thoughts on 2nd hand 16"

[Paddy]

Dear all,

I have the opportunity to obtain a 2nd hand Meade 16" Newtonian for about the price of a new 16" GSO primary. I have been very happy with my 12" gso but contemplate an upgrade to 16-18" in the next few years, but finding a quality 16" primary at a good price could accelerate my plans. The vendor says that the mirror was crafted in the US in 1992 and is optically superior to the current Chinese primaries (quoting 1/4 wave error for the current Meades vs 1/8 for the older model). Do people think that this would be true and would the difference be significant? Is the difference between a 12" and 16" under dark skies significant? I had been planning to take some time looking through various scopes at star parties before upgrading, but this opportunity has pre-empted this groundwork.

Any thoughts would be greatly appreciated.

[astronut]

Hi Patrick,
Firstly as you already know 12" of aperture, gives you an excellent balance of light gathering ability, size and portability.
Will a 16" be that much better? YES!!
It gathers 77% more light than the 12"
the only negative of a 16" scope is the physical size and possible weight.
A good way to check the health of the 16" (aprt from mounting it in a scope) would be to have it tested by a reputable optician/mirror maker.:thumbsup:

[Satchmo]

I've refigured a handful of the older Meades 16" which which, as presented to me, were good for low power only. I'm not sure on what basis you could say that the USA ones were better than Chinese ones..no mass produced mirrors are rated on a measured wavelength pass/fail basis : I think its the average batch quality that is monitored, you can get some that are clearly better or worse than the mean. You get what you pay for in the sense that you don't get the same level of quality control with low cost optic.

I would recommend use the telescope before you buy it. Medium to high power ( depending on the seeing ) will tell you all you need to know.

[tnott]

Having used both 12" and 16" at a dark site I'd say yes, there is a noticeable difference between them on DSOs. As to the quality of the old 16" Meade mirrors I cannot say but the actual telescopes I have seen are (extremely heavy) junk.

If you can get it for a good price and put the optics in a truss dob the mirror should be good enough for DSOs at least.

[Satchmo]

I think the concept of deep sky objects being 'best with' or 'only requiring low magnification' has gone out the window with the general improvement in optical quality over the last 15 years.

[Starkler]

I have to agree there. Its a wonderful thing to be able to crank up the power in a large dob when seeing allows to closely examine internal structure in a planetary neb for example.

[Paddy]

Thanks for the input all. tnott, I must say I have been quite inspired by your tridob and envision a similar project in the future - just a question really of lashing out on an 18" mirror, or settling for a 16". This current possibility would only bring the whole thing forward and make it cheap. This would only be worthwhile if I was sure the mirror was very good and I'm not and I can't imagine getting the optics independently tested. So I reckon it's probably plan a - keep star hopping with the 12", which I'm very happy with, look through others' fatter scopes at star parties and when I reckon I've worn out my scope and my observational skills, then upgrade.

Still, more thoughts would be welcome.

[Paddy]

Oh, I just noticed that your tridob will be up for sale in November - that could really throw plan a out the window! I'll be very interested to hear what you're asking for it!

[Ian Robinson]

You might need to have it recoated if it's 16 years old - I'd send the optics off to the USA to get a 98-99% reflectivity dialectic coating (that would be like adding a inch or two of glass (based on standard Si02 protected Aluminium mid 80s reflectivity). It'll probably be pretty mucky and thin , and probably badly pitted too.

You might also consider asking for the figure to be checked (Nova Optical perhaps - will give you a super mirror in the end , do that fist ....).

Sounds like a nice find nonetheless as all the above are eminently fixable.

[Starkler]

Ian this can be done locally in Sydney.

[Chippy]

Hey Geoff,

Who does the high reflectivity coatings in Sydney?

Nick.

[Starkler]

Oops I meant mirror re figuring and coatings can be done in Sydney.
I dont know if they do the special 'enhanced reflectivity' coatings.

[Satchmo]

Quartz protected coatings if properly done with 1/4 wave protective layer do not cut reflectence of fresh aluminium, and come in at 89-90%. Typical dialectric coatings are TiO2 layers and are closer to 94-95%.

[Satchmo]

Paddy, PM me if you would like to arrange a proffessional test of your mirror.

[tnott]

As someone who has used higher power on planetaries, small galaxies and the Homonculus I would concur as well. It's best to get good quality if you can.

[Paddy]

This is certainly what's on my mind as I observe with my 12". How much more detail will I see through a bigger scope? I've set an upper limit on aperture fever, though, as I don't want to be using step ladders etc. I'm looking forward to the Border Stargaze in August to get more of an idea. I think I'll shelve this current option until I'm more prepared.

Thanks for all the input!