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Discovery vs. Zambuto Optical Shoot-out

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#26 deepskydarrell

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Posted 01 December 2011 - 01:27 AM

Carl Z's 7 criteria are very convincing. The 4th one is excedingly so. http://zambutomirror...oopticalce.html

Optical companies don't / won't talk about surface roughness. There doesn't seem to be a statistical test for it. But boy can you see it when you take a look at it on a focault testor. And it shows up in glare or fog next to a bright object.

I still believe the visual test in contrast is in faint objects near brighter ones. Such as the galaxies hidden within M 44.

DSD.

#27 Darenwh

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Posted 01 December 2011 - 10:58 AM

Even if it comes down to Zambuto mirrors being better than those in Discovery scopes it becomes apparent based on how close the two mirrors were that anybody who owns a Discovery dob (at least an Ostahowski vintage) should be very happy with the scope they have for the money they spent. Discovery scopes are easily premium scopes at bargain prices.

I happen to be one of those people who have one and I am quite happy with it.

#28 azure1961p

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Posted 03 December 2011 - 06:49 PM

Hi Tim,

I would say you have to test them on the planets. I have 13.1" dob yep old coulter but Carl Zambuto refigured the mirror in 1995 and it's 1/11th wave where before it was 1/2 wave. My scope performs better on planets 312x is easy and have pushed it to over 700x before. It rivals 6" APO refractors on planetary detail. It also does better on globulars and detail on nebulas.

I am not surprised the discovery scope was brighter it has more aperture in the review and more surface area. Carl Zambuto does make some fine mirrors and never seen a bad one. You can get to that 50x magnification per inch if the seeing is right with his optics. But with a dob without tracking sometimes that is hard to do.

Good article enjoyed the review. One of our club members has a discovery premium dob 17.5" and enjoys it and it does have good optics too.

James Bielaga


I would bet big bucks that your reflector would out perform any 6" apo on a night that allows its potential to be realised. On common so so nights it might seem rivaled, but on a better night with 1/11 on the wavefront in that aperture youd also best a 7" apo.

Pete

#29 oldtimer

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Posted 05 December 2011 - 01:38 PM

I have read several 'good' reports as to Discovery's mirror quality, however the 14" I bought several years ago is nothing to brag about. Oh its fine for deep sky, which is what I use it for, but fails badly on planetary.

Yes yes I know all about alignment, seeing conditions, cool down time and mirror cell pinch but its just not that good. My 10" newt with a mirror produced by an 'acomplished amateur' kicks its butt on the planets.

#30 Bowmoreman

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Posted 14 December 2011 - 08:55 PM

Fascinating review, and it pretty much mirrors my review experience and thread earlier this year... There is something hard to quantify about the 'smoothness' of Zambuto that is hard to quantify... That said, I am sold...

Disclaimer: I have not viewed thru other premiums... Only a Tak M300... And FSQ106... The key to me was the contrast delta... Darks darker, lights lighter.. And linear in between...

Nice review

#31 Calypte

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Posted 16 December 2011 - 03:46 PM

I have read several 'good' reports as to Discovery's mirror quality, however the 14" I bought several years ago is nothing to brag about. Oh its fine for deep sky, which is what I use it for, but fails badly on planetary.

What vintage is the Discovery scope?

#32 photiost

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Posted 25 December 2011 - 12:15 AM


The quality of the secondary plays a significant roll in the systems overall image quality.

This has to be taken into consideration.

#33 Víctor Martínez

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Posted 25 December 2011 - 05:27 AM

Hi,
Has anyone compared directly one mirror Zambuto mirror with a recent Ostahowski mirror (since he set up his own business) on same conditions?

#34 oldtimer

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Posted 26 December 2011 - 12:25 PM

The 14" size miiror was one of the last they produced...maybe 1998???

#35 ScumotheUniverse

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Posted 26 December 2011 - 12:59 PM

In the ones that were optimized, though, I've generally seen that the star images are a little tighter and have a little less "fuzz" in the edges and/or diffraction rings in the Zambuto-mirrored scopes--obviously less light scatter.


Justifying Zambuto's decision not to use enhanced coatings. Apparently his rationale for using only standard coatings. Or at least that is what he used to say. Is he still recommending standard coatings only? I belong to the ZOC yahoo group, but have not kept up with the most recent posts.

#36 Calypte

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Posted 26 December 2011 - 06:57 PM

The point about secondaries is interesting. Discovery made their own secondaries (note that this was a "diagonal" in my day, and Terry still uses that terminology, as do I), but at one point they considered buying some from China, to cut costs. They rejected an entire shipment and went back to making their own, but another scope maker was using those same secondaries in production scopes.

#37 deepskydarrell

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Posted 27 December 2011 - 02:15 AM


Justifying Zambuto's decision not to use enhanced coatings. Apparently his rationale for using only standard coatings. Or at least that is what he used to say. Is he still recommending standard coatings only? I belong to the ZOC yahoo group, but have not kept up with the most recent posts. [/quote]

Carl Z told me: "We use a standard aluminum with one layer of silicon dioxide overcoat. Its a good coating. Provides 92% in the visible
and it preserves our contrast."

I believe one concern might possibly be that enhanced coatings don't last as long and are harder to remove for recoating, sometimes requiring refiguring (which defeats the whole purpose for the excellent figure) The single overcoating keeps the micro finish from getting too bulky / lumpy? and that would defeat contrast.

Darrell Abrahams.

#38 Starman1

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Posted 27 December 2011 - 12:00 PM

[quote name="deepskydarrell"]
Justifying Zambuto's decision not to use enhanced coatings. Apparently his rationale for using only standard coatings. Or at least that is what he used to say. Is he still recommending standard coatings only? I belong to the ZOC yahoo group, but have not kept up with the most recent posts. [/quote]

Carl Z told me: "We use a standard aluminum with one layer of silicon dioxide overcoat. Its a good coating. Provides 92% in the visible
and it preserves our contrast."

I believe one concern might possibly be that enhanced coatings don't last as long and are harder to remove for recoating, sometimes requiring refiguring (which defeats the whole purpose for the excellent figure) The single overcoating keeps the micro finish from getting too bulky / lumpy? and that would defeat contrast.

Darrell Abrahams. [/quote]

Carl may be right about the multi-layer aluminum "enhanced coatings" of the 1980s. But today's dielectric-layer enhanced coatings (usually 2 or more transparent layers added to the silicon dioxide) will not fail earlier than a standard coating.and are no more difficult to remove. The thickness of the coatings will still be in the small number of nanometer thickness area, so what it really boils down to is the quality of the coating, and most coaters who offer enhanced coatings are pretty good at it. The ones we've tested here were very good.

What is a matter for debate in the physics arena is the nature of how multiple dielectric layers handle off-axis light. There is the possibility of increased scatter and constructive/destructive interference with off axis rays.
I haven't seen lab reports that show spectral results or photometry of light scatter, so I think those "reports" are anecdotal and suspicious from the standpoint of the physics of reflective surfaces and likely to be related to a justification to keep costs down rather than a true examination of the results of the enhanced coatings.

From the standpoint of failure of the aluminum surface, enhanced coatings should be MORE durable than simple silicon monoxide (which becomes silicon dioxide) overcoating.

What is true, though, is that the slight difference in reflectivity for the enhanced coatings would be sub-visual (i.e.not noticeable), and might not be justifiable from the cost standpoint.

#39 Jeff Morgan

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Posted 27 December 2011 - 02:29 PM

.... so what it really boils down to is the quality of the coating, and most coaters who offer enhanced coatings are pretty good at it. The ones we've tested here were very good.



Are there coaters in the Pacific northwest that offer (and are good at) enhanced coatings?

Shipping mirrors isn't cheap and has to be reflected in the mirror price.

And if you haven't noticed shipping costs have gone up dramatically in the last year or so.

#40 Starman1

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Posted 27 December 2011 - 03:05 PM

Here are some links. There are information articles about coatings as well as coaters:
http://www.alcoat.net/
http://www.majestic-...otectedAluminum
http://c-optical.com/
http://www.clausing.com/
http://www.dentonvacuum.com/
http://www.evaporatedcoatings.com/
http://www.flabegusa...ce_mirrors.html
http://www.galaxyopt...ngservices.html
http://www.llopt.com/mc.html
http://www.majestic-coatings.com/
http://articles.adsa...000303.000.html
http://www.newportlab.com/
http://www.nova-opti...com/Coating.htm
http://www.opticalme...ror Coating.pdf
http://www.opticalme...ing_primer.html
http://www.opticwavelabs.com/
http://www.emf-corp.com/
http://www.astronomy...uide/ag373.html
http://www.quantumcoating.com/
http://www.glasscoater.com/id2.html
http://www.reynardco...lm_coatings.php
http://www.sciencedi...168900204001627
http://www.opticalsp...um coatings.pdf
http://www.gemini.ed...pt-te-g0073.pdf
http://www.page.sann...o/emsultima.htm
http://www.page.sann.../silvertest.htm
http://www.spectrum-...rror-Prices.htm
http://www.youtube.c...h?v=_ToAkH7u3lY
http://www.thinfilms....php#Evaporated
http://www.vaculayer...CFSNQagodOUoxKg
http://zcrcoatings.c...CFRekiQod6y3_QQ

#41 RAKing

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Posted 27 December 2011 - 05:35 PM

Justifying Zambuto's decision not to use enhanced coatings. Apparently his rationale for using only standard coatings. Or at least that is what he used to say. Is he still recommending standard coatings only? I belong to the ZOC yahoo group, but have not kept up with the most recent posts.


Carl Zambuto is not the only mirror maker who uses standard coatings.

I had a long discussion about this with another one of the top quality mirror makers. He told he that he would use enhanced coatings if the cutomer demanded it, but he considered it a "matter of pride as an optician" that he could create a mirror good enough that you wouldn't need any enhancements. He asked me to test his mirror with the standard coatings and if I didn't think it was good enough, he would fix it.

I haven't talked to Carl about this, but I suspect his philosophy is similar. My last two mirrors have come from Zambuto with standard coatings. The view through the eyepiece speaks for itself.

Cheers,

Ron






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