Settings last night:
Shot Rate: 10"
Tv normal Limit: 1/4"
Tv low limit 12"
ISO default: 100
ISO Upper limit: 1250
Exposure ramp rate: medium
Aperture setting: min_Av
Use ND Filter: eneabled
Raw Enable: Disabled
Those are pretty much the defaults other than the ISO Upper limit (changed from 400 to 1250) and Tv low limit from 10" to 12". Should be okay.
One thing occurred to me immediately that I should probably have mentioned and it's why I wanted to see the log files. My strongest suspicion is that this is related to the camera's ND filter engaging/disengaging.
When I tried using the versions of the script by the previous authors, I would see a jump like that when my camera automatically introduced or removed the ND filter. Cameras with adjustable apertures (i.e. user settable f-stops) do not tend to automatically engage the ND filter - camera with fixed apertures (other than what changes with zoom position) do. So I added code to control the ND filter and rather than just force the ND filter off, I added logic to control it as part of the exposure adjustment code.
The catch here is that I assumed the inserting ND filter was the equivalent of changing by 3 f-stops. That seemed to work well on the camera I was using at the time (A1200) and matched testing of the camera and my research on the forum. I've since noticed some variation between camera models in that number and so you may need to "calibrate" the factor used by the script.
To change the factor today, you'd need to edit line 89 of the script where it says :
nd96=288 -- ND filter's number of equivalent f-stops
Changing the 288 to 192 gives you 2 f-stops, 288 to 96 gives you one f-stop, and so on.
Or you can just disable the ND filter altogether using the available script parameter in the CHDK Script Menu.
All of the above is dependent on seeing if the ND filter position was reported as changed when the exposure suddenly jumped.
There are a couple of things I can do here. First of all, I should make the ND filter calibration factor something that can be set in the script parameters so future users do not have to edit the code. And I can pretty easily provide a simple script that will provide the correct calibration factor. I'll do those tonight regardless of what you find. (I suppose I could even make it an automatic part of the program that runs at the start for a few seconds if ND filter mode is enabled).
