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Testing the manual focus and ISO range of Canon A75 camera

January 7th, 2006

My compact digital camera, Canon A75, is pretty slow. Even in manual mode when I set the aperture and exposure time myself, the lag between pressing the shutter button and the picture being taken is annoyingly long - a good half a second. This means that when I shoot fast moving objects, i.e. a car driving by, I have to press the shutter ahead of time by just the right amount and hope that the object is fully within the frame when the picture actually gets taken. Another example is taking pictures of people posing - when someone's told that I'm about to take a picture they expect it just happens right then; people don't like holding a smile for too long.

This got me thinking why the camera would be so slow? One obvious reason is the auto-focus. When I press the shutter button, it has to do some measurements to determine the correct focus. So I tried manual focus and there was a very noticable improvement in the lag. However, using manual focus on such a small camera presents other challenges.

Firstly, it's not easy to set because there's no focus ring around the lens like there is on SLR lenses. Secondly, because the display is so small the changes in focus are not really noticable, so it's difficult to judge what the right focus is. The only indication that it's set correctly is to estimate the distance between the camera and the object being photographed, and set the focus to that distance. But all of this adds up and the setup time for taking a single picture gets quite long. So I wondered if I could find a happy medium setting such that I can set the manual focus once and have the whole scene in focus, and just use this setting for most everything. The idea here is the same as using a large depth of field - if everything from front to back is in focus, then I'm happy.

Below are the results of my tests. It looks like using a large depth of field (i.e. a small aperture) and focus set to distant, almost everything in the scene is sharp. However, this in turn poses another challenge because this camera needs a lot of light and with a small aperture I'm limiting myself in when I can shoot pictures. So then I tried to play with the ISO setting, which did not provide good results. Basically, ISO 400 is useless because the image is so noisy, ISO 200 is better and would be acceptable in dire situations when it's down to taking a bad picture or no picture at all, ISO 100 is OK, and ISO 50 (the default) is definitely fine.