Astrophotography. Photography of astronomical objects that dot our own galaxy and the ever expanding universe. While it may sound complicated and riddled with jargon, it is a discipline that can become as complex and expensive as you allow it to be. One of the mainstays of astrophotography is long exposures, measured in seconds and extending well into multiple minutes all while battling or at least reducing the effect of earth rotation. The answer is deceptively simple, just rotate the camera at the same rate at which the earth rotates.
Those who attended the star trail sessions organized by the kind owner of this website have been treated to the photographic manifestation of the earth’s rotation. In some of the pictures, you’ll notice that the star trails rotate around a “fixed” point. That is the North Celestial Pole (for the Northern hemisphere in which Kuwait is located in) which is near the star Polaris. You’ll also notice that the stars rotate in a circle or an arc, depending on the length of the exposure taken. The brighter members of society who have been reading this post (and I hope that is all of you considering the nature of this blog) would conclude from what is said that one needs a platform replicates the rate of earth’s rotation around the North Celestial Pole. Luckily, a very cheap and deceptively simply platform called a barn door tracker is the answer to this physical and mathematical conundrum. I built this after attending the Star trail session IV just to see what can be accomplished in the realm of astrophotography in Kuwait. I’ll spare you the theoretical/design details and focus on how to actually build one. I opted to build a curved rod/bolt barn door tracker since it does not accumulate tangent error as a straight rod/bolt would (at least the type 1) and it is easier to build than the type 2-4 barn door trackers. In essence, it’s a curved rod opening a hinge bolted to two pieces of wood.
Now onto the juicy stuff. First is the list of parts needed. Those who tried DIY projects will now how difficult it is to find some quite simple parts in Kuwait so I’ll also list where I got them as well. While this service sounds quite simple, it will save you A LOT of time and headache. This was the most consuming part of the project.
- 1/4″-20 threaded rod. Nuts and washers that fit said 1/4-20″ rod. Kuwait mostly uses metric bolts/rods so this was difficult to find. I found it at a store opposite Jawad AlSaffar in Shuwaikh Industrial area. There is an intersection near Jawad Al Saffar. When it is on your right take a left and you’ll find a couple of stores dealing with nuts and bolts. Sorry I can’t remember the exact name but the first one on the right had them. Six nuts, six washers and a 2 meter 1/4″-20 rod was 750 fils. This is almost the exact location
- Wooden boards. You can use any wood but choose some at least 1cm thick. Depending on the equipment you’re going to mount, it can be thicker to be more stable. It can be any size you want but make sure it is at least 30cm wide. This is the only critical criteria. I bought a 150cm wide by 20cm high and had the carpenter cut it into 40cm wide boards and got the leftovers. All for 1 kwd
- Sturdy hinge. You can use a piano hinge or door hinge. Make sure it is sturdy and does not have any play within it. I bought a sturdy one from Al-Ostad in the same street you can find the 1/4″ rod. It was 1.250 kwd for two. They come with correctly sized screws.
- Large piece of paper and a smaller piece of paper. This will be used to draw a radius. I used a large piece of paper from a local stationary and an A4 paper for the paper compass.
- Pencil/compass/pencil sharpener/30cm ruler
- Sandpaper (40grit)/metal file
- Electric drill with various sized bits.
- Wood saw and hack saw
- Vice grips/pliers/screwdriver etc
- Epoxy
- Old CD
- Old tripod head
Total cost would depend on how much of the equipment you already have. Counting the major parts only, it cost me 3kwd for a platform (with extra material left actually) that will accurately track stars for 1+ hours.
Please be careful, you are going to deal with potentially dangerous equipment. Please use heavy gloves, safety goggles and practice proper precarious precautions.
Q8Geeks™®© and I are not responsible for you being abducted by UFOs and aliens after tracking their movement using this tracker. We are also not responsible for any subsequent probing and the resulting psychiatry bills. Q8Geek is not responsible if you got abducted by cows. I, on the other hand, will happily accept that responsibility after proper authentic documentation documenting said abduction.
Step 1 – Tracing an arc
Since we are using a 1/4″-20 threaded rod, the rod needs to have a radius of 11.43″ or 29.03cm. To accomplish this, draw a 29.03cm line on an A4 paper and puncture two holes at each end. One will be a pivot point to keep it in its place and you can use a needle or a compass to accomplish this. The other hole will be used to draw the actual curve. Select an appropriate spot on the large piece of paper/cardboard and carefully draw the arc without tearing the A4 paper.
Depending on the screw/rod you use, this radius will need to be adjusted. You can search the internet for the radius needed for different sized rods/bolts. I used a 1/4″-20 because when bent and positioned correctly, it will need to be rotated at 1 rpm, greatly simplifying timing the rotation of the nut.
Step 2 – Get bending
Now is the difficult part. Bend the rod around a circular object. Routinely put it on top of the arc to check if it is true or not. Bend, bend and continue bending until you can get it to a 29.03cm radius as much as you can. I only used my hands since I did not want to possibly damage the threads using pliers/vice grips.
An ingenious fellow suggested attaching screws/nails to the arc draw on a piece of wood to assist bending. After trying it by hand I would certainly entertain his idea.
After some time, you’ll achieve this.
Cut the most accurate portion of your rod using a hacksaw. Sand down the ends so a nut can spin freely.
Step 3 – Hinging the hinge
Put your two pieces of wooden board that will make the bottom and upper boards next to each other. Put the hinge in between them and make sure they are as parallel as possible. Make sure the hinge is fit as snugly as possible in between the boards. When the hinge is correctly orientated and positioned, drill some pilot holes for the screws with the hinge in its place. I used a 3mm drill bit but it will vary depending on the hinge and screw size. A trick to make sure you are drilling straight is to use a CD or mirror and to see if the drill bit forms a continuous image or not. It will make sense when you try it. The screws have sharp edges and extend out of the wooden boards. I recommend sanding them down/filing them with a metal file to reduce risk of injury.
Step 4 – The vital measurement
The next important measurement. The distance from the center of the hinge to the driving nut that will open the hinge. This will also vary depending on the size of rod used. For a 1/4″-20 rod, 11.43″ or 29.03cm (metric sure is easier) is the correct distance. Please note that the distance is measured from the center of the hinge (as shown) not from the edge of the wooden board. Since my hinge had a 15mm diameter and therefore a 7.5mm radius, the line on the board is actually 28.28cm long and the rest is made up by the radius of the hinge (7.5mm) to give 29.03cm
Here I made a couple of points using a pencil 29.03cm away from the hinge and drew a line through them to make sure this is the correct distance. I drilled a hole using a 8mm wood drill bit in the middle. If the two pieces of wood are identical you can stack them on top of each other after you correctly drilled one to make an identical hole in the other.
Step 5 – Attaching it to a tripod
I have a cheap tripod with a quick release plate. How do I attach the barn door tracker to the tripod? Luckily, the 1/4″-20 rod is the same size used for camera tripod inserts/bolts. I drilled a hole with a 4mm drill bit near the center of gravity of the wooden board (you can try balancing it on your finger to find the CoG – great fun). I cut a small piece of the rod and put it through the hole. I removed the old threaded rod on the quick release plate, threaded it through it and attached a nut on the other side to make sure it is secure. I attached another nut on the other side of the bottom wooden plate to secure it even more. Note that this step may vary depending on the make and model of your tripod.
Step 6 – Completing it
Now onto the upper board. Cut a rectangular piece of wood diagonally. This will elevate the tripod head so you can move the camera freely without bumping into the tracker. Make sure it is longer than the one I used though (was around 10cm). Drill a hole in the upper board wherever you like, I kept it around the center of gravity because my cheapo tripod won’t handle the stress if I moved it to the edge. Attach a length of 1/4″-20 rod or screw through another hole made in the diagonal piece of wood. Epoxy this to the board and epoxy the bolt/screw into the diagonal piece of wood. I used a screw so I can epoxy the wood and tighten it to make sure it is completely secured to the upper board (yes I know the pictures show a piece of rod) Drill another 3mm hole into the other end of the diagonal piece of wood and insert a short or long 1/4″-20 to mount the tripod head to it. Epoxy this as well since we don’t want any oopsies with fine expensive antiquated (ok modern) photography equipment. Different tripod heads have different size threads so use the appropriate one. How did I make drilling 3 holes so complicated???
I have cut the excess wood and shortened it to be around 31cm wide.
You are almost finished. Fetcheth your curved cut circle of rod. Thread it gently through the two holes which you have elaborately and deliberately positioned perfectly perpendicularly 29.03cm from the hinge (perpendicular circles???? must be the epoxy). Attach a washer and nut on the above and below the upper board. Attach another nut above the lower board (or below the upper board depending on your mood). I can hear you begging for an illustration already
You’re finished. Attach it to the tripod and you’re done. Now you can profusely perspire in our forthcoming inferno of a summer tentatively tracking the heavenly heavens (exactly like chocolatey chocolate)
Or are you? How do you drive the tracker? Remember you need to turn it at 1 rpm (revolution per minute – non-politically related I swear)
Use this: disc.docx
This is a circle I made that fits on top of a normal CD. It is divided into 12 sectors. Each sector represents a 5 second interval (60 seconds / 12 = 5 seconds). Or instead, you write each sector the focal length of your lens so you know how often you need to turn it. For example, a 50mm lens needs to be rotated every 15 second intervals only so you can write 50mm on every 15 second interval and so on. I got the idea from This website also lists how often you need to turn the CD to prevent star trailing. Another website has another useful calculator to know how long your exposure needs to be for the different deep space objects. Glue the template to a CD. Then, glue a nut on top of a washer and glue both on top of the CD. The result is:
You can vaguely see that I drew a line above the CD. This is so I can accurately match the line from the CD to the bottom board. I suggest adding a dim light, preferably red to preserve night vision, on top so you can see what you’re doing in the dark. As I said previously, rotate it once per minute to match the sidereal time (earth rotation)
Now we built it and know how to drive the board. However we are not done. The third most important goal is proper polar alignment. This basically means the hinge of our tracker needs to point at the North Celestial Pole (NCP). If you remember, this is where the stars rotate around in the Northern Hemisphere. The longer the focal length of your lens, the more accurate polar alignment and your tracking needs to be. I stuck a large drinking straw as parallel as possible to the hinge. This is surprisingly effective to align it to the NCP or for our needs, Polaris would be accurate enough. Even though I could not see Polaris (!!!) from the light polluted skies of Bayan, a rough alignment using Ursa major as a guide was good enough for 2 minute exposures. Using an actual rifle scope or finder scope would be quite a bit more effective and I will probably add one in the near future.
And that’s it basically. You can motorize it but that’s a different story (don’t even know where to begin searching for a 1rpm motor or stepper motor/microprocessor).
Just to conclude.
- Build one as accurately as you can, keep track of the various measurements that will vary depending on the threaded rod you chose, I used a 1/4″-20 (1/4″ diameter, 20 threads per inch) and the measurements listed apply to this rod only. If you want to use a different threaded rod you can find calculators or you can use the websites referenced to help you recalculate the dimensions .
- Drive it at 1 rpm using the CD disc as a guide. Add a quartz clock or timer or light or whatever you want that helps you, it’s a flexible design.
- Make sure you polar align it as practically as possible. I did not say accurately because if you’re using wwwwiiiidddeeee lenses such as less than 30ish mm you’re not going to notice much star trails unless your alignment is way off. So it would not make much sense to do a drift alignment or using a polar scope. I used a 50mm with only a rough visual alignment and got minimal trailing (not zero) at 2 minutes. For 135mm or 200m+ you’re going to need it to be more accurate, even possibly necessitating a rifle scope/finder scope/telrad. A sturdy tripod definitely helps.
- Most importantly, have fun. This is not supposed to be a stressful project. It’s easy, fun and hopefully you’ll learn new things. If you mess up, try again. This is an example of what can be accomplish. Astrophotography can be a really humbling experience, seeing objects millions of light years away (the actual object or light you receive is millions of years old. Some of the stars you see may have actually “disappeared”). I can only conclude this post by quoting the late Carl Sagan:
from: http://www.skyimagelab.com/pale-blue-dot.html
Clear skies everyone,
Bader (an unemployed biochemist/molecular biologist turned gardener)
If you have any questions or suggestions, just ask.
References:
http://homepages.nildram.co.uk/~sbuniak/BarnDoor/Barn-door%20Index.htm
http://www.petesastrophotography.com/
http://massapoag.org/astro_2/Equipment/Barndoor_Tracker/Barndoor_Tracker.html
DISCLAIMER: Uhhhhh