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11-11-2016, 03:40 PM   #1
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mysterious underexposure

Hi Forum

I am a frequent user of my Pentax 645n.
I use in auto function and it has always been flawless.
However......
Recently got I back 30 rolls of portra 400 120 from a holiday and exactly half are dramatically underexposed.
There is an obvious day in which the metering shifts from perfect to very very wrong.

The mystery is all dials are correct - iso set to 400, all film used is 400, dials not shifted to minus anything
i have cross checked through lens meter readings with my Pentax 67ii and a light meter and the Pentax 645n is apparently reading correctly but results look 4 stops under.
It is not lens dependent either as I used two lenses through out the trip.

Please please help
any suggestions?

11-11-2016, 03:54 PM   #2
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A problem with the shutter mechanism, perhaps?

Adam
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11-11-2016, 06:46 PM   #3
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I am interested in the thread. I have a 645 and it also underexposes sometimes. Not by 4 stops though. I haven't figured out the pattern yet. Most noticeable with Velvia, sometimes portra 160 on a cloudy day, but not fuji acros 100... Maybe there is no pattern and it's just random...
11-11-2016, 06:50 PM   #4
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Exactly what conditions are the photos being taken under? Sometimes a cameras metering can be thrown off drastically when metering a dark scene by strong light entering the eyepiece.

11-12-2016, 02:41 AM   #5
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By the way holidayformat, welcome.
I'm curious about your problem also since I use the 645. You might want to query the members in the Medium format forum here in PF or search past posts. Many who regularly comment there have much experience in Pentax 645 cameras.
11-12-2016, 02:43 AM   #6
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Thanks for the quick response

Photos are being taken in a wide range on conditions. It seems the underexposure is consistent across all rolls and frames.
It seems very much like the information on the dials and the reader is not what is being implemented inside.
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