achew, no, it depends entirely on how bright the place is. It might not choose F11, it might choose F4.5 or any aperture depending on how bright it is.

Program Mode works like this:

1) Set aperture to brightest and ISO to lowest of Auto ISO range (e.g. 300mm F2.8 ISO200)

2) Calculate reciprocal of focal range as your "needed shutter speed"

For an APS-C body, 300mm * 1.5 = 450mm equivalent, so 1/450s is what is used. But that doesn't exist so they round it up to 1/500s.

4) If shutter speed is slower than "needed shutter speed", increase ISO so that the shutter speed is correct.

Let's say at 300mm F2.8 ISO200, it meters at 1/30s. So it increases the ISO to the maximum defined by Auto ISO, let's say ISO1600 - now it's at 300mm F2.8 ISO1600 1/250s. Sure, it's not able to hit 1/500s... but that's where Super SteadyShot helps!

As you can see, Auto ISO prefers to use a good shutter speed to avoid having to use Super SteadyShot much.

On the A900 however, Auto ISO is a bit more relaxed... at 135mm for example, it picks 1/100s as the "needed shutter speed" instead of 1/160s.

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Added on May 25, 2009, 12:18 amAny of you with an Alpha can try it out; put your camera in P mode or Auto mode and walk around the house.

The camera will not pick F8 or darker unless you take a macro shot of a lightbulb!

In fact, if weigie had used Auto or P mode, the camera would've selected F3.5 or whatever brighter aperture the lens allowed in such a condition. Given that the shutter speed doesn't even hit 1/30s (it was 1/13s if using F3.5 at such lighting conditions). Honestly, P mode is very useful to avoid such situations where you forget to set your aperture again!

creepydslr, what I meant by that, is:

Supposing you were out in bright daylight, and you had a F2.8 lens and were using ISO200, you might for example get 1/8000s when pointing at the sky in Aperture Priority. So if you choose F11, the shutter speed would be 1/500s.

In bright sunlight, there is the classic Sunny F16 rule:

Set your lens to F16, and your shutter speed to the ISO. For example if you were using ISO200 then your shutter speed should be 1/200s. On old film SLRs, some might not even count to 1/200s!



My old Olympus OM-2000. So, in such a case, I'd choose 1/250s instead. (1/125s is orange because that is the flash sync speed.)

This is true manual exposure mode (not the metered manual that everybody thinks is manual, but isn't truly manual if you're still setting your aperture and shutter to make your meter read 0. You might as well be using A mode for this!)

So, based on this Sunny F16 rule, that's how I estimated that a F2.8 lens on ISO200 could give 1/8000s... because at F16, ISO200, the shutter speed would be 1/250s.

tanjq87 has got it right.

Honestly, a lot of people are:

- wasting their time in M mode when they should be in A mode
OR
- wasting their time in A mode when they should be in P mode
OR
- wasting their time in P mode when they should be in Night Scene mode

Once you understand what M, A, P and Night Scene mode do, you'll know which to choose for which situation. Yes, I wish I had a Night Scene (slow sync flash) mode on my A900!

landscape..


flower~