Tinker

I took some images of the Milky Way while at Monument Valley recently, but with a 30-second exposure there is a bit of star trail evident - very slight, only about three times or so the diameter of the star image itself. Is there any way in PS or is there another app to reduce that effect so the stars are sharp? Appreciate any help from all the experts in astrophotography! Bill

wdross Loc: Castle Rock, Colorado

I am fairly certain that there is very little to be done, but you should go to our directory and pose this question again in our astrophotography section.

Jrhoffman75 Loc: Conway, New Hampshire

Basically no. Once the digital file is created all you have is pixels with RGB data. The file doesn't know how they were created and can't differentiate between a line source of light captured a 1/1000 of a second (for example) and moving point source which results in a line a 30 seconds exposure.

If you are new to astro then the section wdross recommended can give you hints for future shoots. In particular the 500 rule and its variants depending on the camera you are using.

Longshadow Loc: Audubon, PA, United States

15-20 seconds max;
or get an equatorial tripod?

mborn Loc: Massachusetts

Longshadow Loc: Audubon, PA, United States

What ƒ-stop is the lens you used?

nikonnate Loc: Woodbury MN

Follow the rule of 500 (500/ focus length = max time of exposure before trails start to appear) for a start. Personally, I don't like to go more than 80% of the way there myself.

larryepage Loc: North Texas area

You don't tell us what camera, lens, and exposure time you used, but it was demonstrated at a workshop I participated in last summer that the old "Rule of 500" is no longer adequate to determine shutter open time with today's high resolution cameras. For cameras like the D850, and for 21MP and greater DX cameras, exposures should be limited to about half of the time indicated by the Rule of 500. I tend to limit myself to 20 seconds when using a 14mm lens.

The good news is that these newer cameras also have much improved dynamic range at higher ISOs, meaning that with the D850, I can even reduce ISO to 3200 while using the shorter exposure, then very satisfactorily bring the stars up in post processing.

It is also possible that you can simply ignore the star trails. Even good extreme wide angle lenses will "stretch" the stars in the corners of the image. Some of that stretch will remain after distortion correction. I've found that it doesn't matter...even on fairly large prints (16x24), and even on prints that I have sold.

Night sky photography is one discipline where equipment does matter. I still have and use my trusty D300. But it is in no way capable of doing what needs to be done to reliably capture iimages of the night sky.

Tinker

Thanks for all the considered - and considerate - responses. You all basically confirmed what I had suspected: I blew it with too much exposure time. My shooting partner used about 20 seconds and his images are really impressive. Lesson learned; I was just hoping against reason that some way to improve the final product exists. Apparently such is not the case. Too bad Monument Valley is over 1000 miles distant. Thanks again to all who responded.

67skylark27 Loc: Fort Atkinson, WI

Always take a few insurance shots, some at 30 like you were thinking, then do some
at 25 and 20. Then you can see the differences and have a variety to learn from.
Make up a chart ahead of time of what you will shoot. Plus the milky way moves
pretty slowly so you can grab plenty of shots!!

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

500 rule for milky way
For full frame camera's
Set camera to ISO of 3200 to 6400
Aperture at 2.8 or as wide as possiable
set shutter speed to 500 divided by the focal length of lens, ie. using a 50mm lens, 500 divided by 50 equals 10, so 10 seconds, using a 24 mm lens, 500 divided by 24 equals 21, so 21 seconds

For crop factor lens on a Nikon (1.5)
so, 50 mm lens on crop camera is 500 divided by 50 divided by 1.5 equals 6.6 so 7 seconds.

Bill_de Loc: US

Wouldn't 30-second exposure mentioned in OP's first line qualify as being the exposure time?

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jerryc41 Loc: Catskill Mts of NY

Some good links -

https://petapixel.com/2017/06/23/improve-astrophotography-focus-bahtinov-mask/
http://www.diyphotography.net/guide-astrophotography-will-shooting-stars-no-time/
http://petapixel.com/2014/01/29/picking-great-lens-milky-way-photography/
https://www.davemorrowphotography.com/p/tutorial-shooting-night-sky.html
https://www.nikonusa.com/en/learn-and-explore/a/tips-and-techniques/photographing-the-night-sky.html

larryepage Loc: North Texas area

You are correct. I either just missed it or else my brain slipped into neutral for a second. I do stand by the rest of what I wrote, though.

jeep_daddy Loc: Prescott AZ

Try to reduce the time from 30s to perhaps 25s or less. That's the only thing you can do. Up the ISO and reduce the time.