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  #1801  
Old 08-09-2017, 01:26 PM
m11 (Mel)
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Hi Forge,

I am still new as well. My view on collimation is to align the primary and secondary mirror to achieve a good focus. The lower f number requires more accurate alignment. I use a laser collimation tool as it is easier for me. Just need to ensure the laser is pointing to the middle of the primary mirror and looking from the back of thr scope in the bulleye of the laser collimation tool.
If the alignment is really bad then you wont even get a decent image to focus with the scope.
Due to the dob design, the mirrors will enventually move over time depending on how often and when you move the scope.

Hope it helps.

M11

Quote:
Originally Posted by Forge View Post
Hi all,

I'm very new to this and only just put together a collapsible dobsonian 8. Waiting for a clear sky in Melbourne to give it a go.

I have a question - what is collimation and how often should you do it? From what I've understood it's simply a process of aligning the eyepiece and the primary mirror. Is that correct and do I absolutely need a laser accessory to do it as a beginner (it was suggested to me by someone else)? Also why does it need to be routinely done i.e. why does it go out of alignment after a while?

Thanks
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  #1802  
Old 08-09-2017, 03:42 PM
Forge
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Thanks m11, I'll see if I can collimate without buying the laser tool
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  #1803  
Old 08-09-2017, 04:43 PM
m11 (Mel)
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Nps, i usually collimate before every viewing as it usually a bit off.

A couple of times when i have pick up a second hand dob its completely off and it took awhile to align.

My philosophy is to minimise time spent on setting up as the wife anf kids really kills me on my viewing time

M11


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Thanks m11, I'll see if I can collimate without buying the laser tool
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  #1804  
Old 09-09-2017, 07:13 AM
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doppler (Rick)
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If you tighten the lock bolts carefully but firmly enough the collimation shouldn't need adjusting very often.

I find the best tool is a Cheshire eyepiece.
http://www.ebay.com.au/itm/142458779558

You can make a basic one yourself out of a 35mm film canister. Drill a very small hole in the exact centre of the cap (there is a dimple there that makes it easy) and cut the bottom of the canister, these are a good fit to an 1.25" eyepiece holder.
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  #1805  
Old 09-09-2017, 06:24 PM
Forge
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Thanks doppler. Another question, as I continue to wait for a non-cloudy night in Melbourne , with something like a Dobsonian 8, would I be able to see something from a backyard in the inner-suburbs of Melbourne?

Or do you have to be somewhere, where it's pitch dark with no street lighting around?
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  #1806  
Old 09-09-2017, 10:53 PM
m11 (Mel)
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Hi Forge,

With a 8 inch the planets - Saturn and Jupiter will be visible with good detail. Bright open clusters like jewel box , southern pleaides and globular cluster 47 tucanae and omega centauri.

Other objects will be pleasing which you will discover which objects you like to view.

Mel

Quote:
Originally Posted by Forge View Post
Thanks doppler. Another question, as I continue to wait for a non-cloudy night in Melbourne , with something like a Dobsonian 8, would I be able to see something from a backyard in the inner-suburbs of Melbourne?

Or do you have to be somewhere, where it's pitch dark with no street lighting around?

Last edited by m11; 11-09-2017 at 11:43 AM.
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  #1807  
Old 11-09-2017, 10:38 AM
Forge
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Thanks again m11. Last night was one of the first relatively non-cloudy skies in Melbourne, so we took it out for a look with no luck.

Just to recap - the first thing we did after assembly was look through the eyepiece at a distant object and then made sure the crosshair in the finder's scope was centered at the object. This was during daytime last week. Last night we left the telescope out in the backyard for an hour to let it cool, and stayed outside ourselves for a good 10 minutes to let our eyes adjust to the dark.

The moon wasn't about so I used the finders scope to point to the brightest star in the sky (there were quite a few) and looked through the eyepiece but couldn't see anything. Infact we couldn't see any light at all through the eyepiece, even after adjusting it a bit.

What could I be doing wrong? I've read references to light pollution maps on these forums. Could it be that the street lighting could be affecting the viewing? How can I check?
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  #1808  
Old 11-09-2017, 10:50 AM
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iborg (Philip)
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Hi Forge

If the focus is way off, then you won't see any stars. Did you move the focus from one end of its travel to the other? If not, try it.

If still no luck, try looking at the moon. That is big enough and bright enough, that even without a finder, you should be able to point the scope close enough to see the light at least, then adjust focus.
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  #1809  
Old 11-09-2017, 11:39 AM
Forge
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I certainly did play with the focus from one end to another. I also had a pair of binoculars with me and I could definitely see a few stars from it, so I'm guessing the ambient light pollution from street lighting couldn't be a major factor when I use the telescope?

I'll try the moon when I get a chance.
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  #1810  
Old 11-09-2017, 11:48 AM
m11 (Mel)
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Hi Forge,

Street lighting and cooling aside, you should be able to see objects, just with less detail.

It sounds like you collimation is off a bit. I would recommend checking your collimation.

Mel


QUOTE=Forge;1334716]Thanks again m11. Last night was one of the first relatively non-cloudy skies in Melbourne, so we took it out for a look with no luck.

Just to recap - the first thing we did after assembly was look through the eyepiece at a distant object and then made sure the crosshair in the finder's scope was centered at the object. This was during daytime last week. Last night we left the telescope out in the backyard for an hour to let it cool, and stayed outside ourselves for a good 10 minutes to let our eyes adjust to the dark.

The moon wasn't about so I used the finders scope to point to the brightest star in the sky (there were quite a few) and looked through the eyepiece but couldn't see anything. Infact we couldn't see any light at all through the eyepiece, even after adjusting it a bit.

What could I be doing wrong? I've read references to light pollution maps on these forums. Could it be that the street lighting could be affecting the viewing? How can I check?[/QUOTE]

Last edited by m11; 12-09-2017 at 08:43 PM.
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  #1811  
Old 11-09-2017, 12:46 PM
Forge
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Oh thanks! A colleague of mine with a bit more experience than me is coming over to help me out. However if we still aren't able to fix the problem I might take you up on your offer

Are there community gatherings organized from this forum by the way? I reckon I'll learn a lot by meeting others.
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  #1812  
Old 11-09-2017, 12:51 PM
m11 (Mel)
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Great to hear. I remember starting off and it took me 40mins to find the full moon. Really frustrating and it took me awhile to learn what worked for me. Still learning as i go along, its a rewarding hobby but it requires patience between work, family, weather and motivation.

Best if you keen is to check out the asv/mpas.

No problems

Mel

Quote:
Originally Posted by Forge View Post
Oh thanks! A colleague of mine with a bit more experience than me is coming over to help me out. However if we still aren't able to fix the problem I might take you up on your offer

Are there community gatherings organized from this forum by the way? I reckon I'll learn a lot by meeting others.
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  #1813  
Old 11-09-2017, 05:19 PM
gaseous (Patrick)
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Ambient light pollution aside, you may find your finderscope has shifted slightly since you first aligned it. I have an 8" collapsible dob also, and find the finderscope can move a very considerable amount between viewing sessions, even with a lot of care taken when moving it. This may account for your difficulty in finding a star through the eyepiece after finding it in the finderscope.
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  #1814  
Old 01-10-2017, 08:16 PM
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NewBee101 (Robert)
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Hi all,
Got a inquiry for those that use Stellarium to guide their mounts. I have just configured Stellarium to giude my EQ6-R mount, when i pick a target off the comp'(Stellarium)screen enter it into the hand controller the mount will slew straight to the target, when i pick an other target and use ctrl+1 the mount will start and stop,start and stop, slewing for at least 30 seconds or more then it will decide to slew continues to the target, to me this does not seem normal.
Can anybody offer any reasons for this, or is this normal? I have watched Yu Tube vid's on the configuration and there is no hint of this start and stopping.
Rob
@ Stawell
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  #1815  
Old 05-10-2017, 03:31 PM
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Jen
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Quote:
Originally Posted by NewBee101 View Post
Hi all,
Got a inquiry for those that use Stellarium to guide their mounts. I have just configured Stellarium to giude my EQ6-R mount, when i pick a target off the comp'(Stellarium)screen enter it into the hand controller the mount will slew straight to the target, when i pick an other target and use ctrl+1 the mount will start and stop,start and stop, slewing for at least 30 seconds or more then it will decide to slew continues to the target, to me this does not seem normal.
Can anybody offer any reasons for this, or is this normal? I have watched Yu Tube vid's on the configuration and there is no hint of this start and stopping.
Rob
@ Stawell
G'day Rob
You might get a better response if you post this question starting a new thread instead of in this beginners thread 👌 But your problem sounds familiar to me when I'm choosing targets near the South Pole. It seems to be a glitch there that annoys the hell out of me I'm not sure if your having this issue all the time or is it just certain targets? And another issue I can have sometime is that my ascom location doesn't match my Stellarium location so check these. Every time I move location from home to snake valley I have this issue it's only taken me a few years to work that out hahahaha I'm on to it now cheers and good luck

Jen
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  #1816  
Old 05-10-2017, 04:36 PM
that_guy (Tony)
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personally i dont use stellarium for eqmod control. You might have better luck using cartes du ciel? I hear stellarium can be troublesome when it comes to telescope control.
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