Posts Made By: Thomas Dey

Another picture - I don't know how to put more than one in the original post. Enjoy! Tom Dey

And another pic...that's me. Tom Dey

And as it sits in my computer room...Tom

I just posted to Billy but noticed your comment regarding insects here! I'm 66 now, but collected insects for the Dept. of Agr. in the Jungles of Panama way back around 1970. What an AWESOME place to collect for 20 months straight. Resulted in such best-sellers as "Antireflection Properties of the Chitenous Moth Cornea" and "Polarization Sensitivity of the Compound Eye of Hymenoptera Bombus." Tom Dey

I notice that your focuser looks similar to my LUNT Pressure Tuners (all 5 of them!). And indeed one has gotten frightenly stiff when turned in far. I have always assumed they are brass on brass and just greased up. These tuners have 4 identical threads phased 0, 90, 180, 270 (of course). Especially stiff when it gets cold - I assumed it was the non-synthetic grease viscosity climbing. I keep planning on at least cleaning and regreasing them but never get around to it. But here's a thought: if the M, F are of different BASE materials, then their different CTEs would result in best match pitches and diameters at the original lapping ambient. Anything other temp would result in a mismatch...which need not be much at all, considering the close tolerance of lapped threads. And THAT would be a function of how much engagement is involved. My inclination would be to disasemble (if easy), clean, re-lap, clean, grease, reassemble and use. Risk is that further abrading surface-hardened materials can subject them to galling...disasterous. At work we more than once ruined surfaces by breaking thru the anodized surface of aluminum. Al is notorious for galling unless it's the cast stuff. It astounds me that our hardware works as good as it does, considering all the little gremlins that affect performance.

WHOOPS - I OF COURSE MEAN OCTOBER 22nd. Tom Dey

Aperture will completely transform Deep Sky, if you would like that. A Dob in the 13.1-16 inch range could fit your budget. And rolling it out of the barn for use would be easy. Little known secret for planets is to just make a cheap off-axis stop for the Dob. I made a 6.5 incher for my 17.5 Dob and the planetary views were magnificent! As good as the best Apos of similar (6-inch) size. Trick is you rotate the stop to find the mirror's best wavefront "sweet-spot" while you are looking through the eyepiece. So you have the best of both worlds: Large aperture for deep-sky AND high-res, unobstructed apo just by plopping on the stop. Bonus: I'd enjoy Saturn with the stop on and then take it off to see all those little moons hovering close around. Tom Dey (Thomas Dey)

Nuts, It's cloudy here today and I do an imaging session nearly every favorable day (not that often here in NY). But the sun has indeed been hanging in there nice and active ever since it perked up a couple years ago! Tom

Years (decades?) ago I did hundreds of multi-hour DS pics "the old fashioned way" pushing the 4 buttons on an old Cave Astrola 12.5-inch. The gears were terrible so I couldn't relax and sometimes temps were sub-zero! Then the miraculous ST-4 came out and I replaced the RA gear with a Byers 11+ incher and made a precision tangent arm for Dec. Miraculous! That Astrola locked onto guide star like a bulldog. I would actually sleep and come back to that wonderful sound of the solenoids still clacking. On topic - I had it in a powered dome so set my laptop on a heating pad set on low. Only precaution would be to not inadvertently OVER heat your PC. But they have auto shut off even of that were to happen. The DSLR manual would spec temp tolerance. Even there a heater strip would probably keep it happy. Tom Dey

Hi Stephen. Most fundamental rule of thumb is based on Rayleigh res (radians) being 1.22 wavelength/diam with assumption that two monochromatic stars of equal brightness are being observed and seen bright enough to of course look directly at the pair. Other assumptions are that effective wavelength is in the middle of the photopic visual ~0.55 um and that the eye resolves 1 arc-min (can just discern two dots separated by 1 acr-min as seen thru the eyepiece). Plug that in and an e.g. 6-inch telescope has a Rayleigh limit of 0.908 arc-sec (Rayleigh) 0.76 (Dawes) and 0.74 (Sparrow). These correspond to mags of 66, 79 and 81. But you really need around 4 times that mag to render the airy disc(s) comfortably resolved. That's why 1.5-inch theodolites typically have mag thru the eyepiece of ~60x. (This is bases on actual USE rather than theory!) So if we increase those 3 example mags by 4x it gives 264, 316 and 324 for Rayleigh, Dawes, Sparrow using a 6-inch scope. Your rule yields 358X...which is reasonably close to the 324. And I note that if we had assumed a wavelength of 0.5 um...the 324 becomes 356...virtually identical to the rule you cite. To ans your direct question though...I don't know who came up with that or how. Add to all this seeing, polychromatic, central obstruction, convolution...I wouldn't put too much stock in rules of thumb. In practice, I would crank up the mag until bright stars are quite comfortably bigger than dots. In fact, you will NEED to comfortably see fairly stable little Airy Discs on individual stars to even HOPE to have a good night splitting doubles to the capability of your scope! Tom Dey