Image of the day

Captured by
Douglas Rollain

M20 Trifid Nebula in LRGBHa

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Posts Made By: Doug Scobel

August 16, 2005 02:06 AM Forum: Telescope Making

Looking for air filter ideas

Posted By Doug Scobel
Thanks for all the ideas, everyone. I think the trick will be getting a balance between filtration and airflow. I'm going to try Bill's idea and use the air conditioner filter material first. I picked up a package today for $2.99. I'll post a picture once I get something rigged up.

Doug

August 17, 2005 01:03 PM Forum: Equipment Talk

Power supply for Kendrick Heater

Posted By Doug Scobel
In looking at the answers to Tom's question I'm amazed. How much power do the Kendrick heaters use, anyway? I use a 7 amp-hour gel cell for my scope and I can run it all night if I have to. Total current draw is under an amp, but I'm running two three-inch computer fans, plus home grown dew heaters on the Telrad and both ends of the 8x50 finder. Everything stays bone dry even under the wettest of conditions (common here around the Great Lakes). Why do the Kendrick heaters suck up so much juice?

One of my observing buddies has a 12" Portaball and he also has power problems when he has to use his Kendrick heaters, so I don't think it's unique to their corrector plate heaters.

Doug

August 30, 2005 12:43 PM Forum: Telescope Making

Looking for air filter ideas

Posted By Doug Scobel
Here's my solution. I used 1/4" screening cut just a little larger than the openings and pressed in, then some cheap air conditioner filter foam also cut a little oversize and pressed in. Quick and (hopefully not) dirty. I don't know how well it will work, but it ought to keep out any big chunks, and the bugs. Easily removed if it restricts the air flow too much. We'll see how it works at the BFSP.

Doug

September 6, 2005 02:48 PM Forum: Telescope Making

Sonotube for 12.5 inch DOB

Posted By Doug Scobel
Jon, find a genuine "Sonotube", available at real building supply stores. Wall thickness is about 5/16" in the 14" size. My 13 inch Dob uses a 16" Sonotube and it is more than robust enough. It has survived more than eight years of drenching dew with no deterioration.

Use fender washers when mounting the spider. They will distribute the tension force over a larger area and reduce deformation of the tube.

Many folks use the term "Sonotube" rather loosely, but it is a brand name. The "Quiktubes" sold at home improvement stores are not the same thing.

Doug

September 7, 2005 12:41 PM Forum: Equipment Talk

Packaging a mirror

Posted By Doug Scobel
John, if you use the packing method prescribed by Spectrum Coatings (http://www.spectrum-coatings.com/Telescope-Mirror_Packing.htm), then all you really need is the large tissue available at gift shops. With the hard foam they recommend, nothing bears against the concave face except at the extreme edge. Just wrap the entire mirror with two or three layers of tissue and you're good to go.

Doug

September 8, 2005 01:19 PM Forum: Equipment Talk

Aperture and nebulae, OH, MY WORD! (LONG)

Posted By Doug Scobel
Amazing, huh?! Wait 'til you get out under truly dark skies. You will see another quantum leap in the views!

I upgraded from a 6-inch to a 13-inch more than 20 years ago, and I still haven't felt the need to go to a larger scope.

Yes, aperture is a good thing! grin

Doug

September 10, 2005 04:39 PM Forum: Solar System Observing

Huge sunspot AR 10808 2005-09-10

Posted By Doug Scobel
Here's a full disk shot that illustrates how large this sunspot is.

Doug

October 6, 2005 01:52 AM Forum: Deep Sky Observing

NGC6791 - harder to detect than NGC4236?

Posted By Doug Scobel
Inge, in my log I see that I observed these two objects on different nights, so I can't comment on one being easier to detect than the other. But I describe NGC 4236 as having a low surface brightness, and NGC 6791 as "Not bright; Stars seem to be very faint, making it look mottled rather than resolved; Looks more like a faint face-on galaxy than an open cluster". These observations were in my 13" f/4.5 Newt, under about mag 6.0 skies.

Sounds like my observation resembles yours. Were you able to resolve any stars in NGC 6791 in the 18"?

Doug

October 7, 2005 05:19 PM Forum: Beginning Astronomy?

How did you start?

Posted By Doug Scobel
Here's my story:

http://www.umich.edu/~lowbrows/reflections/2005/dscobel.21.html

Doug

October 11, 2005 01:27 PM Forum: Deep Sky Observing

Aperture vs. magnification

Posted By Doug Scobel
Jeff, I think the key is when you said "Now, I didn't have the 8" set up the same night...". Without a direct comparison it's all subjective. Bad seeing on one night is not the same as bad seeing on another night. It can even change minute-to minute. To make the comparison valid you need to do a side-by-side comparison.

Happy testing!
Doug

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