High ISO speeds and Noise

[redruthann]

Hello again,

I am new to dslrs (Canon XTi) and manual photography techniques for which I have many questions...I'll post each separately (hope that's ok).

Please explain ISO speed, re higher speeds and noise.
I have not gotten the fstops down, but I experiment a lot - changing them to the exposure I want. But when I use 400 or more ISO, there's so much noise.

I have been taking pics of birds in my yard. Obviously they do not pose for you. I play with the f-stops and try faster ISOs. What situations use higher ISO speeds?

Using: Canon XTi; Sigma DG 28-300mm 1:3.5-6.3 - Telephoto/Macro

[Ian]

Re: High ISO speeds and Noise

Hello again,

I am new to dslrs (Canon XTi) and manual photography techniques for which I have many questions...I'll post each separately (hope that's ok).

Please explain ISO speed, re higher speeds and noise.
I have not gotten the fstops down, but I experiment a lot - changing them to the exposure I want. But when I use 400 or more ISO, there's so much noise.

I have been taking pics of birds in my yard. Obviously they do not pose for you. I play with the f-stops and try faster ISOs. What situations use higher ISO speeds?

Using: Canon XTi; Sigma DG 28-300mm 1:3.5-6.3 - Telephoto/Macro

Welcome to DPNow, Ruth!

In simplified terms, ISO speed is a representation of the sensitivity of the camera's sensor. The lower the number the lower the sensitivity, so ISO 100 means you need more light to obtain the correct exposure than, say, ISO 400.

The optimum ISO for your camera is usually the lowest number - if there is good brightness. You will need to raise the ISO to enable the camera to record correctly exposed images when there are lower light levels illuminating your subject.

The cost for raising ISO can be reduced dynamic range, lowered saturation and, most noticeable of all, increased noise - which looks like an unwanted graininess in your picture. You can lose resolving power too as one solution for addressing additional noise is to blur the image.

With your Canon XTi, (known as the EOS-400D in some countries) you should be able to get noise-free images at 100 and 200 ISO, and even 400. at 800, the noise will start to show.

To avoid having to use a higher ISO than you want, you will have to use slower shutter speeds, or wider apertures (f-stops) or use flash to supplement the available light.

Ian

[redruthann]

Re: High ISO speeds and Noise

PERFECT!
This has really helped.

[Pops]

Re: High ISO speeds and Noise

I also have the 400D and take hundreds of bird photographs.
I very rarely go higher that 200 with the ISO. At 400 the noise is very slight and can be removed easily but once you go above 400 you are looking at excessive noise. Here again it can be removed with editing software but it gets time consuming if you have a large amount of images to process.
I'm sure 200 will give you satisfactory results even on cloudy days.