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08-07-2015, 12:09 PM   #1
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Zenitar 16mm slow aperature lever

My Zenitar 16mm aperture lever seems to be slow or something. It over exposures with 1/200 and faster when stopped down on my K-3

In M - mode I have set the aperture, hit the green button and lens stops down for metering. I can hear that. I get nice 1/500 speed with 8.0 for example.
Metering is almost same as in old ME so metering works. Also preview works.

Then I release the shutter and only usable parts are shadows. Way too much light. Am I doing something wrong? (50mm works OK in same workflow) or can this be resolved in the lens?

My best guess is that lens is still closing while shutter is already open and too much light enters. Difference between 500 and Zenitar in lever feeling is noticeable.

Has anyone else had similar problems?

08-07-2015, 02:40 PM   #2
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QuoteOriginally posted by anemone Quote
Am I doing something wrong?
It looks like you are doing it right and it is possible that your Zen is not cooperating. Is the aperture responsive and snappy at all settings with the lens off camera? You might also want to do an exposure series at constant EV (Exposure Value). If you get the same basic histogram for each exposure in the series, there is no issue with the lens.


Steve
08-07-2015, 05:56 PM   #3
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This happened to me with a Sigma 70-200 2.8. Pictures at F2.8 were fine but other apertures were overexposed. I can sometimes even see that the aperture is slow to close when I look into the lens from the front. I think the aperture mechanism needs to be cleaned/replaced.
08-07-2015, 07:28 PM   #4
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Looks like I have to get dose for my LBA and learn to disassemble, clean and assemble lenses.

I did quick look to problematic scene where I noticed this problem. I remember starting from wide open and then stopping down one notch at a time and every time I hit the green button to measure. And I have five good pics. Two from wide open end and three from stopped down end. Rest are more or less overexposed. But I need to take that test.

08-07-2015, 11:18 PM   #5
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QuoteOriginally posted by anemone Quote
every time I hit the green button to measure. And I have five good pics. Two from wide open end and three from stopped down end. Rest are more or less overexposed. But I need to take that test.
I think may find that metering is not linear for stop-down metering with your K-3 with this or other lenses. I suggest that you take a well-lit daylight scene and determine a reasonable exposure in M mode using the green button and fine tuning with the histogram. Once you have that baseline, do the appropriate calculated exposures (no additional metering) for larger and smaller apertures. The EV table at the link below may be helpful for finding the combinations.

https://en.wikipedia.org/wiki/Exposure_value#EV_as_an_indicator_of_camera_settings

I will state again, a little more explicitly...the Zenitar, as with many ultra wide angles is very good at fooling the meter on your camera. This is made worse by the lack of consistent accuracy of the K-3 for stop-down metering. The reason for that is complex, though it is enough to say that the K-3's stop-down metering is much much better than the likes of the K10D and K20D, but still different than open-aperture metering with A-contact lenses.

Your overexposure may not be due to any mechanical failure of the lens.


Steve
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