What’s Your Preference?

dcclark · #1 (**permalink**) 12-14-2009, 11:07 PM

Hello all -- I've been experimenting for some time with time-lapse photography. In particular, I've been learning about star trail photos, and playing around with an interesting technical setup. This thread will cover my experiences, tips, hints, and frustrations.

The final result is this photo -- technical data below:

Click the image to go to its flickr page -- even more technical details available at Cliffs and Ruins.

This photo is a composite of 144 separate photos, stacked together to form a singe "star trail" image. This is not my first try at such a photo, and not all attempts worked out well!

Where: This is the Quincy Mine #2 shaft-rockhouse, just north of Hancock, Michigan. This building was once part of the great Quincy Mine, one of the largest (and deepest) copper mines in the world. I've been playing around with using this abandoned structure as a subject for my star trail photos. You can check out the geotag on flickr for exact coordinates.

Gear: Now we get into the technical details. Here are the physical parts of my setup (software and method are covered below this):

Camera: Nikon D40x
Lens: Nikon 10-24mm, a truly enjoyable lens to use!
Computer: Apple MacBook Pro 15". This was used to control the camera during the shoot.
Miscellaneous: One USB cable (A to B type), and a cheap tripod with pan-tilt head

Exposure Info: This photo consists of 144 individual shots. Each shot had these settings:

Shutter speed: 30s (the maximum non-bulb length for the D40x, also avoids sensor overheating problems which could result in "purple clouds" in the photos).
Aperture: f/3.5 (see below for why I used such a large aperture)
Focal length: 10mm (I love my ultrawide!)
ISO: 400 (see below for the high-ish ISO explanation)
White balance: Incandescent (which gives the sky that lovely blue-ish color)
Mode: Manual (exposure and focus)

Software and Technical: To actually take the photos, I tethered the camera to my laptop using a USB cable. On my computer, I used gphoto2 to control the camera (Mac OS X installation instructions on my blog -- based on my painful experiences required to get an up-to-date install!). I used the following command:

Code:

gphoto2 --capture-image-and-download -I 34

This instructs gphoto2 to take a photo every 34 seconds, and download the photo to the laptop when the exposure is done.

Why 34 seconds? This is a technical, but annoying, detail. The exposure is only 30 seconds, but the camera and laptop require a few seconds to start the exposure, and to download the photo after it has been taken. If a smaller interval gets used, the camera somehow gets "backed up" and may stop taking photos (or stop sending photos to the laptop) after a while. 34 seconds seems to be the perfect interval to keep this working -- and for some reason, the photos still ended up being taken continuously, with almost no delay between them!

After capturing all 144 photos (at which point my camera's battery died), I stacked the photos using the Windows-only program Startrails, which does an excellent job of stacking photos correctly. Every other photo stacking app I've tried seems to try to be smart about aligning the photos, and as a result the star trails end up being jerky.

Composition: From an artistic standpoint, the photo is OK. I deliberately placed the north star behind the shaft-rockhouse, so that the stars would appear to rotate around the top of the building.

Unfortunately, a few low-level clouds came through. Those are the brownish streaks which you can see crossing the photo -- they reflected nearby streetlights and car lights.

The photo required a bit of post-processing (other than stacking the photos) -- mostly curves, to bring up the overall contrast and brightness.

Problems: The main problem with this setup is that gphoto2 refuses to operate the D40x (or any Nikon, for that matter) in bulb mode -- it can't tell the camera to start and then stop an exposure, only to start the exposure (and let the camera stop it after the chosen shutter speed, on the camera).

As a result, to get enough light into the camera, I had to set the camera to shoot at 30s (longest non-bulb shutter speed available), f/3.5 (widest aperture), and ISO 400 (as low as I could get it!). Luckily, the photo stacking process tends to remove the small amount of noise which the moderately high ISO setting added.

In addition, this photo was taken with only a 1/4 waning moon, so very little light came into the scene from the sky. This is good for stargazing -- not good for my setup though!

Lessons learned: There are a lot of random things which I've learned while taking star trail photos.

One is that a strong subject is still necessary: star trails alone aren't a very good subject. The shaft-rockhouse has helped me a lot in this way.

Another: setting up and focusing on your subject at night is hard. Get to your site early, set up your gear, focus, set the focus to manual, and don't touch it!

One more: Although this photo worked out, technically, better than my previous attempts, I kind of prefer some old my older ones, in which I didn't compose with the north star "head on" -- the result is that stars appear to move farther! Here's a previous example:

(Click for the photo's flickr page.)

Despite the weird stutters in the stars (due to the camera randomly stopping, when it shouldn't have!), the apparent movement of the stars is much larger. Also, this photo was taken during a full moon, which lit the building much better.

Overall, I've thoroughly enjoyed the trial-and-error process involved in star trail photos, and I fully intend to go out and keep trying, on our next clear night!

GarenT · #2 (**permalink**) 12-14-2009, 11:44 PM

That is so cool! I love the shed as your foreground, such great lines and textures... I would love to try that someday, but there's WAY to much ambient light down here by Chicago, guess I'll have to wait to go back to Hancock someday! ALthough I almost got killed on a snowmobile the last time I was there, so not sure the wife will let me go back!

Garen

dcclark · #3 (**permalink**) 12-15-2009, 12:45 AM

Quote:

Originally Posted by GarenT

That is so cool! I love the shed as your foreground, such great lines and textures... I would love to try that someday, but there's WAY to much ambient light down here by Chicago, guess I'll have to wait to go back to Hancock someday! ALthough I almost got killed on a snowmobile the last time I was there, so not sure the wife will let me go back!

Be careful calling it a shed -- it's 150 feet tall! :P

Thanks very much -- snowmobiles are the local hazard, much worse than bears or wolves. I live a stone's throw from this location, so it's a great place to practice.

vandergus · #4 (**permalink**) 12-15-2009, 04:17 PM

Very nicely executed dcclark. I like that you are using the star trails to enhance the subject rather than simply making the star trails the subject.

I know you're using the stacking method to avoid long exposure noise, but have you tried a single exposure with dark frame correction just for the sake of comparison. Sounds like the stacking method has some drawbacks, too (the jittery look), and the trade off might be worth it. Just a thought. Thanks for the detailed explanation.

dcclark · #5 (**permalink**) 12-15-2009, 05:09 PM

Quote:

Originally Posted by vandergus

Very nicely executed dcclark. I like that you are using the star trails to enhance the subject rather than simply making the star trails the subject.

Thanks! This is one of my pet peeves about star trail photos: far too many are only star trails, and don't have a real subject. It's good to have these things nearby to use as subjects.

Quote:

Originally Posted by vandergus

I know you're using the stacking method to avoid long exposure noise, but have you tried a single exposure with dark frame correction just for the sake of comparison. Sounds like the stacking method has some drawbacks, too (the jittery look), and the trade off might be worth it. Just a thought. Thanks for the detailed explanation.

I have done some long exposures, but there are a few problems with it. The main problem is that my D40x will only go for 30 minutes in bulb mode. It's not a battery limitation, the camera just stops!

As a result, the single long exposures don't have as long of star trails. That may or may not be a problem -- but it is a bit frustrating.

Perhaps now that it's winter, the cold will keep the amp noise down!

Agata · #6 (**permalink**) 12-15-2009, 05:31 PM

Thanks for the tutorial!

I won't be going out to take any star trails anytime right now - way, way too cold for me but I will get back to this in the summer when I'm away from the city. It looks very interesting and I am inspired to try it! :-)

Thank you again!

My Life is Pink · #7 (**permalink**) 12-15-2009, 08:20 PM

Wow! I appreciate all the time and effort you put into taking this glorious photograph! Thank you for sharing!

GarenT · #8 (**permalink**) 12-16-2009, 03:58 AM

Quote:

Originally Posted by dcclark

Be careful calling it a shed -- it's 150 feet tall! :P

Thanks very much -- snowmobiles are the local hazard, much worse than bears or wolves. I live a stone's throw from this location, so it's a great place to practice.

Shed, Shaft, 220,221 whatever it takes!