A Wedge and Pier of ^/ood The first obstacle facing a beginning astro-photographer equipped with a forkmount CAT is the need to buy "more stuff." In addition to cameras and computers and software, the tyro imager must also obtain a wedge in order to set the telescope up in equatorial mode for serious long-exposure photography. Even basic wedges sold by Meade and Celestron cost a pretty penny.
My friend Pat Rochford, was in this position some years ago as he embarked upon CCDing with his new 8-inch LX200. Like me, Pat is loath to buy anything when it can be made or modified. What he came up with was a wedge of (ply)wood. We originally looked on this concoction as a temporary fix, something to be used until a better one could be purchased. The wedge of wood worked so well, however, that Pat never had reason to buy another for his Meade SCT. Since the scope was to be placed in a permanent observatory, he also designed and constructed a wooden pier to go with the wedge.
The pier is made from 1/2-inch plywood (3/4-inch might be even better), with all pieces being glued and screwed together. Double-thicknesses of ?-inch were used in places where it was thought necessary: the base plate at the bottom of the pier and the upper plate on which the wedge rests. The dimensions for Pat's pier were 20-inches x 20-inches for the base, a height of 40-inches, and pier body 9-inches square, but these can be modified to fit the needs of a particular scope and observer. There is a 4 ?-inch square opening near the top of the pier to allow for tightening or loosening of the bolt that holds the wedge to the pier top. Gussets running from the base were used strengthen the pier, and the whole thing was varnished and sealed and bolted to a concrete footing in the ground beneath the observatory.
The wedge (Plate 81) was slightly more complicated to make than the pier, but not much. Since as much stiffness as possible is desirable in a wedge, Pat used 3/4-inch plywood throughout. The main hurdle for wedge builders is providing a means for fine altitude adjustment for polar alignment. This particular wedge would be used in a permanent observatory, so only a small amount of altitude adjustment was required, just a degree or two. If a portable wedge is needed, it wouldn't be hard to devise an altitude adjustment scheme that allows for greater range—maybe copied from the metal wedges Meade and Celestron sell.
The wood wedge's dimensions are 18-inches long x 8-inches wide and 12-inches high. This is for an 8-inch CAT; naturally, there will need to be considerable upsizing (and strengthening, perhaps) for larger telescopes. For Pat's "permanent" wedge, the side plates were cut at an angle equal to our latitude, 30 degrees. Adjustment up or down is accomplished by four 7/16-inch bolts inserted into T-nuts installed in the corners of the wedge base plate. These bolts turn through the T-nuts and push against the pier top plate to raise or lower either the north or south end of the wedge, as required. Wedge azimuth adjustment is even simpler. Leaving a little slack in the bolt that attaches the wedge to the pier top gives fine enough action when moving the wedge by hand to do a good drift polar alignment. When azimuth is perfect, the center bolt is tightened down carefully by reaching through the hole left in the side of the upper pier.
How well did the wedge and pier of wood work out? Over the months, there was no detectable change in scope alignment due to shrinkage or expansion of the wood—one of our big concerns. Stability? Outstanding. Pat was able to produce excellent unguided 1-minute CCD exposures with the LX200.
Astro-Imaging ^/eight The astrophotography gurus preach that a telescope needs to be kept "east heavy" for best tracking during picture taking. And that's true.
But how is that done with a fork mount? A GEM is easy to balance, but a fork, it appears, will need the addition of store-bought balance weights on the fork arm. Not so. Hang a small bucket or jug full of rocks, fishing weights, or water (if a jug is used) from the eastern arm by means of a bungee cord (one with a hook on either end) long enough to suspend the weight well away from the mount/telescope. This simple hack can dramatically reduce both backlash and tracking errors.
Milk Jug Weights A larger container filled with water can help reduce a tripod's annoying shakes. A 1-gallon milk jug filled with water (or the beverage of choice) is perfect for this purpose. Most milk jugs have integral handles molded into them that allow the jug to be easily suspended from the CAT's tripod. Use nylon line rather than a bungee cord for this weight, and tie one end securely around the top of the tripod so it extends down between the legs. Knot the free end to the handle of the water-filled jug so it is suspended a couple of inches from the ground. High power views will now be considerably steadier. This scheme also works well to help hold the scope still during focusing. Be careful not to bump the jug while viewing, though, as moving it will introduce swaying that will ruin the view and tend to make observers seasick!
Paint Can Lid Accessory Tray and Tripod Leg Spreader An accessory tray mounted on the telescope's tripod is a handy thing to have. It provides a convenient place to keep eyepieces and other small items handy for immediate use. Unfortunately, the tripods of most fork-mounted SCTs and other CATs do not feature these trays. Some GEM scopes do have accessory trays, but they are usually poorly designed and don't feature much space for astro-stuff. A nice tray that can be used with most fork and some German mount CATs can be made for just a dollar or two and takes less than five minutes to make.
The only material this project requires is the lid from a plastic 5 gallon paint bucket; empty ones are available from most home improvement stores. Discard the bucket or use it for another project (empty buckets are great for carrying small items to the observing site). Drill a hole in the center of the lid the same diameter as the threaded rod the tripod's leg spreader is attached to. Loosen the knob holding the spreader in place and remove it temporarily. Slide the paint lid onto the threaded rod, orienting it so that the lid's lip is facing up. That will keep eyepieces from sliding off. Replace the spreader on the rod and tighten it down. That's all there is to this simple, but remarkably useful, project (Plate 82).
Ersatz Shake Enders Celestron, Meade, and Orion sell an accessory called "Vibration Suppression Pads." These tripodfootpads are shock-absorbing disks that fit under each tripod leg tip to reduce vibration. They are a very desirable item and really do improve telescope steadiness. They are also relatively expensive. That seems
Plate 82. (Accessory Tray) Many SCT tripods lack handy accessory trays. This can be rectified at almost no cost with the lid of a 5-gallon paint bucket. Credit: Author.
surprising, but close examination reveals they are not as simple as they look. They appear similar to the pads that go under furniture legs to prevent scuffing but are actually cleverly made, consisting of an inner cup the tripod leg end tip rests in, which is isolated from the rest of the pad by a layer of "Sorbothane" rubber. Could the enterprising amateur make her or his own? Well certainly! Homemade shake-suppression pads may not be as effective as the real thing, but when combined with other vibration-reducing strategies, they can help.
The simplest homemade pads are nothing more than upside-down bathtub drain stoppers. The best stoppers to use for this purpose are those with an inner ring molded into their surface. This ring would normally face down and would be inserted into the tub drain, but we'll place the tripod leg tip into this depression. The opposite side of the stopper has a narrow raised portion for attachment of a metal ring and chain that may be trimmed off with a sharp hobby knife. If there's a wide raised area, just leave it in place, as it will add to the stopper's vibration-reducing characteristics. Remove the metal pull chain, if present. Placing three tub drain stoppers under the tripod legs might seem to be a slightly humorous and overly hopeful method of trying to stop a CAT's palsy, but users report that this really works. The person who suggested this trick experienced a reduction in "shake time" from 5 seconds to an excellent time of less than one second.
What else can be pressed into service as homemade shake-enders? Well, what looks like a Shake Ender? The aforementioned furniture carpet or scuff protectors for furniture. Sadly, these do little or nothing to reduce the shakes. But that can be fixed! Buy three carpet protectors—hard rubber ones are the best choice. On the way home stop off at the office or computer supply store and buy a couple of neoprene mouse pads. At home, take the three carpet protectors and the mouse pads and make little "sandwiches." Cut neoprene circles from the pads the same diameter as the carpet protectors. Place one circular cutout piece of mouse pad on the bottom of each protector and another piece on top, where the tripod tip will rest. The pieces of neoprene can be glued into place with contact cement or Super Glue. Place a completed "shake ender" under each tripod leg and enjoy.
Strengthen Tripod Legs with Sand If the telescope is still too shaky despite weights and homemade vibration suppression pads, the problem may be that the tripodis just too light. As a last resort, try a trick that many scope users, especially those saddled with the light extruded aluminum tripods, swear by: fill the legs of the tripod with sand. This can, in some instances, have a dramatic effect on scope steadiness. Use nice clean sand from the home improvement store (it will be in the same area as the concrete mixes). One bag should be more than enough. How the tripod is filled and sealed will depend on the particular model. Often, the easiest method will be to pour in sand from bottom of the legs after having removed their tips. Before doing that, remove mount head or wedge, of course. If the tripod is an extruded aluminum job (light square leg sections), it will probably be necessary to seal small gaps in the tripod to prevent sand from leaking out. Any type of silicone sealer (RTV) will work well. Make sure the sand can be removed if this trick doesn't work out—don't glue tip ends back on permanently.
"Permanent" Polar Alignment for portable CATs Polar alignment is a pain, but a necessary one for astrophotography and for accurate go-to with some GEM telescopes. Is there some way to avoid having to do a polar alignment every time the scope is used? If the CAT is used in the backyard or at a site owned by a club, it is possible to preserve a good alignment by marking the exact positions of the telescope's tripod legs. If only middling accuracy is required, do this by placing some simple markers. These can be three stakes driven into the lawn next to each tripod leg tip after a good alignment. Just don't forget and run the lawnmower over these stakes the next time the grass needs to be cut.
An even better solution involves three lengths of PVC pipe. Go to a plumbing supply store and purchase a length of 3- or 4-inch diameter PVC pipe a couple of feet long. Cut off three 6-inch-long sections and, using a hammer, drive them into the ground at previously determined and marked positions appropriate for the telescope's tripod, leaving maybe a half-inch of each section above ground. Each leg tip of the tripod will be placed in the exact center of one of the protruding pipe ends. The pipe ends should not touch the tripod legs. That could cause vibration. Their only purpose is to act as position markers.
When the three pipes are in place and the tripod is properly positioned, do a good polar alignment. When the alignment is complete, make sure the wedgeor GEM altitude and azimuth adjusters are tightly secured. Observe as normal and return the scope to the house when the run is over. The fun part comes on the next evening. Instead of polar aligning, just set the scope up so the tips of the tripod are again positioned in the centers of the pipe ends. The scope's polar alignment should still be very close. The most that will be needed will be a quick fine-tuning drift alignment if astrophotography is on the evening's agenda. Likely that will not even be required. Naturally, if the altitude or azimuth of the wedge or GEM head is changed, either purposefully to observe from another site or accidentally, a new polar alignment will be required.
If driving PVC pipe sections into the ground is not possible at a particular observing site, there are other ways to "mark" polar alignment. If the telescope is set up on a concrete pad, a driveway, or a deck make small marks with paint or a permanent marker to indicate leg positions. A nice solution, and one that's super-permanent, would be pouring three round concrete pads in the yard for the scope legs to rest on. That is not hard to do, since small, easy-to-use bags of concrete ("Sackcrete," "Quickcrete") are readily available at home improvement stores. If placing permanent concrete pads on the lawn isn't practical, building supply houses sell concrete paving blocks or "stepping stones" that will work as scope leg pads. These can be found in sizes as small as 6-inches x 6-inches and in various pastel colors.
A Permanent Telescope Without an Observatory Thanks to superb and inexpensive pre-fab observatory domes like the Skyshed Pod, more amateurs than ever can realize the dream of a permanent backyard scope installation. Some can't, however. Some neighborhood ordinances restrict the use of even "temporary" buildings. If a permanent observatory isn't possible, how about a permanent pier? A sturdy and weatherproof pier, either homemade or store bought, can provide at least some of the benefits of an observatory. If used with a fork mount scope in equatorial mode, the wedge can be left in place, and the CAT will not need much—if any—polar alignment before an observing run. Some amateurs take this a step further and leave scope and mount out in the yard on a pier all the time. Before contemplating that, be sure that bugs, the elements, or theft won't be problems. A good weatherproof cover is a must.
Shortening Tripod Legs Some CAT tripods are too tall. Even when fully collapsed, they are difficult to use seated, especially if the telescope is placed on a wedge. Some tripods can be improved by removing the legs and cutting off 4 or 5-inches from top or bottom. This will not be easy for all tripods, but if it's possible to do so, cutting down a tripod a bit may have a benefit in addition to more comfortable observing. A shorter tripod may be considerably more stable when fully collapsed.
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