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04-14-2011, 11:06 PM   #1
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Aperture + *minimum* speed -> iso ??

Hi !
I have a question for the K7 experts here
In TAv mode, one can fix the aperture and the speed. The K7 then chooses an adequate ISO.
Is there a way to define an aperture and a *minimum* speed, and let the K7 define an adequate speed&iso?
That would really be helpful for shootings from my paramotor...

04-15-2011, 07:49 AM   #2
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If you shoot in 'P', you can set the program line (in custom settings on k20d) to high shutter speed and set your auto iso appropriately. That's probably the closest you are going to get.
04-15-2011, 08:00 AM   #3
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You can use P-mode or Av-mode and set your apperture.

In the INFO menu you can set the top and down ISO-setting. You can also use the way the camera handles this iso-setting, by setting it to slow/normal/fast in wich you give the camera the go to set iso at different settings according to your commend.

I have K-5 now and it is a little different in this way then K-7, but to my memory this should work.
04-15-2011, 08:01 AM   #4
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if you shoot in Av mode, with auto ISO, I htink all pentax cameras will adjust ISO to follow the optimum lens MTF function, or at least minimum hand holdable shutter speed for the focal length,

04-16-2011, 10:47 AM   #5
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Thanks, Av with auto iso is probably my best shot..

Thanks
04-17-2011, 11:09 AM   #6
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I'll speak of my K20D, with Auto-ISO:

In Av mode (any lens) with the aperture wide-open and SR on, the cam changes the ISO before changing shutter speed. It seems to pick a nominal shutter speed based on the focal length detected (or input to the SR'bot). So if I use an M42 100mm prime in less-than-bright light with SR on, shutter speed is almost always 1/50-1/100, and ISO goes up or down as the 'bot decides. With that same lens and SR off, it varies shutter speed too, and I'm not sure of the relationship.

In P mode (A-type or newer lenses, with aperture at A) the 'bot optimizes exposures based on the Program Line settings. (MTF optimization requires FA or DA lenses.) For different shutter speeds, I twist either dial. How the 'bot decides on ISO in this mode varies with Program Line choices. I.e., the algorithm is non-trivial.

To automatically grab the least-blurred images in motion shots, I'll use Tav mode (A-type or newer lenses, with aperture at A). In Tav, I *know* what the shutter and aperture are. If shooting from a moving vehicle with an AF lens, then SR and AF-C are on, aperture is wide, shutter is fast, and the ISO goes wherever is best, insh'allah. Next best would be Sv mode (same lens requirement): a known fast shutter, and let the rest go where they will. Av only provides a known aperture and nothing else.
04-18-2011, 06:58 AM   #7
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This problem annoys me as well. I'd like an Av mode where I can set the minimum shutter speed with the front scroll wheel. This would be so easy to implement and be a huge help to my shooting style.

As others have mentioned, the closest bet is Av with slow, med, or fast auto-ISO setting. I just get tired of those settings not matching the speed I'm looking for and being so hard to drill down and change on the fly.

Another mode that's similar but not quite perfect is Sv with program line set to narrow DOF and the custom function controlling to the front wheel set to "P-shift". In this mode you can set the ISO with the back wheel and the aperture with the front wheel, plus the green button will return you to the largest aperture.
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