star trails

posted November 15th, 2012
Hey guys

Wondering if any of you have ever tried to take shots of star trails? Gonna try and give it a go this weekend and was hoping for some tips if you have any.
posted November 15th, 2012
go with the stacked approach, DSLRs aren't up to the noise issues related to 30+ minute exposures.
shoot raw, and disable any long exposure or high ISO noise reduction (to prevent lag between exposures).
CHARGE YOUR BATTERY. that bears repeating... CHARGE YOUR BATTERY. use an aux battery pack, if that's an option.
acclimate your gear for an hour before shooting... your camera is going to heat up, you don't want condensation blowing a full night of work.
and of course, point at the north star, and get the heck out of Dodge, light pollution will blow your shots.
have I forgotten anything? oh yeah, get a more stable tripod, you'll never be happy no matter what you got. bring a hat, gloves, and a good book. snacks help, and never leave home without a bag light. (I use a mini maglight does double duty in my macro and close up light painting shots.)
posted November 15th, 2012
There have been a number of previous threads with great advice and amazing examples. You may find them back by doing a discussion search
posted November 15th, 2012
@scatcat @cameronknowlton @mikegifford Thnaks guys. Great help. Was using the startrail.de programme to stack but the ps-c5 action gives great results too. I actually setup my camera this morning in my garden when I went out for a walk. Got over 50 shots but there was a fair bit of cloud so only around 15 were usable. Stacked them, adjusted contrast and messed with the huw a little bit. Just a test run really but pleasing results as a start.



posted November 15th, 2012
A lot or all of this maybe in the links provided above, but I can't get to them now, so I'll just type it out here...

Divide 600 by your focal length and that will give you the amount of seconds you can keep the shutter open w/o seeing trails (or the minimum shutter speed for beginning to capture trails)

It helps if you're using a headlamp at all or there is ambient light, to cover your view finder. It sounds silly but even digital cameras have minute light leaks onto the sensor from the back of the camera. You won't notice this probably ever, but if you have light shining in the back, repeatedly or even once, over a long period of time (long exposures) in complete darkness, some have seen and documented light leaks or pollution. Some models have even seen it from using the backlight on the top LCD settings display. Better safe than sorry!

If you happen to have a mac book here is a very easy way to set up your camera and walk away....doesn't have to be with a D90 either, any camera that has a USB input should work.
http://olliegapper.wordpress.com/2010/01/07/how-to-create-a-time-lapse-on-a-nikon-d90/

Here are my results using that method:
http://www.flickr.com/photos/shadesofgrey2012/7627162124/in/photostream

I only used 30 sec exposures because that is the longest my camera will go before using the bulb setting, however I think that system will let it go longer, acting as a shutter release, more experimentation is neccesary.

If you can't use that method make or buy a remote shutter release for your camera. www.instructables.com has a lot of DIY camera remotes especially for Canon, just depends on how handy you are. Use a stable tripod too. Weigh it down with rocks or sandbags if it's windy out, you don't want any shake.
60-80 miles away from any major city is preferrable, if you don't want light pollution.

A directly Northern view (in the N. hemisphere anyway) will give you the vortex look, any other direction will produce long arcing trails across the horizon, play with perspective and the surrounding landscape.

If you decide to blend them in PS, there is a manual way to do it w/o an action. File>Automate>Batch Stack>select files>change each layer blend mode to lighten, the process as desired (contrast, brightness, etc). If that is all the action does, then you're ahead of the game. If it does it's own adjustments past that, this will give you more control.

Definitely turn off Image review and noise reduction. It allows your camera to cycle faster, resulting in more continuous trails and uses less battery power. If you take either the first or last frame with the NR on, it will reduce the noise for all the frames. If you don't know what NR does, I'd be glad to explain.

Have fun and definitely bring a chair, snacks, a book, warm clothes (even in the summer) and any adult beverages you may require.
posted November 15th, 2012
I was able to check the links from Mike.....great stuff in there.

The first one goes way more in depth into stacking and the action looks good, does what I explained, only probably a bit better....

The only thing the second link fails to mention is the 600 rule but he basically explains it, w/o directly mentioning it!
posted November 15th, 2012
Everything Shades of Grey wrote @shadesofgrey is what I've been told to do; however some on this site may disagree with turning off noise reduction. I find you have to since the camera will require time to process (should be the shutter time length). Everyone has different techniques. A pro who does this stuff told me also to focus on the brightest star first before assuming the infinity focal setting is right. If shooting at night in the cold you may also need those warmer packs to put around the lens so that condensation doesn't form. Posting processing is required too....lightroom.
posted November 15th, 2012
@shadesofgrey, you rock. can't wait to try this. I especially like the div 600 trick.
posted November 15th, 2012
@shadesofgrey amazing detail. Thanks so much. Hoping for a clear night this week. Out of intrrest what white balance do you guys use? Heard awb aint that great
posted November 15th, 2012
This was my first and only attempt. Far from fantastic but I was tickled pink at the results for a one time shot. Look closer for the results from what others have said about turning off the NR in the camera, you get a dashed line of a trail. Didn't learn that trick until after I finished but next time I'll be prepared.

Good luck! Aside from me freezing it was really fun, esp to see the results.

posted November 15th, 2012
@brav I totally forgot to mention that! Thanks for bringing it up.

You definitely DON"T want to use auto WB...I found that the hard way. It will show a different amount of light and shading across almost all of your frames, creating a very uneven look when you blend the frames. Find what works for the enviroment and time you are shooting and stick with it....

I have experimented a bit with tungsten and with my "cloudy" setting. Basically, I would play with it a bit and chimp until you get something that looks pleasing to your eye. This might result in 5 or 6 shots to get your settings right but will end up with a better result.

(to chimp is to look at your screen after every shot rather than trusting your settings and meters)
@cameronknowlton Thanks! See above for one tip I forgot to mention...
posted November 16th, 2012
It's worth mentioning that the 'Rule of 600' is both a bit of a myth, and also not particularly relevant when photographing star trails -- it's intended for shots where you intentionally want to freeze the motion of the stars.

The (claimed) purpose of the Rule of 600 is to give the maximum shutter length that you can use without seeing star trails in your photograph, effectively freezing the stars in place in your image. However, it doesn't actually do that.

The actual effect depends on where you point the camera (stars closest to the axis of rotation of the planet appear to move less), but taking the worst case scenario, a star will appear to move across the sky at a rate of 15 degrees every hour.

We can calculate the time taken for the image of a worst-case star like this to move a given distance across our sensor with the formula:

(Pixel pitch / focal length) * 13750

Taking an average full-frame camera resolution of 5760 x 3840 on a 36x24mm sensor, that gives us a pixel pitch of 36/5760 = 0.00625mm between each pixel. We can plug this into our formula above, and taking as an example a 50mm lens, we get a time to move from one pixel to the next of (0.00625/50)*13750 = 1.72 seconds -- a far cry from the 600/50 = 12 seconds the rule would have you believe. In simple terms, an exposure of longer than 1.72 seconds with a 50mm lens will start to show trails on a modern camera.

Now, for the intended purpose of the rule of 600, that's not necessarily a problem. The rule is to tell you the longest exposure necessary to freeze star motion, and motion of 5-6 pixels is close enough to suffice for most web usage (most star photographers who print their work will use a rule of 500 or 400 though, as when printed, the streaks from the rule of 600 exposure times are visible). Also, an interesting fact is that a longer exposure won't actually make the stars brighter (except for those very close to the pole star) -- the majority of stars will have moved on and be illuminating different sensor sites.

What does all this mean for star trail photography? Well, not a lot. It doesn't really matter if your shots are longer or shorter than the rule of 600 -- or any other rule -- as long as you are taking them continuously. When you blend the shots together, the result will be smooth trails, regardless of whether your individual photos show a trail or not. All you need to do for star trail photography is make sure that adjacent sensor pixels are illuminated at some point during your sequence of shots.

However, there is one useful way that we can use the information above when photographing star trails. We know that a star will move from one pixel to the next in 1.72 seconds with a 50mm lens -- so we know that, to avoid gaps, we need to make sure the gap between each shot is less than 1.72 seconds.

This becomes particularly relevant when using intervalometers (which typically only have a granularity of 1 second). We can see from the formula above that, once we use a lens longer than 85mm, a 1 second pause between photos will introduce gaps in your star trails. If for some reason we wanted to use a telephoto lens, the problem becomes even worse -- at 300mm, we need just 0.29 seconds between photos before gaps would start to show -- a definite problem for many cameras!
posted November 16th, 2012
@abirkill great info. This might explain why I had problems using the 600 rule and three different lenses last summer. I'll try this again soon.
posted November 16th, 2012
@brianl @abirkill @shadesofgrey @cameronknowlton @geocacheking Thanks for the info guys. Really helpful.

Had another attempt last night/this morning. Experimenting with ISO, white balance, durations etc. Most of all having fun doing it. Here is the results of my efforts so far. A lot happier with this second attempt.

posted November 16th, 2012
@abirkill Good to know! I had not seen that anywhere but it seems to make sense. Where does the number 13750 come from?

This will definitely come into play if/when I get a chance to do some star field photography and try to capture the milky way.

@brav Beautiful! Experiment with different focal lengths and lenses if you can too!
posted November 16th, 2012
@shadesofgrey thanks a bunch. Was with my 35mm so will give my next attempt with 18-55mm
posted November 16th, 2012
@brav Great job, very clear trails and a wonderful dark blue back there. Also experiment with some foreground elements to give the photo a bit more interest. If you get brave enough you could even use a torch/flashlight to illuminate the foreground elements a bit more with just a tad bit of light painting.

Have fun. :)
posted December 29th, 2012
Many thanks for the ideas (@brav @geocacheking ). It would be great if you could include some information on the ISO, Shutter Speed, Aperture and Focal Length used for your excellent photos, then at least I can have some settings to start with!
posted December 29th, 2012
@dac I forgot that info was stripped when combining the images. Let me check.....For the one I did there is ISO 800, f11, 18mm, with a bunch of 30 sec exposures. :)

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