Posts Made By: Darren Drake

Well after losing the original post thought I'd put it up again. The latest style includes a locking ring in the 2 inch drawtube and also has internal baffels in the drawtube to further reduce glare. The 1.25 inch adaptor not pictured here is also different. It has an extended gripfriendly lip so it is easy pull out whereas before you had to put your fingers inside the adaptor and pull it out.

The latest Orion catalog does not include their highest quality eyepieces but they still appear on their website. Anyone know what's going on?

For Sale: 8" APO YES 8" APO
No f ratio and no maker and only a bank to bank transfer. Sound fishy or is it me?

Well Markus has really outdone himself in add #308857 he has an 80mm f/6.25 OTA for only $9990. I better make an offer quickly before it's gone

About 2 1/2 years ago a good friend of mine spent a lot of money for an 8 inch f/8 mirror. It cost more than most 8 inch dobs. After only 2 nights of using the new scope there was a major mishap and the mirror took a very bad scratch. He dismantled the scope and moved on to other projects.

Recently he gave me the all the parts to that scope including the mirror. I had my good friend Dan Joyce test it with his Foucault tester. It had a badly turned edge and a significantly rough surface along with a poor overall figure . After assembling the scope I saw a poor star test and rough surface with a null test at the focuser using a knife edge; confirming Dan's test results.

I then decided to refigure the mirror under Dan's instruction. He has over 1500 mirrors to his credit. After only 3 sessions the scratch is gone and the figure is almost complete. It's already vastly superior to what it was originally and hopefully in a few days will be done and on it's way to Clausing. I won't mention who made the mirror (it wasn't Zambuto or Swayze) but that person does have a decent reputation and supposedly uses state of the art testing methods including the use of an interferometer.

After looking at the Foucault of that figure it's hard to imagine anyone putting it out for over $100. It could be that it was a fluke and I don't want to trash any reputations based on one data point but people out there need to be familiarized with the star test so as to be able to protect themselves from such circumstances. But soon the mirror will have a KILLER figure and ready for the upcoming planetary season.

I have an 18 inch f/4.4 dob with excellent optics and a 17.5 inch mirror on loan with only one inch longer focal lenth. Problem is it has strong undercorrection of about 1/2 wave. (It was a Coulter) My question is can the Aries SAFIX be used to corect this SA to bring it to a high quality optic? If so what is the availability like? It would be nice to have a backup mirror. Thanks.

I saw an add for this scope here and the owner swears it doesn't have a barlow built into the focuser. How could this be true if it's an f 8.8 as is stated?

http://www.walmart.com/catalog/product.gsp?product_id=2684096&cat=5182&type=1&dept=4125&path=0%3A4125%3A4143%3A5182

Check out the image on page 103 of the March issue of Astronomy of Neptune. It appears WAY to sharp for any back yard scope especially a 6-inch which this was appaerently taken through. Even the image of Triton appears much smaller than an airy disk would for a 6-inch. Any thoughts?

For a few years now I have been using a laser to help determine 2 things about an eyepiece: light transmission and glass purity/cleanliness.

Using my green laser to help judge light transmission I simply shine the beam at close range into the eyepiece and see how bright the reflections are. The better coated eyepieces have dimmer reflections than the inferior coated eyepieces. Sometimes the differences are obvious. My Pentax XWs show the dimmest relections of all with the Naglers a close 2nd.

To determine glass purity and cleanliness, I shine the green laser on the white wall maybe 5-10 feet away and hold the eyepiece up so that the bright pointlike reflectoin is centered in the fov. I then look through the eyepiece and look for any dark splotches and other impurities. Apparently clean eyepieces can look filthy. Also any inconsistencies in the coatings will be obvious as well.
One premo eyepiece I had showed the whole fov to be splotchy even after cleaning all accessable surfaces. This surprised me and explained why contrast was not 100% as good as it should have been. Casual inspection did not reveal any problems.

I should mention that this test is so sensitive than almost no eyepiece will show no impurities whatsoever but a couple of tiny spots will appear even on a new premo eyepiece. Even after cleaning an eyepiece and then using it carefully for one observing sesssion can reveal all tiny dust particles that accumulated during the session.
I hope these ideas can help some of you a little in evaluating eyepieces in the future.

I recently obtained a second hand 17.5 inch f/4.5 Coulter mirror which was tested to be 74% corrected from sphere to parabaloid. Star test does show pronounced undercorrection. Images are quite noticeably inferior to my Sky Designs 18-inch f/4.4 mirror which has an excellent star test and has long been a proven performer. Soon I will work with friend and colleague Dan Joyce to make the mirror excellent and have a back up mirror. What a nice thought. Anyways I've been wondering if the undercorrection is evenly spread does anyone know what the wave front rating would be? I'm guessing around 1/2 wave or slightly better based on the star test. Thanks