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Posts Made By: David Simons

August 12, 2006 08:13 AM Forum: Astro-Physics

Stuck Traveler focuser

Posted By David Simons

Hi Folks,

I have been trying to replace the focuser on my vintage EDT smooth paint Traveler without much success. I have tried rubber strap wrenches to unscrew it.

Any success stories out there ?

Thanks !


February 11, 2007 11:48 PM Forum: Refractors

Testing an Achromat lens

Posted By David Simons

Hi Folks,

I did a quick search of the old Astromart threads and could not seem to find a description of how to bench test an achromat lens.

I have access to optical flats, Ronchi screen, filters, etc. I kind of got the idea a lense could be tested like a mirror if a flat was placed behind it?

Maybe there is an ATM thread on this also ?

Thanks !

March 22, 2007 04:56 PM Forum: Telescope Making

8in f6 Comet sweeper

Posted By David Simons

Hi Folks,

After reading Keith's posts, I finally got motivated to work on my 8" scope also wink

I decided to use the same method of heavy wall paper tube and wood parts that Keith used, as it would be easy to modify, and a cheap way to get the scope built while I finalize the drawings for the metal shop. End plates and lense mounting rings are both routed from 8 layer plywood.

I was surprised the collimation was very close for my astigmatic eyes, so no adjustments yet.

As an f6 it makes a good comet-finder type scope. Yep, easy to spot chromatic aberration on mag 0 stars, but for deep sky fuzzies, it is not noticeable. I think there is some spherical aberration, and critical star testing has yet to be done. Saturn did show a bunch of moons though.

I setup the scope last night in the front yard, (street lights –bah !) to look for Galaxies around Virgo/Leo. Just sweeping back and forth (1.75 degree FOV) I counted 28 obvious ones without checking at a star map. I did need a map inside Leo, and saw 5 more without too much effort. The fun part was seeing the groups of galaxies together, three or four at a time.

The mount is a Lightspeed "Wagon" fork mount, that seems to handle the scope without too much shaking. Length of scope is about 42" with racked in focuser. Weight somewhere around 25lbs. Setup time was a few minutes, and no counter weights !! Tube painting, inside flocking and baffles to follow later.

smile

March 22, 2007 05:04 PM Forum: Refractors

8in Comet Finder

Posted By David Simons

Hi Folks,

Here is a pre-metal version of an 8" f6 refractor I am working on.

Info and short observing report in the TM forum:

http://www.astromart.com/forums/viewpost.asp?forum_post_id=517377&poll_id=&news_id=&page=

April 19, 2007 01:02 PM Forum: Telescope Making

Fun with Flats

Posted By David Simons

Just a little eye candy to show some attempts to test one reference flat against another. The bottom perforated flat is already aluminized, and the top flat is double polished to show the interference lines.

I think the interference lines are too close together though. Comments welcome smile

The bottom picture just shows a red laser bouncing around the inside of the double polished flat. I thought it looked cool. 8)

May 10, 2007 09:50 AM Forum: Eyepieces

Vixen LVW 42

Posted By David Simons

Hi Folks,

I just received my Vixen LVW42 from the Vixen America closeout sale. I have been looking for the ultimate rich field eyepiece for my 8" f6 scope, and this ep may be it.

I tried it last night in somewhat foggy skies, so I know my eye pupil was no where near 7mm, but the view was very comfortable, with just a hint of softness near the edges of the field. Very nice even with my glasses on. If my calculations are right, I was getting:

Mag=1200/42 ~29X
The specs on this ep list a 72 degree FOV, so

True FOV = 72 degrees /29 = 2.48 degrees

I was using a correct image diagonal, and it felt like I was looking through an 8" finder scope.

However the 72 degree spec on this ep deviates from the rest of the series at 65 degrees. Has anybody made any measurements to verify Vixens claims on this 72 degree?

June 10, 2007 01:12 PM Forum: Deep Sky Observing

M24 in the Wine Country

Posted By David Simons

We had our clubs monthly public night at Robert Ferguson Observatory last night at Sugar Loaf Ridge State Park, located between Sonoma and Santa Rosa, California in the heart of the Valley of the Moon and the Northern California Wine Country no less. Not quite a Mag 6 location, but very clear last night.

I had been using the clubs 8" f9 APO refractor showing Saturn and the Ring Nebula to crowds of kids and their parents most of the night. When it was over, I was itching to use my own refractor still packed in the car, an 8" f6 Achromat. I had just purchased a Vixen 42LVW eyepiece at RTMC and with a clear dark night was ready for some wide field views. I was getting almost a 2.5 degree FOV with this combination, and 8" of unobstructed aperture will show some objects in a whole new way. I tried various combinations of O3 filtered and regular views of large objects such as the Veil, and NA Nebula. This was the first time I could really see the NA Nebula etched into the surrounding background. The Veil was showing some nice details, like a semi-transparent scarf all twisted up.

Scanning along the Cygnus Milky Way area was great fun. Panning down through the Scutum Star cloud near M11 was a treat, as the mist of stars just dropped off into the black abyss next to it. On my way to Sagittarius I stopped over at M24. The whole cloud neatly fit into the 2.5 FOV of the 8" lense. This was maybe my favorite area. For me, it's something like looking at the sky all at once in one field of view; it's easy to find asterism for almost anything in this region with so many stars. Although I have seen this area many times before in other scopes and binoculars, the view is different in each kind of scope. What really struck me this time were the delicate strings of stars snaking their way through the area. A couple of the "s" curved strings seemed to find their way together in the shape of a wine or Champaign glass. Maybe it was just being surrounded by all the vineyards, but to me, the glass shape just seemed to jump out! If you can indulge my imagination, I have tried to sketch the pattern on top of the picture in Desktop Universe.

The Sagittarius region was still a bit low on the horizon and in the sky glow haze, but in another month or so should be just right for some more wide field viewing.


August 6, 2007 05:44 PM Forum: Refractors

Re: Refractory history question

Posted By David Simons

Hi Greg,

From the 'net I found fresh speculum had a 66% reflectivity, and IIRC he did not use a secondary due to the large light loss. So on a good day he was at 66% of a 72" mirror, which would give ~ 58" equivalent light transmission aperture, which I am pretty sure bested any achromat of the time.

I think one of his biggest problems was it was frequently cloudy cwy >sad :S

Greg Nowell said:

When Lord Rosse started his 72 inch Newt in 1840, I'd like to know what the competition was in the refractor domain. With speculum coatings he was going to get only .4 x .4 or 16% light throughput, and that was when the mirror was "fresh." So he was basically getting the equivalent of a modern 20 inch.

But refractors such as they were then didn't have modern coatings, so they probably lost a lot of light too. So here are my questions:

1. Light throughput of an 1840s era achromat doublet?
2. Maximum refractor aperture achieved in 1840?

thanks
Greg N

August 31, 2007 08:25 PM Forum: Refractors

Ronchi on a refractor

Posted By David Simons

Here is a Ronchi (100 lpi) picture of a Ukraine made 8" f10 refractor lense against a flat mirror. I think the mirror was around 1/4 wave. This is the first time I have tried a picture like this smile

The before and after focus picture were very similar, so I am only showing one picture. For reference I included a shot of a 60mm f8 fluorite lense.

Comments welcome !

November 12, 2007 08:35 PM Forum: Telescope Making

How did I live without this ? (Bandsaw)

Posted By David Simons

Just got myself an early Xmas present, a Sears 10" bandsaw. After getting it setup and adjusted, I tried it out on some scrap aluminum. It sawed through a 1" square, 1/8th thk. aluminum tubing without much fuss, also some 1/4" aluminum plate with ease. It was quiet enough to use at night in my garage without worrying about waking up the kids.

I used to use a hacksaw, saber saw, sawzall and circular saw with varying degrees of success.

This is the way to go !