On this page, I take a look at the amount of noise introduced in images using various different ISO settings on the Sony A100 Digital SLR Camera. If you own a digital camera of any sort, you are probably already familiar with "noise" - this is the coloured splotchy appearance that occurs sometimes on pictures; most commonly seen in darker areas of the picture especially when taken in low light. Digital cameras are getting better at reducing this all the time - a lot of people rate Canon DSLR's (such as the EOS 350D) for being particularly good at producing low noise images (although some comparisons suggest the images are sometimes a little softer as well), whereas other brands are perhaps not so good. When Sony first brought out the A100, it was criticised for poor noise control, especially at high ISO settings. This page attempts to examine this by comparing shots where the only change to the camera was the ISO (of course the shutter speed is altered by the camera to expose correctly).

Noise occurs in images due to fluctuations in the signal coming from the cameras sensor. This can be due to the electronics in the camera, stray photons and all sorts of other factors. This means that each individual pixel has it's signal altered slightly from what it should be, leading to the coloured blotches.

A lower ISO setting means that the camera "records" the image for longer thus improving the signal to noise ratio (i.e. over a given time, the image you are taking forms a bigger percentage of all the data the camera sees, when compared to the little fluctuations that cause noise). A higher ISO setting is useful, because the shutter speed can be higher (shorter), but this means that the noise factor is much increased.

To get a lower ISO setting, without the shutter speed becoming so slow the image blurs, you have a few options. For 'static' scenes, mount the camera on a tripod. When this isn't possible, you need to try to get more light into the camera with all other things being equal. More expensive lenses are usually faster, meaning they let more light in, so you can use a lower ISO while keeping the shutter speed the same. Alternatively, better light (perhaps a flashgun or improved lighting of your subject) means you can achieve the same result. In addition, use a larger aperture on the lens (although this has the side effect of reducing the depth-of-field which, although often is a good thing, might not work for all situations). Finally, there are some software packages available that reduce the noise in images once on your PC, such as Noiseware from Imagenomic.

The images below were taken after mounting the A100 on a tripod and using a remote-release, so camera-shake shouldn't be a problem. The Swiss Army knife was placed on the table in a fairly dark room (lit only by a 40W lamp in the corner and a monitor that was also on). Asides from changing the ISO settings in between shots, everything was left the same. The camera was on "portrait" mode, and the images are camera processed JPG, not RAW. For each setting I have shown a fullsize crop of part of the image, and also a thumbnail link to the original full-size image.

ISO 100 - 5sec@F5.6

At ISO 100 the image is excellent, with rich, accurate colours. Noise is hard to spot.

ISO 200 - 2.5sec@F5.6

At ISO 200, noise is still very well controlled. The colours are different, however as white balance was on Auto, it could be a change in the image on the monitor altering the colour cast.

ISO 400 - 1.3sec@F5.6

At ISO 400, noise is still well controlled, but is becoming more evident, especially in darker areas of the metal, and also on the red plastic in the upper portion.

ISO 800 - 0.6sec@F5.6

At ISO 800, noise is more prevalent across the whole image. The quality is still good, and this image could be resized down for web use or printed at normal photo size without the noise being an issue. Larger sized prints would suffer though.

ISO 1600 - 0.33sec@F5.6

At ISO 1600, noise is very evident, although it could be said the grain in the image is perhaps not much different to using 1600 film. The colours compared to the first image are also much less saturated (although this could be amended in post processing).