Posts Made By: Gary Weber

I own a few Naglers and Pentax XLs and I love them dearly - I also have a set of UO orthos (cone top) from 9mm and up. In my 12.5" f/6 Dob I have tested a 9mm UO ortho with my 9mm Nagler (T6) on galaxies. I too prefer the orthos for getting a bit more detail from galaxy structures.

The difference is small, but immediately apparent. I still love the wide view for providing greater spacial context and perhaps a better emotional view. But on very transparent nights when I know conditions will allow me to eek out the most detail in galaxies, I choose an ortho.

Gary Weber

Although I live in Canada, it works pretty much the same here. The one problem I have encountered with my agents is after buying a used dob, they wanted the telescope appraised. I asked who would they accept an appraisal from and the agent replied "a certified telescope appraiser".

Upon further exploration of this topic, they admitted they had no idea where I might find one, or who certifies them, but that's the minimum they would accept. There are no telescope shops in my province.

So although everything you say may be true, determining the appropriate value on used equipment can be a bit of a trick.

Gary Weber

It's amazing how many of those "special" nights are accompanied by active cooling. I have been doing some experiments on this with my 12.5" and the difference is simply stunning.

Gary Weber

My limited experience with the use of cooling fans on both my 8" tube dob and my 12.5 truss dob suggest that what is often attributed to poor seeing can be significantly mitigated by active cooling. I suggest you install fans to cool the main mirror AND to wash the boundary layer of air off the optical surface of the primary.

It's amazing how much better my high power planetary viewing is after using the fans.

Gary Weber

The first problem is trying to figure out which numbers are mentioned and how they were derived. 1/4 wave at the wavefront (EP) means the mirror surface is 1/8 wave off of perfect (the error is doubled because of the bounce). There are many other inconsistencies about RMS, MTF & Strehl.
see http://www.rfroyce.com/standards.htm

In the March 1992 issue of Sky & Tel, there is an article that discusses this very topic. In order to determine what can be seen in the EP, Peter Ceravolo (a very respectable optician) built four 6" f/8 Newtonian Telescopes with wavefront accuracies of 1, 1/2, 1/4, 1/10. These were compared by two veteran observers and they were asked to determine which scope had what figure.

The 1 & 1/2 wave scopes were easy to cull out of the experiment. Only in very good seeing conditions were these people able to determine which was better between the 1/4 and 1/10 wave scopes. Terrence Dickinson, one of the observers for the article, said of the experience "Clearly this excercise suggests that there are huge gains in visual performance as optical quality improves to 1/4-wavefront, and less conspicuous benefits with further improvements"

Three of these scopes were also at 1991 Stellafane, and people were asked to view and try and tell the difference. People who knew how to star test were quicker to note the difference between the 1/4 and 1/10 wave scopes. As the seeing improved during the evening, the confidence of the observations went up. Overall, about two thirds of the 103 people were able to tell the difference betwen the two best telescopes.

When it comes to buying a mirror, to get this kind of quality (1/10-wavefront), I think you will have to buy from premium makers - Swayze, Spooner, Royce etc. to increase the confidence that you will be delivered a mirror that actually meets these specs. Or if you are upgrading to a new scope, consider a Starmaster or Portaball for the Zambuto mirror.

Gary Weber

I always thought postal money orders in Canada were like cash. I bought a money order last week (for a telescope transaction) and asked if I could pay for it with a credit card. I know I can pay many other postal fees with a credit card. The woman said "No, cash or debit card only". This confirmed for me that the money order was as good as a certified cheque, as they would accept nothing less than cash (electronic or otherwise - but cash nonetheless) to purchase one.

I don't honestly know what happens to my money order once it arrives in California, but they ensure their can be no liens against the money order before issuing one.

Gary Weber

Actually there is quite a difference between light pollution (broad-band) filters and nebula (narrow-band) filters.
Here some great articles to help you in you rdecision.

http://www.prairieastronomyclub.org/filters.htm
http://pages.sbcglobal.net/raycash/filters.htm

Gary Weber

I will be ordering a new three vaned secondary mount and a ULS Quartz diagonal from Protostar soon. I have purchased two mounts and secondaries from Protostar in the past and I have been very pleased with their products.

I also like that Bryan Greer is part of the astronomy community and writes informative articles for Sky & Tel and has a lot of useful information on his web site. I also know I can phone him and ask questions and get a balanced opinion on what will meet my needs.

Gary Weber

Leave it alone.

No mirror can pass the "flashlight down the tube" test - it is most unforgivable. Look at your mirror in daylight to determine if it should be cleaned.

Cleaning a mirror should be done sparingly, perhaps once every two or three years. There are many people who believe it should be cleaned less often. Part of it depends on your location. Does pollen build up on your mirror; does grunge somehow make it onto your mirror from frequent dewing (rare) or industrial pollution; have spiders found a new home on your mirror?

Aside from cleaning a mirror, I do rinse my mirror once each year. I first soak it in a tub with a mild soapy solution for a couple hours. Then, using a shower head with fine, high pressure spray, I pass the spraying showerhead about an inch off the surface of the mirror while it's under the water. I go over the surface (without touching the mirror of course) two or three times. That will release most dust and bits of whatever that my mirror has collected. I remove the mirror from the tub and rinse with 99% isopropol alchohol and let it rest for a few minutes and rinse again with distilled water (lots). I then use a bottle of compressed air (a no no for many people I know) and blow the water droplets off the mirror, so they don't dry and leave spots or streaks. I put the mirror back into the scope and nothing other than fluid has touched the mirror. It may still show a few small blotches, but nothing to make me touch the surface to overcome.

Gary Weber

It's interesting how a great deal of the dicussion with reflectors is directed to the optics and little is said about mechanics.

In general, most dobs in the size you are looking at will not be of a "premium" pedigree. Consequently they can all use some tweaking and puttering to make them more of a joy to use. Tweaking the movement is one of the items most considered. There are many good discussions on this topic on the yahoo group Skyquest-Telescopes.

I have a premium truss Dob and the movement is sublime. I also have a Discovery Premium 8" and it works OK, but planetary viewing at 450x shows the mechanics could use some tweaking. I have no experience with the current crop of Asian scopes, but everyone has a different level of tolerence for nudging the scope. The short focal length Naglers begin to look a whole more inviting for planetary viewing however.

Gary Weber