Originally posted by sterretje P mode
The camera will calculate a combination of shutterspeed and aperture and set that as the default
P mode will choose what it thinks gives the sharpest picture based on light level, focal length, lens sharpness data, knowledge about sensor noise and the shutterspeed>1/f rule of thumb. P mode is pretty smart and it deserves some respect.
Originally posted by sterretje M mode
You set both; the green button just does a calculation for a default combination (not sure based on what)
Based on P mode.
1. When light is plenty, P mode will choose a lens sweet spot aperture, base iso and a fast shutter speed to match.
2. When light diminishes, P mode will open the aperture and lower the shutter speed according to some complex system that I haven't figured out, until it hits max aperture and the shutter=1/f rule of thumb limit. I suspect it looks at lens sharpness data and weighs it against some expectation of blur from camera shake at the current focal length.
3. When light diminishes further, P mode will up the ISO until it reaches the set ISO limit.
4. When light diminishes even further, it will slow the shutter speed below the 1/f rule.
Then there's the scroll wheel (P shift). It chooses alternative, equivalent exposures by trading aperture for shutter and ISO.
That's how P mode works on my K-x, if I remember correctly.
Sincerely,
--Anders.