With a number of Dobs going at resonable prices at the moment, I'm looking for opinions on what is considered to have an edge against the competition.
We have :
BINTEL
MEADE
GSO
All state that they have top optics, etc. , but it's hard to really know what you are getting?
Are there any differences in the manufacturing quality of the optics?
If I were purchasing a mass produced 16" dob, I would purchase it from Bintel simply because of the fact if the mirror is a dud (as what happened with me) than they can test it and replace accordingly.
If I were purchasing a mass produced 16" dob, I would purchase it from Bintel simply because of the fact if the mirror is a dud (as what happened with me) than they can test it and replace accordingly.
wouldn't Andrews do that to?
and yeah, GSO make all 3 scopes, so optically there is nothing to choose from, more the design, fit & finish, accessories etc. i know some people are very happy with them, and i have only looked through 2 of the GSO 16" scopes, a lighbridge and a GSO, and both wear shocking optically.
TBH, i wouldnt buy any of them, i would get the Skywatcher "14 with full goto for the same price from Andrews Coms.
I have 16" Lightbridge. With all the mass produced telescopes paricularly the truss tube type collimation is the difference between great performance and mediochre performance. There are quite a few other threads on collimation. The basic tests that are usually the only ones done by most people are only part of the job. Real collimation is much more tedious in getting the wave front in phase so that the full use is made of the mirror. Only a star test diffraction pattern will show you this is OK.
Spoke to Roger at Bintel , Melbourne shop. They have some means to have a look via ronchi and further investigation , but there is no routine bench testing of these scopes before they go out besides collimation. I don't think anyone in the country would offer that service.
It must be so hard to choose when one is expecting so much for so little in the way of quality control. What exactly constitutes a dud with a large low cost mass produced mirror? I guess it would take a statistical analysis of large sample to make a judgment if any particular one is outside the tolerance envelope. The two that I tested including Mohammed's suppled to me for testing by an our much loved local OEM telescope maker were not a large enough sample to make a qualified judgment.
Thanks for the feedback gents.
Well, it appears that purchasing such a scope is a gamble, ...........especially if the structure of the scope needs to be modified or even reconstructed before something near accurate collimation is to be obtained
I had a suspicion that all were made in the same factory and re-branded, but needed some input on that theory.
I know this Chinese made stuff is cheap and consequentially attractive, but I have read the reviews where flimsy plastic parts and components need replacing or modifying.
Only after this has been carefully executed does the optical capability reveal itself......................this is a bummer!
As one person has stated on this thread that the optical performance was shocking when a few of these scopes were looked through, I don't think I can trust shipping over a scope at 2-3 hundred bucks a pop to have to send it back because the optics suck.
As I beleived that larger aperature revealed more in planetary viewing/and or imaging, I'm tending to lean more to a refractor of large aperature???
Your last post poses a question- what do you want to do with the 16"? Visual or photo? Reason being, if for photo, man, you are going to need a BIG mount.
Yes, the larger the apeture, be finer resolution you can obtain. But ultimately it comes down to what is both practical and financially viable.
There are many folks who do planetary imaging with 8", 10" and 12" newt's. Mounts for these are tried and tested, and with quality barlows, provide excellent imaging quality. If you did go down the refractor route, you would still be needing a quality barlow to achieve the necessary magnification.
So where do you want to go, 4" refractor or 10" newtonian for imaging? Similar focal length, but markedly differing resolution.
If money is not an option, you have the 16" Meade SCT!
If visual is more your thing, a 16" dob is still a good option. If you could get the retailer to examine the thing before dispatching it, you are also on a winner with that fellow for service, who ever they may be. Something you may be able to insist on to overcome the tyrany of distance.
Yes, size, size, size
Alex, I see where you are coming from. I have a recently acquired an 8 inch, old Orion F4.4..........massive secondary mirror/obstruction.
At the moment with rough (By eye) collimation there is severe astigmatism even at low power. Could be the no brand 25mm plosslyl that came with it(lot's of C.A. also)?
This could be due to the clamps on the mirror which I noticed where tight when I removed the mirror for cleaning, so I did the same.....tightened them against the mirrors surface, firmly.........mistake?
Using higher powers (again with cheap -ass eyepieces) is a joke.
I know the mirror/optics is better than this......surely?
Cheap eyepieces, such as cheap plossls and wide field EPs, perform best in slow scopes, f/6 or slower. In a fast scope, they will show astigmatism, especially in an f/4.4 scope. No way around that one other than purchasing expensive EPs, from $300 +.
The shorter the focal length of these cheap eyepieces, however, the astigmatism is greatly reduced, but it becomes really hard to use these cheap eyepieces.
Tightening the mirror in the cell is not a good idea, as it distorts the figure. The clamps should just stop the mirror from sliding around as it is moved in altitude.
If the figure in the mirror is distorted by the clamps, using higher powers really makes for an impossible image, regardless of quality of eyepiece.
Relax the clamps a little and retry your high power EPs.
I have an 8" f/4 dob. I use a 30 year old Edmund Scientific 28mm RKE eyepiece- no astigmatism. That is because it is designed for use with a fast scope. This is the only 'cheap' eyepiece that is of low power with bugger all astigmatism. At high powers, this little scope is fantastic. I made its mirror cell, and it is held securely, but not tight. I've pushed it to 260X, beautiful. See what I mean.
I'll relax the mirror clamps this weekend and start looking for a good eyepiece.
Thanks for the heads up on the Plossl's and fast newts......I suspected something foul going on there
What would you recommend as an eyepiece for low AND high power?
I have a 16" home built Truss Dobsonion with which I have had the best views of Jupiter and Saturn I have ever seen
Ask some of the attendies at Astrofest
Can I say that if you want to go down the visual route buy the mirror and build it yourself or get someone to build it for you
that way you control the situation.
Most mass produced telescopes are built to a price not quality
You cannot get a Rolls Royce for a Holden price
cheers
I have a 16" home built Truss Dobsonion with which I have had the best views of Jupiter and Saturn I have ever seen
Ask some of the attendies at Astrofest
Can I say that if you want to go down the visual route buy the mirror and build it yourself or get someone to build it for you
that way you control the situation.
Most mass produced telescopes are built to a price not quality
You cannot get a Rolls Royce for a Holden price
cheers
Ron, I see your point, but what about the optical quality of these Chinese GSO's and BINTELS etc?
Is there a consensus that the optics are good but the scope build is crap???
I am in a similar situation; looking for a large dob to give me the visual thrill that I lost with my 6" since I started AP.
When I understand right than the majority is rather against a 16" factory dob for various reasons especially collimation. Is it then better to go with a 12" GSO (non truss design)?
I am after a large scope that lives in the kitchen near the terrace door (2m roll in/out), that is ready in a minute (apart from cooling), easy to use and offers views of galaxies and nebulae similar to pictures of it.
I was leaning towards the 16" lightbridge but donīt feel like collimating primary and secondary everytime Im gonna use it. Or is it just not the right tool for imaging but otherwise planets look fine (maybe with a barlow)?
Ron, I see your point, but what about the optical quality of these Chinese GSO's and BINTELS etc?
Is there a consensus that the optics are good but the scope build is crap???
Ron, what brand is your mirror?
Rob, You have hit it in one as I suggested buy the mirror or buy the scope and modify yourself.
Collimation of a truss Dob with a mirror cell of the Kreigie design scopes Ie Obsession is a breeze
As I mentioned in your other thread my Mirror is a 16" f 4.5 Meade, bought about ten years ago.
If you buy the mirror seperatly and it is no good then that is all you have to send back, not a whole scope.
I think you can buy the optical kit from GSO
Cheers
I am in a similar situation; looking for a large dob to give me the visual thrill that I lost with my 6" since I started AP.
When I understand right than the majority is rather against a 16" factory dob for various reasons especially collimation. Is it then better to go with a 12" GSO (non truss design)?
I am after a large scope that lives in the kitchen near the terrace door (2m roll in/out), that is ready in a minute (apart from cooling), easy to use and offers views of galaxies and nebulae similar to pictures of it.
I was leaning towards the 16" lightbridge but donīt feel like collimating primary and secondary everytime Im gonna use it. Or is it just not the right tool for imaging but otherwise planets look fine (maybe with a barlow)?
any comments greatly appreciated.
Max, a couple of points, you will not get views similar to the pictures of galaxies unless you go quite large.
Imageing and visual are two entirely different beasts.
you should not have to collimate a scope every time you use it unless you bang it about, but hey after a little while it comes second nature to do it
Decide which one you want to do, Imaging or Visual and go for it
Ron, the BINTEL 16inch F4.5 mirrors claim 1/16 wave accuracy or better..................if that's true, it MUST have a very good optical performance if mounted and supported correctly.
I have noticed that it is very hard to find a ready made 18 point flotation cell for such a large mirror(or any cell for that matter). Same goes for the secondary?????
What gives here?..............do I have to make these ?.............if so, any links?
B.T.W...............how much is Mark's 16'' mirror?
Mark's mirrors are very well priced against other top US mirror makers.
We are talking world quality here. I won't put the price on here because it's Mark's business.
Quote:
Originally Posted by robz
Ron, the BINTEL 16inch F4.5 mirrors claim 1/16 wave accuracy or better..................if that's true, it MUST have a very good optical performance if mounted and supported correctly.
I have noticed that it is very hard to find a ready made 18 point flotation cell for such a large mirror(or any cell for that matter). Same goes for the secondary?????
What gives here?..............do I have to make these ?.............if so, any links?
B.T.W...............how much is Mark's 16'' mirror?
.
Max, a couple of points, you will not get views similar to the pictures of galaxies unless you go quite large.
?????
