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Posts Made By: David Simons

February 1, 2006 08:50 AM Forum: Astro Binoculars

Wide Angle Finder for 20x125s

Posted By David Simons

I have been using my 20X Vixen Big bino's for a few years now, but need a somewhat unique finder. The bino's give a 3 degree FOV. Although I have used a Rigel on it, I occasionally find myself in a sky area without enough bright stars to start the Rigel from, and need a few more stars to align to. I also have a 6X30 correct view finder, but the FOV is not a whole lot bigger than the bino's.

So for fun I modified a 45 degree diagonal by adding a 25mm binocular lense inside the front tube of the diagonal. This allows a 25mm Plossl to focus, and gives a correct view, 4.5X, 11 degree FOV, very long eye relief finder. Although there is some edge of field illumination drop off, the view is very nice. It pulls in the little mag 7 and 8 stars that allow easy star hopping and alignment to a star chart. It fits inside the Chinese finder scope mount pretty well also.

February 6, 2006 12:37 AM Forum: Celestron

Old 16x70 Celestron Giant finder

Posted By David Simons

Does anybody have any pictures or info on these old finders ? Likes dislikes ?

I think I may have one, but there are no markings of any kind.

Thanks !

February 25, 2006 03:24 PM Forum: Astro Binoculars

Canon 10x30 IS

Posted By David Simons

Just received a pair courtesy of Astromart. However we are getting thin clouds sad

Does anybody else have a pair of these ? Favorite targets ? Best use ?


March 20, 2006 05:59 PM Forum: Equipment Talk

Loose SCT secondary

Posted By David Simons

I just received an Astromart "special" Meade 10" f6.3 SCT OTA and it is in need of some corrector cleaning, and also has a loose secondary. I have been reading the secondary position is very sensitive for collimation.

Has anybody adjusted their secondary before? I have been rooting through the MAPUG site and have picked up some good pointers, but I'd like to know if I can lean on anybody's experience here ? smile


April 6, 2006 07:25 PM Forum: Pictures of Me and My Telescope and........

Fooling around with a four and a half

Posted By David Simons

I just received this little Meade 114NT from their clearance web site, and put it on my pipe mount test stand. I was looking forward to tweeking the collimation, but it was pretty much dead-on out of the box. It makes for a decent grab and go setup, and the f8 light cone is very kind to even the budget 9mm and 25mm MA type Meade ep's included with the scope. I barlowed a Takahashi LE 7.5mm to get 243X on the moon and the little scope was still showing a decent image. Saturn looked great as well. For less than $50 I think there is a lot of bang for the buck here !

The other picture shows it next to it's bigger brother grin

April 6, 2006 11:27 PM Forum: Refractors

Re: Restoring A 20 Inch F/18 Refractor

Posted By David Simons

Herbert Highstone said:

Hello to all the folks--

.... I believe that it was also repolished and refigured, but I can't find the details of this work. Can another forum member tell us more about the optical side of this ambitious restoration?

This classic refractor, whose name is Rachel, is routinely available for public viewing sessions every Friday and Saturday night. I'm sure that this venerable instrument has planted the amateur astronomy idea into the heads of thousands of kids who have looked through the giant lens.

Best wishes from Herbert Highstone

Hi Herbert,

I seem to recall reading about the lens being thoroughly cleaned, but can't recall that is was actually re-ground or figured. My optical mentor Bob Schalk who used to work at Tinsley had the measurements made on the lense, and it tested very well. He would regularly inspect and clean the lense after the restoration every so many months. However Bob has moved to Oregon, and is no longer doing this work, not sure who will be taking over.

With the fog below the telescope level, the seeing can sometimes get very good there. The 20" gave some jaw dropping views of the Moon one time I there. It was loafing at 800X and the detail just kept on going.

The new Chabot Science Center is a real showpiece now. The Telescope area seems almost like hallowed ground with the giant silver domes perched on the hillside overlooking the foggy San Francisco Bay.

I think the restoration was about 6-7 years ago ?? I only recently started going there when I started a little mirror grinding project. Have you been there since the restoration ?

Here is a picture of Rachel inside the huge dome.

April 8, 2006 12:23 PM Forum: Pictures of Me and My Telescope and........

Re: Back to the Classics Again...

Posted By David Simons

Hi David,

Do the handles add much ? I was thinking of getting some, but I don't have too much problem with my classic 12" as-is.

April 8, 2006 02:55 PM Forum: Refractors

Re: Restoring A 20 Inch F/18 Refractor

Posted By David Simons


A Master Optician and long time Chabot volunteer Bob Schalk sent me a link to an article he wrote for the East Bay Astronomical Society's newlsetter on Rachel.

Bob has compiled a nice history of the scope and lens along with some good restoration info. It doesn't sound like the lense needed any polishing though. The fringe diagram picture from the article shows the high quality of the 20" lense.

April 11, 2006 11:46 PM Forum: Refractors

Re: Restoring A 20 Inch F/18 Refractor

Posted By David Simons


There is of course another large refractor at Chabot that is not yet setup. It has an 18" achromatic lens using modern glass.

The old Swedish Solar Telescope.

My understanding is this will be useful for nighttime observations also. Nice feature of this scope is you can stay seated while the scope tracks with the two large flats. It will be interesting to compare the images with the two classic refractors.

June 16, 2006 11:43 PM Forum: Telescope Making

Maksutov Mirror and corrector spacing

Posted By David Simons

Well I finally got around to mounting up a set of 10" Maksutov optics I bought from Markus Ludes many years ago.

I thought I had the spacing of the mirror and corrector right, as I measured them with a simple optical bench arrangement while looking at the moon reflected by a front surface flat mirror.

Turns out I was close, but the tube ended up a little long.

Now I know the spacing of the elements is pretty touchy, but does anybody have a rule of thumb for mirror spacing to focal point change? It looks like there might be a 5:1 or so ratio. I'd like to only cut the tube one more time, and if I can measure how much farther I need the focus to move, then I can cut the tube accordingly ??

I believe these are f12.5 optics.

Anybody have some ideas ??