Improving a Meade 4500 question

[henrylr]

I'm trying to improve the performance of my Meade 4500 and have sent emails to some makers asking for spec.s of their 4.5" primaries. While waiting for replies I started thinking about the secondary. I imagine the stock secondary is, at best, an A/8. So would replacing the secondary with an A/30 secondary result in a visible improvement? The calculation, for a secondary minimum minor dia., result is 1.13" I did check out Edmunds and they have a perfect size for the meade but it is A/8 and the surface quality is only 40-60 which is considered a low quality rating and will likely produce some scattered light. The smallest A/30 secondaries have a minor of 1.3". Would that work or would it block to much light?

Thanks,

henrylr

[Peter Drew]

An A/8 specification for a secondary is still a pretty good standard.  I don't think the higher quality A/30 would show very much difference other than on a very good night and high magnification.  A small aperture does not benefit as much from this type of upgrade as a large aperture.  A slightly larger secondary mirror than necessary  will not obstruct a noticeable amount of light, a slightly smaller than minimum would lose more.   Welcome to SGL.     🙂

[henrylr]

Thanks for the reply. I recently sold my custom made 10" newt. It had excellent mirrors. So that is why  I want to improve the optics in the Meade. My other concern is the surface quality of 40-60 for A/8 mirrors available. Another question I have is would you know where I could get a good 4.5" parabolic mirror. The ones from china don't provide any info like strehl ratio and wavefront RMS.

 

Thanks,

henrylr

[John]

This USA based optical company have a good reputation I believe. The smallest aperture they list is an 8" but they might be prepared to do something bespoke for you:

http://www.rfroyce.com/stand_mirrors.htm

You could wind up investing a lot in upgrading a 4.5 inch newtonian to deliver slightly better performance than stock when, for less cost, you could purchase a larger aperture optical tube complete that would offer a somewhat larger performance upgrade.

 

Edited August 20, 2021 by John

[henrylr]

Thanks again. I'm 75 years old and don't do much viewing but thought it would be a fun diversion to improve the old Meade. Robert Royce has retired. 

Edited August 21, 2021 by henrylr

[henrylr]

Seems almost all of the 4.5" mirrors are spherical and are made in China. Now I don't want to buy a pig in a poke so I sent emails to several Chinese makers/sellers asking for strehl ratio and wavefront spec.s. Replies were all the same..."do not have those specifications". Now the mirrors I inquired about  were not cheap, selling for $100 to $150. It strikes me as odd that folks would spend that much without any spec.s.

[John]

I think you will find that there is very little demand for a spherical 4.5 inch mirror purchased on it's own. Probably not much for a parabolic one of that aperture either.

I suspect that most people would buy a complete optical tube for a scope of that aperture, accept the optical quality provided and make the best of the scope by ensuring that the collimation is as accurate as possible and the scope is properly cooled.