Posts Made By: david roberts

I almost gave up on finding M55 tonight. I'm sure I've seen it once before, during a Messier Party, but in urban skies, its surface brightness is nil and unremarkable. Guess I forgot. It is large though and once I found it and settled down to take a look, it resolved nicely but it is quite diffuse. I was trolling through Sagittarius tonite looking at the globs and nebulas and as a last observation decided to look at M55. I'm looking just above a 6' tall wooden fence and a tree to the left. I now know I must have slewed past it probably twice thinking the core was brighter than it is. What with the sweat streaming down my face, body heat fogging the ep, and swatting mesquitos and such, I feel lucky to have found it 8O . Anyways, that's my story and I'm sticking to it

BTW there are alot of nice doubles in the field below the teapot that distracted me. A nice distraction for a change. One double in particular. It makes an approximate triangle with Epsilon and Zeta, the bottom two stars of the teapot. Only a few arc seconds of separation and mag 9 or 10. Typical cat eyes.

regards

DCR

I placed a very small dot (using white out) at the center of my secondary believing that lining it up with a cheshire would be made easier. It also aligns very well with a laser. I can see the laser hit the dot (using a hand-held mirror) and hit the center of the donut.

But when I collimate my primary the dot does not appear inside the donut. It is just out about halfway between the center of the donut and the edge of the cheshire tube.

It could be I have not found the exact center of the secondary. However the previous owner had placed a very small black dot on the secondary that I took to be the center. I used the white-out to see the dot better. It measured out close enough to be the center.

I've read about optical verses mechnical alignment but I'm stumped. I would appreciate some help in understanding whether or not the dot should appear in the donut for the scope to be properly collimated. Or is this evidence of the proper offset I've read about. The scope is a Coulter 13.1 inch f4.5 with the original secondary.

Thanks

DCR

What the the optimal secondary mirror size for a 13.1 inch f4.5 mirror?

Thanks

DCR

When I read a Dec and RA for a star or object in some book or magazine, I know I can go to my star atlas and find that coordinate. It doesn't matter what time of night or my location.

But a given Dec and RA for a planet or comet or astroid is different. How do I find a planet, such as Neptune, from a published Dec and RA. Do I need to know GMT and subtract my time? Where do I go from there. Have I opened a can of worms :S

Thanks

DCR

I read a while back in one of your posts that you have a Coulter 13.1 inch and that you are well pleased with the modifications you have made to it. I own a mostly original Coulter 13.1 inch and want to replace the focuser, secondary holder and mirror, and mirror cell. I also want to add some fans. Not necessarily in that order. I'm very interested to know about your modifications - what worked and what didn't, as I'm sure other Coulter owners with similar experience that I have would also be interested.

Any information you would care to part with would be appreciated

Regards

DCR

I was surfing astro sites and came upon this beauty at:

http://ourworld.compuserve.com/homepages/david_ratledge/tm12.htm

Just couldn't pass it up and had to show somebody.

Last week I took my mirror out of the telescope (not out of its cell though) and cleaned it with soap and water. First time for me. It looked so clean, shiny like a new car. That screwed my collimation up so I took it to a star party for a friend to collimate properly. My friend is an old pro and he took one look at my mirror and laughed at the bluish tint. He said "you washed your mirror with soap". There was no denying it. Here is the recipe he gave me for washing a mirror:

1/2 part water (best ionized and distilled)
1/2 part rubbing alcohol
1 drop of soap.

To much soap leaves a residue that will hardly come off with water alone. You only need a drop of soap to act as a surfactant, to wet the mirror.

Moonless nights (most of them anyways)

david

I'll bite I've learned that collimation is a fine art. Even highly experienced amateurs shutter at the thought of precise collimation. Luckly, I'm not one of them, highly experienced that is! It's almost an obsession for me to obtain perfect collimation. But nothing is perfect, only within a certain tolerance. I had problems collimating until I figured out my focuser was slightly out of alignment. I was starting to think my primary was screwed up. I suspect, at least on older scopes, or ATM scopes, the focuser is an overlooked problem, maybe because it's difficult to align it perfectly. I haven't attempted to realign my secondary to be off-axis just a bit, as proposed by some of the more detailed collimation sites. I haven't seen a clear enough night in weeks to do a star test. I drove over 100 miles tonite to find clear skies and turned around empty handed. I'll take mosquitoes vs. overcast any day, anywhere

Hope your skies are better

David Roberts

I'm pretty new myself. Here is what I would consider:

1. Is the laser collimator properly aligned. I have a howie glatter model and its pretty rugged. Some models are more misalignment proof than others.

2. I always align the secondary to hit inside the donut on the primary first, then align the primary. I may go through this step 2 or 3 times before both the secondary and primary appear aligned.

3. If you are using a rack and pinion focuser, there may be some play in the focuser. The further I focus out (run the tube out) the worse the alignment seems. Use the laser with the focuser tube mostly in close. Also the focuser may have some up and down, left and right play. Can you wiggle the laser collimator around a bit in the focuser?

4. I thought when I bought the laser I would rule the collimation world. Not so. The puny $20 cheshire sighting tube with crosshairs gets it closer, to just a tweak of a turn on a collimation screw. Suprisingly accurate. I'm constantly off more with just the laser alone.

5. Have you checked the angle of the focuser to the OTA. Just a 1/4 inch of 90 degrees can through you off considerably. The focuser alognment should be the first on the ota checked, otherwise, the scope just won't collimate very well. And frustration sets in.

Hope this helps

David Roberts

My three guesses:

1. Old piece used some way in land surveying

2. Used in a piece of old maritime navigation equipment.

3. Old viewfinder from a telescope.

Does it have a set of lenses?