Photography questions

[Rik Booth]

I have a Canon Ixus 500, which is great, but I do have some questions:

1. How does the ISO level affect a picture? Is it better to leave it on 'Auto'?
2. As a general rule, should I leave the exposure as 0?
3. Is shooting at resolution 1600x1200 sufficient? Anything bigger results in huge filesizes and means I have to keep resizing them on my PC.

Thanks in advance. :)

[paulsaz]

1 the lower the iso the less noise there should be in your image, unless you're happy messing with it leave it on auto, or experiment and see what you think.
2 hmm not sure what you mean exposure is a combination of the length of time the shutter is open and the different apertures of the lens to capture the image so for sports and fast moving items you use a short shutter time and to get a sense of movement (ie to make flowing water look cloudy) you would use a longer shutter speed. Aperture affects depth of field or how much of the image is in focus, a low value ie f1.8 would be used for portraits to have just the subject in focus whilst a high value ie f22 would be used for landscapes. As the aperture number gets higher so does the shutter speed.
Do you mean exposure compensation? if say you are taking a pic of a tree surrounded by bright sky the tree may not come out as the camera will take an average reading over the whole viewfinder in this case you can set exposure compensation to +1/2 or +1 and it should help.
3 depends what you want to do with the image, 1600x1200 will be more than enough for 6x4 prints.

[PC_Bod]

There is a formula for working out what size prints which resolutions will give you.

it's Resolution / DPI = Inches

DPI. Usually a figure of 200 will suffice for small scale printing. So.

1600/200 = 8
1200/200 = 6

1200x600 = 8" x 6" :)

[GreyJackal]

1 the lower the iso the less noise there should be in your image, unless you're happy messing with it leave it on auto, or experiment and see what you think..

That's a side effect rather than anything else. It's easier to explain in film terms - the ISO number indicates a film's speed. The faster the film speed, the quicker it reacts to light, so, all other things being equal, you don't need to have the shutter open as long to get a correctly exposed photograph.

This then ties it in to the relationship between aperture and exposure length as you have to balance all three to get the exposure you want. For example, if it's dark and you don't have a tripod, you can use a faster film to try and capture more light and thus reduce the shutter speed and hopefully reduce/eliminate camera shake. Conversely if it's really bright and you want to have a slow shutter speed to try and capture some movement as a blur (eg an aircraft propellor), you can lower the film speed. That's simplifying it a bit, but you get the gist.

The noise comes from the grain of the film as a less sensitive stock has a finer grain. The faster film is rougher.

I have to admit though, I haven't the foggiest what the technical reasons are for it occurring with CCDs in digital cameras :D

[wseed]

I have to admit though, I haven't the foggiest what the technical reasons are for it occurring with CCDs in digital cameras :D

I've always assumed (no technical knowledge to back this up) that the camera turns off an array of pixels in order to have less processing. The resulting gap is than mad up by averaging those pixels around the turned off ones.

Just thought of that and it wouldn't help increased low light performance so not sure.

[DaveH]

On a ccd with a high ISO setting, the gain (amplification) is increased. A side effect of this is more noise in the picture which occurs if the input signal is too great and as a result is clipped.

[KeyserSoze]

about exposure, i think Rik is talking about the "exposure compensation" on Canon digis. Read the manual for that, it tells how to use it. Adjust it according to how much background light you have on the subject.