Posts Made By: George Golitzin

beautiful image dietmar! a favorite target of mine when I've finished looking at nearby 5903--these three give a nice test of the evening's transparency in my 16".
--george

Jon--

I like this spider design by steve swayze:

http://www.europa.com/~swayze/spider/spider.html

you'll have to work out your own secondary holder though!

Another idea that worked well came from an S&T article (December 2001) on a portable 8" --this uses a typical steel ruler for a curved spider--it's very easy to build, a bit trickier to install, and avoids the usual 3-point collimation screws--something that gets hard to fabricate for smaller secondaries.

--george

Well if you picked it up for cheap, maybe it would be worth it to attach an after-market focuser. The question would be whether you have sufficient in-travel, I suppose. Can you tell where the mirror is stuck, that is, towards the front or the back? All I can say is, if you can resurrect the OTA, it'll probably be worth it--the only scope sale I regret is my old mk-67. Absolutely first-rate optic.

There are many sources for observing programs on the net. Here are a few.

The herschel 400 comes to mind:

http://www.astroleague.org/al/obsclubs/herschel/h400lstn.html

These are other good lists:

http://www.astronomyboy.com/saa/saa100.html

http://pages.sbcglobal.net/raycash/dmcon.htm

This is a great resource, esp. steve gottliebs ngc data:

http://www.astronomy-mall.com/Adventures.In.Deep.Space/

--george

This stuff's getting me down! I usually have mag 5 skies on these clear summer nights, but the past week, the bowl of the big dipper has been extinguished while still 20+ degrees above the horizon, while Albireo has been just visible at zenith. Incredible. And no place really to go, except the beach, to get away from it. At least the seeing was semi-decent on Jupiter tonight...made some mods to the trusses on my 16" today and had a nice view of the big guy. Hope the rest of you are having a better season!
--george

Wow. Looks fabulous already. I remember a thread here when you acquired that glass--surplus shed was it? I was muy jealous!

I had some decent seeing here in Petaluma one night last week on Jupiter--hopefully you'll get some too and give us a report on the new monster's planetary performance.

--george

I've compared it to the stellarvue f/7 102ed, not exactly an apo--so I don't know if you're interested in that comparison or if you're looking at how the 100ed stacks up against more expensive offerings. But I can give you my general impressions.

Physically, the 100ed is 35" long vs the 102ed at 27.5"; the distance from a typical balancing point to the eyepiece is 16" on the 100ed vs 12.5" on the 102ed, which doesn't sound like much but comes into play when the scope is pointed near zenith. Both scopes have an operating weight about 10.5 pounds (4.8 kg)--that's including rings/clamshell, finder, and 2" diagonal, but no eyepiece.

Optically, the color correction on the 100ed, at f/9, is superior to the 102ed--there is virtually no violet visible on the moon or planets at high powers (200-250X)--and I am picky about that. Whereas the 102ed shows small amounts on those targets at those powers. The color on the 102ed is seeing-dependent, with much more visible in poor seeing. However, spherical correction is another story. I have had two lenses in the 102ed--the first had mild undercorrection, and the current one has excellent correction, yielding extremely nice detail on low-contrast targets like Jupiter. My 100ed has noticeable undercorrection; yet it yields very nice stellar images and good planetary detail. But it also throws up a little more haze about jupiter than I think it should--whether due to under-correction or smoothness (or the lack thereof) or poor baffling I don't know--but my overall sense on the 100ed is that you are taking potluck on the spherical correction--you won't get a dog, but you might not get tip-top optics either.

Mechanically, the focuser on the C100ed is just barely serviceable, a little rough and coarse--the crayford on the orion model might do better. The 2-speed standard focuser on the SV is quite nice, a little rough on the coarse focus, but very smooth on the fine focus, and it can take a lot of weight. The one-touch adjustment on the SV clamshell is really nice when you go from a 1/2 pound type 6 to a 1.5 pound type 4 nagler. The supplied clamshell with the Celestron is crap; I use rings with it, but these make it harder to adjust the balance in the field.

hope that helps
-geo

IMHO that thing has really ugly lines. What is the point of a truss tube with a rocker box that's as tall and heavy as a solid tube dob? And which is overall heavier than the solid tube offering? Kind of defeats the purpose...
sorry for the rant, just a gut reaction.
-george

Well that's a huge subject. Maybe you could narrow it down a bit. Have you read Tom Trusock's articles at the other place (e.g. http://www.cloudynights.com/documents/naglers.pdf http://www.cloudynights.com/item.php?item_id=1723 http://www.cloudynights.com/item.php?item_id=1737 )
Hate to send you over there, but these are pretty good for starters.
--george

Walt,
There are sort of two issues in your question--Larry addressed one of them. That is, a good ep for dso detail is one that gives an exit pupil somewhere between, say, 2 and 3 mm--although like Larry I really like my 17 nagler, which gives a 3.4 mm pupil in my f/5 reflector. At your f/4.7 ratio, if you're looking at hyperions/stratus, the 13mm length might be the first one you want, and a 17mm down the road.

But the other issue is having an eyepiece that gives you the maximum possible real field consistent with a usable exit pupil, which, depending on your age, might be anywhere from 5 to 7 mm. This is important for finding things, as well as just enjoying wide views of the galaxy--you have no idea how constricted your field of view is until you look through something wider (ok, that's a tautology, but what the heck). For example, on my f/5 I use a 27pan (someday to be a 26 nagler), because I can't go too much above 5mm for an exit pupil. That gives me almost 1 degree actual field. So this is where having the widest AFOV is important, because it increases your true FOV without increasing the exit pupil. (But that's expensive.) At f/4.7, a 30mm ep yields a pretty big pupil--something like a 26mm might be better, for example, the orion 26mm Q70 might be a good bargain, with a 5.5mm pupil, and over 1.5 degrees of field. But I have no idea how well corrected they are at that focal ratio.
--george