Skywatcher 16" Dob primary.

[NGC 1502]

Hi all. Went to Astrofest on Fri 4th. Couldn't help noticing the SW

16" Dob. Had a good look, and all seemed as I expected, until I

noticed that the primary mirror has no clips.

So I looked at the mirror cell from below. The mirror is thinner at the

edges ( like an SCT ) with prominent radial ridges moulded into the

glass. It is secured in the centre only, but I couldn't see by what

method. The only other Newtonian mirrors I've heard of secured at

the centre only, are Royce mirrors from the US, although of course

this is common with SCTs & Maks.

I would think that this design of mirror would cool faster, and track

shifting night time temps better.

Is there is a down side to this type of mirror in a Newt ?

Thought this may be of interest to some.

Best regards, Ed,

Edit : link to Royce mirrors

http://www.rfroyce.com/conical/

[xboxdevil]

It sounds like a better design than the old skywatcher flextubes. As you say the thinner mirror should give quicker cool down times and the lack of mirror clips will also help reduce diffraction spikes too.

Now if I only had dark skies....well actually if I had any skies without cloud!

[Peter Drew]

No downside to this design other than perhaps cost, more grinding unless molded and somewhat more care needed in polishing due to less material edge support. I made several 10" scopes in the late 70's using thin edged, centre mounted mirrors by David Hinds, these gave excellent performance and are well worth looking out for s/h.

[NGC 1502]

I made several 10" scopes in the late 70's using thin edged, centre mounted mirrors by David Hinds

Thanks Peter, had no idea that David Hinds had ever made mirrors

like that.

Regards, Ed.

[derekm]

Thanks Peter, had no idea that David Hinds had ever made mirrors

like that.

Regards, Ed.

That's how he started.