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Posts Made By: Doug Scobel

August 17, 2004 05:02 PM Forum: Telescope Making

questions for glass pushers

Posted By Doug Scobel
Hi, Jeremy.

Regarding 1), have you tried alternating MOT/TOT to minimize FL change? Should still bring you to a sphere. Also, someone suggested using rouge to slow down the polishing action while figuring. It also may result in a better polish (less micro-ripple). But it is messy and stains everything in which it comes in contact, so be careful with it.

Regarding 2), I usually end up with a too-short radius outer zone when figuring with a full-size lap. Is that what you mean when you say that you have a still-spherical outer zone? I haven't come up with a solution either. I'd be interested in hearing others' solution to that. I ended up parabolizing my 8-inch using a 4" lap, after getting a sphere with the full-sized lap.

FWIW, knowing the trouble I had with my "easy" to figure 8-inch f/8, I can only imagine trying to do a 10-inch f/5 with a full size lap. 8O

Hope this helps, if only a little.

Doug

August 17, 2004 09:00 PM Forum: Equipment Talk

Dew Removal

Posted By Doug Scobel
Jeff, here's an article I wrote on the subject for our club newsletter several years ago. Hope you find it useful.

http://www.umich.edu/~lowbrows/reflections/1996/dscobel.3.html

Doug

August 23, 2004 05:11 PM Forum: Telescope Making

Using Doll House Wire Tape

Posted By Doug Scobel
Hi, David. I have used it with good results on my 13". IIRC, there was a clear, vinyl film over the top (non-adhesive) side that I was able to peel off. This left the two conductors bare. I left the adhesive side alone. Of the two copper strips, one had some kind of dark colored ink on it, the other was copper colored, presumably to manage polarity in a doll house. I used sandpaper to clean the top surfaces of both, at both ends, and then applied it to the side of a spider vane. I then soldered thin copper wires (single strand telephone wire) to each, using a 25 watt soldering pencil. They soldered on nicely, without damaging the adhesive side. I then connected the wires to an RCA jack on the outside of the telescope tube, and to the heater wires behind the secondary. Because there's no tension on the connections to the doll house wiring tape, there's no reason to think that they'll ever come loose.

I can take some pics tonight and post them tomorrow.

Hope this helps,
Doug

August 23, 2004 05:33 PM Forum: Star Parties

Black Forest Star Party....Who's In?

Posted By Doug Scobel
I'm in! Third year for me. grin You won't be disappointed, Alan, especially if we have a good, clear night (or nights)!

I hope to bring both my homemade scopes, 13" f/4.5 and 8" f/8. Look for me at "Camp Lowbrow" (there's a good ten of us going).

Doug

August 31, 2004 04:33 PM Forum: Eyepieces

Radians, first light.

Posted By Doug Scobel
Thanks for the report, Floyd. I'm wondering how they'd compare in a slower scope, yours being f/4.8. At the BFSP next week I hope to do such a comparison in my 8-inch f/8. I own a few Radians (4, 5, and 14mm). I'll see what I can borrow to compare against. I'll use the same test objects you used.

As someone else mentioned, the Radian is a good choice if you need a single eyepiece for both planetary and deep sky work. I'm on a tight budget so I currently don't have the resources to buy a separate optimal design for each kind of observing.

Doug

September 1, 2004 11:54 AM Forum: Equipment Talk

Telescope sizes: inches vs. mm

Posted By Doug Scobel
"This way we will have our aperture sizes, focal lengths, and eyepieces on the same unit, which would allow for easier calculation of magnifications(no english/metric conversions)."

Speaking purely WRT telescopes, the FL of my 13" is 58.7 inches or 1491mm. Dividing a 13mm EP (for example) into either has to be done with a calculator, so I don't see an advantage. Unless you can do that kind of division in your head! 8O

I've set up a spreadsheet for calculating magnifications for all my eyepiece/telescope combinations so I just let the computer do it for me anyway.

But in general, I agree that the metric system would be easier overall. Powers of 10 are obviously more natural since we all use a base 10 number system (computer geeks like myself notwithstanding).

Best regards,
Doug

September 3, 2004 11:45 AM Forum: Equipment Talk

Sky Atlas 2000

Posted By Doug Scobel
I like the white stars on black because it's easier on my night vision. You're looking at a predominately dark background that way. Black stars on white means you're looking at a bright background.

Whatever you choose, get the laminated version to prevent damage from dew.

Doug

September 3, 2004 12:35 PM Forum: Equipment Talk

Telescope sizes: inches vs. mm

Posted By Doug Scobel
Here's something that always bugged me until I found out the reason. The conversion from inches to centimeters is 2.54. Not 2.54012623478 or 2.540003776234 or some other similar number. Why exactly 2.54? :S

The reason is that the inch is "officially" defined to be 2.54 centimeters. Not sure where I read it but I sleep better now. smile

Doug

September 15, 2004 05:15 PM Forum: Deep Sky Observing

M 13

Posted By Doug Scobel
Gee, I dunno, Jim. I was there also, and on Friday night (at least early) I was seeing 16th magnitude stars in my 13" - I've never been able to do that before. Saturday night the transparency was not as good. What night are you referring to? Last year's BFSP was late August, and I remember poor transparency, but steady, which was perfect for Mars observations. Friday night's transparency was way better than last year's.

But admittedly there was a lot of moisture this year, in the form of dew. And in the wee hours of Saturday morning, everyone's mirrors, including primaries, were fogging up due to ground fog. The field was just too wet from the several inches of rain Frances dropped on it Wednesday. Perhaps you had the start of some dewing problems and you didn't realize it?

Best regards,
Doug

September 21, 2004 12:03 PM Forum: Star Parties

Home from the Black Forest Star Party

Posted By Doug Scobel
Ditto, Dave. This was my third BFSP and it never fails to impress.

For those interested, here's a link to the BFSP web page with reports from the event.

http://www.bfsp.org/starparty/bfsp2004/index.htm

Doug

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