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DPChallenge Forums >> Tips, Tricks, and Q&A >> Star trails - how to do it properly?
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09/21/2010 10:47:01 AM · #1
What prompted me to start this thread was this:

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How can we get such noise free images at ISO 800?
I've tried a couple of times to do star trails, and I know it's a bit of trial and error, but are there any special settings? Do you use black frames, or in-camera long exposure noise reduction? The only successful one I could manage is

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and it's cheating because it's a ton of 30 seconds exposures...

Cheers,
Joao

Message edited by author 2010-09-21 10:50:30.
09/21/2010 11:28:28 AM · #2
I'm curious about the answer to this one. I didn't think it was cheating to do the multiple 30 second exposures. I actually thought that's how you did it... (but I've never done it, so what do I know?)
09/21/2010 11:31:37 AM · #3
Originally posted by vawendy:

I'm curious about the answer to this one. I didn't think it was cheating to do the multiple 30 second exposures. I actually thought that's how you did it... (but I've never done it, so what do I know?)


Well, it is easier and safer to do like this, since if one photo is ruined we can just remove it, but it's a pain on the camera's buffer, since they are all in sequence, and after about 100 my camera stopped, so I had to reset (hence the missing trail in the middle).
09/21/2010 11:41:40 AM · #4
oh yes, please tell us, cos my star trails look like this"
shot at ISO 100

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09/21/2010 12:02:51 PM · #5
Originally posted by JulietNN:

oh yes, please tell us, cos my star trails look like this"
shot at ISO 100

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Hey Juliet, what other settings did you use? It does look a bit grainy for ISO 100.
I don't have noise on mine because they were with ISO 100 each, so if there is no noise on one, there isn't on any of them, and I use software to stack them.
09/21/2010 12:20:48 PM · #6
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One 60 minute exposure, because that's what the advanced ruleset requires. The rule is poor, if you use multiple exposures it's a DQ. I sent a ticket prior to the challenge, but the answer came late, but supported the issue that it's not allowed.

However, multiple exposures is the best way to get it right.



Message edited by author 2010-09-21 12:26:33.
09/21/2010 12:44:29 PM · #7
Originally posted by bspurgeon:

However, multiple exposures is the best way to get it right.


Using a mechanical camera with film works very well too. No DFS or batteries dieing to deal with. :)
09/21/2010 12:48:01 PM · #8
Originally posted by bspurgeon:

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One 60 minute exposure, because that's what the advanced ruleset requires. The rule is poor, if you use multiple exposures it's a DQ. I sent a ticket prior to the challenge, but the answer came late, but supported the issue that it's not allowed.

However, multiple exposures is the best way to get it right.


What Ben said. The SC's ruling is a bummer, but it is what it is.
For those occasions (hopefully many) where DPC legality does not matter, then multiple exposures is the way to go. Specifically, choose an exposure time that gives you a *reasonable* number of exposures for your total time. So if you want a two-hour total exposure, you might break it up into 24 5-minute exposures, or 12 10-minute exposures. Be aware that the brightness of the sky background (dependent on local conditions) will dictate what that maximum exposure time is.
For star trails, it's really not necessary to shoot at anything above ISO 100. You are not aiming to capture really faint stars, in fact you want only the brighter ones, and you want to retain the star colors, so the trails must not be blown out. The settings required for best results actually depend on the focal length used, strangely enough, because that affects how quickly the stars move across the sensor, and thus how bright the trail will be.
When shooting multiple exposure star trails, do not use in-camera long-exposure noise reduction; it will produce big gaps in the trails. Shoot dark frames before and after and manually subtract them. This will deal with the fixed-pattern noise, and combining the multiple exposures will deal with the random noise. The end result should be a very smooth image.
09/21/2010 12:59:11 PM · #9
The rule sucks but then again...can it be a reasonable expectation to upload 200+ images if the originals are requested? I think we're allowed 5 or so though aren't we? Or is even that small number out?
09/21/2010 01:00:45 PM · #10
I thought it was 10...
09/21/2010 01:03:26 PM · #11
Originally posted by kirbic:

Originally posted by bspurgeon:

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One 60 minute exposure, because that's what the advanced ruleset requires. The rule is poor, if you use multiple exposures it's a DQ. I sent a ticket prior to the challenge, but the answer came late, but supported the issue that it's not allowed.

However, multiple exposures is the best way to get it right.


What Ben said. The SC's ruling is a bummer, but it is what it is.

It's an excellent job under the DPC limitations -- my camera could never do anything like that (see below).

For clarification, under Advanced rules you can stack up to ten images to reduce noise, but you can't "join" images to create a new feature, i.e. a really long star trail, when any one of the frames shows only a short one; it's essentially the same as stitching landscapes into a panorama, also prohibited under Advanced.

Maybe someone can suggest (write up) an astro-photography challenge running under Expert rules to deal with this problem, perhaps with a Special Rule to prohibit compositing-in a spaceship ... ;-)

With my camera I can barely shoot stars at all -- my longest exposure is 15 seconds and I get horrible noise above ISO 200 -- though it did OK capturing Venus ...

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BTW: I'll correct the title typo ...

Message edited by author 2010-09-21 13:05:50.
09/21/2010 01:09:39 PM · #12
Originally posted by vawendy:

I thought it was 10...


Correct
09/21/2010 01:48:26 PM · #13
i just had one experience with my digital camera on startrails, but the best way i know to deal with the noise, as kirbic said, is taking dark frames once in a while.
the stacking software i use (startrails.de) has two parts for presenting pictures. one for the main pics & another one to present dark frames. and it will subtract them automatically.

btw, Michael Covington's book, "Digital SLR Astrophotography" is a very helpful guide for beginners like me.

Message edited by author 2010-09-21 13:51:13.
09/21/2010 03:39:26 PM · #14
Originally posted by GeneralE:

With my camera I can barely shoot stars at all -- my longest exposure is 15 seconds and I get horrible noise above ISO 200 -- though it did OK capturing Venus ...


Sure you can. I did this with a superzoom Fuji that take 15 second shots:

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Flight patterns by alohadave, on Flickr

09/21/2010 03:49:01 PM · #15
Originally posted by sarampo:

Originally posted by JulietNN:

oh yes, please tell us, cos my star trails look like this"
shot at ISO 100

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Hey Juliet, what other settings did you use? It does look a bit grainy for ISO 100.
I don't have noise on mine because they were with ISO 100 each, so if there is no noise on one, there isn't on any of them, and I use software to stack them.


I know! isnt it disgusting, I think it was like a 3 min exposure. manual mode
09/21/2010 04:16:19 PM · #16
I might do this, although my camera only takes 8 second shots. How do you stack all the photos together in photoshop, is it simple?
09/21/2010 04:24:24 PM · #17
14 four minute exposures, stacked. I used a freebie star trails stacking software I found. Some foreigner made it.

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Hot pixels were still a problem in the 40D, but I didn't have it set to do it's own processing. Once upon a time I did a star trail shot with my Rebel in a single, one hour exposure, and let it do it's own hot pixel processing. It came out pretty well.
09/21/2010 04:27:58 PM · #18
just ask ol' will ;D

Message edited by author 2010-09-21 16:28:10.
09/21/2010 04:29:01 PM · #19
Originally posted by alohadave:

I did this with a superzoom Fuji that take 15 second shots ...

So you did -- very nice work. I can set my camera up to do time-lapse exposures, but I think only in one-minute intervals, otherwise I could automate the process. What ISO/Aperture did you use for that series, and what did you use to merge them?
09/21/2010 04:46:18 PM · #20
Originally posted by bspurgeon:

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One 60 minute exposure, because that's what the advanced ruleset requires. The rule is poor, if you use multiple exposures it's a DQ. I sent a ticket prior to the challenge, but the answer came late, but supported the issue that it's not allowed.

However, multiple exposures is the best way to get it right.


Wow, this is like the best star trail shot on DPC. It actually requires more than one brain cell to process.
09/21/2010 04:49:08 PM · #21
Originally posted by adamelliott111:

I might do this, although my camera only takes 8 second shots. How do you stack all the photos together in photoshop, is it simple?


Here's the software I used. I don't think you'll have much luck with 8 second exposures, though, pretty short.
//www.startrails.de/html/software.html
09/21/2010 05:02:55 PM · #22
Originally posted by GeneralE:

Originally posted by alohadave:

I did this with a superzoom Fuji that take 15 second shots ...

So you did -- very nice work. I can set my camera up to do time-lapse exposures, but I think only in one-minute intervals, otherwise I could automate the process. What ISO/Aperture did you use for that series, and what did you use to merge them?


ISO 100, f/3.2, 6.3mm (36mm equiv), 212 15 second shots. I basically pressed the shutter button every 15 seconds for almost an hour.

I used this action for Photoshop: //www.schursastrophotography.com/software/photoshop/startrails.html

It basically opens one file and stacks and flattens each picture in succession automatically.

If you want to do it manually, you add each picture as a layer in PS and set the layer mode to Lighten. That will let the trails show through, but the dark stays dark.

As a final step (whether manual or with the action), use a dark frame (single exposure the same shutter speed, with the cap on, as each other picture, and add that that as a Layer, set to Subtraction. That will remove the hot pixels but nothing else.
09/21/2010 05:18:22 PM · #23
I sent William88 a PM asking him to look in at this thread and maybe offer some advice.

I tried a 5 minute star trail exposure last week which was pretty crappy, so I'm very interested in how he gets such great results also within the DPC rules.
09/21/2010 05:30:09 PM · #24
Originally posted by Strikeslip:

14 four minute exposures, stacked. I used a freebie star trails stacking software I found. Some foreigner made it.

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Hot pixels were still a problem in the 40D, but I didn't have it set to do it's own processing. Once upon a time I did a star trail shot with my Rebel in a single, one hour exposure, and let it do it's own hot pixel processing. It came out pretty well.


What's with the distortion? That wasn't the 100-400 lens you used, right?
09/21/2010 07:20:21 PM · #25
Originally posted by DrAchoo:

Originally posted by Strikeslip:

14 four minute exposures, stacked. I used a freebie star trails stacking software I found. Some foreigner made it.

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Hot pixels were still a problem in the 40D, but I didn't have it set to do it's own processing. Once upon a time I did a star trail shot with my Rebel in a single, one hour exposure, and let it do it's own hot pixel processing. It came out pretty well.


What's with the distortion? That wasn't the 100-400 lens you used, right?

That was my 10-20, and probably at 10mm on my 40D crop sensor. Call me weird, but I like the distortion when I shoot at 10mm, especially tall buildings. :-)
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