TheSkySearchers

I will preface this by saying I know my mirror is in NO need of resurfacing, and I do NOT plan on having it resurfaces any time soon.

But having said that, I cannot help but wonder - how much would a Zambuto resurfacing improve the mirror?

https://zambutomirrors.com/zambutoopticalc1.html

sorry i can't help you but it would be intresting to find out the "realworld" performance of the optics other then by going from the numbers. ie is the extra percentage realy worth it for general use ie observing, imaging/''artistic proccessing''. maybe there is a gain when imaging towards the uv end or high resolution planetary work , i'm going do some research on strehl ratio

i just checked some mirror re coaters here in the aus online, it turns out it's almost cheaper to just buy a new coated mirror , about 14-16'' and over the value of recoating is alot better .

I think the OP is asking about refiguring not recoating?
Zambuto mirrors are famous for very fine figure.

It’s unclear to me that it’s worth it though. The scope is obstructed by the secondary so that is a significant Strehl ratio handicap. I’d rather spend the money on a larger aperture GSO mirror.

notFritzArgelander wrote: ↑Wed Aug 05, 2020 1:44 pm It’s unclear to me that it’s worth it though. The scope is obstructed by the secondary so that is a significant Strehl ratio handicap. I’d rather spend the money on a larger aperture GSO mirror.

Yeah, it's more of a "thought experiment" along those lines - like I said - I am not considering it at all with my current mirror - just wondering if it would make any difference with it. I would suspect not enough to justify the cost.

KingNothing13 wrote: ↑Wed Aug 05, 2020 1:48 pm

notFritzArgelander wrote: ↑Wed Aug 05, 2020 1:44 pm It’s unclear to me that it’s worth it though. The scope is obstructed by the secondary so that is a significant Strehl ratio handicap. I’d rather spend the money on a larger aperture GSO mirror.

Yeah, it's more of a "thought experiment" along those lines - like I said - I am not considering it at all with my current mirror - just wondering if it would make any difference with it. I would suspect not enough to justify the cost.

Ultra smooth mirror surfaces are costly. The main physical difference is less scattered light at the objective. It’d be interesting to see what the trade off would be with other methods of reducing scatter like baffling the OTA. IMHO the most cost effective way to get rid of scattered light in a Newtonian is to install knife edge baffling in the OTA.

i also wounder if the reduced scattering would help push a sct magnifaction a bit futher with a barlow

yobbo89 wrote: ↑Wed Aug 05, 2020 3:26 pm i also wounder if the reduced scattering would help push a sct magnifaction a bit futher with a barlow

I suppose one could get a somewhat higher magnification. I don't think it is preferable. By magnifying 2X with the barlow the whole image will become 4X darker. That means the advantage is gone.
IMHO : It is nicer to enjoy the better contrast with the same magnification. Far more pleasing.

There is refiguring, but there is also recoating.

Re-coating
In 1978/79 I ground and polished a 6" mirror under the supervision of an expert mentor. He pushed me to keep working on it until near perfect. It's first coating was done by an excellent optical coater and the scopes performance was exceptional.

It's second coat, about 12 years later, was mediocre and the scopes performance reflected that.

That coat stayed on for 20 years during which time, I was doing very little observing. Two years ago, I had it recoated with a very high quality expensive coating - I could have bought a finished 10" GSO mirror for the same money and had money for a mid-priced eyepiece left over. But it was very worthwhile. Those of you from AF may remember my post about the comparison we did between a 6"f7 newtonian and a Takahashi TOA-150 6"f7.5.

Alas, AF has shut down now and material is unavailable but the comparison is still posted on my website.
https://joe-cali.com/astronomy/articles ... ctors.html

Was it worth it? In my case - yes, definitely. Rob is correct that if you have an off the shelf mirror, and given the reasonable quality of GSO & Synta mirrors, it's probably not worth it. You might even get a better mirror out of the swap.

Refiguring
I can't comment specifically on the refiguring. I can say that detail seen through a high quality optic is exquisite. But the improvement depends on how bad your current mirror is.

Cheers

Joe

cheers joe, i'll enjoye the read.

KingNothing13 wrote: ↑Wed Aug 05, 2020 1:48 pm

notFritzArgelander wrote: ↑Wed Aug 05, 2020 1:44 pm It’s unclear to me that it’s worth it though. The scope is obstructed by the secondary so that is a significant Strehl ratio handicap. I’d rather spend the money on a larger aperture GSO mirror.

Yeah, it's more of a "thought experiment" along those lines - like I said - I am not considering it at all with my current mirror - just wondering if it would make any difference with it. I would suspect not enough to justify the cost.

My observing buddy has a 20” f/5 scope with what many of us thought an excellent mirror. Mike Lockwood, of Lockwood Optics, said it was god, but he could make it even better. After months of humming and hawing, Harry sent the glass to Mike. It is now one of the sweetest pieces of glass one could wish for!

Without knowing the qualities of your existing mirror, the question of refiguring can not be answered. Most machine made commercial mirrors are fair to good, but very few are excellent. I love walking around the observing field to peek through all the telescopes. My unscientific estimation is at least 70% of them are in dire need of collimation. I’ve seen a few with strong spherical aberration and some with obviously rough surfaces.

I imagine proper recoating by a world class optics producer would be benifical.

Either way I do like the owners attitude:

There is brightness, which is provided by aperture, and there is contrast, which allows one to see detail. I have been accused of overstating the importance of contrast, so please let me be clear. “Contrast is not everything. Outside of aperture, contrast is the only thing”.

-Carl Zambuto