Astronomy
Small things
November 30
Applying lessons from The West and just getting off my duff to take care of some small things that will make life better:
1) Remount the A-P rings at the end of the Losmandy bar. Didn't even need to drill new holes (although I did drill one before I realized this). Now that I am no longer using the home-brewed reversible aluminum shield (heavy) but rather the AstroZap roll-up shield, there's no reason to leave room skyward of the rings to accomodate the reversed shield when the telescope is stowed for travel. Now there's room between the mounting rings for the AstroZap shield to be wrapped around the tube for storage and travel.
2) Replace the bolts that hold the tailpiece in place with 10-24 button-cap socket screws. They are more secure than the smaller thumbscrews, are more easily found in a store if lost, and don't hang up on the LowePro case I packed the tailpiece in.
3) Finally! Supplemental support for the Linhof's legs so I can extend them as needed to level the rig on uneven ground. No more digging holes and hunting rocks, let alone carrying boards for shimming. Over the years, I've sketched many ideas to add strength and reliability to the extension clamps. Half-blocks, set screws, sets of fixed width collars, cotter pins, even a couple of wild-hair cable schemes. Then George told me about ordering his new bicycle and about reserving his present one for guests. In my mind, I saw his current Trek. And for some reason one detail was highlighted: I saw the seat post clamp fairly glowing with vivid presence. D'oh! Of course. I measured the Linhof legs' downtubes, ordered cam-operated clamps -- 31.8mm please -- one for each leg. $5.99 each. Perfect!
D'oh! That's the way you do it.
Tonight, weather willing, I'll make some unguided DSLR exposures of fading Comet Holmes and we'll see if there is any creep in the solution.
Success! I left the Canon shooting consecutive 2-minute frames for a couple of hours. The first and last align very nicely, so there's no significant creepage in the tripod legs. Of course, the 5-inch and DSLR with a single 11-pound counterweight on the G11 is about the lightest load it ever carries. With more counterweights, a guide scope and the 200mm F2 in addition to the 5-inch, I don't expect any problems. But it's not yet tested.
Testing the new clamps:
Comet Holmes.
120s Canon 20D, iso 1600. A-P 5-inch @ F4.8
(Click image to enlarge)
One of a sequence of about 50 images
to see if the tripod sagged.
Comet on a String, frame 20 something.
120s
Canon 20D, iso 1600. A-P 5-inch @ F4.8
(Click image to enlarge)
The best frames aligned on the comet's
nucleus and combined.
(Click image to enlarge.)
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Cameras behind Telescopes:
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Text & Photos by David
Cortner
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