How do aperture priority, manual focus, and exposure work on a Canon PowerShot SX20?

Question

I’m learning photography on a Canon PowerShot SX20 and using CHDK for RAW and a histogram. I understand that compact cameras have much deeper depth of field than DSLRs, but I’m confused about a few controls:

1. In aperture priority, the SX20 only offers about f/2.8 to f/8, and I don’t see much visual difference between settings. What is aperture priority useful for on a small-sensor point-and-shoot?

2. In manual focus, the distance scale goes from close focus to infinity, and there’s a magnified center area for fine adjustment, but small focus changes don’t seem very noticeable. Is that normal on an electronic viewfinder compact camera?

3. For exposure, I try to keep ISO at 100 to reduce noise, and I adjust shutter speed when needed. The camera has an exposure indicator and I can also view a histogram with CHDK. How can I tell whether exposure is really correct in practice?

user3375 · Accepted Answer

1) Aperture priority: even in the widest range mode, where it has from 2.8 to 8, I don't see any difference in the picture. I know that AP is used for DOF, and that P&S have huge DOF because of the sensor size, but then why is this mode here? What's supposed to do in a P&S?

You are correct in saying that a P&S has a huge DOF, however on these types of cameras the Av mode is often used as an alternative for Macro (little flower icon) mode. Having the aperture wide open is a common characteristic of Macro photographs.

2) Manual Focus: the slider goes from 0cm to infinity (Depending on the zoom) and even you have the option to see a zoomed zone in the center of the picture for a refined focus, I don't see much difference between little steps. May it be because it's an electronic viewfinder instead of optical?

I'd definitely agree that it's far more difficult to see focus adjustments on an LCD (the electronic viewfinder) rather than an optical eyepiece. Again, it's not an entirely useless feature, but rather a more advanced version of a possibly pre-existing function. Setting focus in manual on your P&S would be useful when shooting landscapes (the mountains or hills icon, normally) or again if shooting Macro (little flower).

3) Exposure: I've read that you should get a proper exposure. There is an indicator that warns me if the picture is going to be too dark or too bright, but the only options I have to change the exposure are the shutter speed and ISO, which I always try to be at 100 in order to avoid noise (of course during daylight or in a well-lit room). How can I know if it's really proper? Right now I have a post processing plugin in photoshop which does exposure compensation so I'm checking how much does the picture change.

I dare say the comments above handled this nicely: read up, research. You'll understand it, it's something all photographers have to wrap their heads around.

How do aperture priority, manual focus, and exposure work on a Canon PowerShot SX20?

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