Posts Made By: dan hilts

I distinctly remember looking at a Celestron silver top in the auctions. The bids at the time I saw it seemed strangely high; high enough that they caught my attention and I wondered what the attraction was. I didn't notice anything about green lettering but I wasn't planning on bidding so I didn't read too closely.

dan

Coulter used a double sided tape to mount their secondaries. It holds incredibly well even years after the tape has completely dried out. I wouldn't be at all surprised to see this as your source of astigmatism. Remounting with silicon will tell you easily enough. Coulter secondaries are heavy pieces. Make sure you start with clean surfaces and allow enough time for the silicon to cure.

good luck,
dan

So we'll sit around and chat, have hot chocolate and eat key lime pie. I'm gonna have fun.

dan

Those Ronchi lines are going to straighten out quite a bit at IR wavelengths. If this mirror was for IR communications, it may be a reasonable sphere for the application.

dan

I had a set of Hyperions that I used in my 120mm/F12.5 refractor. I wanted something that would also work at F4.5 so I replaced them. If I had stuck with just the refractor, I would still have them.

The 24mm was not the greatest and was my least favorite of them all. (I had 24, 17, 13, 8) The others were just great but the 8mm was exceptional value for the money and the views through my refractor were very good and so very comfortable. I can't imagine the Pentaxs you have would be anything but better.

Why not keep what you have until you see how they perform? With eyepieces, they just keep getting better as the F ratio slows down. I bet they will be simply wonderful at F15!

dan

Hi John,

You have stated that you don't want to be nagged too much by a dim FOV, but you love the 30x.

If much of your viewing will be in the daytime, the image brightness will be determined by your eye pupil, not by the aperature of the binoculars. The useful daytime aperature can be determined by the magnification times your eye pupil which is probably about 2mm. At 30 power you can only use about 30 X 2mm = 60mm of objective in the daytime. At 25 power, this is somewhat smaller at 25 X 2mm = 50mm. This applies anytime there is enough light in the view to restrict your eyepupil and that includes any daytime use, any nightime use when you have lots of light around, or any time you are looking at a bright target such as the moon or a lighted billboard.

Large binoculars are really great for sweeping dark skies when your eyes are dark adapted and your eye pupil is opened up to 4-5mm. If you can't get these conditions, the large aperature never comes into use as I have stated above. So, if your viewing is not in dark conditions, the difference in aperature of the two binoculars you are looking at, should not be an issue.

Have you considered the value of a smaller scope such as an 80 - 100mm? One of these would allow you to change the eyepiece to obtain much higher powers as you want but still allow some pretty nice low power views if you should get dark conditions.

I have a 100mm F6 refractor that I use with a 32mm Erfle eyepiece that provides about 18X. I can just get all of Orion's belt in the field of view. Open clusters and star fields are excellent at this power. I use a 19mm eyepiece for 32X, and a 9mm for 66X. It is not a binocular but I decided for my purposes, the ability to change viewing power was more important than the binocular view.

Good luck,
dan

Since my original post here my wife has had one additional transfusion and has gotten much stronger. This morning at 6:00am she had the surgery to correct the problem that caused her initial grief and she is expected to recover fully.

Many thanks to all who offered prayers and support.

dan

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I had always thought that the Nexstar was just a ST80 on a hyped GOTO ALT-AZ mount. Is it really an upgraded and well built 80mm scope? That would be good news.

I had one of the original ST80's from Celestron and while it had a metal focuser and tube, the lens cell was plastic and the focuser was the worst of the rack and pinions. If the Nexstar is typical, I would think it is the same. Sliding the dew shield off revealed the three mounting screws for the lens cell. The tips of these screws were just slightly too long and were easily visible with a casual look into the objective. There is a possibility that it could be as much as a couple of degrees out of alignment if one of the mounting screws is in crooked. The lens cell on this scope was easily distorted so much with just hand pressure that it would be almost impossible to move the retaining ring if you gripped the cell tightly. I don't think there is any real hope of permanent adjustment on this type of cell.

I still have one of these lenses and the plastic cell. It is OK at low power but it is not sharp once you crank up the power.

dan

That's a good looking scope. I have built a couple of wooden tube refractors and they worked quite weel. I'll bet your friend's scope with a D&G lens gives really nice views.

dan

I think the difference is probably due to the weakest link in the system and that would be the accuracy of the alignment of the Cheshire in the focuser.

What amazes me is that anyone can see any amount of astgmatism in a decent lens close to the axis. If you look at the published spot diagrams that are available, astigmatism doesn't show until you are well off axis. If you look at any of the wide angle photos published, even the hi-res versions, there is little to no trace of astigmatism even at the edges. I certainly don't see astigmatism in any of the refractors I've cobbled together and these don't have sophisticated adjustments built in.

So what is it you folks can see that I don't?

dan