P vs A vs S - I don't get it

[Rob vdKam]

I used a real SLR for years (years ago) and now have an A200, but while reading the manual, I slowly came to the realisation that I don't understand the difference between P, S, and A program modes. Of course, I thought I did - it's rather obvious after all. But when it comes down to it, what is the difference between wanting an aperture of 3.2 and being in S or P and choosing a shutter speed that gives it to me instead of switching to A? I must be missing something here... :confused:

[Rob vdKam]

Okay (egg on face) - a friend told me it's to compensate automatically for different lighting and etc without changing aperture (or shutter speed). I suppose that's important. If there's more, though, I'd appreciate hearing about it.

Am I not correct, though, in saying that the A200 does not give any indication of just how far off the correct exposure your current settings are? The Sony H1 I tried would tell me I was 0.3 or 0.7 or 1.0 plus/minus EV at the current aperture/shutter speed settings. I don't see anything in the A200 except for the red numbers indicating I'm under/overexposed beyond the ability of the camera to compensate. Isn't that important to know? I don't enjoy rolling the settings and waiting for the readings to turn black. I'd like to know how far off I am. If for example, I knew I was -0.3EV, I could decide if that was okay, and use it instead of chaning the EV setting, for example. But with the red readout, I have no idea.

[Geoff Chandler]

Well, as I see it - through my possible share of the egg -
P = program which is pretty much Automatic, correct exposure unless you compensate.
A = Apperture priority - still a form of Automatic but you have anchored the apperture to your desired opening, the camera will, as far as possible - light permitting, select the correct shutter speed to balance
S = still a form of Automatic but you have anchored the Shutter to your desired speed, the camera will, as far as possible - light permitting, select the correct apperture to balance.
M = Manual - Not automtic - you select the Apperture and the Shutter speed - the two are displayed in Blue if the exposure is considered OK by the camera - or Red if it is under or over exposed. Trouble is it doesn't tell you wether it is under or over - you have to work that out by adjusting one or the other up and down through the Blue zone.
Hope I am not stating the obvious in any way - If I have missed the point - do forgive
Geoff

[Rob vdKam]

Thanks - especially for the comments about not knowing how over (or under) exposed one is. Too bad about that...

[Coltess]

There is a third part (in some instances) to the Aperture/Shutter speed "equation", namely ISO setting.
If your A200 is on Auto ISO, the camera can change the ISO to get a closer match between A and S. At least that is how I understood it in the manual ;)

[Geoff Chandler]

RE ASA comments: -
It will depend on which mode you are in and also, really, how the designers set it up. If you are in Auto ASA - I would imagine it would bias towards a lower ASA to preserve image quality - but when the light gets lower it will still bump up. If you are in Sports mode it will definately sacrifice a bit of ASA quality (IE go up higher) in order to preserve the faster shutter speeds, again - it depends on what Logic has been applied as it can lower the apperture first.
I'm not sure about the quoted manual wording - I'll have a look sometime as I don't quite understand what was meant by "change the ISO to get a closer match between A and S" Apertures are holes, Shutter speeds are speed of shutter - they can both be expressed in terms of stops and one times the other equals the exposure - but match between??
I usually select my own ASA setting and try to keep it down as much as possible - mostly 50 ASA or 100 ASA. Incidentally - the difference between 50 ASA & 100 ASA is also one stop.
Think I've said enough for now!
Geoff

[rjromero10]

Rob,

Don't forget when you use S (Shutter Priority) you can choose how fast you shutter is. Stopping motion(fast), Blurring Motion(slow). The camera adjust Apature accordingly. Also A(Apature Priority) you adjust apature for depth of field. Small number causes background and foreground blur while keeping subject in focus. A large number will allow for more of the background and foreground to be in focus. The camera will adjust the shutter accordingly for correct exposure. P(Program Mode) is almost automatic, it allows you to compensate flash and exposure.