Posts Made By: Lorne Johnson

March 14, 2003 02:02 PM Forum: Equipment Talk

Comparison between two Newtonians

Posted By Lorne Johnson

Last Sunday I spent the eveing out with my 8 inch Spooner dobsonian, and with a friend's 16" truss dobsonian. The images in the 16" were awesome. M 3 and 13 resolved to core at about 70x. All kinds of galaxies cropped up in unexpected places. Detail in the larger glaxies was less than I had hoped to see, but I was looking to see what would happen with largerinstruments, so I had my hopes up too high. I could see spiral structure in M 101 and 51, as well as a dark lane in 104 (way down in the soup). It was a very exciting night, but I am realy happy with my 8 inch Spooner. It's a wonderful blend of great views and no set up time, with planetary views limited by the seeing in Vermont.

March 18, 2003 09:56 PM Forum: Equipment Talk

Deep sky - SCT or APO?

Posted By Lorne Johnson

$3500 gives you a lot of choices. APO's are supposed to give you nicer views. The SCT 12" will let you see more and further, it has about 9 times the light gathering power, and greater resolving power. Then there are all the other possibilities, a high quality dobsonian truss (say 14-15 "will give you better, brighter, views and is probably about as portable as the Meade and its massive tripod, should cost half as much, and be more reliable. A Maksutov either Cassigrainian or Newtonian will give you sharper views than the SCT, although you won't get to 12 inches set up at that price.

March 26, 2003 06:22 PM Forum: Equipment Talk

To Plossl or to XL?

Posted By Lorne Johnson

I've been using two televue plossls in an 8" f/6 dob and they work very well, (within their 50 degree field of view). The 15 mm gives an exceptionally strong tonal range on the moon. I used the 10.5 with a 1.5x barlow to find the trapezium stars a through f. The limitations are field of view and eye relief.
This is not to suggest that the pentax XL's do not work well, I simply haven't used any.

March 28, 2003 08:13 PM Forum: Equipment Talk

How much light is twice as much?

Posted By Lorne Johnson

In acoustics a just noticeable difference is double (or at least double the wattage).

For me, a 30% increase in area of primary, is clearly noticeable. That is about the difference between a 70 mm Ranger and an 80 mm Vixen. From 5 inces to 8 inches is a clear, well, an order of magnitude (probably a little over that).

April 1, 2003 10:34 PM Forum: Deep Sky Observing

Question about M3 and resolution

Posted By Lorne Johnson

I use an 8 inch reflector, f/6 and it resolves M3 to the core at 240x. It largely resolves M3 at 165x. I can see some structure in M 51 and M81 and M 82, began to see the dark lane in M 64 last month. If you can't, in your 13 inch it may be a problem with collimation or the mirror.

April 8, 2003 03:56 PM Forum: Maksutovs

Intes Micro 503 optics ?

Posted By Lorne Johnson

I would agree with Jim. I don't have a 503, but do own an MN56, same company same size scope (wider field, less portable). It's optics are very sharp indeed. Mine came trough with 1/6.7 ptv (ie. the biggest error in the system, but a 96.3% strehl ratio which says more about the overall smoothness of the system). Those values are for the whole system: corrector plate, primary and secondary combined, not just the primary.

April 8, 2003 04:01 PM Forum: Eyepieces

Widescan 30mm Type III

Posted By Lorne Johnson

There was a substantial thread on here a few weeks ago about this. And, Markus has been very upfront, in that. Edge sharpness should be the same as the type II, the lense edges are blackened on this and they like the new supplier better. Design is the same. I think that there was a typo on the APM add from last week. Markus e-mailed me a shipped from Germany price of $235.

There are two reviews of the type II on cloudy nights. It's better on edge a higher focal ratios.

April 12, 2003 01:46 PM Forum: Equipment Talk

D&G vs Meade APO ???

Posted By Lorne Johnson

Without wishing to knock Meade, I must say that the views through a D&G 5" f/12 are beautiful. The mechanics are excellent. It's a pretty big tube though.

April 13, 2003 03:24 PM Forum: Equipment Talk

Motor Drive Options for Super Polaris

Posted By Lorne Johnson

There are three lower cost options that I know of. One is the JMI drive reviewed on Cloudy nights recently. The next is the currently produced CG5 drive from Celestron $165 dual axis. Third is the Orion version of the Celestron CG5 drive at $119 plus about $15 for shipping, which I believe is functionally identical to the Celestron. I purchased an installed the Orion on my Super Polaris. It attaches with one bolt for each drive instead of the set screws and has fewer slewing options than the real Vixen drives, but it works just fine for tracking, and I think for guiding (but I only do visual). It's certainly the best buy, unless straight AC will work for you. But, it doesn't come with covers and so the plug recepticals for the cables are exposed to abuse. It's perfectly workable, but not a throw it in the back of the car and go arrangement. On mine there was also a trick to installing the RA drive through all those damn little holes that involved filing a purchased washer so it would fit through the first hole and holding it in place with a piece of thread while I threaded the bolt through it, and the purchase of a slightly longer metric bolt for the Dec motor. I can explain this more thoroughly if you actually get one. The instructions from Orion were surprisingly useful considering that this was going on a different mount.

April 13, 2003 08:51 PM Forum: Telescope Making

Truss or tube?

Posted By Lorne Johnson

My instincts would side with your current lean toward a tube. But, you should probably look at Bob Royce's sight rfroyce.com. His personal scope is a 10" f/8 newtonian, and he went the other way--started with a tube and went to a truss. I think that it is in the personal scopes and musings section.