Flash and P mode ISO oddity

[matthew miller]

I posted this in another forum and no one seemed to care. Maybe people will here. :)

 

So, here's an interesting thing about P-TTL and P mode on the K10D with a flash

mounted. This is with the Metz 48 AF-1, but I assume it's with any flash ? it'd

be interesting to have confirmation.

 

At ISO 320 or below, it tends to pick things like shutter speed 1/60th and f/2.8

or f/3.5. (This is a f/2.8 max lens, in MTF P mode ? I should test the other P

options too.) But at ISO 400, there's a sudden jump to preferring f/8 (same

shutter speeds).

 

It makes sense, of course, that higher ISOs allow smaller apertures, but the

interesting thing is that there's a clear jump in behavior right at that point ?

the 1/3 stop increase in ISO causes a 2 1/3 stop decrease in aperture.

(Either way, the flash power is automatically adjusted to the right exposure.)

[mountainvisions]

Hmm, let me give this a reply.

 

Matt, this is very interesting. Thanks for the research.

[michael_kuhne]

To me there is a certain logic here. Flash effect being seen as apropos to ambient lighting, when increasing to greater ISO, a smaller aperture for greater depth of field can be set, because increased ISO sensitivity will pick up more detail well beyond the reach of the flash range. But that should also change according to the amount of ambient light being read by the meter.

 

When moving outdoors in daylight, using the flash will result in auto fill flash being adjusted, producing both a smaller aperture and a faster shutter speed than when in a dark interior.

[matthew miller]

Michael, am I missing something in what you're saying? I get that it makes sense for aperture to decrease as you increase ISO, but the interesting thing to me is the jump at ISO 400 -- it's like the program suddenly shifts priority.