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EIGHT-INCH SHOOTOUT

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#1 Charlie Hein

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Posted 14 July 2012 - 07:07 AM

review of 3 eight-inch telescopes

By Lawrence Carlino

#2 mwedel

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Posted 14 July 2012 - 03:01 PM

Very interesting, fair, and useful review. Many thanks for doing all the work, and writing it up so the rest of us can benefit. :bow:

#3 Scott in NC

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Posted 14 July 2012 - 03:26 PM

Nice review, Larry, and a very interesting read! I've never looked through a Mak-Newt before, and always wondered how they were optically. :waytogo:

#4 David Knisely

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Posted 14 July 2012 - 04:30 PM

Very interesting, fair, and useful review. Many thanks for doing all the work, and writing it up so the rest of us can benefit. :bow:


I dunno about being exactly 'fair'. The Mak-Newt is Intes, which is a premium telescope maker. The others are mass-market and probably can't match the Intes optical quality (kind of like comparing the performance of a Ferrari to a Chevy). Maybe if the Dob's mirrors had been refigured by Lockwood, and an optical window installed, then one might be able to come to some conclusion, but as it stands now, all we can say is that the author compared the scopes. Clear skies to you.

#5 mwedel

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Posted 14 July 2012 - 07:49 PM

Very interesting, fair, and useful review. Many thanks for doing all the work, and writing it up so the rest of us can benefit. :bow:


I dunno about being exactly 'fair'. The Mak-Newt is Intes, which is a premium telescope maker. The others are mass-market and probably can't match the Intes optical quality


All points that Larry acknowledged, frequently, in his writeup. For example:

Having obtained an 8” Russian-built Intes-Micro Maksutov-Newtonian from Astronomics last spring, I was anxious to determine if a standard Newtonian and a Schmidt-Cassegrainian could stand up against its well-documented optical quality.


and, regarding the dob:

This scope was the real surprise of the trio. Despite its bargain price, this conventional Newtonian optic delivered sharp, high-contrast images.


and concluding:

Overall, considering the strengths and weaknesses of all three telescopes, one might conclude that no instrument “blew away” the other two. That COULD occur with a defective unit, pinched optics, bad collimation, or a thermal disaster – but it didn’t happen here. In essence, you do “get what you pay for,” and only each individual’s priorities can determine if a premium instrument is worth its purchase price.


So, since Larry acknowledged that the three scopes come at different price points up front, and still found that no one scope consistently blew away the other two, what part of that is unfair? :shrug:

Or are you saying that it's not Larry's shootout in particular that is unfair, but that any comparison of three scopes at such wide price points would be unfair?

In which case, and speaking as a Chevy driver, I appreciate knowing that the Ferrari did not blow the doors off the other two. My "car payments" are already expensive enough! :roflmao:

#6 jrbarnett

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Posted 14 July 2012 - 09:30 PM

I certainly concur with your conclusion, Larry. A well-made refractor of larger than 5" is more than a match for *any* 8" obstructed scope in my experience, at least on double stars, planets and the Moon. On the other hand, give the Tak and any of those 8-inchers a go on something dim and extended, and see if it changes your ranking (NGC 188 about 4 degrees from the Pole Star, for example).

Regards,

Jim

#7 jrbarnett

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Posted 14 July 2012 - 09:33 PM

Intes is Russian. Ever been in a Russian car? Plane? Tank? I think you're putting too much stock in Intes word-of-mouth marketing and the little pieces of paper they ship with their scopes. Ferraris are Italian. Ladas are Russian. :winky:

Regards,

Jim

#8 stevew

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Posted 14 July 2012 - 09:55 PM

Excellent article.
Although I was not surprised at the results.
As the Lawrence said, if I was only able to own one scope it would be the C8.

Steve

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#9 Mauro Da Lio

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Posted 15 July 2012 - 03:49 AM

I think that comparison has been carried out at too low magnification to be meaningful. I read of 140x on Jupiter and 240x on Mars.

A well cooled scope, decent figured, on fair seeing should be able to get crisp images at higher magnifications. I used to go 400x and more with a GSO 8" dobsonian on Mars, revealing crisp images with details not seen at 200x. Jupiter holds less magnification but still a lot more than 140x (300x and plus were not infrequent with the GSO).

Overall, the magnification that a scope can hold while keeping crisp images (the roll-off magnification, see Mel Bartels' page on the end http://www.bbastrode...atemirrors.html ) is the primary indicator of image quality.

Overall I think that comparing scopes at so low magnification means that the bottleneck is not the scope but some environmental condition such as seeing, local seeing, local thermal disturbances, internal thermal disturbance, and so on.

One question: did the newtonian have a boundary layer extraction fan? It makes a huge difference: http://www.cloudynig...ll/fpart/1/vc/1

#10 rflinn68

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Posted 15 July 2012 - 07:49 AM

I own an 8" & 10" Newt and a 8" & 10" SCT. I just bought the 2 sct's used for a great price thinking I would sell one but I love them both and dont see me parting with this lightweight jewel anytime soon.

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#11 Daniel Mounsey

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Posted 15 July 2012 - 09:04 AM

This is a great comparison because it teaches beginners what really happens in real world situations. Members should take note of this and start making comparisons of their own. There's WAY too much optical theory going on in the forums and way less hands on experience in real world comparisons and it shows. There's not enough reviews like this anymore.

#12 Daniel Mounsey

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Posted 15 July 2012 - 09:06 AM

Very interesting, fair, and useful review. Many thanks for doing all the work, and writing it up so the rest of us can benefit. :bow:


I dunno about being exactly 'fair'. The Mak-Newt is Intes, which is a premium telescope maker. The others are mass-market and probably can't match the Intes optical quality (kind of like comparing the performance of a Ferrari to a Chevy). Maybe if the Dob's mirrors had been refigured by Lockwood, and an optical window installed, then one might be able to come to some conclusion, but as it stands now, all we can say is that the author compared the scopes. Clear skies to you.


Regardless, it helps others understand how certain telescopes compare to others in real world situations.

#13 Jim Rosenstock

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Posted 15 July 2012 - 10:02 AM

Regardless, it helps others understand how certain telescopes compare to others in the real world situations.


Concur. :bow:

#14 Mauro Da Lio

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Posted 15 July 2012 - 11:14 AM

There's WAY too much optical theory going on in the forums and way less hands on experience in real world comparisons and it shows. There's not enough reviews like this anymore.


I totally disagree. Any experience has to be "interpreted" (it is so even when it does not seem). In facts "conclusions" are nothing but "theories". The conclusion that scope A is better than B might be flawed by some factor that has been not recognized (it was the case of boundary layers before Alan Adler for example).

Carrying out comparisons, means trying to set the experiment within a theoretical framework and identifying all the interference factors. Otherwise one might come out with believing that "objects only moved as long as they were pushed" as has actually been the case for nearly two thousands years ( http://csep10.phys.u...e_dynamics.html ).

Were people before Galileo correct? Yet they were doing experiments. The fallacy was they were doing ONLY "interpretation" of the outcome of the empirical data.

#15 Daniel Mounsey

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Posted 15 July 2012 - 01:08 PM

I understand what you're saying and I agree but not entirely. The observer may not know why a certain telescope is performing better of worse than another. It happens sometimes with what little comparisons are made these days but that's not the point. The point is that beginners need to be taught more about what actually occurs in the field. In the meantime, people are throwing numbers around like it's lifes bread. There's plenty of that to gargle in the forums. It's the observers responsibility to get themselves up to snuff on what's going on with the instruments in the field but field testing and comparisons are the REALITY of what is taking place whether the observers know what is going on or not. It may not always be conclusive unless the observer is highly experienced and knows what he or she is talking about but I'd rather see these kind of reviews rather than listening to these continuous lengthy threads from people reading about optical theory, not getting in the field. People are passing judgements about telescopes they have no experience using or comparing and drawing premature "conclusions" based on some stats. So what, anyone can read a brochure. You think all those performance specs on supercars are reality? Not even close. You are correct, but you are also incorrect. I am correct, and I am also incorrect BUT 95% of forums are optical theory NOT actual experience based on enough field comparisons. With that said, it's great to see some comparisons for a change.

#16 tonyt

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Posted 15 July 2012 - 07:30 PM

I think the most important point from the review is that they're all good scopes and observers can be happy with the scope they already own.(assuming it's a decent sample)

#17 azure1961p

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Posted 15 July 2012 - 10:06 PM


I enjoyed Larrys article a lot.

I think the comparisons were fair in that there were not external issues warping the comparisons, ie; one scope over looking a roof another a grassy meadow for example. The scopes are hardly equals but thats what made this review one of the more interesting. I think Larry did a terrific job. He loves his refractors - that I know from previous reviews hes done and done quite well. Still, I never detected an unfair bias that needlessly slighted the other scopes.

Im a big believer that a great factor in leveling the playing field in terms of visual observation is the dedication and persistance of the astronomer. An experienced and seasoned observer often sees more despite CO size, etc etc.

I thought the whole article was a success.

Pete

#18 KeithC

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Posted 16 July 2012 - 03:32 AM

Larry, I had a lot of fun reading your article and it sounds like you had a lot of fun doing the comparisons. I always enjoy it when people do hands on, direct comparisons, in the field. Thank you for sharing your observations with us!

KeithC

#19 Chucky

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Posted 16 July 2012 - 06:16 AM

<< There's not enough reviews like this anymore. >>

Certainly not in American astronomy magazines.

#20 Mauro Da Lio

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Posted 16 July 2012 - 08:17 AM

Filed testing and comparisons is the REALITY under the condition that the "experimenter" perfectly knows what is going on. Otherwise conclusions might establish the wrong cause-effect relation.

It had been so for long time for reflector scopes, addressed as intrinsically poor for high resolution, until the boundary layer phenomenon was discovered.

Knowing from theory that reflection is not different from refraction shuold have forced people making "real life test" to search for another explanation (searching the real cause of poor performance), but that did not happen. So, framing an experiment in a theoretical solid pre-existing background is of paramount importance.

In the case of Larry's test there is a weakness that is worth to be considered: magnification were too low.

#21 Larry Carlino

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Posted 16 July 2012 - 09:28 AM

My sincere thanks to everyone who made comments on my review. A few points do need clarification, especially regarding the use of "too low" magnification and the primary mirror boundary layer effect. To put things in perspective, I have been an active, serious visual observer for over 45 years. I have owned over 150 telescopes in that time and have looked through hundreds more. I have built a dozen or so scopes, including 16, 17.5, 22.5, and 28-inch Dobs. From the late 1960's to the early 2000's, I contributed regularly to the various ALPO planetary sections with detailed visual observations and sketches. The generally poor seeing conditions in Western New York where I reside are somewhat compensated by the blessing of 20/15 vision in my observing eye. I am very familiar with optical physics and can spot an optical system not in thermal equilibrium with ease. My larger scopes are generally equipped with fans and other devices to ensure that a boundary layer on the primary evacuates expediently.
As to magnifications used in the review, my fortunate visual acuity allows for lower powers to be adequate and conformal to less-than-excellent seeing conditions. Please note, that all four of the telescopes in the article have been tested on the night sky and with an artificial star at magnifications in the 400x to 500x range, though this was not mentioned in the review. The result was the same. Nowhere in the review did I say anything about intrinsically poor performance of reflective telescopes; on the contrary, the inexpensive Newtonian put on a fine performance - but it is absolutely NOT the equivalent of an 8-inch refractor. The secondary obstruction, spider vanes, and nature of light itself make this impossible given equal optical quality. Many of my most detailed planetary sketches in the past few decades have been made with 10" and 12.5" Cave Newtonians, so I DO recognize the virtues of this simple, effective optical system. The whole point of this "shoot-out" review was to illustrate that differences in optical design and arcane technical details are secondary to experience, some basic knowledge, and enjoyment of our magnificent universe with the equipment one has. I have no other "agenda," nor can I be relegated to the "uninformed" or "inexperienced" category.
Again, my thanks for all of the kind comments.
For Mauro: Because you have mildly offended me, I'm not going to share my Grand Unification Theory equations with you. (hint: the 6 quark varieties "lock up" the 6 "missing" dimensions from the Big Bang)

#22 KeithC

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Posted 16 July 2012 - 10:09 AM

Larry,

One of the things that I liked most about your review was that it was so gentle. I picked up a keen sense of awe, wonder, fun and discovery....the very things that drew me to this hobby as a child. I applaud your work and would love to see more of it!

KeithC

#23 Mauro Da Lio

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Posted 17 July 2012 - 03:15 PM

Sorry Larry. It was not my intention to offend you. Criticism is not offense.

I disagree with the conclusions and the way they are drawn.

I pointed out that magnification was too low to be meaningful, and I still believe so (despite higher acuity 140x is far lower than the roll-off magnification of 20 cm apertures). By the way I also have high visual acuity but still find advantageous going in the 30-50x per inch whenever possible. If that magnification is not achieved the bottleneck is not the scope (or it is a bad scope).

As for compensating bad seeing with visual acuity, sorry, but that is another incorrect statement in my opinion: seeing degrades the MTF of the scope and you cannot recover lost contrast with visual acuity (you can do somewhat on photography by running deconvolution filters). With an example: take a photo on your desktop, apply a gaussian blur and look it with a magnifying glass: it does not help.

#24 Larry Carlino

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Posted 17 July 2012 - 05:30 PM

Mauro,
If you would please re-read my last response, you will see that I DID use magnifications of 400-500x and found the results to be the same as for those obtained at 240x(30x per inch of aperture). This was not mentioned in the original review as I wanted to give an impression of the telescopes' performance at powers normally used under mediocre seeing conditions, something, unfortunately, many of us in the NE U.S. are plagued with. I stand by my original conclusions.
I absolutely did not say or imply that visual acuity compensates for poor seeing conditions. Excellent visual acuity, however, DOES allow the use of somewhat lower magnification to obtain the desired angular resolution. That is a scientific fact.

#25 grom

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Posted 18 July 2012 - 08:09 AM

This is a great comparison because it teaches beginners what really happens in real world situations. Members should take note of this and start making comparisons of their own. There's WAY too much optical theory going on in the forums and way less hands on experience in real world comparisons and it shows. There's not enough reviews like this anymore.

I couldnt agree more. Great article.

I disagree with the conclusions and the way they are drawn.

I pointed out that magnification was too low to be meaningful, and I still believe so (despite higher acuity 140x is far lower than the roll-off magnification of 20 cm apertures). By the way I also have high visual acuity but still find advantageous going in the 30-50x per inch whenever possible. If that magnification is not achieved the bottleneck is not the scope (or it is a bad scope).


And this is an example of the "way too much optical theory". Mauro, you can throw all the theory you want, and you probably will be right theoretically. However, in my experience of years using scopes between 3" and 8", the vast majority of Jupiter observations I settle for less than 200x, in order to get the most pleasing image. So, I am not surprised at all the author used 140x.

In this other 5" apo shootout (link below), Jay Reynolds Freeman states that, on Jupiter, "We all independently settled on magnifications between about 125x and about 175x as providing the best views".
http://www.cloudynig...php?item_id=506

So, again, it is practical experiences at the eyepiece what I sometimes miss in the forums, not theory.






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