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anybody ever use acrylic primary mirror ???

Started by BABOafrica, 09/30/2011 07:18AM
Posted 09/30/2011 07:18AM Opening Post
Have any of you ever tried using a parabolic acrylic mirror for the primary on a Dobsonian?

I'm asking because they are so much cheaper than glass mirrors.

Cleers,
Joe

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm
Posted 09/30/2011 08:03AM #1
Joseph Babendreier said:

Have any of you ever tried using a parabolic acrylic mirror for the primary on a Dobsonian?

I'm asking because they are so much cheaper than glass mirrors.

Cleers,
Joe

Hi Joe:

I've never even heard of an acrylic telescope primary. Is someone making them? It would seem to me that you would have thermal expansion problems and maybe atmospheric water absorption problems with a plastic. Also, is acrylic rigid enough for a primary? Can it take an optically smooth and accurate polish?

These would seem to be huge problems, but like I said, I've not heard of anyone trying acrylic for a primary and I don't have any useful engineering knowledge of the material characteristics of what might be highly specialized types of acrylics developed to be mirror substrates.

Jim
Posted 09/30/2011 08:11AM #2
Well, there are those $10 refractors with 60 mm plastic objectives...a 16" Dob with a plexiglass mirror should be a real treat for the senses. 8)

Jim McSheehy
Posted 09/30/2011 01:14PM #3
About a decade ago I came across a site for a company that made cast first surface mirrors up to 6" diameter. They claimed 1/4 wave accuracy. They were quite inexpensive as I recall. I don't know of anyone who ever made a scope from one of these but if they were still available, I think a large light wieght finder might be a good place to try one.

I searched for the manufacturer a while ago and couldn't find anything similar and until now, hadn't given it another thought.

dan
Posted 09/30/2011 09:44PM #4
If you check eBay item # 180683239702, you'll find an example of what I'm talking about.

It's labeled as:

HUGE 25" ACRYLIC PARABOLIC MIRROR CONCAVE

I was just wondering if this thing could be used to make a dob.

Cleers,
Joe

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm