Do any of you large Newtonian users employ a secondary heater for anti-dew/frost use? I've never used or needed any kind of optic heaters; a conventional tube acts as a really long dew-cap. I was wondering if dew or frost is a problem with open-frame, truss-tube Newtonians? Oops, I have used a small chemical hand-warmer rubber-banded to the eyepiece, but that's it. Prevents fogging in cold weather, and brain freeze. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Hi Chuck, Bruce Grim has an open tube scope and I think he has mentioned his primary frosting up. Bruce doesn't hang out here on U-A so I'm CCing a copy of this message to him so maybe he can reply. Patrick On 22 Dec 2006, at 21:31, Chuck Hards wrote:
Do any of you large Newtonian users employ a secondary heater for anti-dew/frost use?
I've never used or needed any kind of optic heaters; a conventional tube acts as a really long dew-cap. I was wondering if dew or frost is a problem with open-frame, truss-tube Newtonians?
Oops, I have used a small chemical hand-warmer rubber-banded to the eyepiece, but that's it. Prevents fogging in cold weather, and brain freeze.
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Thanks, Patrick. That would be a big concern for a portable scope, since Bruce's is in an observatory, and next to a structure (his house). I'm wondering if the humidity from the millpond contributes to it? I'll let everyone know what Bruce says. --- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
Hi Chuck,
Bruce Grim has an open tube scope and I think he has mentioned his primary frosting up.
Bruce doesn't hang out here on U-A so I'm CCing a copy of this message to him so maybe he can reply.
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Guy, when I first got started in astronomy and telescope making in the late sixties, Bruce was already well advanced in the hobby and an expert. He's also very busy in his retirement at the moment and like many of us, astronomy isn't his only hobby. He's a man of many talents and his time is in demand from multiple quarters. If Bruce hadn't been around, there would literally be no SPOC today, and probably a much diminished SLAS. --- diveboss@xmission.com wrote:
Quoting Patrick Wiggins <paw@wirelessbeehive.com>:
Bruce doesn't hang out here on U-A...
What??? That's blasphemy!
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I hope to meet him someday. ;) Quoting Chuck Hards <chuckhards@yahoo.com>:
Guy, when I first got started in astronomy and telescope making in the late sixties, Bruce was already well advanced in the hobby and an expert. He's also very busy in his retirement at the moment and like many of us, astronomy isn't his only hobby. He's a man of many talents and his time is in demand from multiple quarters.
If Bruce hadn't been around, there would literally be no SPOC today, and probably a much diminished SLAS.
--- diveboss@xmission.com wrote:
Quoting Patrick Wiggins <paw@wirelessbeehive.com>:
Bruce doesn't hang out here on U-A...
What??? That's blasphemy!
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Heh-heh, I know you already know him well. I wish you could have known him when he was 30 years old, not a grey hair on his head (or beard- the beard is almost as old as Bruce is). Get him to tell you about the day we moved the old 16" from his in-law's yard in Bountiful out to Stansbury for the first incarnation of SPOC. About 30 mph on a flatbed truck, all the way! --- diveboss@xmission.com wrote:
I hope to meet him someday. ;)
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Sounds like a bucket of chicken and a six pack of beer drive to me. For my politically correct and activist friends, that would not be "Free range" chicken! ;) Quoting Chuck Hards <chuckhards@yahoo.com>:
Heh-heh, I know you already know him well. I wish you could have known him when he was 30 years old, not a grey hair on his head (or beard- the beard is almost as old as Bruce is).
Get him to tell you about the day we moved the old 16" from his in-law's yard in Bountiful out to Stansbury for the first incarnation of SPOC. About 30 mph on a flatbed truck, all the way!
--- diveboss@xmission.com wrote:
I hope to meet him someday. ;)
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On 23 Dec 2006, at 12:24, Chuck Hards wrote:
...I wish you could have known him when he was 30 years old, not a grey hair on his head (or beard- the beard is almost as old as Bruce is).
Bruce then... http://www.trilobyte.net/paw/slas/patrickw/PATRICKW471.JPG http://www.trilobyte.net/paw/slas/patrickw/PATRICKW367.JPG And now... http://www.trilobyte.net/paw/slas/patrickw/PATRICKW385.JPG pw
Back in New England, either a dew strip or a hair drying was a standard part of the kit if you had a refractor or SCT. On large reflectors, I tended to see heaters on the finder scope and the eyepiece.. On Dec 22, 2006, at 9:31 PM, Chuck Hards wrote:
Do any of you large Newtonian users employ a secondary heater for anti-dew/frost use?
I've never used or needed any kind of optic heaters; a conventional tube acts as a really long dew-cap. I was wondering if dew or frost is a problem with open-frame, truss-tube Newtonians?
Oops, I have used a small chemical hand-warmer rubber-banded to the eyepiece, but that's it. Prevents fogging in cold weather, and brain freeze.
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Michael Carnes MichaelCarnes@earthlink.net home.earthlink.net/~michaelcarnes
Although I've had the parts for this big scope for over 20 years now, including the spider and secondary holder, I think I may opt for a new secondary holder/spider from Protostar, and purchase the optional built-in heater. Very clean design: http://www.fpi-protostar.com/options.htm I've heard that the Protostar secondary holders are much easier to adjust than the older Novak designs that I've favored in the past (which are no longer available), so that's a bonus as well. Bryan Greer recently dropped his line of Pyrex diagonal mirrors completely in favor of fused quartz exclusively. The quartz mirrors should show essentially no deformation from the gentle warming of a dew chaser. Remember that a good dew or frost preventer merely raises the temperature of the optic above the dew point- it doesn't make the optic warm to the touch so there should be no induced distortions from differences in air densities close to the optical surface. You know, Michael, I've never had a dew or frost problem on anything but eyepieces- and then only when I place my eye close to it. A small chemical hand-warmer, which come in the form of a bag, solved the problem. They last for hours. You just shake it to mix the ingredients and start the catalytic reaction that generates the heat. Rubber-banded around the eyepiece, the problem went away. On all-nighters, I would cover the scope during occasional breaks and I think that helps as well. I'm sure our average humidity out here is much less than that of New England. Ever see a swamp cooler in Boston? --- Michael Carnes <MichaelCarnes@earthlink.net> wrote:
Back in New England, either a dew strip or a hair drying was a standard part of the kit if you had a refractor or SCT. On large reflectors, I tended to see heaters on the finder scope and the eyepiece..
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I think I may opt for a new secondary holder/spider from Protostar, and purchase the optional built-in heater. Very clean design: I put a Protostar secondary holder in my 10" a couple of years ago. It's the 2-legged curved holder and I think it's really great. Some people love diffraction spikes. I hate 'em, and they're gone. The adjustment is really easy too. The whole block is a stiff rubbery composite. I had my doubts at first, but it takes adjustment easily and holds it.
I'm sure our average humidity out here is much less than that of New England. Ever see a swamp cooler in Boston? Never even heard of one till I got here. Average humidity in the summer is such that your scope chases the dew point all night long. Some nights, big drops of water would roll down the collector plate. In the winter (one of the best times for observing in New England, except for the frostbite), everything would frost up. There are lots of things to miss about New England, but humidity isn't one of them.
I use a home-made curved spider in my 4.25" f/5 and have no spikes. Thought I would try it before I went with an optical window, just to satisfy my own curiosity, and it worked so well, I never used the window (have a couple of surplus windows from Edmund Astroscans). What I'm told is that the total resolution loss due to diffraction from the curved supports is still there, just not visible as spikes since it's spread-out to a level below the threshold of visibility. I don't think Protostar offers a curved option for large spiders, however. I'll check into it as time permits. --- Michael Carnes <MichaelCarnes@earthlink.net> wrote:
It's the 2-legged curved holder and I think it's really great. Some people love diffraction spikes. I hate 'em, and they're gone.
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Yep, a check of the Protostar Website shows that the curved option is only for "tubes" up to 15". IIRC, the reason was unacceptable vibration when you go larger due to more massive secondaries. Thickening the spider 'vane' sections to compensate cancelled the diffraction-fighting quality of the curved supports.
I don't think Protostar offers a curved option for large spiders, however. I'll check into it as time permits.
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Yep, a check of the Protostar Website shows that the curved option is only for "tubes" up to 15". IIRC, the reason was unacceptable vibration when you go larger due to more massive secondaries.
Drat. Maybe you could make them out of that transparent aluminum from Star Trek 4, the whale episode. I think the whales were humpbacks, but one of them could have been Shatner.
Nope, Doohan (or Nichols...). --- Michael Carnes <MichaelCarnes@earthlink.net> wrote:
Drat. Maybe you could make them out of that transparent aluminum from Star Trek 4, the whale episode. I think the whales were humpbacks, but one of them could have been Shatner.
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What I'm told is that the total resolution loss due to diffraction from the curved supports is still there, just not visible as spikes since it's spread-out to a level below the threshold of visibility.
There might be more to it than that. I think the total amount of diffraction components is lower because there are only two vanes instead of three or four. The vanes themselves are pretty thin, since much of the rigidity of the structure is provided by the spring tension of the vanes. But certainly there's still schmutz in there, just spread around.
My point is that assuming the same obstructed area, there is the same total amount of diffraction. It is just not concentrated in the "spikes" with a curved spider. I use a single-stalk secondary holder in my 6" scope. Since the diagonal is only 1" minor-axis and very low mass, I use a rod of much thinner section than most commercial single-stalk rods. I get only two spikes, diametrically opposed. My 4.25" uses a curved spider that is one curved section of sheet metal, with the secondary holder at the mid-point. Neither of these options is particularly good for a larger telescope, with much more massive secondaries supported much further from the tube walls. Wire spiders have gained popularity recently because they obstruct very little area. A curved spider, whatever the number of vanes, is really a type of apodizing mask. Straight-vaned spiders can reduce the intensity of spikes, at the expense of greater total diffraction, by covering them with a thin mask with a non-straight edge, like an undulating wave pattern. Deep-sky objects are so dim that we never notice diffraction effects with large telescopes. It's usually only on bright stars and the planets that it is noticeable, or when imaging. For the average "light bucket", an optimised spider is really no big deal. Schmutz- There you go with those technical terms again. I think Ingalls comments on schmutz in ATM book 2. --- Michael Carnes <MichaelCarnes@earthlink.net> wrote:
There might be more to it than that. I think the total amount of diffraction components is lower because there are only two vanes instead of three or four. The vanes themselves are pretty thin, since much of the rigidity of the structure is provided by the spring tension of the vanes. But certainly there's still schmutz in there, just spread around.
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It HAS come in handy, now that I've gotten-into Klesmer hip-hop... --- Michael Carnes <MichaelCarnes@earthlink.net> wrote:
Schmutz- There you go with those technical terms again.
Hey, everybody ought to know a little Yiddish...
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participants (4)
-
Chuck Hards -
diveboss＠xmission.com -
Michael Carnes -
Patrick Wiggins