End of my astronomical timelapse shows?

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End of my astronomical timelapse shows?

Postby Magmatic » Thu Mar 22, 2012 3:22 am

I'm writing to announce the great difficulty I have had doing an astronomical timelapse slideshow. I just thought you'd like to know. With my camera, exposures are not consistent shot to shot. So, it's just not practical.

I did a timelapse slideshow of Venus and Jupiter recently. Pulling the shots into Proshow I discovered the brightness alternated light, dark, light, dark, light dark. That gives a strange flicker effect. I can change the brightness of each slide in Proshow, but that is very time-consuming. (By the way, in Proshow 5, it flashes "loading". Proshow 4.5 doesn't do that, but just blinks, which is just as bad.)

Even when I tried to adjust each slide, that didn't work because the brightness difference is not consistent across the slide. I can adjust the brightness for the center, but then the edges still flash. If I adjust for the edges, the center flashes.

So, this just doesn't work.


I use a low-end Nikon D3100. 4 second, f2, shot every 5 seconds. I did not use an intervalometer. I just stood there and hit the button. ISO400, manual, all the fancy-dancy adjustments such as D-Lighting turned off. Noise reduction was on, but should not be a factor because the exposure was too short.

Maybe the exposure time was not consistent. Perhaps it's the long exposure time. Perhaps it would be different at very long times. Or very short times. Perhaps a longer interval would help. But it needs to be fast or the stars move too fast. Maybe the aperture is not consistent on the lens, a 35mm DX 1.8.

With all the variables, is this really my last try? Probably not!

I wonder What kind of camera I need for this. I don't know how the big boys do it, such as with the incredible videos I've seen on Universe Today lately.

Here's the most-excellent demo:
http://www.youtube.com/watch?v=kiMkoU9TsKU
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Re: End of my astronomical timelapse shows?

Postby gpsmikey » Thu Mar 22, 2012 7:21 am

First thing that came to mind was being on auto expose, but you indicated you were set on manual. The alternating light and dark sounds like a problem I created for myself some time ago that took a while to figure out what was going on - I had set the camera to bracketed exposure (3 shots). It expects me to take those 3 shots of the same object then combine them later. I didn't realize what I had done, so one shot would be correct, the next over a stop and the next under a stop. The next one was right on again. Took a bit to figure that one out - one of those "duh" moments when I did solve it. :roll: I would have expected that if you were in manual mode, all the exposures would have come out the same - the fact they didn't indicates to me that something was changing. It did take me a bit to figure out that if I want a picture of the moon, I need to spot meter on the moon not average (which blows out completely).

One consideration on your camera is the number of shutter activations it is rated for. Most people are not aware of that issue since they came from the film era and were unlikely to easily get to 50,000 shots with film. I don't know what yours is rated for, but my D70 supposedly is only rated for about 50,000. My D300s is more like 150,000 if I remember correctly - doing timelapse can start to push those numbers a bit. Something to keep in mind.

There have been a number of really cool time-lapse sequences of the night sky on Vimeo etc with information posted there as to what they were using so it can be done - the trick is to figure out what you are doing different from them.

mikey
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Re: End of my astronomical timelapse shows?

Postby debngar » Thu Mar 22, 2012 8:31 am

I don't know if you have any thought to taking a workshop but Ben Canales offers them and he looks like he's mastered the technique.

Some of his videos look like he uses a mechanical contraption for automatically moving the camera on a dolly using a timer of sorts to get multiple perspectives.

http://www.dynamicperception.com/ Pretty costly unless there's a way to sell the results and recoup the costs.

http://www.youtube.com/watch?v=Upv_IKhcBI8

http://www.uncagethesoul.com/

http://www.thestartrail.com/

~~~~~~~~~~~~~~~~~
This tutorial covers a single shot, not time lapse and turns out to be on Vimeo.

Landscape Astrophotography Tutorial
http://vimeo.com/16833554
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Re: End of my astronomical timelapse shows?

Postby Ron » Thu Mar 22, 2012 12:18 pm

maybe the aperture is not consistent on the lens, a 35mm DX 1.8.

It could be the aperture but I think it would be highly unlikely, you probably would have noticed it earlier. I love the 35mm f/1.8 it's such a great value piece of equipment. If your settings on manually were 4 sec @ f/2 then either as Mikey said your camera is set for bracketing, which we all have done, or some other setting must be changing.. Although highly unlikely, what about your ISO ? Was it set manually as well

I think I would compare the exif data of a light & dark !! This should tell you why your seeing a difference! I'm curious what you find .
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Re: End of my astronomical timelapse shows?

Postby Magmatic » Thu Mar 22, 2012 6:04 pm

Well, Debbie, that guy is a true big boy. With big sponsors too. Very impressive. Thanks for the tip off.

I am sure the exposures were all at 4 and f2. Manual. ISO was set at 400 and not automatically altered. The camera does not have auto bracketing. I have had to laboriously adjust exposures before, but this one was different because it was so regular: light, dark. I've had inconsistencies with an advanced point and shoot too.

Remember the brightness inconsistency was not constant across the frame. Perhaps there is some vignetting going on.

Yes, I know the shutters are only claimed good for a certain number of cycles. I'm not too worried about that though. I just hope it's not programmed to shut down once the limit is reached. I don't even know how to check how many cycles have been done.
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Re: End of my astronomical timelapse shows?

Postby gpsmikey » Thu Mar 22, 2012 8:08 pm

No, they aren't "programmed to shut down at x cycles", however, like with my D70, someone had found the information indicating it was rated 50,000 if I remember correctly. When this discussion came up in the Nikonians forums some time ago, they were quoting something like $250 or something like that to have the shutter replaced. As far as how many shutter actuations you have, if you look at the EXIF data on the most recent image, you will see a number like "total pictures" or some such (I was just looking at it with Irfanview) that gives you the number of pictures taken with the camera (in my D300s, it indicates 23,886 (my D70s indicates just over 18,000)) -- the number reflects the total at the time that picture was taken :D I forget where I originally found that information - I think someone mentioned it in the Nikonians forums. One frame every few minutes does not rack them up too fast, but you often see timelapse stuff where they were shooting ever couple of seconds for hours which starts to run those actuation numbers up. I assume other cameras have similar information, but I am only familiar with the Nikons on this issue.

mikey
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Re: End of my astronomical timelapse shows?

Postby MG - Admin » Thu Mar 22, 2012 8:32 pm

Pardon the pun, but I'm taking a shot in the dark here to suggest trying again with the noise reduction turned off. A 4 second exposure isn't very long, but the fact that the camera is taking a second blank exposure and then "processing" the two images it may be the culprit.

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Re: End of my astronomical timelapse shows?

Postby Magmatic » Fri Mar 23, 2012 4:28 pm

Mikey, I'll see if I can find such a shutter count field in the EXIF.

Mike, I wish I had thought of that, the pun, I mean. Noise reduction was not "off", but it was not in operation. It would kick in at 8 seconds, not 4. Plus, I was shooting about every 5 seconds, so with a 4 second exposure, there was no time for a blank 4 second exposure.
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Re: End of my astronomical timelapse shows?

Postby chezeury » Fri Mar 23, 2012 6:35 pm

Hi,
I didn't know the answer to your question, but it got me curious so I had to go and research and the answer seems to be that it is the bane of time-lapse photographers simply because a DSLR is a mechanical device. So the shutter needs to open up and close and there are slight variations of how long they are open caused by friction etc., Normally you would not notice unless your attach 2 photos side by side, then obviously you can see the difference and that is what you are doing. I read this on a few websites, so I think it is correct and makes sense to me. Also suggested, using completely manual lenses. Because the camera stops the iris down from fully open to the chosen setting right before the shutter opens, and then resets after. One solution they found was to use manual Nikon lenses, since with those you set the aperture manually by turning a ring on the lens itself, and the camera never moves it.

This website shows a lens twisting tip that you can do to make an automatic lens work like a manual one if you don't have a fully manual lens.

http://blog.planet5d.com/2011/11/getting-rid-of-flicker-in-timelapse-the-lens-twist-method/

It's very cool as it offsets your lens just enough so the camera is not talking to the lens, but still allows you to take your photos.

For the time-lapse you already did, many people use de-flickering software that takes a look at the histogram of each frame and averages them and corrects them so they are all even. It will work as long as you don't have any clipping, as with clipping it cannot cannot correct something it doesn't have all the data for, but since you are taking time-lapse at night, I would imagine you don't have this problem. Apparently though, it is difficult to get perfect in post.

Hopefully, something that I found while roaming around can help you.
Best of luck
:-)
Maggie
To see my slideshows visit:
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Re: End of my astronomical timelapse shows?

Postby Magmatic » Sat Mar 24, 2012 6:09 pm

Well, thank you so much for that research, Maggie. Lens twist. A dirty trick! It's too bad my camera doesn't have a depth of field preview button. Anti-flicker software! Normally, that would help, but I don't think it would touch the inconsistent brightness across the frame. It could fix one part of the image, but not the other.

But you gave me an idea for another dirty trick. Simply delete every other frame. Bingo, no more flicker! It makes the motion twice as fast though. Alas, dirt has it's price.

I did some more experiments tonight. I said I had turned off all the fancy settings. But there was one setting I forgot about. I used the "quiet shutter" mode, thinking it was save wear on the shutter. However, my test tonight proved that was not the problem. I also tried it with noise reduction turned off, and that didn't help either. (Even if it isn't doing blank exposures, there is still noise reduction going on, with it turned on. Even with it turned off, just not as much.)

I had used a 4 second exposure. I tried 8 seconds, and no flicker! That's either because of the longer shutter speed, or the smaller aperture used. I wouldn't be surprised if it was the aperture, as in your suggestion. I might have tried another lens, but it started to rain.

I did use another lens earlier when it was still daylight, but a normal fast exposures, and no flicker. More tests are needed.
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Re: End of my astronomical timelapse shows?

Postby gpsmikey » Sat Mar 24, 2012 8:07 pm

I could buy the "inconsistent shutter" if the effects were random, but the fact that it is every other one is very puzzling. Have you looked at the EXIF for the images and verified that the camera thinks the shutter and aperture were the same in all the shots ? It used to be pretty easy to check the shutter - you opened the back of the camera, put a photocell or photodiode in the film plane hooked to an oscilloscope with a bright light in front and fired the shutter a number of times looking at the scope to check the time. Unfortunately, with these new digital thingies, there is no way to easily put something in the "film plane". This "every other one" is certainly puzzling and does not sound like a random shutter issue (or it would be random).

mikey
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Re: End of my astronomical timelapse shows?

Postby chezeury » Sat Mar 24, 2012 8:58 pm

Magmatic wrote:
But you gave me an idea for another dirty trick. Simply delete every other frame. Bingo, no more flicker! It makes the motion twice as fast though. Alas, dirt has it's price.


Yes, I'm also surprised that it is every second one.

As for the speed by taking out the offending frames:
How about making a duplicate of each frame; it would slow down the final result and no flicker. If you have Lightroom, you could simply select them all, right click and choose create virtual copies, and it would make a duplicate of each of them and place them right beside the original. Then reselect them all, (originals and duplicates) and export to a folder with a name and check the box so that they carry the the name and numbers in sequence and they will all be saved in the proper order.

It is worth a try.

Good luck
:-)
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Re: End of my astronomical timelapse shows?

Postby heckydog » Sun Mar 25, 2012 6:27 am

I don't think it would be necessary to duplicate the frames that are removed. All you have to do is change the frame length in PSP to twice the normal length.

For example, an NTSC video is 30 frames per second or .033 seconds for each frame. If you remove every other frame and change the frame length to .066 seconds the total length of the video stays the same.

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Re: End of my astronomical timelapse shows?

Postby chezeury » Sun Mar 25, 2012 7:33 am

heckydog wrote:I don't think it would be necessary to duplicate the frames that are removed. All you have to do is change the frame length in PSP to twice the normal length.

For example, an NTSC video is 30 frames per second or .033 seconds for each frame. If you remove every other frame and change the frame length to .066 seconds the total length of the video stays the same.

Joe



Heh, I just thinking about this, this morning, and realized how complicated I had made things, :roll: as it dawned on me that just making it longer in Producer would work. Thought I'd come and rectify my post, but you beat me to it.
:-D
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Re: End of my astronomical timelapse shows?

Postby Magmatic » Tue Mar 27, 2012 6:31 pm

Yes, I would just lengthen the time of each slide, which is what I've done as much as possible and still avoid a jerky feel. I'm down to about 11 slides a second. Down from 12. I'm posting my finished result in the sample show forum.
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