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07-12-2018, 11:03 AM   #16
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QuoteOriginally posted by MJKoski Quote
Yes. Only aperture which worked good with Leitaxed Zeiss 28/2 was wide open. And that was when shutter speeds were "fast" under 1 second. Even wide open started to fail when light levels dropped ~10 seconds being some kind of limit. However in Av mode histogram updates as aperture is selected and it works in good light.
It appears that yours is a special case with very low light levels perhaps with that lens and perhaps with the K-1. Since I don't have that camera, I should probably stop typing. But, since my previous results were based on actual tests with my K-3 and other users have reported satisfaction with other models, I will continue.

I had previously compared Av and M in live view with manual aperture, but did the test series under conditions where ambient light was strong enough to allow a full range of apertures to f/22 without going below 1s shutter speed. Just now, I found a dimly-lit closet where the light was measured (Gossen Luna Lux) at EV 3.* An exposure for that EV (f/2 @ 1/2s) of a blank white wall resulted in a centered and symmetrical histogram. I recorded metered shutter settings for the range f/2 - f/16 in both Av and M modes using my Helios 44M with aperture in M mode. Av and M agreed at all apertures, but both were only linear** to f/11 (EV -2 at the sensor). Based on that, I consider EV -2 as the practical low light sensitivity limit for live view metering.

As mentioned before, I don't have access to a K-1 and would welcome some findings for stop-down metering using a controlled process with that camera.


Steve

* I hate using "EV" in this way since the term originally referred to a combination of shutter speed and aperture (quite literally "exposure") independent of film/sensor sensitivity. The values above are for metered EV at ISO 100.

** By linear, I mean a doubling of metered exposure time for each full stop as the aperture is narrowed.


Last edited by stevebrot; 07-12-2018 at 11:10 AM.
07-12-2018, 01:57 PM   #17
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Well, I had M 300/4* lens too and it was not any better when stopped down to f/8 or smaller. F/4 and /5.6 were okay but I used that lens only on daylight.
07-12-2018, 05:49 PM   #18
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Thanks everyone. Since I would be primarily using this lens for landscape, hence need to find a way to calculate the optimal exposure when stopped down to f8 or f11. I may not be using this lens wide open. With f22 I will have to use EV compensation to -5 to get correct t exposure. But again it changes with aperture setting. As advised , I will try to meter exposure at f2.8 and then will manually calculate the shutter based on the aperture and see how well that works out.
07-13-2018, 04:49 AM   #19
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QuoteOriginally posted by matroxication Quote
Thanks everyone. Since I would be primarily using this lens for landscape, hence need to find a way to calculate the optimal exposure when stopped down to f8 or f11. I may not be using this lens wide open. With f22 I will have to use EV compensation to -5 to get correct t exposure. But again it changes with aperture setting. As advised , I will try to meter exposure at f2.8 and then will manually calculate the shutter based on the aperture and see how well that works out.
The green button metering with manual K-mount lenses was problematic from the K10D onwards as has been outlined above. However my experience with the K1 is that it meters very well. I have just done a little test in the garden with the SMC 24mm 2.8 (your lens) and I get consistent metering throughout the f-stop range. Perhaps a half stop overexposure at f16/f22 but not the five stops you are getting.

Method is Manual exposure; optical viewfinder; green button. Dont forget that with optical viewfinder you get centre-weighted metering or spot.

One of the things I noticed immediately i bought the K1 was that the green button exposure was correct again after the problems I had with my old K10D. I have an extensive collection of K-mount manual lenses and I have yet to find one that the K1 does not meter correctly with.

Does your 24mm have sticky aperture blades ?

07-13-2018, 06:14 PM   #20
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The Pentax 24/2.8 was my first foray into old Pentax glass. Great lens, but mine turned out to have some issue with the diaphragm mechanism, not sticky blades but gave a similar result to what you're describing. I hope that's not the issue you're having, because I was unable to get mine fixed. If you're getting 5 stops overexposure at f/22, that means the lens is hardly stopping down at all when you release the shutter. Which could be sticky blades (easy fix), or could be a faulty diaphragm such as mine had. In either case, the lens isn't going to work properly, no matter how you meter -- you will always be shooting wide open or nearly so. So find a competent camera tech and take or send it in for an evaluation.
07-14-2018, 03:34 AM   #21
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Thanks baro-nite. I just purchased the lens from Pentax Market place for $AU130 including shipping within Australia. Am not sure how much its going to cost to get this fixed
07-14-2018, 06:05 PM   #22
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I have reset all in-camera settings and did testing indoor and outdoor. On indoors, the lens is working as it should across different aperture range and the green button does metering and selected the correct shutter speed to get the right exposure. I even tried with different ISO setting.
But when used outdoors, the lens metering system (Spot or Center) is not able to calculate the correct exposure I believe and it overexposes. Am not sure if anything that am doing wrong or this is the behavior. Please find the images as attached with center and spot metering (Aperture f22). The building which I was trying to focus, is overexposed and spot metering does a bit better job but still not good. I have to manually use the exposure compensation to get it to expose correctly.

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PENTAX K-1  Photo 
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07-15-2018, 02:28 AM   #23
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QuoteOriginally posted by matroxication Quote
Please find the images as attached with center and spot metering (Aperture f22)
You are trying to capture a very high contrast scene (the buildings on the left are correctly exposed (in number 2) while the subject building is blown out). But I would have expected the subject to be correctly exposed at least with spot metering.

Look through the front of the lens as you press the green button, then shutter release, at small apertures. Does the diaphragm close quickly, stay closed for the duration of the exposure ?
07-15-2018, 02:47 AM   #24
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Exactly. At least on spot metering it should have correctly exposed. When I press and release the green button, the diaphragm stops down and opens for the duration of the green button. Do I need to keep the green button pressed when I hit the shutter ?
07-15-2018, 03:08 AM   #25
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QuoteOriginally posted by matroxication Quote
Exactly. At least on spot metering it should have correctly exposed. When I press and release the green button, the diaphragm stops down and opens for the duration of the green button. Do I need to keep the green button pressed when I hit the shutter ?
No. You press the green button and release, you should see the aperture close and re-open as the camera takes a meter reading. Then you press the shutter button.

Does it stop down all the way (f22) during both green button and shutter press ?

Make sure you have no EV compensation dialed in.

---------- Post added 07-15-18 at 11:09 AM ----------

QuoteOriginally posted by matroxication Quote
At least on spot metering it should have correctly exposed
Well, the subject should be correctly exposed. The buildings on the left should be very dark.
07-15-2018, 04:15 AM   #26
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Correct , when I press the green button the aperture closes and reopens. It works fine indoors and the green button produces correct exposure. Not sure what is different outdoor when it's too bright. Even I was expecting the building on left to be dark which was not the case

---------- Post added 07-15-18 at 04:26 AM ----------

Regarding the EV compensation , I have double checked it. Not sure what the problem is.
07-15-2018, 04:27 AM   #27
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QuoteOriginally posted by matroxication Quote
Correct , when I press the green button the aperture closes and reopens. It works fine indoors and the green button produces correct exposure. Not sure what is different outdoor when it's too bright. Even I was expecting the building on left to be dark which was not the case
So the aperture closes the same amount on grren button and shutter operation.

You get correct exposure indoors, but not outdoors/ Is this the same for your K-mount 50mm lens too ?
07-15-2018, 04:46 AM   #28
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If I can remember, the 50mm seems to be fine outdoors in the same scenario and the issue is only with 24mm. How ever I will double check on the 50mm again next weekend.
07-15-2018, 07:48 AM   #29
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The most puzzling thing is your observation that Green Button metering with the 24/2.8 is working correctly in some circumstances (indoors) but not others (the scene above). Here's a suggested approach for figuring out if the lens itself is the issue. Shoot some neutral subject (e.g. evenly-lit interior wall) wide open, manual mode, with settings that give you correct exposure. (Actually you could use any scene but an evenly-lit blank wall would be my choice.) Continue with a series of shots, each time stopping down one stop and doubling the exposure time. If each exposure turns out more or less the same, the lens diaphragm is working properly. If that's the case, the issue you're having must be camera-related.
07-15-2018, 08:29 AM   #30
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I may be misunderstanding this or perhaps it was explained and I missed it but why is Spot metering being used? Spot metering can easily cause the problem being discussed.
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