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Full Version: holy grail darkening in sequence
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Setup: Nikon D800E with google Nexus7 tablet.

The holy grail for LRTimelapse works great, but there is one problem. I think it might be a Nikon problem but am not sure.

I set up my parameters like this:

Longest Shutter: 15.0"
Max ISO: 6400
Connection Direction: Sunset

Then I set the current exposure and ISO, typically maybe 1/800 and ISO 100.

When I start the Auto Holy Grail, everything goes fine at first. As it gets darker, the exposure time increases until it reaches the longest (15.0") and then the ISO starts to go up. The problem is that around ISO 400 it stops increasing as it gets darker. I can see the histograms moving to the left indicating that the frame is underexposed. Then, after maybe 100 exposures, the ISO starts increasing again. After the next maybe 100 exposures, the ISO catches up to where it should be.

The result is that in LRTimelapse, the exposure curve looks nearly flat at first, then there's a dip followed by an increase, like a "U", and then it's flat again.

Does this make sense? I can correct for this problem in LRTimelapse to some extent, of course, but it would be better if the problem didn't exist.

Any ideas?

Is this reproducible? I did not experience that yet - could you post a screenshot of the curves in the LRT preview please?
It is reproducible. Here I was using a 28mm f/2.8 wide open but I see it also with other lenses. The attached screenshot covers a time from near sunset to a couple of hours after darkness starts. One frame every 30 seconds. I had DSLRDashboard set up to make corrections in 1/3 stop. After starting the sequence with DSLRDadhboard, I didn't touch the camera.

I can of course fix this dip in LRTimelapse and Lightroom 5, but when I do it adds some flicker that even the deflicker option doesn't completely fix.

Oh, I think I know what happened. I had DSLRDashboard checking every third frame, (90 sec in this case) and making only 1/3 EV changes when needed. I think the light was changing so fast that 1/3 EV every 90 sec wasn't fast enough. So it got behind. Maybe this caused a problem in DSLRDashboard, or maybe it just took a long time to catch up.

Anyway, I just made a similar set but with the change in DSLRDashboard changed to 1 EV when needed. This worked well. I didn't see the dip in exposures this time.
Hmm - hard to say for me without knowing the exact sequence. Please note that the Auto Holy Grail is meant to be like an auto pilot: sometimes you should check while shooting and maybe adjust the reference value by clicking +/- beneath the "set reference" button.
If the previews are getting too bright press - to shift the reference down, and vice versa.
Please keep observing this and keep me posted.