Astronomy
Version 3.0 Micrometer Focussing adapter.
December 21, 25
It suddenly occured to me how to make this much more compact and get more range and increase the drive ratio into the bargain. See photos at right.
At top is the version I messed with all day.
At bottom is the variation that occured to me all at once late in the evening. I expanded the milled slot into a flat and drilled a new hole to mount the existing split-block. I didn't have any small bolts to accomplish this so I used a huge 3/8x16 thing just to get it cobbled up and mounted for measurements and a plausibility check.
It fits, it works, it's just a little crowded at the drum. The newest version has a focus range measured to be 38 thousandths at the draw tube. It does not bind. It can be rendered neater, (even) more rigid and more ergonomic simply by making a new and longer split block to hold the micrometer and drilling one more hole in the newly milled flat. The geometry will remain essentially unchanged, so call it v3.1. But use reasonably small bolts, OK? And wait to see if one of the pair of micrometer heads enroute from eBay is better for this application. The price was way low, probably because of the custom scale engraved that looked like something I would have happily specified for dialing in filter offsets.
And while you're at it, how about shooting some photographs sharp enough to justify all this trouble?
Dec 25. Clouds for now. The next clear spell will probably coincide with a trip to the Mint Museum to see an exhibition of Hudson River art. So much for field trials. I've rebuilt v3.0 as v3.1. Some changes: a longer straight arm so that the flat milled on the round clamp contributes to rigidity and a larger micrometer with twice the travel. V3.1 offers 50 thousandths of focus travel. It still needs refinement, but it's ready to go to work under the next clear skies.
50 thousands is about 1,250 microns, or 10-15x the depth of the critical focus zone behind this telescope. Now we're getting into a useful reach without compromising the ability to find best focus. While tweaking this or the next iteration, I need to be sure the micrometer has the range to focus in all channels (L, R, G, B, and H-a).
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Text & Photos by David
Cortner
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