noise to the image although some of the newer pro-DSLR bodies out recently are getting amazing reviews for their lack of noise at high-ISO.
You can try to remove the noise by using tools such as Noise-Ninja.

You're doing the right thing by increasing the ISO to compensate for a low-light environment however perhaps you're expecting too much from it - for the best quality images you need a low ISO. This does have the trade off of forcing a slower shutter speed and the only thing you can do here is buy expensive lenses with even wider apertures or go with the easy option of using a tripod.
 
Worth bearing in mind that if you are using the 'shutter speed must at least equal lens focal length' rule mentioned above, you will need to add in the crop factor for your camera also, e.g. if you're using a 100mm lens and your crop factor is 1.5, you'll need a shutter speed faster than 150th, etc.
 
Not popular with many I know, but a tripod is a great tool for reducing camera shake and allowing low noise, sharp pictures.
 
try to optimise on an iso which delivers the quality you want
i stick to 64 and put up with its shortcomings on speed
carry a soft clean rag to use as a pad to steady the camera in low light situations

or a tripod..:D
 
I would say the highest ISO for the 450D would be 400 Max. Thats only from what I have heard from other people. There is also software like Noise Ninja. Anything more than 1/30 and you should be using a tripod.

There's a article in the June 2008 Digital SLR Photography all about ISO. About 4-6 pages of it. If you want I can scan you a copy if you want to read it.
 
clud17 said:
are they really that unpopular? i take mine everywhere with me, a simple 234 equation.
me 2 legs
tripod 3 legs
dog 4 legs

and my car is on its last legs!
Click to expand...

:clap::D:D

good old fido to the rescue
 
Andy said:
There's a article in the June 2008 Digital SLR Photography all about ISO. About 4-6 pages of it. If you want I can scan you a copy if you want to read it.
Click to expand...

I'd really appreciate a copy of this please Andy! Thanks!! :thumbs:
 
viewfromthenorth said:
Worth bearing in mind that if you are using the 'shutter speed must at least equal lens focal length' rule mentioned above, you will need to add in the crop factor for your camera also, e.g. if you're using a 100mm lens and your crop factor is 1.5, you'll need a shutter speed faster than 150th, etc.
Click to expand...

I didn't know that:shrug: Thanks:thumbs: Thats why it hasn't been working for me.
 
450D and the kit lens??

you can get away with ISO 400 or 800 in that environment if haev the IS version of the lens.
just cradle the camera properly, and breath out as you shoot. but check your shutter speeds
I agree with someone's comments about low ISO soft shots due to camera shake
post up some examples with the EXIF so people can help you a bit more
 
It sounds fantastic doesn't it increasing the ISO from say 200-400 ISO, but each doubling or halving of the ISO number only equates to one f stop. In practice that means if you were shooting at 200 ISO and gettig 1/60th at f8, you'd need to change the shutter speed to 1/125th at f8 or 1/60th at f5.6 to maintain the same exposure value.

Increasing the ISO is a necessary evil, forced on us by not having enough light in the prevailing conditions. What that usually means is we need to increase the ISO to get a fast enough shutter speed to eliminate camera shake and any subject movement.

Like everything else in photography it's a balancing act between what you'd like to do and what the prevailing light will allow you to do.
 
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