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Posts Made By: Thomas Dey

September 16, 2015 03:25 PM Forum: Digital SLR AstroPhotography

Double Cluster

Posted By Thomas Dey
Very nice! I actually kinda like the "diffraction spikes" remind me of the view thru a scope with a spider. Decades ago I did photographic constellations and would add a tape cross over the lens pupil to get that affect. Purists would of course suppress spikes, arguing that they are "unnatural" AKA Not characteristic of the object, but of the instrument. But in the limit, stars technically would be completely unresolved DOTS much smaller even than single pixels. In that sense, Everything that we see is almost entirely artifactual. Even the Airy Disc is instrumental artifact! Reductio ad absurdum. Nice pic! Tom Dey

September 18, 2015 05:03 PM Forum: After Dark

"NAKED EYE" SUNSPOT(S)

Posted By Thomas Dey
here's an image taken with a 1.8x barlow Tom

September 23, 2015 02:12 AM Forum: Equipment Talk

Threaded spacers 5mm or so

Posted By Thomas Dey
Agree with Floyd. Spacers were always needed at work and I recall we found spacer "sets" for C, T etc. that had a whole stack of spacers and even ring-shaped shims so in theory you could get ANYTHING you want just by stacking them in different ways to accuracy of 0.001 inch! I think they may have been Newport but just don't recall for sure. The sets weren't cheap...but neither was out program time. That was the nice thing about work. Hobby stuff is mostly plywood and cardboard for me now! Sorry for bloviating so much... Tom

September 26, 2015 10:50 PM Forum: Home Observatories

My first pier

Posted By Thomas Dey
Very nice, Charles! I've hand-dug 31 post holes 40+ inches down in the name of Astronomy! And two MASSIVE piers. One needed a ladder to get out of... My will directs that I be frozen in liquid nitrogen and pounded into the ground beneath my dome... ~RIP~ Tom

September 27, 2015 05:52 PM Forum: ASTRONOMY

Hubble Animated View: Veil Nebula

Posted By Thomas Dey
Hi Rod. Nice! I thought that looked familiar, so I dug out a picture I took on film decades ago. It is that region of the handle of the "Witch's Broom" highlighted in the yellow box. Many of the stars appearing in the Hubble pic should be easily seen in a biggish amateur scope and also plenty of the bigger neb structure especially with a reasonably strong nebl filter. This is a very bright section of the Veil. The attached pic is a scan of a print of a (region of a) TP2415 neg that I took with my ancient 12.5-inch Cave Astrola! Tom

October 3, 2015 09:01 PM Forum: Equipment Talk

Safty "button?" On counter weight shaft

Posted By Thomas Dey
Good idea. If there's a threaded hole there you could make a stop. I had an ancient HEAVY Cave Astrola with a single 100-lb Lead counterweight held onto the SMOOTH shaft by ONE SETSCREW! BIG setscrew - but still primed for a Darwin Award. I drilled and tapped the end of the 2.5-inch steel shaft (3/8-16) and added a stop. Also added a collar below the weight so it had two things holding its position. Maybe someone will chime in with a stock part for you. Tom

October 4, 2015 02:57 PM Forum: Deep Sky Observing

NGC 7048

Posted By Thomas Dey
Rod, it that 2048 or 7048? We were looking at planetaries last new moon. Thanx for the tip. Perfect object for my Big Dob.

October 4, 2015 04:32 PM Forum: Equipment Talk

Notes on Zeiss 20x60S Stabilized Binoculars

Posted By Thomas Dey
Thanx, Paul. Excellent, thorough review! I have same binos and love them. My bloviating appears on your site. Caution to visitors: If you DON'T have these binos yet ... Paul's review will keep you up at night Wanting Them! Maybe that's redundant for astronomers, though. Tom

October 7, 2015 04:18 PM Forum: Equipment Talk

Diagonals

Posted By Thomas Dey
Yeah - I did an exhaustive comparative study of 15 star diagonals - measured alignment, wavefront, spectral throughput, etc. Most were deficient. Of the two Meades, one had terrible angular alignment and one had fairly low strehl (but measured over the whole diam so probably still fine when used in traditional way). Of the two TeleVues, one had a slightly low strehl and the other was very nice indeed. Here's a copy of the summary sheet. I can send anyone the entire paper if they like. If I had a web site I would put it there. Final comment - it you are doing polarization studies the dielectrics can induce phase changes that could screw up your measurements of IQUV (Stokes Parameters) or the Jones Matrix ... but Very Few here would be doing that kinda stuff! Tom

October 7, 2015 04:19 PM Forum: Equipment Talk

Diagonals

Posted By Thomas Dey
Here's the summary sheet - Tom

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