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05-26-2009, 01:59 PM   #1
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'Normal' program line on K10D?

I was a strictly aperture priority (or pure manual) film camera guy before I got my K10D, so I've never used Program mode on an SLR before, and I'm a little puzzled about it. I know on the K10D you can set the program line method to prioritise aperture, shutter speed or MTF, and I'm pretty sure I understand the effects of doing all of these. You can, though, just leave it on 'Normal', and this is the one I don't understand. How does the 'Normal' program hit upon the combination of aperture, shutter speed and ISO needed? It presumably has to prioritise something or the settings would be effectively random.

05-26-2009, 02:15 PM   #2
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These are good questions.
And it also seems that the depth of field program line strives for a deep field instead of a shallow, thin field which most often is what I prefer. I set mine on MTF and spin e dials.
Someone will come along and give us things to think about or point out the obvious remarks in the owner's manual I am sure.
05-26-2009, 02:49 PM   #3
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Yeah, good point.
Who knows what the 'normal' algorithm prioritises...
How did P modes work before MTF/aperture prioritisations?
This may explain the 'normal' setting...
05-26-2009, 03:31 PM   #4
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Based on my K200D, which doesn't have multiple program lines and is presumably the same as Normal, it works roughly like this, assuming Auto ISO and going from dark to light:
  • starting at wide-open aperture, max ISO, necessary shutter speed
  • increase shutter speed until it's fast enough to not show camera shake (dependent on focal length, and ignoring SR)
  • reduce ISO until it hits bottom
  • increase shutter speed a bit more, just to be sure
  • slowly close aperture while still increasing shutter speed
With the brightest conditions I have available right now, I end up at ISO 100, 1/1600", f/10 on the 18-55mm kit lens.

So I'd say its priorities are, in order: avoid blur due to camera shake; keep ISO at minimum possible; put aperture in a decent place that's neither wide-open nor stopped down too much.

With the flash up it likes stopping down a bit and keeps shutter speed at 1/60" or faster, but I'm not sure what it aims for beyond that.


Last edited by Quension; 05-26-2009 at 03:38 PM.
05-26-2009, 06:09 PM   #5
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QuoteOriginally posted by J2R Quote
I was a strictly aperture priority (or pure manual) film camera guy before I got my K10D, so I've never used Program mode on an SLR before, and I'm a little puzzled about it. I know on the K10D you can set the program line method to prioritise aperture, shutter speed or MTF, and I'm pretty sure I understand the effects of doing all of these. You can, though, just leave it on 'Normal', and this is the one I don't understand. How does the 'Normal' program hit upon the combination of aperture, shutter speed and ISO needed? It presumably has to prioritise something or the settings would be effectively random.
No, they're not random. They are essentially based on EV values. This plot is fairly typical of a basic "program mode."

05-27-2009, 01:59 AM   #6
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QuoteOriginally posted by Quension Quote
So I'd say its priorities are, in order: avoid blur due to camera shake; keep ISO at minimum possible; put aperture in a decent place that's neither wide-open nor stopped down too much.
That certainly seems an intelligent approach and one I should think before overriding. Thanks!
05-27-2009, 02:00 AM   #7
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QuoteOriginally posted by Duck Dodgers Quote
No, they're not random. They are essentially based on EV values. This plot is fairly typical of a basic "program mode."

I'm sorry, I don't really get how that works. What is this chart telling me?
05-27-2009, 04:26 AM   #8
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QuoteOriginally posted by J2R Quote
I'm sorry, I don't really get how that works. What is this chart telling me?
If we start at the left, the beginning, lowest amount of light on this particular plot is EV 0 (Exposure Value 0). Following the diagonal line for EV 0 gives us a shutter speed of 2 seconds at f/1.4. That is the aperture/shutter speed chosen by the camera's exposure system (again, only for this particular graph). Increasing the amount of light by another stop to EV 1 gives a shutter speed of 1 second at f/1.4. So this camera will hold a maximum aperture of f/1.4 until reaching EV 4. At EV 5 it begins opening the the diaphram by one-half stop, and increasing the shutter speed by a half stop. It continues on along that slope on the graph until EV 18, whereupon it has reached its smallest aperture and continues to increase the shutter speed as light increases.

The high-speed progile would attempt to to hold the shutter speed at 1/4000s (in this case) for as long as possible, as light decreased. It's "weighted" towards higher shutter speeds, just like you might tend to do when shooting sports, for instance.

The DOF profile would do the opposite; attempt to hold a high f-number for as long as possible.


BTW, the first "Program Mode" was implemented in Canon's A-1 back in 1978. (Yes, I was there! )

05-27-2009, 11:37 AM   #9
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Yes but I would still imagine there is a large amount of predetermined settings involved especially taking into account that non Pentax lenses will be used. I know it is fun to play these games but something tells me that when a lenses without a proper Pentax chip is connected, much of that profile algorithm goes out the window and a preset course is taken with small variations.

But I make stuff up all the time.
05-27-2009, 11:03 PM   #10
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QuoteOriginally posted by Nowhere Matt Quote
These are good questions.
And it also seems that the depth of field program line strives for a deep field instead of a shallow, thin field which most often is what I prefer. I set mine on MTF and spin e dials.
Someone will come along and give us things to think about or point out the obvious remarks in the owner's manual I am sure.
I don't hardly use P mode but this thread got me curious and my owner's manual is somewhere in storage.

What is MTF?

The camera ain't gone tell me for sure and I don't want to guess.
05-28-2009, 02:59 AM   #11
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MTF is modulation transfer function, and it's a way of objectively measuring sharpness. There's a good explanation here: Understanding Lens Contrast. The MTF data for modern lenses is apparently stored in the lens chip and can be queried by the camera, allowing it to set the aperture to where it is sharpest, according to the MTF data (or at least, prioritise that aspect, as opposed to depth of field or shutter speed).
05-28-2009, 09:59 PM   #12
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QuoteOriginally posted by J2R Quote
MTF is modulation transfer function, and it's a way of objectively measuring sharpness. There's a good explanation here: Understanding Lens Contrast. The MTF data for modern lenses is apparently stored in the lens chip and can be queried by the camera, allowing it to set the aperture to where it is sharpest, according to the MTF data (or at least, prioritise that aspect, as opposed to depth of field or shutter speed).
Wow! I did not know that! Thanks for the info. I will try it out.
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