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01-09-2013, 11:36 AM   #1
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Aperture Priority Heads-Up?

Hi all,

As I learn to deal with the K-01, I am finding out some of its quirks. Given that some people are saying that their pictures are sometimes flat, I thought I'd see if others have had the same experience as me. I've posted about this before, but since I've now seen the same behavior across many lenses, I'm pretty confident in saying that what I am seeing is camera behavior, and not lens behavior.

In short, when shooting JPGs:
1) going from auto to aperture priority mode produces much less saturated colors, even at the same f-stop; and
2) in aperture priority, as you go to smaller and smaller apertures (large f-stop), the camera tends to overcompensate and produce more exposed pictures.

Now, I find that this behavior is both a bug and a feature. In low light, I find that auto images are sometimes oversaturated, and going to manual apertures produces better (to me) color. In bright conditions, the reverse is true and I find my manual aperture images tend to be very flat (and a little over-exposed from F/8 onward), while the auto images are wonderful.

Keep in mind that I'm a P&S upgrader, so I'm a relative noob and any advice is welcome (except that I'd rather not shoot raw and then adjust the images on a computer). Here's what I will probably try:
1) When shooting aperture priority in bright conditions, I will set the camera to "vibrant" or "bright" (I've been using "natural" so far), with -0.3 to -0.7 eV compensation.
2) When shooting aperture priority in low light conditions, I will keep the natural setting with maybe -0.3 eV compensation (or none at all).

Here are three samples that illustrate what I am talking about (see also those in the previous thread).

These images are with a 35-105/F3.5 Pentax-A (MF) lens, at macro range. They are low light, so in this case the best images is aperture priority at F/9, IMHO - though maybe it needed -0.3 ev? (Again, in bright light I find aperture priority images very flat.) First image is full auto, wide-open (F/3.5), then aperture priority at F/3.5, then aperture priority at F/9:

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01-09-2013, 12:07 PM   #2
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Or it could be because the different perspective in the second shot!

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01-09-2013, 01:13 PM   #3
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QuoteOriginally posted by Adam Quote
Or it could be because the different perspective in the second shot!
If you looked at the examples in the linked thread, the first is a tripod shot. However, it occurs to me that you can't adjust "Custom Image" in Auto mode, and that the default is "bright". This explains the difference in colors that I am seeing (as above between the 1st and the other two shots): switching between Auto and Aperture Priority also winds up switching between "Bright" and "Natural" colors. Which also means, as I thought, that it's probably better to shoot "bright" when there is a lot of light and "natural" in lower light.

As for exposure differences at smaller apertures, I can try a tripod test, but I'm pretty confident. The two Aperture Priority shots above (2nd and 3rd) have very similar framing, though they are both handheld, admittedly. The F/9 looks much brighter than the F/3.5, no? Look also at the 2nd example in the linked thread. Again, it's not a tripod shot, but the framing is very, very close. The F/13 shot is much brighter than the F/2.8 shot...
01-09-2013, 01:28 PM   #4
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As Doundounba said, you are shooting in Green mode, which defaults to Bright exposure. Virtually everyone on this board would advise not to use Green mode. There's nothing wrong with letting the camera choose your settings, especially with a Pentax, since it allows Program Shift, but if you want the camera to control the settings, use P mode. It controls aperture, ISO and shutter speed just like Green mode, but gives you control over all these and more, including Image Tone. I use Portrait with +1 sharpening as my default. For nature shots I bump up the contrast, for portraits I drop saturation to -1.

Regarding differing exposures, I find it difficult to believe that the camera is behaving as you state (overexposing as you stop down). Are you using Matrix metering? That's what Green mode uses.

01-09-2013, 01:49 PM   #5
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QuoteOriginally posted by audiobomber Quote
As Doundounba said, you are shooting in Green mode, which defaults to Bright exposure. Virtually everyone on this board would advise not to use Green mode. There's nothing wrong with letting the camera choose your settings, especially with a Pentax, since it allows Program Shift, but if you want the camera to control the settings, use P mode. It controls aperture, ISO and shutter speed just like Green mode, but gives you control over all these and more, including Image Tone. I use Portrait with +1 sharpening as my default. For nature shots I bump up the contrast, for portraits I drop saturation to -1.

Regarding differing exposures, I find it difficult to believe that the camera is behaving as you state (overexposing as you stop down). Are you using Matrix metering? That's what Green mode uses.
Thanks audiobomber, that's useful advice. AE Metering is set to "Multi-Segment" - not sure if that's what you mean by "Matrix"... Do you use "Center-weighted" or "Spot" metering (the other two options)? Wouldn't you agree that of the 2nd and 3rd shots above (only diff is F/3.5 vrs F/9), the 3rd is much brighter?
01-09-2013, 02:21 PM   #6
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You get exactly the behavior that is expected. Green Auto as many pointed out determines through some algorithm what is the best "Scene" mode to apply while Av uses the parameters that you have set, which are different. Also, you are shooting with an older manual lens. If you are using the lens in "A" mode, sometimes the aperture on older lenses are ever so slightly sluggish, which can lead to overexposure. If not in "A" mode, when the light reading is done at a lower than spec aperture for the light meter, it will also lead to an overexposure.
01-09-2013, 07:13 PM   #7
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QuoteOriginally posted by Doundounba Quote
AE Metering is set to "Multi-Segment" - not sure if that's what you mean by "Matrix"... Do you use "Center-weighted" or "Spot" metering (the other two options)? Wouldn't you agree that of the 2nd and 3rd shots above (only diff is F/3.5 vrs F/9), the 3rd is much brighter?
Yes, matrix is multi-segment metering. I use all three methods, Green mode only uses Multi-segment. That is probably not the cause of your problem though.

I didn't realize you were using older lenses. I have a couple of lenses that behave the same way. The further I get from wide open, the more the camera overexposes. This is not a camera fault, it's due to inaccuracies in the lens. My fully manual Kiron does the same, overexposes with smaller and smaller apertures, on all three of my bodies (K100DS, K-x, K20D). I have an Image A 28mm 2.8 that exhibits the same behaviour. My Sears A 135mm 2.8 exposes accurately with all bodies.

Note also that fully manual lenses will not close the aperture down unless you are in M mode. If you set the aperture manually to say f8 but you are in P, A, or S mode, the photo will be taken wide open. You may know this by now, but just in case.
01-13-2013, 09:45 AM   #8
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QuoteOriginally posted by audiobomber Quote
Yes, matrix is multi-segment metering. I use all three methods, Green mode only uses Multi-segment. That is probably not the cause of your problem though.

I didn't realize you were using older lenses. I have a couple of lenses that behave the same way. The further I get from wide open, the more the camera overexposes. This is not a camera fault, it's due to inaccuracies in the lens. My fully manual Kiron does the same, overexposes with smaller and smaller apertures, on all three of my bodies (K100DS, K-x, K20D). I have an Image A 28mm 2.8 that exhibits the same behaviour. My Sears A 135mm 2.8 exposes accurately with all bodies.

Note also that fully manual lenses will not close the aperture down unless you are in M mode. If you set the aperture manually to say f8 but you are in P, A, or S mode, the photo will be taken wide open. You may know this by now, but just in case.
Thanks again audiobomber. I suppose it could be the lenses, but... all of them? Just yesterday I ran a tripod test with three different lenses, and with *all* of them, the camera seemed to expose more and more for the first few aperture stops, with aperture leveling of at a certain point. The lenses were: the kit 40mm/F2.8 pancake (hardly a vintage item), a Pentax-A 50mm/F1.7 (in very good condition), and a minty Tamron Adaptall 35-70mm/F3.5 with PKA adapter. For the 40mm, I put the lens in manual focus mode after the initial focus, to make sure that refocusing wouldn't change things. I then did at least two runs with each lens, all runs in Av mode, with one run using Bright color profile, and one run using Natural color profile (to see if that changes anything). Each time, I started with the lens wide open, and then went to F16 in either one or two stop increments - shoot, turn aperture dial, shoot again, and so on. What I saw:

- Pentax-A 50mm/F1.7: exposure increases gradually from F1.7 to about F3.2, then stays more or less steady after that.
- kit 40mm/F2.8 pancake: exposure increases gradually from F2.8 to about F5.6, then stays more or less steady after that.
- Tamron 35-70mm/F3.5: exposure increases gradually from F3.5 to at least F7.1 or F9, then stays more or less steady after that.

Is it possible that the changing depth of field changes the Multi-Segment exposure computation that the camera does? No one else observes this behavior? When I have some more time, I'll try spot or center-weighed metering... I'd post more samples, but I don't think they'd add significantly to what I've already posted...

01-13-2013, 01:55 PM   #9
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There should be no problem with modern lenses (DA etc) and I don't think metering would be affected by DOF. I don't think it's unusual for lenses expose a little more darkly wide open. How much variation are you seeing? Is it enough to cause a problem?
01-15-2013, 10:33 AM   #10
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The problem is that in most of my test shots, I tend to like the (exposure) results much better wide open (ie the high f-stop shots often look over-exposed to my eye). To get similar exposure at F8 or greater (which I sometimes want for depth of field), I need to dial in maybe -0.7 EV compensation (sometimes -0.3 EV is enough, and rarely I need a full -1.0 EV). But I'm not sure if I should do it all the time or not... Also, since there's no dedicated dial for EV compensation on the K-01, the workflow to go from, say F2.8 with 0 EV to F10 with -0.7 EV is a little cumbersome. I guess I might shoot using exposure bracketing for a while to get an even better feel for how the camera exposes, but it means (temporarily) reviewing three images for each shot - not necessarily a lot of fun. I might also need to start looking at histograms to get a more quantitative grasp of exposure. (I suppose this is one "benefit" of shooting raw: just shoot it once and then tweak in post.)
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