X-T4 Exposure spikes during interval timer

[madnic]

I use my X-T4 for a lot of timelapses, and have been getting a weird glitch whenever I do a holy grail shot. I'll set it to auto exposure length, electronic shutter. At sunset it ramps nicely from 1/30000 to somewhere around 2.5~5 second exposures, then jumps to a 30-second exposure without using any setting in between. Inevitably this means about ten minutes' worth of frames are over-exposed until it gets dark enough for 30 seconds not to be terrible. After an hour or so stuck on 30 seconds, it'll start varying exposure to match actual conditions around moonlight/aurora activity, still tending towards over-exposure. Then at sunrise, same problem in reverse where it will keep the setting at 30 seconds for around 10 minutes after it should have started ramping, then jump straight to 2.5 seconds.

I've updated camera firmware, tried setting lower exposure compensation, tried with "Interval Timer Shooting Exposure Smoothing" both ON and OFF. Nothing seems to work. This is my second Fujifilm I've used this way, and I never had any problem like this with my old X-E3.
Attached a couple of pics showing what the transition looks like in editing.

Attached video shows preview of the output when I haven't yet gone crazy with the deflicker to try to smooth it out. Sunset spike about 0:08, Sunrise at 0:45.

 

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[jerryy]

Unfortunately the video you included does not play, I tried a few browsers, no joy.

Can you separate out the settings for the camera from the settings you have for the LRT app? Also, include many more camera settings, such as what kind of metering mode you are using as well as where you think the focus point was for the sequence.

Are you setting this up to taking one shot, waiting a while based on the anticipated exposure, then taking another shot and repeating from there?

If you manually blink through the sequence, does anything catch your attention as to what differs between the frames where there is a dramatic exposure change?

If you look at the manual https://fujifilm-dsc.com/en/manual/x-t4/menu_shooting/shooting_setting/index.html#interval_exposure_smoothing

regarding exposure smoothing, it recommends using shorter intervals to keep the big shifts minimized, have you tried this to the extent you can?

To that end, what happens if you use fixed time exposure, adjusting throughout the night? From the way, the LRT manual reads, that approach sounds like it fits their workflow, but maybe not ???

p.s. Welcome to the forum.

Edited November 13 by jerryy

[madnic]

Thanks for the welcome. Have browsed many times for questions others had already asked.
Not sure what went wrong with the video embed. Have tried again below, or this links to where it's stored in my Smugmug gallery.

 

 

Camera setup

• Fujifilm X-T4 with Samyang 12mm at F2.8
• ISO Auto 800-3200 (Dynamic range 400%)
• Auto shutter speed (electronic)
• Long exposure NR OFF
• Photometry CENTRE-WEIGHTED
• IS OFF
• Flicker reduction OFF
• Interval timer shooting exposure smoothing OFF
• Interval set to 14 seconds, which increases to 42 seconds once exposure length ramps up to 30s. 

Last "correctly" exposed frame at 19:38:52, ISO 3200, Exposure 5s.

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The following frame at 19:39:06, 14 seconds later, has ISO 3200 and Exposure 30s.

It doesn't appear to be an issue of too long an interval between shots. It's not that the light is changing too fast for the sequence, it's that the camera changes settings faster than the light. I've sat with the camera more than a few times trying to figure it out and there doesn't seem to be anything physically changing in the environment to cause it. It's just when the shutter speed should step to 5s or 6.5s, it instead steps to 30s. 

Problem with fixed time exposure (and yes, I can keep manually adjusting all night and it won't happen) is that I very rarely set my camera up somewhere readily accessible. It usually goes out before sunset with external battery bank setup and I hike back to wherever I'm staying the night. My most frequently captured shot is trying for holy-grail leading into an Aurora or vice versa at a lookout 30 mins jog from my accom. I'll set it up late afternoon, run back out a few hours later to make sure battery is behaving, then collect after sunset after it's been running some 10-14 hours. Obviously impractical to sit with it 😉

I've wondered whether it's a problem of using an interval setting that's less than the 30s max exposure length it ends up ramping to, which when it works just effectively slows the interval rate after sunset then speeds up again predawn. But I've tired both ways and that doesn't affect it. Did a sequence a couple of nights ago with 60 second intervals to check and it had the same problem as always.

 

[jerryy]

It looks like there may be several options that will affect your sequences.

[For those reading along, a holy grail sequence is explained here: https://petapixel.com/2018/08/02/how-to-shoot-and-edit-a-holy-grail-timelapse-at-sunset-or-sunrise/ .]

I very well sympathize with troubles coming from trying to get remote sequences, but sometimes, well, …, you still have to babysit the camera either in-person or via long distance wifi or ethernet.

I noticed several light sources popping up in and out of your Smugmug video. Maybe try using spot metering with the exposure tied to the focus point. As long as no car lights or flashlights, etc. turn on and off inside the focus area, lights outside of the focus area will have far less effect on the overall exposure. You will have to tie the metering to the focus point as explained here: https://fujifilm-x.com/en-gb/learning-centre/which-metering-mode-should-you-choose/

It would be nice if there is a quick-do-this and everything is copacetic, but probably it will take working each part of the issues you are facing one at a time until you can get results you like better. The most troubling part is giving the camera free rein over the shutter speed with other “auto” features turned on as well. Older cameras did not have as much latitude to do as they wanted.

@madnic edit: Second place to try: Try raising the maximum iso to 6400 and pull the shutter speed back down. The sensor will give you clean files and the algorithms have more room to work in before they over-ride the set shutter speed.

Edited November 14 by jerryy

[madnic]

Hi Jerryy,
I'll play around with metering settings more next time I'm out there. Won't be for another couple of days til I next have a chance. It is unaffected by anything real though, and in the case of that particular sequence the spike was well away from the time of torch light that affected frames around an hour later. Presence/absence of real light sources doesn't change the behaviour. One of the places I usually set it up, the nearest light source in its field of view is a few thousand km away and it will still reliably fail. If I sit there through that period and just press the shutter button repeatedly it won't happen, so I think it's something to do with the interval timer setting. I would put it down to problems with being left unattended, but I haven't had this problem with other Fujifilms.

ISO could be a good one to test. I tend to avoid going over 3200 with my 12mm lens, but anything is worth a shot.

[jerryy]

Hello again,

There is a simple way to see if the internal interval timer is part of causing problems. Switch to the mechanical shutter and bulb mode, then use an external intervalometer such as: https://jjc.cc/index/goods/detail.html?id=483 or one of their competitors, there are several really good ones out there. (In bulb mode, the electronic shutter is limited to one second exposures.)

Keep in mind the sensor is far, far more sensitive to light than our eyes are. It can record briefly lit lights we never see. For example, a one second astrophotography exposure will fill an image with more stars (very very very distant single points of light) than our eye see even in the darkest of places.

Hopefully, setting a low minimum shutter speed in your auto iso menu setting will help as well.

[madnic]

I've had some... not success but definitely a slight improvement playing with different metering modes. Changing the ISO range had no effect.

Not sure what you're suggesting with the bulb setting and external timer. That's just going to be fixed exposure length of what 1/2 second? I've got a similar timer that I've used with a Sony in the past and it doesn't allow for exposure ramping. I realise there are timers that do, but even then exposure ramping isn't exactly what you need for HG because it's not a linear transition over time.