Erratic long exposures

[DandA]

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Hi,

 

This question is from an aquantance who is shooting with the MM1. While shooting a well lit nightime outdoor scene (tripod mounted)n at base ISO 320 and then again at ISO 400 and 640 to look st the differences of noise chsrateristics of each shot (noise reduction kicks in), he observed something strange. Here was his initial observation:

 

ISO 320 (perfect exposure)

ISO 400 (over exposure)

ISO 400 (over exposure)

ISO 400 (perfect exposure)

ISO 400 (over exposure)

ISO 400 (perfect exposure)

ISO 640 (over exposure)

ISO 640 (perfect exposure)

 

Of course thr over exposed pics had longer exposure times.

 

Again all tripod mounted and nothing changed in lighting diring each exposure.

 

In addition he also mentioned when he got home and simply fired the camera continuously, it maxed out at 8 seconds unless he turned off and on the camera which thren it acted normally. Not sure what he meant by this last observation until I get further clarification from him. Any idea why the erratic exposures on his nightime tripod mounted shots described above? Thanks.

 

Dave (D&A)

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[DandA]

Well I have a better handle on his issue .  He was shooting the series of shots as described above at the various ISO's. Instead of waiting between each individual shot till the red light indicating the file and companion noise reduction dark frame was finished writing, he continued to shoot till the buffer was filled.  Apparently by doing so, he interrupted the noise reduction part of the file writing and this caused erratic exposures.  If he waited for each individual low light shot and noise reduction to completely finish before taking the next shot, all exposures were accurate.  Has anyone experienced this or seen it described?  Thanks.

 

Dave (D&A)