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Old 24-05-2018, 07:46 PM
Blackspear (Craig)
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Can't see the Moon

I live on the northern end of the Gold Coast in Queensland, and have purchased a 2nd hand Sky-Watcher Traditional Dobsonian Telescope 254mm/1200mm (10") for Christmas for my 11yr old daughter who wants to be a astrophysicist (at this point in time). The telescope still has 2yrs of warranty (the owner purchased it new from Slacks Creek in Brisbane).


All caps are off, and we can locate the moon with the finderscope, but no matter what we do, we can't see it through the focus tube using a 10x or 25x eyepiece.


I left the telescope outside to come down to temperature for over 30 minutes.


I am seeing a brilliant bright line when looking through the focus tube, it appears in the centre coming from the edge of the angled secondary mirror.


What obvious thing am I doing wrong?



Cheers
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  #2  
Old 24-05-2018, 07:54 PM
StuTodd
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The mirrors need collimating, the primary mirror is way off line to direct the image to your secondary etc.

Many "how-to's" on google but have a look at http://www.skyandtelescope.com/astro...tor-telescope/ for an idea.
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Old 24-05-2018, 08:17 PM
Blackspear (Craig)
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Originally Posted by StuTodd View Post
The mirrors need collimating...

Thank you, now I know what to look for, and it makes sense.


I found this video after reading what you wrote:


https://www.youtube.com/watch?v=8G98RTP6jbY


Does anyone know a good 2nd generation' laser collimator, and can they be purchased on the Gold Coast?



Cheers
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Old 24-05-2018, 08:31 PM
m11 (Mel)
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Hi Craig,

Stu is right in that collimation between the primary and secondary is probably not aligned.

Laser collimation for me makes it easier to do. Laser in the middle of the primary and for the secondary in the bullseye for the laser collimator itself.

Give us an update on how you go and if you need collimating.

M11
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Old 24-05-2018, 08:52 PM
gaseous (Patrick)
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Hi Craig,

I assume you've shifted/nudged the scope slightly when trying to see the moon, and racked the focuser fully in and out to see if you can get a focused image - it doesn't take much for a finderscope to be misaligned with the main scope, so just because you can see it through the finderscope doesn't mean it'll be bang in the middle of the eyepiece. No doubt you probably need some collimation, but I've never heard of a dob being so far out of whack that you can't even get some sort of rudimentary image focused. At this point of the lunar cycle, even a very unfocused moon should present as a fairly blinding light taking up a fair bit of the field of view with the 25mm EP and probably covering the field of view with the 10mm EP.
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Old 24-05-2018, 09:01 PM
Blackspear (Craig)
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Originally Posted by gaseous View Post
I assume you've shifted/nudged the scope slightly when trying to see the moon, and racked the focuser fully in and out to see if you can get a focused image...

Hi Patrick, yes, had 3 of us trying everything. You should have heard the squeals of delight, and the sheer excitement from my little girl seeing the moon through the finderscope, she can't wait to see the moon through the main scope


Cheers
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Old 24-05-2018, 09:06 PM
gaseous (Patrick)
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She's in for a treat! That's great - hope you get it sorted.
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Old 24-05-2018, 10:08 PM
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astroron (Ron)
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Quote:
Originally Posted by Blackspear View Post
I live on the northern end of the Gold Coast in Queensland, and have purchased a 2nd hand Sky-Watcher Traditional Dobsonian Telescope 254mm/1200mm (10") for Christmas for my 11yr old daughter who wants to be a astrophysicist (at this point in time). The telescope still has 2yrs of warranty (the owner purchased it new from Slacks Creek in Brisbane).


All caps are off, and we can locate the moon with the finderscope, but no matter what we do, we can't see it through the focus tube using a 10x or 25x eyepiece.


I left the telescope outside to come down to temperature for over 30 minutes.


I am seeing a brilliant bright line when looking through the focus tube, it appears in the centre coming from the edge of the angled secondary mirror.


What obvious thing am I doing wrong?



Cheers
It also could be that your finder scope is not lined up with the telescope
First thing to do in the daylight is find something like a power pole about a a 100 meters or more away in the main scope using the lowest magnification eyepiece and center it.
25mm,not the 10mm.
Look in the finderscope and see how far out of alignment you are.
With the adjustment knobs on the finderscope align it to the telescope
Not the other way round.
Then you will see if your scope is out of colimation when you can find some stars later on.
I hope this helps.
Cheers

Last edited by astroron; 24-05-2018 at 10:24 PM.
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  #9  
Old 24-05-2018, 10:12 PM
Blackspear (Craig)
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Originally Posted by astroron View Post
It also could be that your finder scope is not lined up with the telescope...

Thanks Ron, I'll try that tomorrow.


I have just ordered a SVBONY 7 Bright Level 1.25” Next Generation Laser Collimator+Adapter Sleeve from eBay:


https://www.ebay.com.au/itm/261854809495



Cheers
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Old 24-05-2018, 10:22 PM
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astroron (Ron)
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Originally Posted by Blackspear View Post
Thanks Ron, I'll try that tomorrow.


I have just ordered a SVBONY 7 Bright Level 1.25” Next Generation Laser Collimator+Adapter Sleeve from eBay:


https://www.ebay.com.au/itm/261854809495



Cheers
Even if your scope is out of collimation the moon should be visible in the eyepiece if your finder is aligned properly.
Don't touch the collimation until you get a bit more confident with the telescope.
Weather can make things like planets and stars fuzzy,so get used to the scope a bit first.
Enjoy your new views into the night sky.
Cheers
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Old 24-05-2018, 11:18 PM
Wavytone (Nick)
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Simpler solution:

Ask here if there’s someone local who could drop by and show you how.
A modest token of appreciation would probably seal it.
Or join a local astro society and take it to one of their members nights.
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Old 24-05-2018, 11:29 PM
m11 (Mel)
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Quote:
Originally Posted by Wavytone View Post
Simpler solution:

Ask here if there’s someone local who could drop by and show you how.
A modest token of appreciation would probably seal it.
Or join a local astro society and take it to one of their members nights.
Second that
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Old 24-05-2018, 11:41 PM
Oddity (Andrew)
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Hi Craig. From the way you describe it, it sounds like the focuser is not functioning.

Does anything happen when you turn the focus knobs? Does the bright light change in size?

Does the focuser/eyepiece move in and out when you turn the focus knob? If not then perhaps it has some kind of focus lock engaged (a thumbscrew you can turn) and/or a focuser traction knob that needs to be tightened. Some focusers/scopes have both, meaning you'll need to disengage focus lock and engage the traction screw.

Last edited by Oddity; 24-05-2018 at 11:53 PM.
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Old 24-05-2018, 11:58 PM
raymo
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It just occurred to me that Skywatcher Newtonians[dobs] have an unusual
focuser/eyepiece adaptor set up, and maybe you are using it wrongly, or not all the parts are there. There is a large black collar about 60mm long with a bevelled end and an opening for a 2" diameter eyepiece at the other end.
This is not used with the 1.25" diameter eyepieces that come standard with the scope. There is a plate with a bevelled side and a short tube for the
eyepiece on the other side. This plate fits directly into the focuser opening,
and is secured by the chrome screws on the side of the focuser. If you are
using the set up wrongly you will not be able to come even close to focus.
raymo
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  #15  
Old 25-05-2018, 12:46 AM
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Quote:
Originally Posted by Blackspear View Post
I have just ordered a SVBONY 7 Bright Level 1.25” Next Generation Laser Collimator+Adapter Sleeve from eBay:
https://www.ebay.com.au/itm/261854809495
Cheers
Just a warning that the cheap laser collimators may need collimating themselves. I have the same one as you ordered and it definitely was not collimated.
It is easy to do, 4 nails in a block of wood and a hex-key will get the job done. Just google "laser collimation v-block".
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  #16  
Old 25-05-2018, 08:19 AM
Blackspear (Craig)
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Originally Posted by Wavytone View Post
Simpler solution:

Ask here if there’s someone local who could drop by and show you how.
A modest token of appreciation would probably seal it.

Thanks for the suggestion, where on the forum would I ask this?


Cheers
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  #17  
Old 25-05-2018, 08:21 AM
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RB (Andrew)
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Originally Posted by Blackspear View Post
Thanks for the suggestion, where on the forum would I ask this?


Cheers
In the General Chat area will be fine.

RB
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  #18  
Old 25-05-2018, 08:24 AM
Blackspear (Craig)
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Quote:
Originally Posted by raymo View Post
It just occurred to me that Skywatcher Newtonians[dobs] have an unusual focuser/eyepiece adaptor set up...

Yeah, I'm out of my depth now, definitely going to need someone who knows how to set up what I have purchased.


Cheers
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Old 25-05-2018, 09:58 AM
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doppler (Rick)
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Skywatcher newt's / dobs have their mirrors setup for astrophotography. My 10" dob needs an extension tube to get focus when using an eyepiece, defiantly don't start messing with the mirrors and collimation yet.
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  #20  
Old 25-05-2018, 10:03 AM
Blackspear (Craig)
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Originally Posted by doppler View Post
Skywatcher newt's / dobs have their mirrors setup for astrophotography. My 10" dob needs an extension tube to get focus when using an eyepiece.

Thanks, yes, I have that extension tube as well, tried adding it, still no go. Time to get some help


My little girl is chomping at the bit to see her present work, and I must say, me too, having seen the craters in the moon with the finderscope, that was just stunning.


Cheers
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