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02-25-2012, 01:51 PM   #1
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K10D metering issues

Hi All,

for a long time I was convinced the meter of my old K10D was seriously ill- over-exposure with more than 2-3 f-stops was no exception, I had a -2 dialled in permanently and still had to dial down after that.. This was with my DA* 16-50 and SMC M 35 mm. So bad actually, that I bought a proper meter and use that when things get tricky. Then, this weekend, I tried an old 18-50 kit zoom. And hey presto- near perfect metering! Even with difficult subjects (lots of reflecting bits on a sunny day)

The 16-50 had aperture issues, but the 35 is in pristine condition.
What gives? Can anyone enlighten me?

Thanks!

02-25-2012, 01:55 PM - 1 Like   #2
Ash
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Are you stop-down metering with your M 35?
If you don't know what this is, please refer to the article in this forum about stop-down metering and metering for M lenses.
It is more involved than with A lenses and beyond. This is the most likely explanation.
Start with being in M mode and using the green button to meter after you've closed down the aperture manually on your lens. Follow the article's instructions and see how you go.
02-25-2012, 02:08 PM   #3
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Hi ash,

Wow, what a quick reply! Sorry, I forgot to mention- yes, green button metering. One of the key advantages of the Pentax in my book (unfortunately it isn't that simple)
Thanks for your response though!
02-25-2012, 02:20 PM - 1 Like   #4
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Over-exposure with a Pentax-M lens? Well, that is a new one. The usual complaint is 1-2 stops underexposure at wider apertures with non-A-contact glass. As for your DA lenses...again, the usual complaint is a tendency to underexpose.

So, the big question is...how does the camera reading compare to your hand-held meter when metering some bland, uniform subject? A blank wall or a leaden winter sky will do. Use one of your DA or FA lenses with the "A" contacts.

If the hand-held meter agrees with the camera (figure within 1/2 stop with the camera suggesting more exposure), the issue might be in one of two areas:
  • Defective aperture mechanism in the lens
  • Defective aperture actuator mechanism in the body
You might also want to check to see if your exposure comp is set to other than zero when used with your DA lenses.


Steve


Last edited by stevebrot; 02-25-2012 at 02:52 PM.
02-25-2012, 02:24 PM   #5
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Hi Steve,

Thanks! To my shame and embarrassment I have to admit I haven't done that yet. Kinda weird when I think of it. Will go out tomorrow and compare the two, and post back. (Couldn't really be the body though- or it wouldn't work with the 18-55...)
02-25-2012, 03:02 PM   #6
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I had an over exposure issue with my K10 when using my Tamron 70-200 f2.8 zoom to the point that I quit using it. Then I found out that the lens had a sticky/defective aperture mechanism. I sent the lens into Tamron for repair and that solved my over exposure issues with that lens. My K10 typically underexposes with all lenses by about .7 of a stop so I have to pump it up by that amount normally.
02-25-2012, 03:17 PM   #7
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The K10D & K20D have a well-known metering problem with M & K lenses, when using the green button. Lowell Goudge posted a chart showing how those cameras over or underexpose manual lenses depending on the aperture used. (I can't find the article, but it's here on the forums.) Supposedly it's correctible by using a focusing screen from the *istD series cameras, or 3rd party screens such as Katz-eye, etc.
02-25-2012, 03:19 PM   #8
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Hi Paul,

Thanks. the blades are quite snappy though, and results are consistent. I doubt it is a lens problem.

02-25-2012, 03:25 PM   #9
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I found one of Lowell Goudge's charts showing green button metering inconsistencies on the K10/20. You should look at the whole thread for more info.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/124627-k-5-met...ml#post1292191
02-25-2012, 04:03 PM   #10
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Interesting link, thanks! I almost thrashed my K10 over this (and focus impossibilities), but it seems there may be hope.. Well, as soon as there's daylight I'll compare my camera with the light meter and see..
02-25-2012, 06:34 PM   #11
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QuoteOriginally posted by paulh Quote
or 3rd party screens such as Katz-eye, etc.
Lowell has reported good results with the *ist screen. I have evaluated my K10D against the Katz Eye (both with and without Optibrite) and can confidently report that it does not help the exposure issue with stop-down metering and that screen.

Like Lowell, I have also done extensive testing of my aperture ring lenses. Unfortunately I lost the spreadsheets in a hard-drive failure. I can summarize in a few bullet points:
  • The problem exists at apertures wider than f/4 and is characterized by underexposure of 1-2 stops
  • The severity of the problem varies by lens and selected aperture. Of those in my "stable" the Jupiter-9 85/2 is the worse with 3 stops underexposure at f/2.
  • Exposure compensation is no help unless you always shoot at the same aperture with the same lens since the offset is non-linear and varies by lens
  • There is a similar lack of meter linearity at narrow apertures in dim light, but I have assigned that one to lack of meter sensitivity at those light levels. This was a known issue with stop-down meter cameras back-in-the-day and not unexpected.
Solution? Be familiar with your lenses and apply appropriate compensation as needed based on the chosen aperture. Chimp, adjust, and re-shoot, if needed.

Cause? From what I have been able to glean and from the correction of the issue in one mode (M) on the K-5, K-7, and K-r; the K-series digital bodies apply a mathematical correction to the meter reading to correct for behavior of the focus screens at wider apertures. This correction is based on the maximum aperture as communicated through the contacts on the lens base and from the aperture to be set by the body. Both are available when an A-contact lens is detected.

That data is missing when using the aperture ring to control the iris with subsequent default to a baseline program that may or may not work too well. This behavior dates back to the *ist film camera and is documented in the user manuals for affected models. The newer bodies have a modified algorithm that is applied in M mode for stop-down metering and which yields essentially accurate readings with those cameras in that mode only. Use Av mode with your M42 lenses and you are back to the same old issues.

All that being said, the general picture is one of underexposure with the K10D in stop-down mode at wider apertures. The OP indicates the opposite with a general pattern of overexposure. Overexposure such as described generally indicates a lens issue (lens is not stopping down to the set aperture as expected when doing an actual exposure). Regardless, it is usually good to rule out the meter as the source of error and go forward from there.


Steve

Last edited by stevebrot; 02-25-2012 at 06:41 PM.
02-26-2012, 05:20 AM   #12
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OK, today it's heavily overcast, so nowhere near the contrast and tricky conditions I had yesterday. Measuring seems to work better now, but when compared to my meter and me, it still overexposes by 1/2 to 1 stop. That's just measuring, not actually snapping the shot. I am starting to think this is a camera/lens issue- since the 18-55 didn't give me any issues.
02-26-2012, 06:46 AM   #13
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You did mention your 16-50 had aperture issues. Maybe your issue there wasn't the meter but the lens was slow to stop down or not stopping down at all. My DA 40 doesn't stop down right in cold weather. It's long been known that manual lenses don't quite meter properly on digital cameras and can vary in errors from lens to lens. I haven't noticed a whole lot of difference since adding a Katz Eye to my K10D, but I haven't really done a test. I'm so used to firing off a shot and checking that I haven't noticed if I'm making less adjustments since adding the new screen.

Once again, it appears the lowly 18-55 kit lens has rose to the occasion. While we're always looking for "higher quality" glass, I always seem to get very good results with this lens.
02-26-2012, 07:09 AM   #14
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If it weren't for being able to fix exposure problems in the computer after-the-fact, I would have sold my Pentax gear long ago. Most of my lenses are older, manual focus lenses and my K10D is HORRIBLE at establishing exposure with them. In the film days, I could confidently shave my exposures to within a half-stop, depending upon the effect I was wanting. These days...pfffttt...if I trust my K10D, I usually start off about 3 stops off from where I really want to be. Despite the technology, I really feel like I've been transported back to the days of selenium hand-held meters.
02-26-2012, 07:21 AM   #15
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QuoteOriginally posted by TaoMaas Quote
if I trust my K10D, I usually start off about 3 stops off from where I really want to be
Seems we have similar issues re metering.

QuoteOriginally posted by TaoMaas Quote
I really feel like I've been transported back to the days of selenium hand-held meters.
That's what I bought recently- fortunately they go for about €5-10 at the local flee market
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