D|ASTRO1  ASTRO2 ! A SIMPLE EQUATORIAL MOUNT FOR ASTROPHOTOGRAPHY Have you ever stood under a clear, dark night sky and wished you could capture all that beauty on film. I have many times. I've spent many hours in a dark-room with my brother-in-law developing films of clusters, nebulae and galaxies. All the exposures were taken with borrowed equipment. The owners of the various clock-drives were very generous in lending me their telescopes and cameras for mostly piggy-back, wide angled photos. However if you're like me, you long for your own equipment. It doesn't matter what the age or its state of repair. Having your own equipment gives you the freedom to pack up and go whenever you wish. The same brother-in-law mentioned in the preceding paragraph and another astronomical friend gave me this freedom in a very roundabout way. The brother-in-law talked my wife into buying the right camera for a Christmas present. The friend pointed me to an article in TELESCOPE MAKING MAGAZINE #7 called "Build this simple astro mount" by Ken S. Hume. The mount is based on one devised by Professor George Haig and is described in the April 1975 issue of SKY & TELESCOPE magazine. (I guess that's why they're called Haig mounts.) You require 3 boards, preferably 2x4s, at least 12 inches in length. Cut the end of one board to the angle of your latitude. Hinge the other two boards together and attach one of them to the angled cut made on the first board. The hinge should be on the right hand side looking down the angle-cut board. What you should have now is something that looks like a "T" that you can take half the top off. Drill a hole in the middle of the moveable board approximately 11.4" from the centre of the hinge. Make the hole large enough to accept a 1/4-20 bolt without binding. Countersink a normal 1/4-20 nut or a T-nut (available at most hardware stores) into the hole you drilled. Round off the end of a 4 - 6 inch 1/4-20 bolt and thread it into the nut from the top. You will find that by turning the bolt far enough, the 2 boards will start to move apart. Attach a large turning knob and some king of pointer (I used a large cotter pin) to the bolt. You may want to place some sort of bearing surface under the bolt where it pushes on the stationary board. Lastly, attach a ball and socket type camera mount anywhere on the moveable board. The camera you use should have a bulb or time setting, allowing the shutter to stay open. A cable release would be of great help. The only thing you need now is a watch with a sweep second hand. (I will explain in a moment.) On a clear night, place your mount on something solid and of reasonable height. Aim the hinge so it just covers Polaris. Pick a target, open the shutter and lock it, finally turn the knob on the bolt at 1 r.p.m. for 15 minutes. How do you know your turning the knob at 1 r.p.m.? Remember the watch with the sweep second hand? Try and match the second hand of the watch to the pointer of knob and voila 1 r.p.m. (Don't worry if your not quite in sync. Close is good enough.) CAUTION !!!. Try and stick to shorter focal length lenses (less than 80mm f.l.) Remember the longer the focal length, the shorter the exposure. A 50mm lens is good for about 20 minutes with no or little trail on 35mm film. A SIMPLE EQUATORIAL MOUNT FOR ASTROPHOTOGRAPHY (Conclusion) Remember the sweep hand watch ? Your going to need it again but this time the watch will not be held in your hand. Instead we are going to attach it to the bolt that pushes the two boards apart. (By the way, the watch should be an old one that works but you are willing to part with.) A small battery fired LED (red of course) should be used to light up the face of the watch. How this is done is left to your ingenuity. One way of mounting the watch is to counter-sink it into the turning knob. In this way the watch will be facing you and the LED can be mounted right along side of the watch. If, like me, you put the bolt right through the knob, the protruding bolt-head makes a convenient reference point for the sweep hand. This is important, you must have some sort of reference mark for the sweep hand or this method will not work. The mark can be anywhere around the circumference of the watch and should be made easy to see. (The LED maybe?) After you have lined up your camera and are ready to shoot wait until the sweep hand points at the reference mark and keep it there by turning the knob. Keeping the second hand on the mark will give you exactly one revolution per minute. It also frees up one hand that you can keep warm in cold weather. My own variation is somewhat more complicated mainly because I'm lazy. My Haig Mount uses a 1 rpm 110 volt electric motor in place of the turning knob. The previous mounts usually have the bolt threaded though the top board, pulling it up when the bolt is turned. On mine the bolt is threaded through the bottom or stationary board pushing up on the moveable board. The one drawback is when I reset the mount for the next picture. The motor has to be removed but the inconvenience is worth it. The reason I say more complicated is where do you find a 1 rpm motor easily and how do you power it away from a convenient outlet? The motor comes from obsolete timers in the plant where I work and the portable power comes from a 100 watt 12 volt DC invertor I built myself. I've explained how to build the mount and even what lenses and length of exposure to take but what about results. My best results were with Hypered TP2415, a 50 mm lens and a 10 minute exposure of the Scutum-Sagittarius region. I had no trailing and the many M objects in that area were easily picked out. I've also had good luck with Kodachrome 200 at -20 deg C of Orion in the dead of winter. As a footnote on winter photography I discovered, much to my chagrin that cold kills batteries in cars, power-packs and modern electronically controlled camera shutters. A word to the wise is to use the simpler mounts in winter or carry spare batteries. The descriptions I have given you of the Haig mount are to say the least, sketchy. If you do want more information on this easy to build camera platform please look up the April 1975 issue of Sky & Telescope, Telescope Making Magazine #7 . The variations of this mount are only limited by your imagination. Above all experiment and have fun. Good luck. -- Fred Boyer