New Project

[Black Pearl]

About the only type of photography I haven't had a crack at is star trails so I've decided its about time to put that right.

To be fair I have had one go ages back using a massive long exposures but the noise was so horrendous the images were just about unusable so after a bit of Googling and asking about it turns out lots of shorter exposures 'stacked' together is the way to go about it.

So......I took a guess at the exposure from random advice and set the camera away in the back garden the other night while I went in search of some software. The Nikon D300s has an intervalometer so I picked (randomly) 30 second exposure times and an interval of 35 seconds.
Turns out there is good star trail (image) stacking software for free on the net and ended up with StarStaX for the Mac.

An hour later I had a CF card of NEF files that I loaded into Lightroom - they were bright orange from the light pollution and over exposed in general......not the best first guess at exposure I've ever had......but I had a fiddle and crunched the resulting images down to jpegs, ran them through the stacking software and got this:



Its awful - actual exposures were 30 seconds - 1600iso - f3.5 on a Nikon D300s + 16-85mm.
This is an example before I attacked it with LR:




So......I swapped out the zoom for a 50mm and tried again using 5 second exposures - f2.2 and 800iso.
Much better looking files with less noise, less over exposure and some actual colours to the stars:



Once LR had crunched its way through 280 14bit tweaked NEF files and I put them through StarStaX I ended up with this:



Very little noise - good blacks - plenty of colour - sharp - BUT - I forgot that the intervalometer was still at 35 seconds so I had big gaps between each shot (yes I did say ARGH) but I'm getting there.


Last night was cloudy and today its raining but I will get this nailed down and I will the go out to some local landmarks to give it a proper run. I'm hoping to get the settings right for my Sigma 10-20mm which will give a nice big sky to let the starts rotate (the earth rotate) in.


More to follow as I (hopefully) progress.

[ajohnw]

One thought for you Robin but it will generate huge files is to use video. I came across some one that did this to get smooth waterfalls. With HD resolution it's not that bad an idea as the images are pretty big allowing some reduction. They used image magic to extract the shots from the video.

I tried some star field shots. The milky way. 10 sec exposures at 400 ISO. It just registered bright stars. Exposure chosen to keep them round.

John
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[Black Pearl]

I'll look into video thanks. The Nikon is only 720 but the Pentax can shoot full HD.

[ajohnw]

Not sure if it would work with stars but from what I have seen it's a good replacement for an nd filter for blurring motion.

I think some of the pentax cameras has star tracking built in. It tempted me but so far I have resisted. The advantage telescopes have though is available filters. Max size is 2in diameter or rather expensive squares off some suppliers.

The exposures I mentioned where on an Olympus E-P3. Lots of in camera processing going on after the shots were taken. Several seconds worth so I'm not sure if they were real exposure times. It might have added several shorter ones up or subtracted a dark frame. Not sure but raw was the same as jpg's.

John
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[Black Pearl]

Mine has the star tracking feature but it requires the GPS unit which is a little to expensive for the times I'd use it. Clever feature mind you.

[Black Pearl]

Attempt number three:

This time the Nikon D300s + Sigma 10-20mm set to 10mm - f5.6 - 800iso - 15 second exposures.



It could do with a little more overall exposure, might try a set with longer times and another with the iso up a little. Need to balance star sharpness with noise and the increasing likelihood of light pollution causing a processing issue.
The bits around the edges are our gutter, a bit of Buddleia and the neighbours roof line.
This was 404 NEF files (about an hours shooting) processed in Lightroom - exported as JPEG's and stacked with StarStaX.

[FootLoose]

This is about stars rather than star trails but the guy's processing technique might be of interest.
https://www.youtube.com/watch?v=Rltg...84503534#t=858

[Mark von Kanel]

interesting stuff rob, gunna have a go when i get home, i have a particular scene i want to try but its quite a treck so i want to have the technique pat before i go the actual venue

[Black Pearl]

Kind of the same here Mark - I've a few shots in mind but its a drive and you get one final image from a whole night of shooting so want it nailed down first.

Raining again so on hold........

[ajohnw]

Nice try Robin. The gaps in the trails make a change. Looks like a tunnel. Pretty effective.

On the star shot processing I feel this is a much better one.

https://www.youtube.com/watch?v=K-PC4Sq0Zho


He can get to a really dark site though. Helps a lot.

John
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[ajohnw]

There is one thing I think Colin mentioned that some of the astro people seem to roughly follow at times. Say shots are being taken at 800 1SO and 100 ISO noise levels are wanted. Take 8 shots and average them. The number mentioned was 3200 ISO and as the idea works on the basis of noise being random the more shots the merrier. The software that's around for doing this sort of thing will align and also subtract dark frames etc. One such package is this one

http://deepskystacker.free.fr/english/index.html

Flats are used to account for vignetting. I believe some photo a pc screen to do those. Probably with a brightish grey being displayed. There is a pretty comprehensive tutorial here

http://lightvortexastronomy.blogspot...ering-and.html. There are simpler ones about as well.

I've been meaning to try it this winter but the weather has been crap in Wales when I I have been there so far this winter. Lots of high mist and clouds.


MAC users might be interested in these

http://www.davidbaumgold.com/tutorials/wine-mac/

http://wineskin.urgesoftware.com/tiki-index.php

and google to find out how to install winetricks. I haven't read these pages and maybe wineskin also installs wine. Unfortunately there is more interest in running windows games on Linux and Macs than more serious stuff but software some times works well. Sometimes it only partially works. Depends on just how complicated the graphical interface happens to be and the techniques the application uses. I have run deepskystacker on Linux a year or so ago so suspect it will still run under wine.

John
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[Black Pearl]

Thanks for the links.

As I said this is a work in progress and really I'm putting my worse shots out for people to see it hope it might help me and others.

I've some really dark skies not too far away - I'm near (ish) to Keilder which has one of the darkest skies in the UK and closer I've the coast with little urban build up in places.
Just need some clear skies for a few more tests then I promise I will take a decent image.

[ajohnw]

In case you miss understood me Robin I meant pretty good literally. It is. Maybe I should have just said it some other way. Great really in terms of the technical bits.

I might loose sleep if I don't clear that up.

John
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[jcuknz]

I am reminded of a time at the home movie club and a woman had a film of some glow-worm caves where photography is not permitted so she had photographed a black card with pin holes in it to include in her film ....
nobody knew this until she fess'd up