16" f4.5 GOTO Dobsonian (current status: underway!)
Since my Celestron 8" is permanently embedded in my observatory until replaced, I need a scope I can easily load up in the truck and take places. Lately I've been reading Albert Highe's Engineering, Design, and Construction of Portable Newtonian Telescopes, so I'm using his ultralight telescope design as a guide for the 16".
Author Albert Highe with a telescope of his design
Originally I posted on Cloudy Nights for a 16" mirror blank that I could grind myself expecting to spend about $500 for a good pyrex blank. I got lots of responses, some much below $500 (for example one person offered a blank that needed to be edge ground for $145!) I was offered a 16" f4.5 Meade Starfinder mirror so for my budget, I was able to skip the laborious grinding of the mirror, and start building structure right away. So I went for it! Images below:
The seller's comments were:
The shots don't show exactly what the eyes can see. On the primary there are several minor sleeks that don't show up as well as number of places where the aluminum coating is starting to show its age. The secondary also has a small defect in the coating at one end. If you look at the photos real close you can see the defects. They will appear as slightly "lighter" spots within the reflected image. None of these appears to be into the glass itself, just the coating so if you intend to recoat them (certainly if you refigure) these will be gone. The back of the primary also has a scallop around 1" square that is about 1/8" deep. I think this must have occurred during the original manufacturing (maybe when removing from the mold?) because it appears to have been ground down. I took a couple shots of this so you could see the extent of it.
I have owed the optics for around 14 years and think there is still a lot of useful life in the coatings but they are probably 20+ years old so these types of defects are perfectly normal. I really don't think any of these cause a degradation in the views but I wanted to be sure and disclose everything I know about the optics so you are not disappointed. If you see something and have any questions or just want some more photos please let me know.
Current status: Waiting on optics
Current status: Building OnStep controller