Secondary mirrors?

[sopticals (Stephen)]

Recommendations wanted: Who makes the best secondary mirrors? Would I notice any difference at the eyepiece between 1/10 PV and 1/20 PV secondary when used with my 1/25 PV 14" primary?

[rmcconachy]

I don't know about "the best" (I haven't tried them all) but three sources that are often suggested are Terry Ostahowski <http://www.ostahowskioptics.com/elliptical.htm>, Protostar <http://www.fpi-protostar.com/> and Antares Optics <http://www.antaresoptics.com/SecEM.php>.

[Geoff45 (Geoff)]

Originally Posted by sopticals

Recommendations wanted: Who makes the best secondary mirrors? Would I notice any difference at the eyepiece between 1/10 PV and 1/20 PV secondary when used with my 1/25 PV 14" primary?

If you can notice the difference between a 1/25 PV primary and a 1/10 primary, then you'll notice the difference in the two flats.
Geoff

Note added: Here is a page to answer all questions about diagonal specs

[Quark (Trevor)]

Hi Stephen,

I am sure there would be several companies that produce high quality secondaries. I am into planetary imaging and to produce hi res images at long focal lengths is a very harsh test of the quality of the optics, both primary & secondary.

I have been working for some time on a new planetary imaging scope, project FRED, and have a thread about it on this forum.

http://www.iceinspace.com.au/forum/s...ad.php?t=71332

I sourced a 1/30 wavelength secondary from Antares Optics, I did so on the recommendation of Anthony Wesley, who is a world class planetary imager. My new scope is currently operational using the new secondary but my 17 yr old Meade primary, while Mark Suchting is working on my new primary. The quality of the images that I have produced since installing the Antares secondary has improved and I am very happy with it.

In the thread that I have linked to this post there are images of the Antares secondary and also the documentation that came with it, including a Zygo interferogram test that supports their claim regarding the accuracy of the surface.

Regards
Trevor

[sopticals (Stephen)]

Hi Trevor,

Thanks for your imput and interesting link. Much appreciated.

Stephen.

[ausastronomer (John Bambury)]

Hi Stephen,

IMO the Protostar quartz secondaries are the best you can get. They are exceptional. The largest size you can get in these is 2.6" which should be the right size for your 14" scope. Whilst they are only rated as 1/10th wave minimum guaranteed, they are way better than this. The 2.6" one I have in my 14" SDM with Zambuto primary came with a zygo certificate at 1/40th of a wave. In addition the protostar quartz secondaries have a minimum scratch dig of 10/5 which is extremely smooth, as they are designed for laser applications. This smoothness helps reduce scatter. At $US 265 you get what you pay for. The Antares 1/30th wave secondaries as mentioned by Trevor are also very good. You wont go wrong with either. Don't confuse the 1/10th wave secondaries from Antares with the 1/10th wave minimum rating from Protostar. If you need a spider also the heated secondary holders and spider from Protostar are expensive and outstanding , with a long wait time, but worth waiting for IMO.

As a matter of interest who made the primary and how do you know its 1/25th of a wave? How was it tested? There are about 6 people on the planet capable of producing 14" mirrors of that quality consistently. Mark Suchting is one and Carl Zambuto is another. Or is that 1/25th of a wave RMS (.040), which is about .9 strehl.

Cheers,
John B

[Acrab (Victor Martinez)]

Originally Posted by ausastronomer

Hi Stephen,

IMO the Protostar quartz secondaries are the best you can get. They are exceptional. The largest size you can get in these is 2.6" which should be the right size for your 14" scope. Whilst they are only rated as 1/10th wave minimum guaranteed, they are way better than this. The 2.6" one I have in my 14" SDM with Zambuto primary came with a zygo certificate at 1/40th of a wave. In addition the protostar quartz secondaries have a minimum scratch dig of 10/5 which is extremely smooth, as they are designed for laser applications. This smoothness helps reduce scatter. At $US 265 you get what you pay for. The Antares 1/30th wave secondaries as mentioned by Trevor are also very good. You wont go wrong with either. Don't confuse the 1/10th wave secondaries from Antares with the 1/10th wave minimum rating from Protostar. If you need a spider also the heated secondary holders and spider from Protostar are expensive and outstanding , with a long wait time, but worth waiting for IMO.

As a matter of interest who made the primary and how do you know its 1/25th of a wave? How was it tested? There are about 6 people on the planet capable of producing 14" mirrors of that quality consistently. Mark Suchting is one and Carl Zambuto is another. Or is that 1/25th of a wave RMS (.040), which is about .9 strehl.

Cheers,
John B

"There are about 6 people on the planet capable of producing 14" mirrors of that quality consistently. Mark Suchting is one and Carl Zambuto is another"
And who are the other four?

[ausastronomer (John Bambury)]

"There are about 6 people on the planet capable of producing 14" mirrors of that quality consistently. Mark Suchting is one and Carl Zambuto is another"

And who are the other four?

Hi Victor,

I intentionally didn't name anyone else because I didnt want to start an argument with someone whose favourite high reputation optician didnt make the cut. I have also had experience with less than premium mirrors coming from some premium high reputation mirror makers, who shall remain nameless. What I can tell you is that from all the mirrors I have used which includes just about all the premium US based opticians, Carl Zambuto's and Mark Suchting's mirrors are as good as anyone on the planet and IMO they stand a small notch above the rest in terms of optical quality. Most importantly, they are consistent in quality because of stringent testing and control parameters.

Cheers,
John B

[sopticals (Stephen)]

Hi John,Victor,Geoff and Trevor,

First in response to J and V, the mirror inn question (14") has the following specs:[claimed]

1/25.4 PV (wave front)
RMS 1/111 (0.009)
0.997 Strehl

Maker: Tong Lui [Hubble optics]

Again I reiterate these are the numbers given by HO. Their testing method I dont know. However even if in the worst case the RMS was only half that claimed it still would be an excellent optic.

As an observational tool its performance is excellent [in my opinion]. When I first put it into use I owned an 8" f8 1/10 wave PV planetary Dob a 12" Skywatcher flextube Dob and another Hubble optics 14" f5 1/10 wave PV optic. Putting these scopes together under the same sky my son and I noted the following: Jupiter; 8" and 12" scopes gave similar with maybe a little better contrast noted through the 12". The 14" 1/10 wave optic and 14" 1/25 wave optics were progressively (noticably so) better. When viewing the moon (around first quarter) the step ups were even more pronounced with excellent sharp views of fine lunar detail with the 1/25 wave 14" optic. When comparing instruments viewing DSOs it immediately was clear that the 14" aperture (both @ 1/10 and 1/25 PV) was clearly well ahead of the 8" and showed noticeable deeper stellar penetration compared to 12" Skywatcher.

I know there has been a lot of critisim regarding HO mirrors, maybe its because their not made in the US or because they are cheap, I dont know but I built a budget scope and am very pleased with the way it performs.

Thank you again to Geoff and Trevor for your imputs. (much appreciated).

Stephen. PS Just finished grinding out my own 22" mirror, polishing next.

[sopticals (Stephen)]

Sorry for digressing from main topic regarding secondary mirror question: I asked if there would be a noticeable difference at the eyepiece between a 1/10 wave pv and 1/20 wave pv secondary? The reason I asked this is because when I first put my 14" Dob under the sky I was using a 2.76" MA GSO secondary (1/10 surface wave [claimed]), then I replaced this with a 3.1" MA secondary from Hubble Optics (1/10 wave pv [claimed]). The larger optic selected to allow for focusser being moved towards primary for binoviewing. Anyway I did in the process note an improvement in image quality at the eyepiece so just wanted to know if even further improvement would be noticed if 1/20 or higher spec secondary was used.

Stephen.