PetaPixel

Building a DIY Barn Door Tracking Mount for Long-Exposure Astrophotography

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Getting quality astrophotography shots comes with several challenges, and one of the main ones is that the starts don’t stand still — or, more accurately, we don’t. Since the Earth enjoys spinning on its axis once every 24-hours or so, exposures in excess of about 1 second begin producing star trails unless you have the camera or telescope on some sort of tracking mount.

Fortunately, if you don’t have the money to purchase a $1,000+ equatorial mount but still want to take long-exposure astrophotography, the DIY barn door tracking mount above will enable you to do so on the (relatively) cheap.

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The mount was built by University of Michigan aerospace engineering student David Hash (also known as Reddit user 0×05), and we had a chance to catch up with him over email to find out a little bit more about the rig and how he put it all together.

“The basic design is based on one I found on Cloudbait, but I worked out the drive mechanism and electronics independently,” says Hash. “The basic idea is to make a simple, hinged platform that is slowly driven open by a rotating threaded rod, so that the rotation of the platform exactly matches the apparent motion of the stars in the sky.”

The thing is, the speed of the rig has to be very precise. Hash shoots with a Pentax K-30 and lenses that range in focal length from 17mm all the way to 300mm. “At the focal lengths I’m shooting … if the rotation of the mount deviates by more than about 5 thousandths of a degree during the length of an exposure, you’ll start seeing elongated stars and other artifacts of poor tracking,” explains Hash.

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The mount itself is made up of a threaded rod driven by a stepper motor that makes one full rotation every 3,200 “microsteps.” The speed of the motor is controlled by a clock timer on board a low-cost microcontroller that calculates when the motor should pulse to ensure the camera is always pointing in the right direction.

That involves pulsing the motor about 50-times per second, as each microstep rotates the camera platform only eight hundred thousandths of a degree. The mount is designed this way so that everything runs extremely smooth.

Here’s a video showing how the single-button operated rig works:

In case you’re wondering what sort of different the mount makes, here’s a 30-second exposure of the star Vega taken before the mount was turned on:

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And here’s the same shot after:

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Since Hash is spending his summer in the Los Angeles area, he wasn’t able to get any good sample shots until he took the mount out to Mount Pinos, about an hour and a half northwest of LA. Once there, however, he aligned the mount with Polaris (something you have to do every time), fired it up and managed to capture a few really good ones.

The first is a shot of the Milky Way taken with a Sigma 17-50mm f/2.8 at 17mm, while the second, third and fourth show M8 (The Lagoon Nebula) and M20 (The Trifid Nebula), M101 (The Pinwheel Galaxy) and a particularly awesome shot of M31 (better known as Andromeda), all taken with a Pentax DA* 50-135mm f/2.8 at 135mm:

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All of the shots are made up of several 90-second tracked exposures that were stacked and combined using a freeware program called DeepSkyStacker in order to reduce noise. Not bad from a homemade rig that cost him approximately $200 to build from scratch.

Here’s a closer crop of Andromeda:

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You can see all of the samples in glorious high-resolution on Imgur by clicking here.

If you’re interested in building one of these yourself, you can get the basic blueprint at the Cloudbait link he mentioned. More info on the complex mathematics and equations of it all can be found on Hash’s Reddit thread on the subject.

(via Hack a Day)


Image credits: Photographs by David Hash and used with permission.


 
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  • Chris Brown

    That’s awesome.

  • Oldcamerman

    Ouch! That typo in the title hit me in the eye………..

  • DLCade

    Oops, thanks for pointing that out! Went ahead and fixed it :)

  • Renato Murakami

    Nice! Did not knew how difficult it was to get a clear shot of stars like that.
    1 second is enough to blur… the opposite end though, trails takes hours and stacked photos, right?

  • Bill

    lol@Pentax/Sigma user.

  • Will

    *Looks at Bill’s comment*
    *Look at star photographs*
    *Looks back at Bill’s comment*

    You must lead a sad life if you care that much about other people’s equipment.

  • Zos Xavius

    wtf? Is there something wrong with shooting pentax? They make very capable cameras. I’m no sigma fan but they do make some nice lenses at times and at very reasonable prices. Same goes for samyang, tokina, and even tamron sometimes. You know what? You are a pathetic troll. Let’s see your awesome astrophotography pictures that you took with your custom designed and hand built equatorial mount? I’m going to refrain from name calling, otherwise I might be saying you were a douche bag or something equally immature. No. I’m way better than that.

  • Zos Xavius

    First of all, this project is awesome and I am already considering trying to build something like this. I mean these pictures are pretty amazing if he is really shooting them with that much light pollution. If the photographer that designed this reads this, how hard would something like this be to adapt to controlling panoramas? The problem I always had was how to move the motors accurately enough to get precise registration. Very nice to see Pentax in a good story for a change.

  • 4dmaze

    I have experimented with many different types of sidereal trackers, from a Byers CamTrak (awesome!) and a Teegul Sky Patrol III to a hand cranked barn door tracker like above. The biggest issue is polar alignment. The author kind of glosses over this part, unfortunately. Normally there will be a finder scope mounted parallel with the hinge, don’t see one above (maybe under the circuit board?).

    And Polaris is actually .7º off, so even if you align direct with the star you will lose your tracking on longer shots (not so much an issue with digital as it is with film). A good polar alignment finder scope will have illuminated rings to help find the true celestial north pole. The $200. mentioned doesn’t include this (or a steady tripod + mounting plates + ball head) but still way cheaper than commercial offerings.

    Definitely a rewarding project.

  • slvrscoobie

    Thats why I just spent the extra $200 and got the ioptron tracker.. comes with a polar scope for alignment, accuracy for ~300mm on FF camera up to 5 min, runs on 2 batteries and has capacity to hold my 5D3 w/ 70-200 2.8. Oh and it has an Iphone app to help with exact polar alignment based on GPS location

  • David Hash

    Thanks. I have looked at the O-GPS1, but I wanted something that would be a little more adaptable (and, as you said, work at long focal lengths where the sensor-shift capability runs out faster).

    It would be very adaptable for shooting panoramas. I have it coded to rotate continuously at the rate that I’ve calibrated, but it could easily be adapted to rotate at different speeds, or step in intervals. The main limitation with what I have now is that the platform is limited to about 40 degrees of travel. For my purposes this is fine, because that still gives me 2.5 hours of continuous tracking time, and I can rewind it whenever I need to.

  • David Hash

    I use Polaris for rough polar alignment, and then fine tune by drift aligning; i.e., aiming in various normal directions and taking pictures several minutes apart. Based on which way the stars move I can adjust the polar alignment and increase exposure lengths.

    I just added an inexpensive reflex sight to the mount today to help with alignment. Previously I was just sighting down the hinge.

  • Typo

    „starts don’t stand still” ???

  • David Hash

    I went with the K-30 because, at the time I bought it, it had the best noise characteristics of any APS-C camera. The Sigma 17-50 because it’s the sharpest normal zoom for that mount.

  • moonshine

    a basic rule of astrophotgraphy with a camera. if you want to avoid star trails with out a rotating mount use a shutter speed no more than 600/effective focal length of your lens (taking into account whether its a crop sensor or not) so a 100mm lens on a nikon d700 crop sensor implies a photo no longer than 4 seconds

  • Zos Xavius

    i’ve been thinking about mounts for a long time now. ill have to look into your reddit thread and see what I need to put together for parts. I was thinking that if you could homebrew a gigapan like mount, it could surely be put together for less than $1000. Far less. I have a background in computers, but don’t know much about controlling motors with embedded systems. I figured once you could set your overlap and figure out how much the motor moved, it would be trivial to program a controller to strep through a panorama. Its like embedded design 101. Unfortunately I never took that class. Your project seems to approach a similar problem: precision. I might have to get some things together and start experimenting here.

  • JoeNoName

    Great job man, nice work!

    I would love to have one of those from you, you should really try to make an effort and sell those rigs, plnty of us will buy them!

  • leeseafish

    with an analogue driven barn door you can build it for under £100 ($150).

  • Farzad

    Hi, I wonder how did you couple the motor’s shaft and the screw? Did you use flexible coupling or rigid? Thanks.