First try: Star Trails!

[Van Isle]

Hi folks,
I finally had a decent night (for the the NW Coast) to shoot some star trails. I've never done it before, and so much of the technique seems so relative to the exact shooting conditions of the moment that I appreciate it's hard to give advice, even though I searched and searched. But here's my attempt:

http://mdrivest.smugmug.com/photos/136221445-M.jpg

despite the glaringly obvious - It's a really boring image! - what other C&C can you give me? Here's the basic EXIF data:

Nikon D70s w/nikkor 50mm f/1.8
exposure ~10 mins w/in camera NR, focus infinity,
Aperature f/4
ISO 200
basic PP in Nikon Capture NX for intel Macs (white balance was critical)
shot in RAW compressed to high quality JPEG
Manfrotto 055NAT3 'pod with 486 RC2 ball on a sandy beach

there were far too many background lights, way more than I had expected for the location, which really affected the noise and colouration...

Thanks for looking! and C&C...

VI

[Mitchell]

I've always wanted to try this myself.

Seems to me that the best star trail photos have other stationary earth bound objects to give the whole image some perspective.

While I can appreciate your photo, the average viewer would look and just scratch their head. If you had some trees or other earthly objects the photo would have much more impact.

[NewCreation517]

I love taking pictures like these, except I also really struggle with it!

My first thought on this was that the contrast was almost non-existant. If the stars were brighter, and the sky was blacker ... this could be much more dramatic. Not sure how'd you go about doing that ... maybe a wider aperture? Or shooting in a place with the less light noise, and using a higher ISO setting?

[dogwood]

Not quite star trails, but a shot of the Milky Way from the Pacific Northwest. It's not always cloudy here :D

http://www.pbase.com/dogwood_digital/image/65955001.jpg

For star trails, most folks use film. With digital, you start getting recipocity failure after a few minutes and it just doesn't look very good. You can get short trails over a few minutes, but the really dramatic circular trails are either a film camera at bulb for several hours, or a 'stack' of digital images over a long period of time.

[Van Isle]

Thanks folks, this is the kind of stuff I was looking for:

Mitchell - I understand it's a boring photo! But I think you're sort of saying that, technically, it's getting there. Cool! This was a "ranging salvo" so to speak, to figure out aperature/exposure in certain conditions to establish a baseline for myself, which I think i did, whilst fluking in getting "okay" looking trails of nothing at all!

NC517 - thanks for the input. There was so much "light pollution" around I think that made it difficult to get a black sky. I was going to capture an image of Orion dancing across the sky for about 10 min, so that at least there'd be something recognizable in the image, but it was waaay too bright to the south last night in my location. I might be able to tweak the contrast more in post, I'll keep playing with it. I don't think I would want to change ISO or aperature because that would make the sensor too sensitive. I mean, the shutter's open for 10 minutes! Think of the noise! I think the trick is to not have light pollution around, if you can. There was also quite a bit of reflection off of clouds, so it was even worse than a normal dark night out here.

Dogwood - Nice capture! :thumb No it's not always raining here (Sooke, BC, west coast of Vancouver Island, across the strait from Port Angeles) but it was the first sort of clear night in a long time. When I get better at the capture and the PP, I'll try stacking. That's the plan anyway. :ivar

Thanks all,

VI

[LuckyBob]

[...]For star trails, most folks use film. With digital, you start getting recipocity failure after a few minutes and it just doesn't look very good. You can get short trails over a few minutes, but the really dramatic circular trails are either a film camera at bulb for several hours, or a 'stack' of digital images over a long period of time.

Just curious - from what I understood reciprocity failure was a film-exclusive "feature", and digitals didn't suffer from it at all. From what I understand it's a breakdown in the ability for the film grains to capture extremely dim lighting, but I've only done a bit of research on it. Increased noise seems to be a major issue with digitals, but most dSLRs are good enough to handle several minute exposures usable noise levels.

http://www.cardboardtech.com/gallery/download/1759-2/CRW_1749.jpg
I shot and processed this one shortly after I got my original Rebel (final image Dec '03); it's a just-under 7 minute exposure on the beach at Camano Island (for all you Northwestern folk :D). The lower right corner is light polution, and there was some major curves going on to bring out what detail existed in the original - it looks fairly close to what you posted.

The things I've found to be critical with star trail exposures is to avoid light pollution as it radically hurts the contrast, shoot straight up or only slightly off as you're looking through the least amount of atmosphere at that point (which helps contrast, although horizon shots look better anyway), and learn the curves tool in Photoshop inside and out.

PS: A quick link I found about reciprocity failure - http://malektips.com/digital_photography_0039.html

[LuckyBob]

Hope you don't mind - I took a stab at your image to see what I could pull out of it in Photoshop. I didn't remove the dead pixels, but those are easy to clone out by hand. Downsizing the image seems to have created some aliasing, but the full resolution version doesn't have it.

http://www.cardboardtech.com/gallery/download/1772-1/Star_trails_small.jpg
Full Rez (http://www.cardboardtech.com/gallery/view/Dgrin/Star_trails.jpg.html?g2_imageViewsIndex=3)

Photoshop screenshot (click for larger version):
http://www.cardboardtech.com/gallery/download/1765-2/Star_trails_PS_screenshot.jpg (http://www.cardboardtech.com/gallery/view/Dgrin/Star_trails_PS_screenshot.jpg.html?g2_imageViewsIn dex=2)

It may not be perfect (I agree about some sort of stationary foreground subject), but I guarantee you that even in our light-polluted cities these kind of shots will still blow away friends and family :D

[NewCreation517]

I did this on my 20D. 30 second exposure, 1600ISO, aperture open as far as I could go (4.0 I think?). I think it came out really nice ... it was up in the Sequouia forests ... no trails on the stars, but i did pick up the blinking light of a plane.

http://identity.smugmug.com/photos/91450607-M-2.jpg

[OneWayMule]

For star trails, most folks use film. With digital, you start getting recipocity failure after a few minutes and it just doesn't look very good. You can get short trails over a few minutes, but the really dramatic circular trails are either a film camera at bulb for several hours, or a 'stack' of digital images over a long period of time.


Its the other way around...

Film has serious issue with reciprocity (> 1sec) while digital doesnt cos its has a "linear process"

[TylerW]

Getting good star trails is all about location. You'll want to go and get yourself somewhere really remote, far away from cities, and ideally at a high elevation. This will get you free from any light pollution which would reduce the overall contrast between stars and sky in your image. Star trail images also benefit from having something in the foreground to anchor the image, to give greater context that the start are moving (well, okay, the planet is rotating).

Bring a good strong flashlight, not only to keep you from tripping over stuff, but it will also let you play around with light painting while you've got your shutter open for such a long time.

[dogwood]

Its the other way around...

Film has serious issue with reciprocity (> 1sec) while digital doesnt cos its has a "linear process"

My mistake. However, digital does often introduce unacceptable noise at longer exposures. This is what I meant.

[MrBook2]

The d70 (and d70s) are quite capable of doing star trails, as long as you know what you are getting yourself into. Here are a pair I took with my d70:

http://mrbook2.smugmug.com/photos/49987364-M.jpg

and

http://mrbook2.smugmug.com/photos/49987087-M.jpg

The first is actually a stack of five 5-minute exposures. I turned off the "automatic" long exposure noise cancellation. All this does is take a second exposure of the same length with the shutter closed after the first and subtracts it. This is known as dark subtraction. I figured I could do just as well myself if I took my own dark with the lens cap on. So those five image were combined using "lighten only" and I subtracted off a dark at the end. This also minized breaks between exposures. If you look very closely, you can see that each "trail" is five short segments with tiny breaks inbetween.

The second image was done similarly, but it is a single 20 minute exposure (with a 20 minute lens-cap-on subtracted.) It was taken not long after sunset, and when the moon was up. Since moonlight is reflected sunlight, it looks like day time.

The only really annoying thing about the d70 is the hotspot in the one corner. The dark subtraction helps, but it can also be cropped out.

So, general tips:
1. I agree with the previous posters, things in the foreground help a lot.
2. Keep your ISO low.
3. Open you aperature as far as you can, you need as much light as you can get.
4. Focus around infinity. You may want to take a couple at slightly different focus settings, and remember that if you twist the lens over as far as it will focus, you probably overshot the correct focus value.
5. Take a "dark" with the lens cap on, equal to the length of your exposure to subtract off later.
6. Be aware of light pollution, including the moon!
7. Use a good sturdy tripod and a remote if you have one.

--Aaron

[Van Isle]

I'm aching to try again in a good location, and to try to actually compose a decent shot now that I have some baselines down for me: fire for effect!:D

Thanks all for showing me what's possible with a little more effort (and conditions!) and some photoshop work...I don't have photoshop, but I've got levels and curves to play with...that's a whole other thread I need to ivestigate for a few hours (days) before I ask any questions. Summer's coming! :thumb

VI

[NewCreation517]

[quote=MrBook2]
The first is actually a stack of five 5-minute exposures. I turned off the "automatic" long exposure noise cancellation. All this does is take a second exposure of the same length with the shutter closed after the first and subtracts it. This is known as dark subtraction. I figured I could do just as well myself if I took my own dark with the lens cap on.

So, out of curiousity, why in the world does it take a second exposure with the shutter closed? Doesn't this just create a plain black image? I can't imagine the camera would need to "take" the shot ... :scratch

[LuckyBob]

[...]So, out of curiousity, why in the world does it take a second exposure with the shutter closed? Doesn't this just create a plain black image? I can't imagine the camera would need to "take" the shot ... :scratch

In that a "dark frame" shot right after an image will have essentially the same noise signature and hot pixels, the camera (or we) can then mathmatically subtract the noise from the image resulting in a much cleaner output. There's a fairly comprehensive article with examples here (http://photo.net/learn/dark_noise/); hot pixels are mentioned within the first few comments .