It's all done with mirrors ...

[Allan]

Originally Posted by ausastronomer

I haven't seen one of his cells in the flesh but I know exactly how his design works and the mechanics and theory behind it. I don't think his cells are any better than Peter Read's. Their 27 point cells are very similar in terms of pad support placement position with the main difference being that John Pratte uses whiffle tree edge supports on mirrors under 32" and a moving cable sling on mirrors over 32", whereas Peter Read uses a cable sling on all his cells, regardless of size. In addition to that however Peter uses a 27 point cell on all scopes over 24" whereas John Pratte is still only using an 18 point cell on his 25" scope. What I can tell you is that I have seen and used scopes from just about all of the custom US scope makers from the last 30 years, with the exception of JP Astrocraft and I haven't seen one yet that is as well designed and built as Peter Reads SDM's. I have no reason to suspect that the build quality of John Pratte's scopes is any better than the likes of Rob Teeter's or Rick Singmaster's. For starters no one else is using powder coated cast and machined aluminium altitude bearings like Peter has been using for the past 8 years.



Well a good bit of that research was done with Phil Townsend's mirror and your American friends are only telling you a very, very, very small part of the story in regard to that one

Cheers,
John B

Hey John, nice post. This isn't the place for me to divulge conversations I've had with Peter about John Prattes mirror cells. I'm sure you can ask him about that yourself. I have managed to organise Peter, John and Mike to work together, and the result will be a dob like nothing ever seen in Australia.

Also, one doesn't spend 50k ordering a scope without researching the people involved. I can honestly say I probably have more information about Phils case, from every side of the story than anyone.

[Allan]

Originally Posted by Kunama

Except Kunama Optical Laboratories

You need to trademark that name Matt, it just rolls off the tongue.

[sally1jack (Phil)]

Originally Posted by Allan

I can honestly say I probably have more information about Phils case, from every side of the story than anyone.

then you would be wrong
phil

[Allan]

Originally Posted by sally1jack

then you would be wrong
phil

Hi Phil. I'm sorry, John brought up your scope in conversation, and I shouldn't have responded by discussing it here. I'll leave it at that.

[Satchmo]

Originally Posted by Allan

I can honestly say I probably have more information about Phils case, from every side of the story than anyone.

Originally Posted by sally1jack

then you would be wrong
phil

I'm going to second that notion.

[Allan]

Mark, mate, what are you saying. You gave me your side of the story at IISAC. But seriously, it's best we don't do this.

[Satchmo]

( Edited for brevity )

Allan , all I can think is you may have conflated some of the info attributed to me second or third hand into that conversation, which I can understand .

[Allan]

Ok Mark, no worries.

[Satchmo]

Matt - Getting your thread back on topic- I think what you were after in questioning your Zambuto specs was something like this :

0.6 Strehl - not great - ok for low power deep sky

0.8 Equivalent of the old Rayleigh criterion - will resolve doubles to theoretical limit - good for low to medium Deep Sky observing - planets will not handle high power well

0.9 Much improved planetary performance

0.96 Pretty much as good as it gets

0.999 wishful thinking in reality

These all assume that the figure causing the degradation is smooth and mainly primary spherical aberration for the sake of simplicity and do not generally take into account degradations due to irregular distortions/astigmatism

Technically 0.96 Strehl mirror can actually have an unacceptable star image and lousy star test - if the figure is not smooth .

Just remember that there is nothing mysterious and high tech about getting these figures . Anyone can put a simple zonal mask on a mirror and use free amateur download software like Figure XP to produce nice figures with PV RMS and Strehl on the printout . Most of the time the tests work very well if used by a knowledgeable and honest operator.

Dont worry that your mirror thickness is antiquated - most good mirrors these days up to 24" are 1.6" thick glass and cools pretty quickly - just have some good fans and you will fine .