Author Topic: 7D shutter speed - 1/48 vs. 1/50  (Read 998 times)

sgofferj

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7D shutter speed - 1/48 vs. 1/50
« on: April 12, 2018, 10:06:35 PM »
I noticed a very odd thing with my shutter speeds in LV mode. While the top LCD shows 1/50, ML actually shows 1/48 on the monitor. I have filmed in a location with very bad CFL tubes and I did get vertical moving artifacts, suggesting that I really was shooting with 1/48. Next lower would be 1/41 and next higher would be 1/62 according to ML. Video mode was set to 1080p25.
Is this a quirk in the 7D Canon fw or is that an ML quirk
18+ years Linux user, wolf-fan, hobby photographer and -filmmaker
EOS 6D, EOS 7D

a1ex

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Re: 7D shutter speed - 1/48 vs. 1/50
« Reply #1 on: April 12, 2018, 10:25:48 PM »
Correct (no question mark => assuming statement). Neither Canon firmware, nor ML will show the exact shutter speed on 7D. The former shows so-called market values (look it up on CHDK), the latter shows an approximation based on Canon's internal representation of shutter speeds (we believed it to be correct some years ago, but found out not to be the case).

More info here (a few models report exact shutter speed in ML, others allow SHUTTER_FINE_TUNING) and here for some experiments on 5D2. The method for getting exact shutter speed has to be ported to all models - easy coding task, but low priority (mostly because it's hard to get tester feedback on such nitpicks, and this one is likely model-specific). Maybe after being able to emulate LiveView in QEMU (to have a way to test it without waiting for months for user reports).

sgofferj

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Re: 7D shutter speed - 1/48 vs. 1/50
« Reply #2 on: April 13, 2018, 06:57:34 PM »
Actually, it was a question - I just forgot the question mark, but thanks for the explanation and the link :)
18+ years Linux user, wolf-fan, hobby photographer and -filmmaker
EOS 6D, EOS 7D