Thursday, December 29, 2005

old mags

Big Al dug into his archives to retrieve his old Telescope Making magazines (issues 1 through 33) including a couple of special issues.

I look forward to reading the How to Build Your Own Observatory with Mom so to get ideas about building something on her property...

As well, he pulled his Tirion SkyAtlas materials, which includes the book edition, loose-leaf desk edition (black on white), and the loose-left field edition (white on black).

Wednesday, December 28, 2005

grey skies

What a disappointment.

I was so keyed this winter holiday to do lots of astronomy, using both 'scopes, applying recently accumulated knowledge from the All About Telescopes book, to successfully use Mom's telescope clock drive to track objects, to do some new long-exposure tracking astrophotography, test my new viewing circles, repeat my star drift measurements, get one last good look at Mars, view the occultation of Spica, to have Big Al over...

And every day and night was overcast!


Monday, December 26, 2005

clock drive works

Reassembled the clock motor drive today, trying to follow the various diagrams in AAT.

page 144 from AAT

page 145 from AAT

As I examined the closest diagram closely, it seemed that I was missing one leather washer required for the clutching action against the main 96-tooth gear. But, happily, being at Mom's house, I knew she'd have some leather bits in her craft supplies such that we could make new leather washers.

I reconnected the drive and clutch to the telescope equatorial mount at a little after 9:00pm and plugged it in. I came out 2 hours later and the 'scope tube was turned about 30°. Woo hoo!

Friday, December 02, 2005

new viewing rings

I wasn't satisfied with the copper wire viewing rings that I made. So tonight I made viewing "rings "for the Celestron 26mm Plössl, the Edmund (assuming it has a 1" focal length and a 40° apparent FOV), and the Meade OR18mm and 4mm (assuming they have 40° aFOV as well) when used in both the 6" reflector and the 8" catadioptric. I also made viewing circles for the Telrad's 3 rings, the Celestron finder scope, and my Bushnell and Mom's Canon binoculars.

I made these circles on a document on my computer, properly scaling them to Tirion's skyAtlas (first edition), and finally (and here's the important bit...) printed it on transparency film.

the unknown eyepiece

Part of reason I obtained All About Telescopes (AAT) book was so I could continue to learn about eyepieces. In particular, I'm trying to definitively, once-and-for-all, know what Mom's unindentified eyepiece (EP) is.

  • included with the Edmund 6" reflector (from Big Al)
  • 1-1/4" shaft diameter
  • front or field lens (near the 'scope) is concave
  • rear lens (near the eye) is convex
  • rear lens diameter is 0.90"
  • no markings or printing
I want to know it's focal length for then I can determine it's power. Of course, if I know the power, I can calculate the focal length. Then I know how this EP rates with the other 3 that Mom and I have. And if it's similar to my (more modern) Plössl then there's not much point using it...

I want to know it's apparent field of view so I can then determine the true field of view.

I'd also like to know the exit pupil size and the relief figures.

Finally, I'd like to know the construction type (Kellner, RKE, Plössl) as that will suggest it's strengths and weaknesses.


My personal perception initially was that it was similar in power to my Celestron 26mm Plössl. My timing of the true field of view supports this: the mystery EP is slightly less powerful.

It was in the '74 and '75 Edmund product catalog that I learned that the included low power eyepiece was rated at 48x. If Mom's EP is the "standard" one included with the Edmund 6" reflector, then it's focal length is 25.5mm or 1".

Somewhere on the web (can't remember where now), I saw something about the field lens (the one toward the 'scope or furthest from the eye) of an EP and if it was concave then the EP was an RKE. But the AAT book shows that a "type 2" Kellner has a concave field element.

AAT mentions a trick to determine the image or focal plane of an EP. Having done this little experiment, I'm confident Mom's EP is not a Huygens.

Power, focal length, etc., I'll determine later.

an old book

Popped into the local branch of the Toronto Public Library to pick up my previously requested copy of All About Telescopes by Sam Brown. As I had hoped there's lots of information about using Edmund telescopes, clock drives, Edmund eyepieces... I should be able to learn about Mom's telescope and the operation of the clock drive. In addition, I should be able to learn a lot of general stuff about astronomy. This old book looks fantastic!