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10-27-2008, 03:12 AM   #1
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K20D overexposure in macro

Hey there
I've been looking on the forum, but couldn"t solve the problem.
K20d pentax 100mm A macro
iso 100
different types of measures (spot...)
A locked Av on camera or Sv all photos seriously overexposed.
Checked lens to see if it got jammed or had a sticky aperture, nope plus it worked fine on K10.
Manual mode green button, f11, 16, 22 different speeds which are all wrong.
It'll say 1:20th while it needs 1/60th or 1/90th...
Did not notice this with af lenses...
It is new and under warranty but still I'd like to understand!

10-27-2008, 03:33 AM   #2
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Hi,

Can you show some example shots.
10-27-2008, 06:25 AM   #3
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http://s241.photobucket.com/albums/ff195/lunacalor/?action=view&current=IMGP0719.jpg




you should the exiffs.
1/20 given by green button and 1/90th corrected by myself, other pics on auto mode are a total disaster too!
pictures are of poor artistic quality, not a brick wall though!

Last edited by Substitute; 10-27-2008 at 07:56 AM.
10-27-2008, 07:16 AM   #4
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QuoteOriginally posted by Substitute Quote
Hey there
I've been looking on the forum, but couldn"t solve the problem.
K20d pentax 100mm A macro
iso 100
different types of measures (spot...)
A locked Av on camera or Sv all photos seriously overexposed.
Checked lens to see if it got jammed or had a sticky aperture, nope plus it worked fine on K10.
Manual mode green button, f11, 16, 22 different speeds which are all wrong.
It'll say 1:20th while it needs 1/60th or 1/90th...
Did not notice this with af lenses...
It is new and under warranty but still I'd like to understand!
If it's an "A" lens why are you using the green button? Is the "A" contacts functioning correctly???

10-27-2008, 07:47 AM   #5
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"A locked Av on camera or Sv all photos seriously overexposed."
As I stated, A was first locked it was a disaster.
A disaster too unlocked with green button.
10-27-2008, 10:26 AM   #6
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QuoteOriginally posted by Substitute Quote
"A locked Av on camera or Sv all photos seriously overexposed."
As I stated, A was first locked it was a disaster.
A disaster too unlocked with green button.
Is "A" functioning? You get Ap confirmation in the viewfinder?
SOME overexposure w/ some "A" lenses at full open is not unheard of (My f1.7 50 is a bit "bright" at wide open). Stopped down a bit and exposure gets more accurate. From what you posted I'm still not convinced (yes you said you set the lens to "A") that the contacts are not dirty or in some manner dysfunctional on that lens...
Green button metering on k10/20 (assuming on the 20 BTW) seems hit and miss w/ the orig screen (K10/20 share the same NEW screen) once your out of the sweet spot of f4-8.
10-27-2008, 10:49 AM   #7
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QuoteOriginally posted by Substitute Quote
Hey there
I've been looking on the forum, but couldn"t solve the problem.
K20d pentax 100mm A macro
iso 100
different types of measures (spot...)
A locked Av on camera or Sv all photos seriously overexposed.
Checked lens to see if it got jammed or had a sticky aperture, nope plus it worked fine on K10.
Manual mode green button, f11, 16, 22 different speeds which are all wrong.
It'll say 1:20th while it needs 1/60th or 1/90th...
Did not notice this with af lenses...
It is new and under warranty but still I'd like to understand!
Just a wild guess, but are you outside the camera's metering range? I've found the Pentax meters to be extraordinarily inaccurate as they approach the edge of their range.
10-27-2008, 11:02 AM   #8
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just curious,
in Av mode, what is the shutter speed reading when spot metering to that green leaf?
Is it closer to 1/90th or closer to 1/20th?

10-27-2008, 11:17 AM   #9
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Hi,

I don't find aperture value in exiff data of your images?

If you have your lens in 'A' position, there should be aperture value saved?!

Is camera working with other lenses? Have you looked that the aperture blades work properly (lens in 'A' position)?

Last edited by kurt; 10-27-2008 at 11:30 AM.
10-27-2008, 12:01 PM   #10
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Kurt this is the manual setting: in lightroom I get this info 1/20th for the first, 1/90th if I recall well for the second.Taken a few seconds later.I know I was in manual mode and set the aperture at f16 or 22.
This was the second set of tests.
For the A position in av mode they were taken yesterday,
some pics, no flash and A mode , aperture priority



Thanks

@Jeff: first set is full manual mode I forgot to precise, second is A mode.
very true about lowsy metering with original screen, I had changed the k10's, that's totally true, K10 with which this lens worked fine!

Last edited by Substitute; 10-27-2008 at 12:13 PM.
10-27-2008, 12:33 PM   #11
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QuoteOriginally posted by Substitute Quote
Kurt this is the manual setting: in lightroom I get this info 1/20th for the first, 1/90th if I recall well for the second.Taken a few seconds later.I know I was in manual mode and set the aperture at f16 or 22.
This was the second set of tests.
For the A position in av mode they were taken yesterday,
some pics, no flash and A mode , aperture priority




@Jeff: first set is full manual mode I forgot to precise, second is A mode.
very true about lousy metering with original screen, I had changed the k10's, that's totally true, K10 with which this lens worked fine!
f16 and 1/15sec is about right for an heavy overcast day (if I got this right).
Only really 2 possibilities
1) Seems to me that your aperature is NOT shutting down. (try a different lens)
I think I'd send the camera in.
2) or the lightmeter is just plain bad (If I remember correctly some (or at least 1) DS had the meter cell slip down off the prism (don't ask me how though) and it caused the same problem.
Problem is if other lenses work fine (say kit lens) then it's probably not the camera.
You have to do some lens mix and matches to check this out.
A very slim possibility is if the 100 had something slightly wrong w/ the aperature arm (where it contacts the body of the k10 fine but is missing on the k20 causing the blades to not shut down correctly.)
Even green metering should work on the k20 and the lens in the f4-8 range. Give this a try (if I missed it my apologies). If it meters OK manually at f4-8 you can always interpolate up from that point to set the exposure correctly. Still won't explain the "A" problem though.
Just a fun link:
Ultimate Exposure Computer

Last edited by jeffkrol; 10-27-2008 at 12:41 PM.
10-27-2008, 12:59 PM   #12
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Interestingly, I get consistent over-exposure with my FA100/2.8 macro on the K10D by about 1.3-2 stops. Lens and camera are fine otherwise. I've resolved to simply dialling down the EC by 1.7 stops to get a decent yet consistent exposure with this combo. Then again, I have the LL-60 screen.
10-27-2008, 01:00 PM   #13
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Hi,

Exiff aperture values:
The first image in second set has f16 (1/15) and the second image f6.7 (1/30), which is a little bitt odd?!

Like Jeff said you should try with other lenses (A lens and DA/FA lens) to compare. If they work correctly, you have some issue in lens or bad contacs, or maybe the blades are not functioning properly. Can you see that the blades work normally when you shoot?
10-27-2008, 01:07 PM   #14
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Jeff : sky was blue as you can guess on second pic,I live on the Riviera so it's like spring here...
The K20d underexposes a bit with the kit lens II, is fine with DA*s but not in manual mode of course.Anyway it has a '-year warranty, so I am not scared at all, and won't leave Pentax or anything, but I will sure check with another screen before I send it in!

Ash, does it have to do with macro 100mms then? Oddly enough, extension rings, manual mode on k10d with any lens worked fine. I'll procees tests with both bodies in similar conditions!
sounds like fun!
thanks anyway.
10-27-2008, 01:27 PM   #15
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I have a D-XENON 100mm macro (same as Pentax) which works just fine (I have not noticed any constant overexposure, unless my own mistake ).

If your other lenses work fine, there might be some issue in your macro lens.

Just made a quick and dirty test with FA 50/1.4 with aperture ring not in 'A' position and K20D in Av-mode. I did not find similar problems like you.
The aperture value f6.7 is somehow odd or the exiff data is corrupted.
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