Never thought about this before. I pulled out the FA20-35/4, FA35/2,
F50/1.7 and FA135/2.8 to see what the P mode did on the DS.
Results --
FA20-35/4: @20mm, starts closing down the aperture at f/[EMAIL PROTECTED]/40
FA35/2: starts closing down the aperture at f/[EMAIL PROTECTED]/25
FA20-35/4: @35mm, starts closing down the aperture at f/[EMAIL PROTECTED]/50
F50/1.7: starts closing down the aperture at f/[EMAIL PROTECTED]/30
FA135/2.8: starts closing down the aperture at f/[EMAIL PROTECTED]/200
All give or take 0.3EV.
Seems to me there are likely only a few Program curves. Seemed to me
that the shorter lenses stop the lens down a little faster, once it
starts to stop down, compared to the 135mm, although I didn't go all
the way and generate a set of graphs... I wonder if the MTF data from
the FA lenses is weighted into the curve too.
The points at which aperture starts to close down seem about right to
me, although the F50/1.7 does seem a little low compared to the
relationship between the 35 and 135.
Godfrey
On Sep 2, 2005, at 3:22 AM, Juan Buhler wrote:
I've been thinking about this for a while.
Typically, in program modes with a FA lens, the camera will keep the
shutter speed high enough to avoid blurry pictures when handheld. On a
35mm sized filmplane camera, this is roughly the inverse of the focal
length, as we all know. So if you have a 50mm lens, 1/60 is the
minimum the camera stays at (1/30 sometimes, but even that is
acceptable.)
It seems as if Pentax didn't update that part of its programs for the
aps sized sensors. With a FA50mm on the istD, I keep getting 1/30s,
even if the aperture is not full open (for example, I will get 1/30 at
f:2.8 with the FA50/1.7, instead of the more acceptable 1/60 at f2). A
50mm on the istD is equivalent to roughly 75mm, so shouldn't 1/60 or
1/90 be the minimum speed the program chooses?
Or am I very wrong?
j
--
Juan Buhler
http://www.jbuhler.com
photoblog at http://photoblog.jbuhler.com
