Jump to content

Amateur Telescope Making (UPDATED 9/23/18) - 20" f/4 Nearly Complete


Recommended Posts

  On 9/14/2017 at 9:09 PM, munlander1 said:

What's the difference?

Expand  

A Chief uses a tilted primary mirror to avoid having a central obstruction entirely, and then uses off-the-shelf lenses to correct for the aberrations. Also known as a Jones-Herschelian. I've met the inventor of the design.

Link to comment
Share on other sites

I once found a new 5" mirror on Astromart. An odd size to be sure, but it fit perfectly into the end of #10 cans, like large coffee cans. I soldered several cans together. I bought a beat up 4.5" telescope just for the focuser and secondary mirror with adjustable 45 degree holder (it was cheaper than buying those new, and I was very broke at the time). I used bicycle spokes for the spider, which the local bicycle repair shop gave me for free after I explained why I wanted what they considered trash. The bicycle spokes were a touch of genius. They have those little hex nuts that make collimation a lot easier.

I was going to add light baffling, but decided that the ribbed nature of the cans with flat black paint would be good enough. The primary mirror has a long focal length, but works quite well, especially for planets in Portland OR's light polluted skies. 

I want to grind my own mirror. The Rose City Astronomers (RCA) has a weekend shop where I can do that with expert advise. Does anyone have a recommendation on where to buy a couple of glass blanks and grinding grit?

Link to comment
Share on other sites

  • 2 weeks later...

I wanted to try out the motions so I built a rocker box for my Edmund 6" f/8 and put it on the f/4's base. It doesn't make it to the zenith but it should work.

f4I8T2l.jpg

UPDATE: Motions are pretty smooth. Saturn, Moon, and DSOs were pretty nice with this scope. Still have to finish the f/4.

Edited by _Augustus_
Link to comment
Share on other sites

The 8" SCT is going to be out of here on Monday; as soon as that's done I can order everything - I already have the money from it but my dad won't let me spend it until I ship it out.

I'm going to be getting:

  • Destiny curved spider (already have the secondary)
  • Orion single-speed Crayford focuser
  • 38 pounds of plaster

And of course I'll have some $ left over for aluminizing.

You might be asking why I'm getting 38 lbs of plaster. The answer to that is basically because ordering in small quantities is a ripoff. For the amount needed for an 8" tool, you're paying about $2.50 per pound. If I buy 38 lbs, I'm paying about $1.42 per pound, and I don't have to order more for my next mirror.

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...