Star Trail Problem

Hi Everyone

I posted the below on the a7iv Facebook page and had a few replies from some helpful people but thought I would broaden the search for some answers

Now that we are coming into cool clear nights I decided to do a trial run for some star trail photography.

Camera A7iv

Sony 20mm 1.8

Pixel TX 283 intervalometer

Camera set to bulb mode with intervalometer set to 25 second exposure with a 2 second interval between shots. I thought all was going well until I scrolled through the images and noticed that the shutter speed would randomly change as follows

The first 21 pics were all at 25 seconds with 2 second interval as expected.

Image 22 - changed to 11 seconds plus interval

Images 23-28 back to 25 seconds plus interval

Image 29- changed to 10 seconds plus interval

Images 30-34 back to 25 seconds plus interval

Image 35- changed to 10 seconds plus interval

Images 36-41 back to 25 seconds plus interval

Image 42 changed to 23 seconds plus interval

Images 43 & 44 changed to 1/10 second with black image due to the faster speed.

Images 45-73 back to 25 seconds plus interval

Another strange thing I noticed is that the time between the end of photos 42-45 doesn’t match what the shutter time changed to plus the 2 second interval.

Image 42 taken at 01.21.05 hrs

Image 43 taken at 01.21.09 hrs

Image 44 taken at 01.21.36 hrs

Image 45 taken at 01.22.28 hrs

Not sure if this helps or makes sense.

I have wrecked my brain trying to figure out what went wrong. I have noise reduction turned off. Sod’s Law weather for the next week or so is rain and cloudy nights so it could be a while before I get out again. I am probably doing something stupid but for the life of me I can’t think of anything other than my memory card not being fast enough. It’s a SanDisk extreme pro SDXC 200MB/S UHS 1 class 10 U3 V30.( write speed 90MB/S) or would it be a camera problem?

Any advice would be greatly appreciated as I’m disappointed that my first try started out well and don’t know what went wrong. Keen to sort it out before next attempt.

P.s I have ordered a couple of uhs-II and despite the breaks in the trail from the drop in shutter speed the pic turned out ok considering i wasn’t in a great location

Many thanks

Higher speed cards will not be a bad idea.

Why use an external intervalometer when the A7iv has one built in ? I use the built in one with the A7iii with good results and a simplified set up. Alternatively use a wired cable release put the camera in continuous shooting mode, press the button on the release and lock it. That works well too.

Your actual problem is sounds like slow card writing to me.

Just noticed your are using bulb mode with a 25 second exposure. Why not just use a 25 second shutter speed on camera. Might also be a good idea to test in the garden before making a trip.

Could be a slow or damaged sdcard as stated above, or it could be a bad intervalometer. I agree with other poster in that you should use the built in intervalometer feature rather than hooking up a separate, and totally unnecessary, device. Look for "Interval Shoot Function" in the Settings.

I would set the Interval Shoot Function to 31 sec and the shutter to 30 sec. That will take a series of 30 sec shots with 1 sec interval between each. Even with a slower sdcard it should work fine. No need to use 2 sec intervals between shots on the newer Sony cameras. The shorter the interval between shots the better the image will look. Too long and you will start to see gaps.

--
Best Regards,
Jack
YouTube channel: https://www.youtube.com/channel/UCAfQN-Ygh9z7qqUXdZWM-1Q
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Sony RX100M3, a6000, and a7

Thanks so much for the replies. I will give the built in Intervalometer a go along with a faster card. I only used an external one as I got carried away on Amazon after reading that some people use a single long exposure for trails. I had planned to give both methods a go but will stick to the 30 second multiple shots.. To be honest I was more concerned that there was a problem with the camera. Can’t wait for my second attempt. Have a great weekend

So, if I am reading this right, that is 27 seconds between shots? Ain't no way that the card is too slow for that.

My bet is the connection to the intervalometer (not the intervalometer itself but the connection between it and the camera). With the camera in bulb mode, my guess is the camera will close the shutter if the connection to the intervalometer is lost / broken.

As others have suggested, use the internal one if possible.

I have an external intervalometer but I haven't used it. To me, the way the R5 does things is confusing but I eventually figure out how I need to set it up before I give up and drag out another piece of equipment. I think I just need to use it more.

Hi Pedz

Thanks for the reply. Yep each shot was 27 seconds in total (25 second exposure plus 2 second interval). Looking back I did wonder off briefly several times to keep warm with the remote of the intervalometer in my pocket. The instructions claim an 80m range, at the most I was probably 10m away but it’s probable that that could have been the issue. I’m going to give the internal one a go inside the house to see if it works ok.

kind regards

adam

I've used the technique of setting the exposure time directly inside the camera, with a drive mode of continuous high or low, and set the interval timer to an exposure time of hours. I would tend to use either fully electronic shutter or the electronic first curtain shutter option but this is probably not critical. I wouldn't have the camera be in a completely silent mode because I find it is reassuring to hear the "heartbeat".

Because all of the critical timing is the responsibility of the camera body there should never be any conflicts that could have an impact on an individual time. There's no way that you would expect to overrun the buffer capacity, and the sequence will have the shortest possible gaps.

--
Wag more; bark less.

Hi!

The full-electronic shutter is much faster on Canon cameras (< 1 sec) compared to the 'conventional' shutter with a lag time of > 2 sec. The downside is that you will have only a 12-bit recording with the full electronic shutter (instead of 14-bit otherwise). I think that is acceptable in this case.

nighthiker said:

Hi!

The full-electronic shutter is much faster on Canon cameras (< 1 sec) compared to the 'conventional' shutter with a lag time of > 2 sec.

Click to expand...

But that would mean that the highest continuous shooting mode frame rate is only 0.5 fps or less, which would not be a viable product offering.

nighthiker said:

The downside is that you will have only a 12-bit recording with the full electronic shutter (instead of 14-bit otherwise). I think that is acceptable in this case.

Click to expand...

nighthiker said:

Hi!

The full-electronic shutter is much faster on Canon cameras (< 1 sec) compared to the 'conventional' shutter with a lag time of > 2 sec. The downside is that you will have only a 12-bit recording with the full electronic shutter (instead of 14-bit otherwise). I think that is acceptable in this case.

Click to expand...

I don't know if this is a typo or what but a lag time of great than 2 seconds is not true.

The lag time is the time from pressing the shutter until the camera starts to open the shutter. According to this review: With an approximately 50ms shutter lag (approximately 81ms using the mechanical shutter)

If you meant frames per second, with the mechanical shutter on the R5 is 6 fps and up to 20 fps with the electronic shutter.

I am very new to astrophotography but typical shutter times are in tens of seconds if not minutes.

--
Thank you,
pedz

pedz said:

nighthiker said:

Hi!

The full-electronic shutter is much faster on Canon cameras (< 1 sec) compared to the 'conventional' shutter with a lag time of > 2 sec. The downside is that you will have only a 12-bit recording with the full electronic shutter (instead of 14-bit otherwise). I think that is acceptable in this case.

Click to expand...

I don't know if this is a typo or what but a lag time of great than 2 seconds is not true.

The lag time is the time from pressing the shutter until the camera starts to open the shutter. According to this review: With an approximately 50ms shutter lag (approximately 81ms using the mechanical shutter)

If you meant frames per second, with the mechanical shutter on the R5 is 6 fps and up to 20 fps with the electronic shutter.

I am very new to astrophotography but typical shutter times are in tens of seconds if not minutes.

Click to expand...

Hi!

No, I don't mean the lag time! I mean the time from image to image in continuous shooting mode. The camera needs additional time for writing the file and getting ready for the next shoot. Just make a test with several longer exposures (a few seconds) in the continuous or fast continuous shooting mode and use the time stamps plus the exposure time to calculate the gap between the images. Believe me, I'm an oldy of night photography

Also see this older posting about the problem: https://www.dpreview.com/forums/thread/4561637

just Tony said:

nighthiker said:

Hi!

The full-electronic shutter is much faster on Canon cameras (< 1 sec) compared to the 'conventional' shutter with a lag time of > 2 sec.

Click to expand...

But that would mean that the highest continuous shooting mode frame rate is only 0.5 fps or less, which would not be a viable product offering.

just Tony said:

The downside is that you will have only a 12-bit recording with the full electronic shutter (instead of 14-bit otherwise). I think that is acceptable in this case.

Click to expand...

Click to expand...

The max. fps depend on the camera settings, mostly the auto-focus tracking and the exposure time. I haven't calculated the gap between the images for the full-electronic shutter with long-exposures, but it's short. Maybe << 1 sec instead of < 1sec. The max. fps is calculated for short exposures and I haven't read the Canon white papers if the gap between consecutive images is exposure time dependent (as it is for normal continuous shooting).

nighthiker said:

pedz said:

nighthiker said:

Hi!

The full-electronic shutter is much faster on Canon cameras (< 1 sec) compared to the 'conventional' shutter with a lag time of > 2 sec. The downside is that you will have only a 12-bit recording with the full electronic shutter (instead of 14-bit otherwise). I think that is acceptable in this case.

Click to expand...

I don't know if this is a typo or what but a lag time of great than 2 seconds is not true.

The lag time is the time from pressing the shutter until the camera starts to open the shutter. According to this review: With an approximately 50ms shutter lag (approximately 81ms using the mechanical shutter)

If you meant frames per second, with the mechanical shutter on the R5 is 6 fps and up to 20 fps with the electronic shutter.

I am very new to astrophotography but typical shutter times are in tens of seconds if not minutes.

Click to expand...

Hi!

No, I don't mean the lag time! I mean the time from image to image in continuous shooting mode. The camera needs additional time for writing the file and getting ready for the next shoot. Just make a test with several longer exposures (a few seconds) in the continuous or fast continuous shooting mode and use the time stamps plus the exposure time to calculate the gap between the images. Believe me, I'm an oldy of night photography

Also see this older posting about the problem: https://www.dpreview.com/forums/thread/4561637

Click to expand...

Wow... if some guy walked up to me on the street and told me about this, I would have laughed hysterically. Really weird. I probably re-read the end of the thread you pointed me to again. I still don't 100% comprehend. I wonder if anyone does.

Hi!

There seems to be some camera-internal issues why many Canon cameras need a few seconds between consecutive long exposures. The exact reason therefore is not clear. I also heard that this 'gap' is shorter for e.g. Sony cameras. For startrails I would therefore use the full-electronic shutter with a much shorter 'gap' in-between. For DS that is not recommended as it reduces the data output from 14 to 12-bit.

nighthiker said:

No, I don't mean the lag time! I mean the time from image to image in continuous shooting mode. The camera needs additional time for writing the file

Click to expand...

That is not correct. Files are first written into the buffer and then are written from the buffer to the card as an independent action that happens during the next exposure (if present). The continuous firing rates that eventually slow down on a long and rapid burst illustrate this relationship. Astro length exposures in continuous sequences should never fill the buffer, there would only be one or no files in the buffer at any time.

nighthiker said:

Hi!

There seems to be some camera-internal issues why many Canon cameras need a few seconds between consecutive long exposures. The exact reason therefore is not clear.

Click to expand...

I'd suspect noise reduction to be the elephant in this room, see below.

nighthiker said:

I also heard that this 'gap' is shorter for e.g. Sony cameras. For startrails I would therefore use the full-electronic shutter with a much shorter 'gap' in-between.

Click to expand...

There will be a miniscule added gap for Electronic First Curtain mode because of the shutter having to reset, and a longer but still small additional gap if the fully mechanical shutter mode is used.

nighthiker said:

For DS that is not recommended as it reduces the data output from 14 to 12-bit.

Click to expand...

The gap time on my Fuji 100S becomes a few seconds longer at the 2 minute point for exposure duration. RawDigger examination shows that a noise reduction, even on Raw files, occurs on exposures of 2m 0s, that does not happen at 1m 59s.

It's also slower to record at the 16-bit depth vs 14-bits because a longer settling time is needed at each and every A/D conversion.

nighthiker said:

The max. fps depend on the camera settings, mostly the auto-focus tracking

Click to expand...

That has no place in this context

nighthiker said:

and the exposure time.

Click to expand...

Of course, exposure N+1 has to wait for exposure N to complete. The advantage of Continuous firing rates is that there is no "worry padding" that must be added to an external interval timer's period, and those are often excessively long out of paranoia. Cameras in a high rate Continuous mode will cycle the next exposure as soon as they physically can. The buffer will be empty before the current exposure ends.

Wow, you guys are beating the bejeezus out of a dead horse! ;-) The OP has not even participated in your discussions for 2 weeks now. And since he is shooting with a Sony a7 iv, why all the Canon talk? That will just confuse him more. I've had Canon and Sony cameras, and they are way different in many ways! I think he is on the right track now that he ditched the external intervalometer for the a7 iv internal Intervalometer function.

With that function he won't have to worry about missed shots for long shutter startrails photography. In all likelihood he would only run into issues when using 1 sec total intervals or less, and that means the time the shutter is open plus the time before the next shot is initiated. In Sony's Japanglish, "interval" translates into the entire duration of time between the start of photo x and the subsequent start of photo x+1. For example, to shoot 30 sec exposures with a 1 sec gap between each, one sets Intervalometer = 31 and Shutter = 30 in the Sony menu. Again, this is not a Canon nor an external intervalometer. On my Sony ZV-E10 and a7C, shooting Interval = 1 sec and shutter = 0.6 or 0.8 sec or 1 sec can sometimes cause a few of the photos to fail to be taken. From Interval = 2 sec and longer, I've never encountered any issues with photos being dropped (not taken). YMMV and hisMMV of course. But once you get out to long shutters for startrails I seriously doubt the buffer will ever be an issue.