Posts Made By: Walter Hamler

Sounds about right to me. A friend has a 15" Obsession that is about that ballpark.
My 10" f/6 sonotube dob is almost 100#.

Walt

I plugged the info into Newt and came up with essentially the same distance as you ( I got 40.675") However, using the 11.25" id newt says your 75% rays are vignetted at the front aperature, meaning the tube id is too small. That was using the 2.14" diagonal which I agree would be a better choice. The vignetting is gone with the smaller secondary but the fully illuminated field is only 0.10". It sounds to me like your tube id is too small. However, I seriously doubt you would ever be able to see it at the eyepiece.

Waly

4, sometimes 3, in my 10" dob

Walt

Sean, in a few words,"been there-done that!" But I don't have the tee-shirt!
I built a fiberglass tube as per the method described in Neale Howard's book, "Making a Telescope". One word description, MESSY!. And a LOT of work.
I polyurethaned and then painted sonotubes for 6", 8" and 10" newts. Very efficient and reasonably light weight. If you put an aluminium ring as a stiffener at the points where the diagonal and mirror cell mount, you gain a lot of rigidity with little additional weight. Effective.
My recent 8" f/6 ota was sonotube with two outer layers of fiber and resin and one inner layer of resin. Very strong but the thickness and weight started to add up.
My current 10" f/6 (12.2" OD) sonotube and heavily glassed inside and out would probably allow me to walk on top of it (all 245 lbs), but it is HEAVY, and I am at the age that I begin to notice unfortunately.
A fellow club member recently procurred a 12" x 60" aluminium tube. With flocking interior, a good automotive exterior finish, and edge guard end rings, it is the consumate tube in my opinion. Lighter than my monster, probably as effective at heat disipation, and a few pounds lighter. That's my next trip, if there is a next!
FWIW

Walt

I broke down and ordered one of these last week. It arrived this AM. Big plus, it uses AA batteries (included). Another plus, it is essentially the same as a Telrad in design but 2/3 the size and weight, maybe even lighter.
One negative- the ring pattern is much smaller than a telrad's and not very sharp. With the intensity very low it is a little easier to discern the rings sharply but they tend to bloom with increased intensity. This is done in a darkroom.
I will attach to a scope and give a test the next clear night and report back.

Walt

Yu, what is the thickness of your mirror? If it is at least 2", maybe even 1.75", I wouldn't bother. You will never be able to measure any difference, much less see it.
If, however, it is a 1" thick plate glass variety, the 9 pt. may indeed help. Get a copy of the book by Kreige and Berry, Building a Dobsonian Telescope. They have some excellent pics and descriptions on multi point cells and how to put them together. Their descriptions will probably be all you need to make a successful mod to the UO cell. The key is that the triangle is able to "float" on the mounting/adjustment point without binding. That would introduce uneven "stress" and cause potential flexure of the glass. Not good!

Walt

Dan, I fully appreciate what you are saying. In my case I clean eyepieces and camera lenses only as often as I have to and then only with the new type cleaning cloths. I have found that they work very well for my needs. Only on the rarest of occasions will I use a small dab of ROR liquid cleaner. I have found that it does not exhibit strong solvent properties. It does wonders for removing oily smudges from eyelashes, but must be used sparingly.
I do appreciate your insight on the field stop situation. I am hopeful that installing one on my wide field will make a good eyepiece even better.

Walt

Nope. That be the correct perspective. Saw lots of similiar examples when that happened a few weks ago.

Walt

You can get some pretty good deals here on Astromart for 6x30 and 8/9x50's. Also check out Scope Stuff. They have some good deals as well.
I recently converted my 8x50 straight through to a right angle. The weather has been so bad however that I haven't had a chance to see how I like it.

Walt

A friend and I were viewing last night through his C14 and his new binoviewers. The image we saw was just like your pic except at moments there was even more detail! I had not seen Mars for several weeks and I was very impressed in how much bigger and clearer it has gotten. I was also wondering how much better the image would had been if we were viewing through a 4" apo. Oops! Sorry, couldn't resist. But I just couldn't explain how a scope with that HUGE central obstruction could give such fantastic sharpness. Had to be the binoviewer.

Walt