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06-23-2016, 06:53 PM   #1
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Unexpected Aperture behavior on K-1

I'm about 3000-odd photos in with my K-1, and I'm generally really pleased with it in basically every way. It has certainly done a great job of pointing out my own flaws as a photographer, but those are too many to list here...

One thing I don't fully understand is how it picks aperture when in program mode. I generally have a fairly high max auto ISO set because I do a lot of toddler chasing (harder to catch than Rupert's squirrels, the North American three-year old...)

Most of the time, when I get into low light, the camera works fine, picking a sufficiently fast shutter speed to prevent most motion blur, an aperture a stop or two from wide open, and an ISO with fewer than five digits.

Sometimes, however, it seems to lose its mind and pick f11-14 and an extremely high ISO, even in reasonable light. This then provides a muddy mess of a photo.

At first I thought this was my lens - I first noticed it on a Tamron 70-300, so I thought it was a "not a real Pentax" problem, but I've since noticed the same behavior on a Pentax FA 28-200 (I know, also a Tamron, but is should have a Pentax program line coded in it). I've taken now to shooting with that lens only in aperture priority or manual because there's basically never a reason for f14 with what I shoot with it.

What made me think it wasn't the lens, though, was when it did it with my 40mm XS (definitely not a Tamron) outside, in open shade. Even indoors, shooting a flat surface, why would it pick f11 and ISO 1600? It could get the same shutter speed at ISO 400 and f5.6, where the 40 is ridiculously sharp.

It has, that I'm aware, never done this with a F or A lens (and certainly not with anything without aperture control). I normally leave the program line set to auto. Am I just bumping into something it thinks is a good idea for some reason I'm overlooking? Or is the auto select rubbish? Or did I find a bug?

I'm out of town, browsing on my phone, and the search got me nowhere except excited about a lens that was sold in 2010... so apologies if this has been answered already. But any insight is appreciated.

-Eric

06-23-2016, 07:15 PM   #2
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@TwoUptons

Going from memory here - - (this is not particular to K-1 - my K-3 Has these settings)

There are three 'curves' available for the amount by which the camera emphasizes increasing ISO versus opening the aperture; Slow, Normal and Fast. MENU | Camera | 1 | ISO Auto Setting.

There are several Program Mode Priority settings (below Auto) in Program Line MENU, which control the camera's selection of DoF / Shutter Speed preference; in Program Auto it wants to expose what it thinks is the best DoF and shutter for the scene it thinks it sees. MENU | Camera | 1 | Program Line: Auto; Normal; Action; Landscape/Portrait Deep DoF; Landscape/Portrait Shallow DoF; MTF.

Combine the two Auto settings and you can get funky choices.

Try Slow ISO and/or Normal, Portrait or Action Program Line for chasing children

Last edited by monochrome; 06-23-2016 at 08:00 PM.
06-23-2016, 08:13 PM   #3
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QuoteOriginally posted by TwoUptons Quote
how it picks aperture when in program mode
Aside from your program line settings, it mainly depends on what metering mode you have set - multi-segment, centre-weighted, or spot.

Note that the metering mode the camera uses may also be dependent on the lens used.

If you use a [A- series or newer] Pentax lens and use multi-segment metering, you will get the full benefit of the K-1 86,000 pixel metering sensor 'smarts', including the ability to read scenes, correct for backlit conditions etc.

However if you use a non-Pentax lens, particularly older ones, multi-segment metering may not work, and the camera may only be able to shoot with centre-weighted metering, and no camera metering 'smarts' will be at work.
06-23-2016, 09:08 PM   #4
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The lens profiles have an effect too as these are factored into the program lines.

06-23-2016, 10:26 PM   #5
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As monochrome said, auto-ISO is not part of the program curve. ISO ramping affects the current EV (shifts it up or down), but does not determine the combination of shutter speed and aperture used to satisfy that EV. That is a property of the program curve settable via the menu system (user manual p46). There is an option for High Speed Priority settable in the menus.

If you want to see the program curve at work, turn off auto-ISO.

QuoteOriginally posted by monochrome Quote
Try Slow ISO and/or Portrait or Action P for chasing children
Yes, that should do it, despite sounding sort of counter-intuitive. The system is designed to ratchet ISO down if possible for highest image quality. Setting ISO to "Slow" will dampen the tendency to do so. ("Slow" refers to sensitivity to change, not subject activity level.)

As far as suggestions to address a need for high shutter speed with exposure automation, the question comes up every once in awhile on this site and usually in regards to people wanting to photograph dogs playing and/or fast children. Here are the points:
  • It is not possible to set a range of minimum/maximum shutter speed for modes where shutter speed is adjusted by the camera
  • Likewise, it is not possible to coerce the camera to do so with any consistent predictability using some exposure automation hack
  • Listed below are strategies to attempt the point above:
    • Set the program line to Hi-Speed Priority such that a higher shutter speed will be set along with wider lens apertures. This will affect P and Sv modes and cases where green button action is to return to the program line.
    • Use a fixed high ISO -or- set both maximum and minimum ISO to values high enough that auto-ISO will coerce higher shutter speed in P, Sv, Av, or green button operation
  • As an alternative to automating shutter speed (the sketchy stuff in the list above), any of the list below is a sure solution:
    • Tv mode, setting the shutter speed appropriate for your needs
    • TAv mode setting both shutter speed and aperture (ISO will vary between max/min set for auto-ISO)
    • Manual mode setting shutter and aperture according current ISO. This approach is very old school, but works amazingly well. Do your settings and shoot freely until either the light and/or your subject changes (think in terms of the light striking the subject, not the light reflecting from it).
Good luck and have fun chasing those kids!


Steve

Last edited by stevebrot; 06-23-2016 at 10:49 PM.
06-23-2016, 10:42 PM   #6
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QuoteOriginally posted by Not a Number Quote
The lens profiles have an effect too as these are factored into the program lines.
Only when using the MTF option for program line and maybe the "auto" option.


Steve

Last edited by stevebrot; 06-23-2016 at 10:52 PM.
06-23-2016, 11:57 PM   #7
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QuoteOriginally posted by TwoUptons Quote
Even indoors, shooting a flat surface, why would it pick f11 and ISO 1600? It could get the same shutter speed at ISO 400 and f5.6, where the 40 is ridiculously sharp.
I went back to your original post and must apologize for running off on a tangent in reaction to monochrome's post. You might want to:
  • Check that you are not using spot metering
  • Check that auto EV compensation is off
  • Try "Normal" program line
  • Try auto-ISO on the middle setting (neither fast nor slow)
There is something familiar about your description of the problem, but I can't remember quite yet the case and cause.

Steve
06-24-2016, 11:41 AM   #8
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I nominate stevebrot to rewrite the User Guides.

06-24-2016, 03:02 PM   #9
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Thanks to all four of you for the suggestions. As soon as I get home (and out of airports), I'll give some of these suggestions a shot to see if I can pin this down a bit better.

-Eric
08-28-2016, 07:06 PM   #10
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I went out with my K1 and the FA77 this morning, and had exactly the same thing happen as noted by the OP two months ago. In P mode, set to the Auto program line, the camera wanted to pick F11 and/or ridiculously fast shutter speeds and ISO 800 or higher, all in good light. For example, on one shot of a bird on a wire, ISO 100 exposure would have been 1/125 F/8. The camera picked F/5.6 1/1600 and ISO 800. Another shot of a house below resulted in F/11 1/200 and ISO 32000 with program line on auto. It seems to me that a more rational starting point would have been F/4, 1/100 and ISO 200. The only unusual thing about these scenes is that there was some degree of backlighting.

Whether the program line was supposed to control the Auto ISO or not, it was, either directly or indirectly. I say indirectly because it was picking insane settings which would require a higher ISO. Unlike the OP, my shots were properly exposed, but the lens and ISO settings were not optimal. Using the MTF line brought the initial settings into a more reasonable line, and sometimes "normal" would, but sometimes not help. I have since removed the battery to see if a reset helps. I have the latest firmware.

PS, I see the EXIF indicates the exposure was "Creative Program based toward depth of field." This is a rather extreme bias for depth of field, and I have never intentionally used that program line. Even if DOF is the bias, pushing the ISO to 3200 seems like a very aggressive choice. The EXIF for the bird on a wire photo did not indicate any exposure program.
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Last edited by GeneV; 08-29-2016 at 05:01 AM.
08-29-2016, 11:27 AM   #11
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QuoteOriginally posted by GeneV Quote
In P mode, set to the Auto program line, the camera wanted to pick F11 and/or ridiculously fast shutter speeds and ISO 800 or higher, all in good light.
One of the reasons to not use "Auto" program line, I'd say. I am not sure, but I believe that the scene evaluation capabilities of the RGB meter sensor on the K-1, K-3/K-3II may result in some unexpected behavior that has been experienced by owners of those cameras.


Steve
08-29-2016, 12:49 PM - 1 Like   #12
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It also means the auto setting on the mode knob is a problem. Bad news when my wife borrows the camera.
08-31-2016, 08:59 PM   #13
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QuoteOriginally posted by GeneV Quote
Another shot of a house below resulted in F/11 1/200 and ISO 32000 with program line on auto. It seems to me that a more rational starting point would have been F/4, 1/100 and ISO 200. The only unusual thing about these scenes is that there was some degree of backlighting.
Maybe it was trying to pick the aperture with depth-of-field such that the entire house was in focus. But I'm not sure that the camera is that smart? That might kind of make sense if you actually had the auto-ISO range set to go up to 32000.
09-07-2016, 08:14 PM   #14
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QuoteOriginally posted by leekil Quote
Maybe it was trying to pick the aperture with depth-of-field such that the entire house was in focus. But I'm not sure that the camera is that smart? That might kind of make sense if you actually had the auto-ISO range set to go up to 32000.
It may know something of the size of the house, if the autofocus and exposure are linked. I tend to think that the program line to maximize depth of field is just too aggressive. To want that much depth of field that badly at the expense of quality, I would think one should just use manual or TAV.
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