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Discovery vs. Zambuto Optical Shoot-out

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#1 Olivier Biot

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Posted 25 November 2011 - 03:46 PM

Discovery vs. Zambuto Optical Shoot-out

By Tim Neubert.

#2 gatorengineer

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Posted 25 November 2011 - 08:48 PM

Pictures of both scopes would have been interesting. Was the custom a home brew? Relative cage ID's and cage heights. Rear end mirror box open or closed. Shrouds.... All of these things and this is literally a stream of thought list could have made differences. No slight to Carls optics in anyway, but fair needs to be fair....

#3 Daniel Mounsey

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Posted 25 November 2011 - 09:46 PM

Actually Discovery makes some pretty nice mirrors. I've tested several and was quite surprised. They're just an inch too thick though and they need to be that way for counter weight issues from what they told me when I visited the factory. I told them they really should thin their mirrors down. Really nice people though. All my scopes are Zambuto and Taks and that's enough to put a grin on my face. :grin:

#4 James Bielaga

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Posted 25 November 2011 - 11:44 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

#5 deepskydarrell

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Posted 26 November 2011 - 01:27 AM

Thanks for the comparison Tim.

Wished you would have tested it on more objects. Such as the faint companions of NGC 7331, or Sephan's Quintette, or even (in winter) NGC 2024-- the Flame Nebula --- How would they both perform with the bright star Alnitak just out of the field. Or even the central star in the Ring.

It would be useful to hear more on this.

Thanks.

DSD.

#6 Jeff Morgan

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Posted 26 November 2011 - 12:18 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



Certainly a longer target list would be interesting, but the logistics of getting the weather, people, and equipment together (not to mention the self esteem of the Discovery owner) all need to be considered.

On the brightness, by my math it looks like a 7% light gathering difference. That should be subtly noticeable all by itself, but the large difference in coating age (7 years and in favor of the larger aperture) would be an even bigger factor. Presumably, the diagonal mirror coatings are of the same age as the respective primaries.

But most revealing was the consistent sightings of the faintest stars which were not visible in the larger aperture. That would indicate to me the smaller aperture was doing a better job of getting all the light on target, and not smearing portions of it randomly around the field.

#7 chollman

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Posted 26 November 2011 - 01:04 PM

If you add pricing as the eight criteria. Would that make the discovery mirror more attractive being that it is $1000.00 cheaper? Charlie

#8 Starman1

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Posted 26 November 2011 - 02:07 PM

The brightness difference can be easily explained as the standard coatings on Discovery mirrors are enhanced, whereas Zambuto mirrors always have standard coatings.
The visibility of faint stars is often determined by superiority of focus, and the Zambuto optics may have had a superior Strehl ratio, putting more light into the star's spurious disc, and, hence, making fainter stars more visible.

I discovered the same thing when using a Paracorr. It obviously cuts the light by a tiny percentage, but fainter stars were visible WITH the Paracorr than without for exactly the same reason--a better concentration of the star's light in a tiny point.

So the results, to me, imply that, whereas the Discovery was an excellent mirror, the Zambuto was a tad better.
This seems to conform to what I've seen through the years.
My current mirror is from the Ostahowski era of Discovery and my next scope will have a Zambuto mirror.

No question the Discovery optics are a bargain among the premium mirror makers. It would be interesting to know if the Discovery mirror was from Terry Ostahowski, or made after that period.

#9 Sean Cunneen

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Posted 26 November 2011 - 02:14 PM

A great comparo, truly enlightening! You always wonder exactly what you are going to get with those mirrors ground with pixie dust... No I have an idea!

Sean

#10 jrbarnett

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Posted 26 November 2011 - 02:32 PM

Thanks for the write-up.

Do you happen to have notes as to which eyepieces were used in each scope for the observations of each target?

Regards,

Jim

#11 Tim Neubert

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Posted 28 November 2011 - 10:36 AM

Thanks for the feed-back guys!!

As for comparing on planets, Saturn was very low in the sky when we did the comparison and just wasn't worth it.

We used both eyepieces (Explore-100 degree and Ethos) on each target. We spent a lot of time back and forth between scopes on each target moving each eyepiece back and forth in an attempt to eliminate variability. We should have also done and Ethos versus Explore Scientific shoot-out as well!!

The differences between the optics was subtle but clearly observable. I actually owned the Discovery and I have to say it is amazing the quality you get for the money with Discovery. The owner of the Zambuto scope was truly taken by surprise. He thought it wouldn't be much of a comparison and was really impressed with views the Discovery produced.

One other thing to take into account is that this only one comparison and it is nearly impossible to take out all the variability. So, get out there and do a comparison of your own. Comparisons from multiple owners that show a clear trend is the only way to prove that Zambuto optics consistently outperform the competition by meeting the seven criteria.

Sincerely,

Tim Neubert

#12 Project Galileo

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Posted 28 November 2011 - 12:57 PM

Thanks for taking the time to compare these two mirrors. Very interesting and insightful.

#13 LivingNDixie

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Posted 28 November 2011 - 12:58 PM

Put the scopes through this on the planets or Moon, and I would expect the Zambuto will pull further ahead. And I have owned a Discovery and love the products they make.

#14 bob irvin

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Posted 28 November 2011 - 03:38 PM

Thanks for putting the review together Tim. I know it takes time to do the work and write it up and it's a value to us readers. :bow:

bob

#15 Qi Dang

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Posted 29 November 2011 - 04:16 AM

This should be a double blind comparison.

#16 hoof

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Posted 29 November 2011 - 10:41 AM

A few thoughts:

1) Were the two 'scopes equally thermally acclimated? If the Discovery is considerably thicker, it could have had some extra thermal distortion effects degrading it's contrast if it hadn't had time to come to ambient temperature.

2) What is the status of the secondaries? Even the best primaries can have their capabilities degraded by a less-than-stellar secondary. If the secondary was noticably better on the Zambuto 'scope vs the Discovery, this alone could explain the difference even if the Discovery's primary was actually better.

Without knowing the situation for the above two situations, it's harder to really judge the situation.

Finally, a dimmer image (due to smaller area and more-degraded coatings) could actually increase perceived contrast in certain situations.

Why? Because the background would be darker. I have observed many times DSOs that were more easily observable when the magnification increased. Since this darkens the overall view, this seems counterintuitive, but it's the darkening of the background vs the DSO that can make the difference. This could easily be affecting the results between the two optics in this test.

Finally, we are only observing with one sample of each manufacturer's optics. That means we can only know how these particular optics performed, which tells us almost nothing about how any other optics would compare from both manufacturers.

So I'd say we can't draw any real conclusions yet based on this comparison. Both are obviously great optics. But which one is better? Hard to tell.

#17 Tim Neubert

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Posted 29 November 2011 - 03:27 PM

Jonathan,

You are correct that this only one comparison and it is nearly impossible to take out all the variability. So, get out there and do a comparison of your own. Comparisons from multiple owners that show a clear trend is the only way to prove that Zambuto optics consistently outperform the competition by meeting the seven criteria.

#18 Jeff Morgan

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Posted 29 November 2011 - 04:18 PM

Finally, we are only observing with one sample of each manufacturer's optics. That means we can only know how these particular optics performed, which tells us almost nothing about how any other optics would compare from both manufacturers.


Small sample size is an inherent problem in testing of astro equipment. Especially since the effort and expense of statistically proper tests are immense, and the profit motive none. If there was a telescope in every garage, maybe someone like Consumer Reports would step in. But of course we know that our small hobby will never generate that type of interest. (Their loss, no?)

But let me turn this around for you: When a significant "sampling" of amateur astronomers over a number of years are universally praising the work of a particular optician (Christen, Zambuto, Royce, etc) in comparison to mass-produced work, and then back up words with a product order, there is something real and significant going on.

I suppose it is possible that very rarely one of the premium makers has a "bad one" get out of their shop. And mass-produced mirrors can be consistently good, and be good value for the money. Maybe a random selection could result in a mass-market optic equalling or bettering a premium one (manufacturing is after all a statistical process). But if you think the odds of this are any more than "remote" you're kidding yourself.

Each type of optic has a place in the hobby, and free-market pricing has sorted it out - as it always does.

#19 Tim Neubert

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Posted 30 November 2011 - 10:15 AM

Jeff,

Your right in saying there are clear levels of optics and that their optical performance directly correlates with their price tag. However, what I am trying to answer is different.

My question is about the Zambuto seven criteria. Do they translate to an observable difference in contrast over other premium optics? Does perfection of the small scale features of the mirror truly make a difference? This is a hard concept to grasp and something that I really only noticed on those special nights of good viewing when I saw detail in specific targets that I never saw before with other optics on equally good nights of viewing. Others have had similar experiences, but is it real?

Tim Neubert

#20 Starman1

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Posted 30 November 2011 - 11:58 AM

Jeff,

Your right in saying there are clear levels of optics and that their optical performance directly correlates with their price tag. However, what I am trying to answer is different.

My question is about the Zambuto seven criteria. Do they translate to an observable difference in contrast over other premium optics? Does perfection of the small scale features of the mirror truly make a difference? This is a hard concept to grasp and something that I really only noticed on those special nights of good viewing when I saw detail in specific targets that I never saw before with other optics on equally good nights of viewing. Others have had similar experiences, but is it real?

Tim Neubert

It's hard to evaluate.
1) Extremely good seeing, where differences in premium mirrors are in evidence, are rare.
2) Cooling, collimation, and cleanliness have to be identical in the two scopes.
3) The difference would result in a "slight" increase in contrast only, which would take some time to establish.
Star images might be the easiest to use to see a difference.

#21 BillP

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Posted 30 November 2011 - 05:03 PM

Tim,

Excellent report :waytogo:

Thanks!!

#22 Mr. Bill

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Posted 30 November 2011 - 05:51 PM

Reminds me of the old saying..."one robin does not herald Spring..."

n of 1 is not a significent sample...period.

:p

#23 Starman1

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Posted 30 November 2011 - 06:27 PM

Reminds my of the old saying..."one robin does not herald Spring..."

n of 1 is not a significent sample...period.

:p

Bill,
You're right. I've looked through about a dozen Discoverys, most of the Ostahowski mirror vintage, and almost twice that number of Zambutos over the years.

Collimation and cooling have not been optimum in most of the scopes I've looked through. Judging from what I've seen, I would not say that I was all that impressed with Zambuto mirrors in most of the samples I've looked through.

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.

The difference hasn't been overwhelming, but the star test reveals a slightly better correction, in general, on the Zambuto mirrors in the optimized scopes.
Ostahowski's mirrors are right up there, though. The ones I've seen were definitely in the "premium" class.

What I find it hard to understand, though, is why not everyone who pays the price of a Zambuto mirror bends over backwards to learn collimation or even use fans to cool the mirror! That's a little like buying a Ferrari and never exceeding 30mph.

#24 Wing Eng

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Posted 30 November 2011 - 07:20 PM

I tried a somewhat similar "Shoot-out" that involved comparing my 12 year old Celestron Starhopper 8 inch f/6 with my 24 year old Coulter Odyssey Red Tube 10.1 inch f/4.5. The images of globulars and open clusters seems about identical for the brightness of these objects - probably due to the coatings on the Celestron being only half the age of the Coulter - even though the Coulter has around 59% more intrinsic light gathering ability.

#25 Mike B

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Posted 30 November 2011 - 09:49 PM

Hi Wing- have seen & read your "web" reviews for a long time! Glad to see you here on CN- your input is appreciated!
:grin: mike b






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