Posts Made By: Mike Ratcliff

Howard,

Good question. The Astronomical League has a list of deep sky objects and double stars in their "Urban Club" observing list, plus some tips on observing in light pollution. Web site starts at www.astroleague.org, then go toward the bottom and find the Urban Club link. Most of the deep sky objects are open and globular clusters that tolerate light pollution better than nebula and galaxies.

M3 will be easy to spot once you are at the right location, being a bright globular cluster. But M3 doesn't have the easiest guide stars for it. With the 80x-100x, you probably have a narrow field of view in your eyepiece, less than 1 degree, so you need a good finder telescope like an 8x50mm to get you to the right spot. I assume you have some star charts too, because just panning around a constellation is like finding a needle in a haystack.

You might try for M53, it has better guide stars leading to it and is a fairly bright globular cluster with an 8" telescope.

Good luck!

Mike Ratcliff

Charlie,

With a fan below the mirror, I think the fins could help. It would be worth exploring in my opinion. I have not tried it myself though. Without a fan, the fins on the bottom may hinder air movement because the hotter air would rise up between the fins and be somewhat trapped. Without a fan, you would want the fins on top where heat rises away from the fins. But of course that's on the wrong (mirror) side.

Another nutty idea is to have some aluminum bars thermally attached to the glass that would extend outside of the telescope and into an ice bath or dry ice container. What was the number to that patent office?

Mike

The powermate will not increase the eye relief like a Barlow will, a benefit for longer focus eyepieces like the 32mm TV plossl. If the eye relief is too long, its harder to find the best head position for viewing.

More details on Televue's website, www.televue.com. Look under eyepieces.

Alan,

I got about 90 Messier objects while in high school 1969-1972, with a 60mm refractor from Sears. But quit stargazing after high school until 1996. Finished the entire list in 1998 with a 6" dob. So that makes it about 30 years for me. I'm sure mine is no record for the longest time.

Mike Ratcliff

I was there Saturday night too.

The highlight for me was the JMI 10" binoscope (two mirrors). I've tried looking through other's binoviewers (one scope but two eyepieces) and they didn't do much for me in the brief time I looked. I did do some fiddling but to no avail. But the binoscope was an instant hit. It had motorized spacing and focus controls. Comfortable wide angle view and no squinting the other eye. Alas, the price is $5000, way too much for me personally. The 6" was nice too but still pricey.

The moon was very bright which really hurt DSO views. And like you said the temperatures were falling fast and that had to hurt the big glass scopes.

I'd prefer a real star party myself, but it was still worthwhile for me.

Mike

Doug,

I can confirm the lunar twilight is very obvious from a dark site, especially when the moon is nearly full.

I remember my first attempt at finding the edge on faint galaxy NGC 891 with a 6". That was a foolhardy attempt when the lunar twighlight was building fast and the galaxy was low in the east at the time. I didn't realize then how difficult a sighting that would be even under the best skies. Just chuckle to myself now how absurd of an attempt that was.

Mike

I'm not a hugely experienced person, but I'm going to suggest two possibilities:

1) Your collimation is off that is making coma worse and you're seeing the coma. At f4.5, you are normally subject to coma which produces an arrow head or comet shaped blur at the edge of the field with the point aimed toward the axis of the primary mirror. So your sketch suggests that coma could be the main problem by the shape of the blur.

You can't get rid of coma, it's a natural effect of a paraboloid mirror. (A Paracorr is a way to get rid of it optically). But bad collimation can make the coma worse, Because the centerline of the primary (where coma is zero) is not lined up with the center of the eyepiece. The fact that you are getting coma (if this really is coma) near the center of the field of view, as in your sketch, suggests that your collimation is off. With good collimation, the coma would be negligle in the center and then gradually increase as you get to the edge of the field of view.

A sight tube would be good to check the secondary alignment with respect to the focuser tube. Tectron tools sells one. The sight tube is about 4-5 inches long with crosshairs. The sight tube plus your cheshire is a good combination.

2) Another possibility is that there are some pinched optics somewhere that gives a triangular shaped blur. If so, that could mean that there is some stress of the primary or secondary mirror. Possibly you introduced some stresses when you reglued your primary. There is a procedure for reglueing to avoid stresses using silicone, by placing some nails between the mirror and the cell and letting the mirror gradually settle on the nails and the silicone blobs. Then you pull out the nails when the silicone is set. Silicone is better than epoxy because it hardens more slowly allowing time for the mirror to settle on the nails stress free.

Turbulence certainly makes things harder to figure out.

Hope this helps.

Mike

Carl Zambuto also points out smoothness and lack of "dog biscuit" roughness as their main advantage over mass producers. This I think would be hard to see with the Ronchi test.

I did a similar Ronchi test on an older 6" discovery mirror and it did fine.

Be sure to watch where the lines meet the mirror edges, and look for curves or hooks, these would indicate turned down edges, bad news.

Mike

About a month ago, I posted on a problem reaching focus with a used Paracorr just purchased on Astromart.

I shortened the truss tubes 1/2 inch, and still had weird problems. I figured something else must be going on.

Turns out the main problem was that I was given both a tuneable top and an older fixed top, and that I had stacked BOTH on each other without realizing what was going on. DOH!

This of course made the paracorr-eyepiece spacing way off, you're just supposed to use just one top. The tuneable top is newer and preferred.

The Paracorr makes a nice difference with the 16" f/4.9 and a 17mm Nagler T4. For me the coma was very noticeable before.

Thanks for all of the suggestions.

Mike

Wow,
Looks like you've got star-hopping down pat!
Mike