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01-30-2020, 02:15 AM   #1
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DA 55-300mm F4.5-6.3 ED PLM Exposure issue ?

I've just come back from, a walkabout using K3 and this lens. The lens is a few weeks old and little used so far - I bought it to rekindle my K3 use.

I've spotted identical shots are underexposed - perhaps 10% of the time this is happening. I've added a pair from when I noticed the issue. Matrix metering. Tripod. MUP. Remote.

When I have time I can test the camera with another lens on this body and this lens on another body. However, before I do, I was wondering if others have noticed this issue. I never seen this with any of my other cameras or lenses. I was wondering if it had anything to do with it being a slower lens than I'm used to, struggling with images that have a narrower tonal range.

I should have added that LV exposing was fine.

Any ideas ?

Thanks.

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01-30-2020, 02:19 AM   #2
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Try to shoot wide open and fully closed, to check if there is a problem with the electronic diaphragm.
01-30-2020, 03:02 AM   #3
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Have you updated the firmware of your camera?

The camera is quite a bit older than the electromagnetic aperture diaphragm introduced with this lens, so it has to be updated to know how to operate the lens properly.
01-30-2020, 03:09 AM   #4
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QuoteOriginally posted by Bertrand3000 Quote
Try to shoot wide open and fully closed, to check if there is a problem with the electronic diaphragm.
I'll add that to the test list. Thanks.

---------- Post added 01-30-20 at 10:09 AM ----------

QuoteOriginally posted by ehrwien Quote
Have you updated the firmware of your camera?

The camera is quite a bit older than the electromagnetic aperture diaphragm introduced with this lens, so it has to be updated to know how to operate the lens properly.
Thanks. I believe the firmware is up to date. I'll check.Edit <I have checked and it's up to date>


Last edited by BarryE; 01-30-2020 at 07:26 AM.
01-30-2020, 05:28 AM - 1 Like   #5
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Looking at your EXIF data the under exposed picture is a shutter speed of 1/15 sec and the better exposed picture is 1/4 sec. That could account for the under exposure of the picture at 1/15 sec with everything else being the same. I typically shoot my PLM (I also have K-3 with firmware 1.40) at higher ISO unless in very good lighting conditions. It may be possible you were shooting at the limits of ISO and aperture for the lighting conditions if the scene.
01-30-2020, 05:31 AM - 1 Like   #6
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I do not think it is any problem with the aperture as the camera is using different shutter speeds for the shots.
1/15s on the first and 1/4s on the second. So it should be 2 stops difffernce in exposure if the aperture is working as it should.

It seems more like the automation for some reason want to use a too fast shutter speed for some shots.
01-30-2020, 07:31 AM   #7
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QuoteOriginally posted by Fogel70 Quote
I do not think it is any problem with the aperture as the camera is using different shutter speeds for the shots.
1/15s on the first and 1/4s on the second. So it should be 2 stops difffernce in exposure if the aperture is working as it should.

It seems more like the automation for some reason want to use a too fast shutter speed for some shots.
It was consistently between 2 to 2.5 stops under exposed when it failed. Aperture ranged from f6.3 to f11. FL was not relevant as failures occurred from 55 to 300mm.
01-30-2020, 08:50 AM   #8
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Perhaps dust on the metering sensor/mirror? But that would mean than this should also happen with other lenses...

01-30-2020, 10:10 AM   #9
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If you use spot metering and coupling with af (I cannot check exif on my mobile) the first picture might be of correct exposure too (looking at the top of the tree, the light parts) and exposure can change drastically with mininal changes of perspective.
Edit: ok, just reread the entry post. Its matrix metering....
01-30-2020, 10:46 AM   #10
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QuoteOriginally posted by BarryE Quote
It was consistently between 2 to 2.5 stops under exposed when it failed. Aperture ranged from f6.3 to f11. FL was not relevant as failures occurred from 55 to 300mm.
As noted above, the underexposure is traceable to higher shutter speed (two stops) in the upper image despite both having the same f/6.3 aperture setting. Is there any chance your eye was away from the viewfinder for the upper image, resulting in metering error from errant light*? MUP might also be a factor owing to the time lag between metering and exposure.


Steve

* This is a long-standing problem for auto-exposure cameras dating back to the late-1960s/early-1970s. As with other makers of the time, Pentax included an eyepiece shutter on the Spotmatic ESII, but did not do so on subsequent models. Our K-3 cameras came with a eyepiece cover for this purpose, though it is easily lost. I shadow the opening with a fingertip.

Last edited by stevebrot; 01-30-2020 at 12:12 PM.
01-30-2020, 12:43 PM   #11
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QuoteOriginally posted by stevebrot Quote
As noted above, the underexposure is traceable to higher shutter speed (two stops) in the upper image despite both having the same f/6.3 aperture setting. Is there any chance your eye was away from the viewfinder for the upper image, resulting in metering error from errant light*? MUP might also be a factor owing to the time lag between metering and exposure.


Steve

* This is a long-standing problem for auto-exposure cameras dating back to the late-1960s/early-1970s. As with other makers of the time, Pentax included an eyepiece shutter on the Spotmatic ESII, but did not do so on subsequent models. Our K-3 cameras came with a eyepiece cover for this purpose, though it is easily lost. I shadow the opening with a fingertip.
Many thanks Steve. Might have been, but it wasn't, as I always hold my hand over the viewfinder to stop light finding its way in when using slow shutter speeds.
01-30-2020, 12:56 PM   #12
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QuoteOriginally posted by BarryE Quote
Many thanks Steve. Might have been, but it wasn't, as I always hold my hand over the viewfinder to stop light finding its way in when using slow shutter speeds.
Metering for MUP is done in advance of the exposure. Were you shading the viewfinder before raising the mirror?

If so, then you might want to consider testing using M mode using continuous lighting. My gut feeling* is this is not an aperture control issue. Leaving the meter out of the equation will allow you to tell for sure.


Steve

* Occam's Razor, actually
01-30-2020, 02:33 PM   #13
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QuoteOriginally posted by stevebrot Quote
Metering for MUP is done in advance of the exposure. Were you shading the viewfinder before raising the mirror?

If so, then you might want to consider testing using M mode using continuous lighting. My gut feeling* is this is not an aperture control issue. Leaving the meter out of the equation will allow you to tell for sure.


Steve

* Occam's Razor, actually
Maybe ... This is my default technique, which I've used for years. I've never noticed this problem before. That's not to say it wasn't what caused it. I did wonder at the time, but dismissed it. Maybe I was just being complacent? Maybe the back elements of this lens and/or its construction might cause more viewfinder light to bounce around? Worth experiment at the weekend ...
01-30-2020, 07:38 PM   #14
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Unless you had nudged your exposure comp or had your eye away from the VF, I can see no reason the camera chose a shutter speed causing under exposure for the 1st photo. Do you wear glasses? Any chance some side lighting got in past the glasses? The 2nd photo is what one would expect. In fact, better than what one would expect. With so much dark area, one would suspect the camera might over-expose the brighter areas.
01-31-2020, 12:59 AM   #15
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QuoteOriginally posted by mikesbike Quote
Unless you had nudged your exposure comp or had your eye away from the VF, I can see no reason the camera chose a shutter speed causing under exposure for the 1st photo. Do you wear glasses? Any chance some side lighting got in past the glasses? The 2nd photo is what one would expect. In fact, better than what one would expect. With so much dark area, one would suspect the camera might over-expose the brighter areas.
It is a puzzle. I went through the obvious things when I noticed the issue. I took around 200 shots and about 20 were underexposed. Thus 10%. But, that's not correct, when I looked back at the images in more detail I haven't noticed any failures when I was just in walkabout mode (= no tripod and 1/100 or quicker).

I don't normally have preview switched on as I've learnt to trust the exposures (if in doubt I choose to bracket as required) - in fact I find I rarely check the exposures in camera for non-tricky shots. As more and more of my shooting is becoming tethered on my FF gear maybe I'm becoming complacent. I'll now switch it on for this lens/k-3 combination, which will catch any future problems.

I'll try and re-create the problem today as I've unexpectedly got a little spare time.

Whoops, forgot to say I don't wear glasses, but if the issue isn't a mechanical one (which seems unlikely as the non-tripod shoots seemed OK), then it was probably a quirk of the woodland shooting I was doing using a tripod. This used to be my core subject matter/technique.

Curious ...
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