Posts Made By: Michael Connelley

Hello:
Last night we had first light on a 12.5" f/15 cassegrain I cobbled together and the views were fantastic! Having mostly used dobsonians, the increase in magnification was quite a shock. The flip side to this coin is that the field of view is rather small. I'm in need of a low power eyepiece and I'm looking at the 41mm Panoptic and the 31mm Nagler. Both have similar true fields of view, and both have good eyerelief which is important since I observe with glasses. I am seeking advice on which one to get. I must mention that I borrowed a 31mm Nagler to use on this telescope and my reaction was mixed. Whereas the image was always tack sharp in all other scopes like the my 12.5"
f/6 dobsonian, the image didn't seem to snap into focus with the cass, and looked a touch astigmatic. This was odd since the seeing was very good, and high power views of double stars and Saturn showed that the optics equal or better than any other scope around (2 C-11s and a C-14). Usually long f-ratio scopes are considered "eyepiece friendly", so the performance of the Nagler is a puzzle that I'll investigate further. Basically, I'm wondering if the Nagler has issues with long focal ratio telescopes, and if so would the Panoptic be better?

Cheers
Mike Connelley

Hello;
I'm in the market for an equatorial mount with at least a 40lbs load (the more the merrier). Naturally I'd prefer it be as inexpensive as possible, but it's for a long focus cassegrain, so it also needs to be quite stable under this load. Unfortunately, the primary mirror alone weighs 23lbs, so I don't think I'll be able to get this one under 40lbs. Among other mounts, I've had my eye on the Orion Atlas and William Optics GT-1. It hit me the other day that the Orion mount looks like a clone of the GT-1 (or vice versa), in much the same style as everyone has cloned the Vixen Great Polaris mount with varying degrees of success. So, my questions are:

1) Is the Orion Atlas mount a clone of the GT-1 (or vice versa)?
2) If so, is one a cheap "made in China" knockoff that is best avoided? Or are they both made in China so it doesn't matter?
3) How do these mounts compare witht he Losmandy G-11? This is the other mount I'm looking at.

Cheers
Mike Connelley

Hello:
I am having a rather frustrating time getting consistently good image quality out of my 12.5" f/15 classical cassegrain. Twice when I've used it, the image quality was great, and twice it was not so good with lots of astigmatism. I use the same collimating procedure that I use for my Newtonian and I don't see why it shouldn't work. First I made sure that the focuser is centered in the primary mirror hole, then I use a cheshire collimation tool before sunset each night to:
1) tilt the focuser to point at the secondary
2) tilt the secondary to center the reflection of the primary in the secondary - since the focuser has been centered in the primary this should accurately put the reflection of the focuser in the center of the secondary
3) tilt the primary to center the reflection of the spider on the actual spider
4) point to a star, put in a 300x eyepiece out of focus, and tilt the primary to center the hole in the donut

This procedure uses the focuser to secondary axis as the reference for the alignment. I have read procedures that call for very accurately centering the spider in the tube, but it should not be necessary to align the optical axis with the tube axis. Step 2 is meant to align the secondary to the focuser. I could try to get the reflection of the cheshire in the center of the secondary, but since the reflected image of the primary is just a little smaller than the seconday I think it is easier (and thus more accurate) to center the edge of the reflected image of the primary in the secondary mirror.
So, my question is: Is there a better procedure to accurately collimate of the telescope? Is there some obvious thing that I am missing? When I go to the star, is it better to adjust the primary or the secondary? I have been adjusting the primary since the primary collimation screws are easy to adjust from the eyepiece. I am coming to appreciate that this telescope is very sensitive to collimation, and that driving it up mountains and packing it into cars isn't good for the collimation. Any help will be greatly appreciated.

Cheers
Mike Connelley

Hello:
I need to get a new spider for my 12.5" cassegrain, mainly becuase the one I'm using now I borrowed from my dob. I've read about curved spiders, but nothing about using them in cassegrains (I suppose since amateurs rarely put together thier own). Would it be a good idea to use a curved spider on a cassegrain this size (it has a 4" secondary in an aluminum cell, pretty hefty overall). I would think that a cassegrain puts greater demands on the spider than a newtonian since the cassegrain seconday also magnifies the image size. Does anyone have experience with this sort of thing?

Cheers
Mike Connelley

Hello:
Would anyone happen to know what is the highest redshift object ever visually seen by an amateur astronomer (no CCDs!)?? I was searching a catalog of quasars, and there are several brighter than 16th magnitude with a redshift greater than 2. There is even one that is magnitude 15.8 with a redshift of 3.05. By comparison, 3C273 is magnitude 13.0 and is "only" at a redshift of 0.158.

Cheers
Mike Connelley

Hello:
I have a cassegrain, and it has small problem. Star images look sharp and I can see lots of detail in Jupiter, but the a star test shows either sphercial aberration or a turned edge. Thus, it's in the "tolerable but I'd like to do something about it" range.
The scope in question is a 12.5" classical cassegrain, about f/15 or so with an f/3.8 primary. I did the star test at 315x with a 15mm eyepiece, and defocused so that the star image was about 30" wide (a little less than the size of Jupiter with the same eyepiece). The test star was Spica, high in the SW, in moderately good seeing. Inside of focus, the image was brighter in the center (around the central obstruction) and fainter at the edge. Outside of focus, the image was brighter at the very edge and gradually became fainter towards the center.
I don't know the prescription for these optics, as they were given to me a while ago. It is possible that spherical aberration is being introduced because the primary to secondary mirror spacing is not correct. My questions are: does the scope have a turned edge or spherical aberration? If it's spherical aberration, how much does the secondary need to be moved to have a noticable affect (say, 1/2 wave) or in what direction?

Naturally, any help will be very much apperciated.

Cheers
Mike Connelley

Hello:
I want to make a new truss structure using thin wall aluminum tubing, to save weight. The tube is only 4' long so it doesn't need to come apart. Since the aluminum tubing is so thin, I am thinking of using epoxy to bond the aluminum parts together instead of welding. I have used epoxy for smaller parts, such as for some parts that hold my spider, but not for the whole structure.
I bought some J-B weld since I read is was quite good for bonding metal. Does anyone have experience using this stuff? Are there other epoxies that are recommended for aluminum? What is the optimal thickness of the bond? Or, is it just plain stupid to try and epoxy a telescope together?

Cheers
Mike Connelley

Hello:
The previous post reminded me of something I've been thinking about. The problem is that flat black paint is still quite reflective at grazing incidence. My idea is to first spray some of that spray stone stuff (a spary paint that gives a rock like texture), then paint over it with flat black. I'm wondering of others have thought of this, or even tried it. This method could be cheaper and easier than making baffle rings, or putting down velvet or flocking paper.

Cheers
Mike Connelley

Hello:
Perhaps I've been asleep at the switch, but I just noticed that Anacortes has listed a 6" SCT from Celestron. When did this happen? Is this replacing the C5 in Celestron's lineup? I haven't seen anything in the way of advertising for these, just the listing on Anacortes. Most importantly, has anyone actually seen a real one?

Cheers
Mike Connelley

Hello:
Is there a binoviewer that accepts 2" eyepieces? If so, which one(s), and where are they available? Has anyone actually used one and can report on how well it works? Thank you.

Cheers
Mike Connelley