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06-21-2021, 05:22 PM   #1
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Star trails question?

Some star trail images are perfectly smooth and each trail has consistent brightness. Other trails vary in brightness and look pieced together. What causes this?

Thanks,
barondla

06-21-2021, 05:39 PM - 1 Like   #2
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I'll try to take a stab at this (might be wrong). If you're talking about what I'm thinking of, where a star streak starts out dim and the trail gets brighter/wider, is done in Photoshop. I've not tried the technique but I read on it a few years ago but don't remember how it's done. Attached shot is for reference, not my work. If you're talking about brightness in general, streaks will vary in brightness depending on how bright the star is. The pieced together look could be due to gaps in exposures and stacking.
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Last edited by cdd29; 06-21-2021 at 06:57 PM.
06-21-2021, 05:42 PM - 1 Like   #3
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Related... here is a star trail technique (again, photo for reference not mine) I would like to know how to do, a vortex affect.
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06-21-2021, 07:24 PM - 1 Like   #4
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QuoteOriginally posted by barondla Quote
Some star trail images are perfectly smooth and each trail has consistent brightness
being of consistent width, color n brightness is likely a normally stacked star trail

QuoteOriginally posted by barondla Quote
Other trails vary in brightness and look pieced together.
if the first example by @cdd29 is what you are referring to is generated in programs i use to stack the time lapse........with starstax it is called the comet effect which is a box that can be checked off to implement during the stack also there is a slider for short to long tails for the effect........with sequator the box gets checked that say motion producing similar results but short or long tail

QuoteOriginally posted by cdd29 Quote
I would like to know how to do, a vortex affect.
not that i know or have done this but appears to be a twisted overlay from shooting north over a nice wide starfield

06-21-2021, 07:43 PM   #5
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QuoteOriginally posted by cdd29 Quote
I'll try to take a stab at this (might be wrong). If you're talking about what I'm thinking of, where a star streak starts out dim and the trail gets brighter/wider, is done in Photoshop. I've not tried the technique but I read on it a few years ago but don't remember how it's done. Attached shot is for reference, not my work. If you're talking about brightness in general, streaks will vary in brightness depending on how bright the star is. The pieced together look could be due to gaps in exposures and stacking.
Yes, the comet effect is what I was trying to describe. Thank you.

---------- Post added 06-21-21 at 09:45 PM ----------

QuoteOriginally posted by cdd29 Quote
Related... here is a star trail technique (again, photo for reference not mine) I would like to know how to do, a vortex affect.
Neat effect. Not as "natural" as the other styles. I also wonder how it's achieved. Thanks.

---------- Post added 06-21-21 at 09:49 PM ----------

QuoteOriginally posted by Aaron28 Quote
being of consistent width, color n brightness is likely a normally stacked star trail



if the first example by @cdd29 is what you are referring to is generated in programs i use to stack the time lapse........with starstax it is called the comet effect which is a box that can be checked off to implement during the stack also there is a slider for short to long tails for the effect........with sequator the box gets checked that say motion producing similar results but short or long tail



not that i know or have done this but appears to be a twisted overlay from shooting north over a nice wide starfield
Good to know the comet look can be achieved in Starstax. Guessing it can also make the continuous concentric rings?
I looked over a few star trail tutorials and never saw an explanation for the different styles.

Thanks for the info,
barondla

Last edited by barondla; 06-22-2021 at 01:10 AM.
06-21-2021, 08:05 PM - 1 Like   #6
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QuoteOriginally posted by barondla Quote
Guessing it can also make the continuous concentric rings?
as in the first example by cdd29 those rings are only achieved when set up looking at polaris (northstar) which appears stationary......more complete rings are made by much longer time lapse stacks............of course there is a central point in the southern hemisphere but in an area as there is not a specific star

see entry #9 for a diagram

How do I predict the arc of star trails?
06-21-2021, 08:21 PM - 1 Like   #7
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QuoteOriginally posted by barondla Quote
Some star trail images are perfectly smooth and each trail has consistent brightness. Other trails vary in brightness and look pieced together. What causes this?

Thanks,
barondla
No ideas on the spirals but I recall seeing a YT tutorial somewhere.

As others have said, the software does it but if you want more control, you can adjust the exposure on the images you are going to stack in postprocessing, then stack normally to get tapered trails - one end or both ends of the star trail....like below. (this was about 72 minutes (36 frames) total with exposure adjusted on the first and last 9 frames to progressively reduce exposure 3.33 stops at each end).





Last edited by Grimmus; 06-22-2021 at 11:15 PM.
06-21-2021, 08:57 PM - 1 Like   #8
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Spiral is probably shot with a zoom lens which is slowly zoomed in or out during the exposure. The result is then combined with the foreground since the foreground can't be shot using the zoom effect. You would need a zoom which doesn't change focus during the zoom (parfocal zoom) and a way to zoom smoothly during the exposure (motorized by some means).

If your star trail vary in brightness, it could be caused by varying the lens aperture during the exposure (if done in a single time exposure for intentional purposes). Also, high clouds which might vary the brightness of the stars could be floating by which could result in variations.
06-22-2021, 12:24 AM - 1 Like   #9
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QuoteOriginally posted by Bob 256 Quote
Spiral is probably shot with a zoom lens which is slowly zoomed in or out during the exposure. The result is then combined with the foreground since the foreground can't be shot using the zoom effect. You would need a zoom which doesn't change focus during the zoom (parfocal zoom) and a way to zoom smoothly during the exposure (motorized by some means).

If your star trail vary in brightness, it could be caused by varying the lens aperture during the exposure (if done in a single time exposure for intentional purposes). Also, high clouds which might vary the brightness of the stars could be floating by which could result in variations.
Great idea, I have to try that sometime. I guess this might work without motorization if I keep the exposure short enough to prevent star trails from happening in each frame and linking the stars of multiple exposures in post.
10-04-2021, 12:25 PM   #10
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Star stax has a setting that'll do the comet thing. Take a stack of images (try 50 or more, each 30 second exposures with a wide lens with your NR turned off). Feed it into star stax and hunt down the comet mode.


https://markus-enzweiler.de/software/starstax/
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