Getting some inconsistent exposures while making time-lapse sequences.

Hello fellow Nikonites! I am new to the site, but I come asking for some assistance from others who have experience using Nikons (specifically the D90).

So, I like to make time-lapse sequences on occasion, for which I have an external timer remote from Phottix. Most of the time the sequences I get look pretty fantastic, but recently I have been noticing some intermittent exposure issues that I can't figure out! To practice, I have mostly been shooting things like moving clouds and similar landscape stuff... however every so often a frame will be exposed a little different than the rest, and the effect this has when stringing the images together into a video is a very distracting flickering effect that is extremely difficult to correct after the sequence has been shot. (Upon closer inspection I have seen the evidence of this in the in-camera histogram.) Bottom line is that (sometimes) every few frames I will get one or two that are slightly brighter than the rest.

After noticing this I double-checked my settings to make sure nothing is set to "auto" as I did make that mistake once or twice before... I have Aperture, Shutter, ISO, and Focus all set to MANUAL... Dynamic Lighting is OFF... Noise Reduction is OFF... White Balance is set to DAYLIGHT... VR (when applicable) is set to OFF due to being on a tripod. So what else could I be missing?

I shot one sequence just a couple of days ago using the 18-105 kit lens that has this problem, then the following day I did another one that looks fine! I am not certain if I was using the same lens when it happened before this or if it happened with a different one. I am beginning to worry that this might be indicative of some sort of intermittent hardware malfunction occurring in my camera. I sincerely hope it is not a fault in my camera, as I checked my actuation count today and I'm only at about 48% of the expected life span of my D90's shutter. Does anyone else have some experience with this that could shed light on my problem? I would greatly appreciate any help! Thanks!

EDIT: An example of the flickering exposure that I uploaded to YouTube a while back can be found here: https://www.youtube.com/watch?v=NPu4w11RBbM

I should also add that I am quite confident that this effect is not the result of the video compression, as I noticed it before even making the sequence into a video.

yrogerg said:

After noticing this I double-checked my settings to make sure nothing is set to "auto" as I did make that mistake once or twice before... I have Aperture, Shutter, ISO, and Focus all set to MANUAL... Dynamic Lighting is OFF... Noise Reduction is OFF... White Balance is set to DAYLIGHT... VR (when applicable) is set to OFF due to being on a tripod. So what else could I be missing?

Click to expand...

This sounds correct if you do not want the exposure to vary. I doubt VR matters if not AF, but it does not hurt to turn it off.

If exposure is varying, then look at your Exif on the problem shots, and verify these parameters in fact are not varying (I don't see how they could vary if all is Manual. Auto ISO will vary Manual exposures, but you said Auto ISO was off.)
My point is, check Exif to make sure you know the numbers are in fact not varying. The camera tells you what it did.

Then, if all is manual and unchanged, and yet exposure is still varying, it would seem like it must the light that is changing. A cloud passing over the sun perhaps? It can make a serious difference. Partly cloudy skies can be a pain.

If your scene shows shadows, the shadows can tell the difference - dark distinct shadows vs weak vague shadows when cloudy. Did the shadows change?

WayneF said:

Then, if all is manual and unchanged, and yet exposure is still varying, it would seem like it must the light that is changing. A cloud passing over the sun perhaps? It can make a serious difference.

If your scene shows shadows, the shadows can tell the difference - dark distinct shadows vs weak vague shadows when cloudy. Did the shadows change?

Click to expand...

This is the part that is so confusing to me... I did check the exif data in-camera before I even downloaded it (in addition to the histogram) and it verifies that the exposure values did not change, as expected. It seems to be the overall exposure that is changing from shot to shot, as the effect is most noticeable in the sky. I looked at the sequence I shot a couple days ago again, but I couldn't tell if anything was happening in the shadows as they are fairly dark (exposing for the sky and all...) and it isn't really possible for the clouds to cast a shadow on the sky anyway, so I don't think it is the ambient light level that is changing... I'll see if I can upload an example time-lapse with the flicker and link it in my original post. Thank you for the reply!

Edit: Here's the link - https://www.youtube.com/watch?v=NPu4w11RBbM

I'm sorry, but I didn't notice much variance. Maybe a quick bit at end of first segment, on the roof at about nine seconds. There was a steady stream of moving clouds, and it seems highly probable that they could have obscured the sun for an instant off and on. With such idea, I did not notice much in the way of a problem.

I think the camera is surely OK, but if worried about it, try repeating a scene indoors with artificial lights, to rule out any variance then.

My base is that in the good old days, before any or many cameras had light meters in them, some of us used hand held light meters. It sometimes was a challenge to take a reading, and get the camera settings adjusted and aimed and the shutter clicked, before a cloud changed everything on us. Things are more instantaneous today, clouds do still change the lighting situation, and current metered exposures adapt, but moving clouds are a pain.