It appears that a large proportion of GSO dobs are shipped from the factory suffering from astigmatism due to either or both secondary and primary mirrors being flexed by being too tight in their holders.
Mine, Dave47Tuc, Icemans and Migs GSO dobs all had this issue.
If you dont get nice circular rings on a startest, and nice tight round stars when in focus its well worth the effort of checking the the mounting of both mirrors and ensuring they are not pinched in their holders.
Im a bit dissapointed Bintel didnt pick these issues up for Mike and Dave.
Mike I'll get a howto on this out this weekend if Im not made to work again.
Well I finally got to send some starlight down the tube and test out the optics.
From a 5 minute test, it's a great improvement. I noticed it instantly, most noticeably on the moons of Jupiter. Last weekend, Louie was saying he was seeing double of the moons.. i wasn't seeing double, but there was a lot of flaring off the moons and it was impossible to bring them to sharp focus without comet like trails or flaring.. and it wasn't coma - was using Louie's 7.5mm Tak LE and it exhibited it in the middle of the field as well.
Tonight, I was able to bring the moons to crisp sharp dots without flaring off the side. Using my 9mm GSO plossl, defocused inside and outside revealed showed virtually the same shape.. collimation was a tiny bit off but not by much. Splitting Alpha Centauri and Alpha Crux was very easy, with bright straight diffraction spikes and no flaring.
Very happy..
Thanks again to Louie, George and John for the help and advice.
In defence of BINTEL you only find these things under the stars and If the ones they looked through were good you might not know of this problem. Im shaw they would like to know about It for future sales .
Thats a fair enough statement Atalas.
The QC in the factory is really at fault not Bintel. I had no real issue with my optics straight out of the box once it was collimated.
So its a bit of a hit or miss affair.
Originally posted by slice of heaven Thats a fair enough statement Atalas.
The QC in the factory is really at fault not Bintel. I had no real issue with my optics straight out of the box once it was collimated.
So its a bit of a hit or miss affair.
Slice
Slice,
One thing I have learned about GS is that they are reasonably quick to address issues with their scopes. This is evidenced by the number of design, manufacturing and specification changes that have been made in the 5 years these scopes have been imported into Aus for. The overtight secondary holder problem was fixed by GS once they became aware of the problem, unfortunately Mike just happened to buy a scope from 1 of the batches that suffered the problem. Current manufacture GS scopes don't have this problem
Sorry, One more thing. The astigmatism issue had nothing to do with QC, it was a design spec fault. All of the secondary holders were specked marginally undersize or the mirrors oversize, 1 of the 2. GS's quality control is very good for a Chinese/Taiwanese mass production organisation, it is way better than Synta and the other Chinese optics manufacturers. I am yet to find a GS dob with a "BAD" mirror after minor issues were resolved. On the other hand some of the GS mirrors are excellent, my own 10"/F5 GS mirror is an absolute cracker.
These GS people seem to be right on to things John ,Its good to hear that they want to give people a good product for there money .
You know yourself John It has been the missing ingredient in all but the higher quality gear. Their optics in these telescopes are the perfect proof. Can't wait to see where these people go over the next few years.
Aus
I was thinking that maybe they fixed the problem after I removed my secondary and it slipped out nicely. Then I read Starklers post near the top of this page. His and Icemans scopes were purchased last year ,I'm guessing, Daves and MiGs were purchased April and Feb this year. Mine was purchased in March this year.
Maybe Bintel still had some scopes with pinched secondaries?
But MiGs was purchased from Andrews, as was mine.
So there is still an issue with QC at the factory.
Throw in the fact that these scopes are still nowhere near reasonably collimated from the factory shows their not listening hard enough, if at all. I think after 5 years someone might have mentioned this to them by now.
I have no qualms with their optics,as I've stated before, its the overall package thats a concern. Its great to have decent ap scopes available at a price thats affordable . But if someone buys one that doesnt know how to address the issues then they will be disappointed.
When it comes to tools, instruments and equipment I'm a CRITIC.
Back on subject, I dont think most people take startesting their scopes serious enough.
Regardless of which collimating tool/tools you use the only real test of how good your scope is performing is the startest.
Someone posted a half decent startest diagram(or a link to one)
to show the problems. Its a quick diagnostic check of your optics and it costs absolutely zilch to do. And it takes no time at all to do. It also shows how good your seeing is for the night as well.
The better the seeing ,the better you can assess the optics. Even during poor seeing I believe you would pick up serious faults .
Everyone wants the best out of their scope and the startest is the best method I've found for ensuring this.
Throw in the fact that these scopes are still nowhere near reasonably collimated from the factory
I'm sure the secondary can probably be lined up quite well at the factory, but the primary will never be properly collimated by the time it reaches your door, after travelling from Taiwan, to Sydney, to your door.
Collimation can be thrown out just by transporting to a dark site in the back of the car, along with temperature differences etc, I wouldn't be too hard on GS - I'd expect it to be pure luck if the scope arrived at your door collimated, even if Bintel or someone does it in their shop after receiving shipment.
I agree that a startest can be quite beneficial for fine tuning, but I think that there are some collimation problems that just won't show up in a startest. My opinion is to use tools first to get as accurate as they allow, and then finetune/check with a startest.
I Agree Ice
You cant expect perfect collimation but having to move a secondary 20mm up the scope is not fine tuning.
Yes, you need tools to collimate the scope first but a pinched mirror would have to show up in a startest IF its affecting your image.
Maybe I am Harsh on gs but like I said "I'm a critic " lol
Hi again chaps,
I dont know, but just in case anyones still interested in the curved types of spiders used in my pics - heres a great article from
CN http://www.cloudynights.com/item.php?item_id=511
I havent taken many pics thru f6 8" dob to show you quality - but here is a rough single shot of mars from august 03 - taken with a 35mm film camera on a tripod /105mm lens pointing from a distance into a 32mm EP, in the backyard - the film is fuji NPZ 800 so not known for good reds ssoooo - colour is in important in planetary views of course :-)
re star testing - they arent that many nights in a year that are good enough for a quality star testing as many of you know - so can be hard - specially with tube currents ect. But on the whole you young astronomy enthuisiasts are soooooo lucky today - When i was young (many many moons ago) a quality telescope was like owning a rare maserati! I didnt get to look thru a good one till i was 30! (not to mention the internet for goodness saake)
Same in just about every area EP's everything (dont get me going on music related equipment/help) - you are sooo spoilt - Large apertures for 300 bucks indeed LOL
Cheers
Fringey (wheres my walking frame?) (the generation before me was raised on bread and drippings!)
