collimination on newtonian

[hookedonsaturn]

I downloaded everything i could find for colliminating my 8" newtonian.Step by step i followed everything getting everything to look like it did in the pictures.The first problem i found when adjusting the secondary mirror was there was no way i could get the circles in the center of the eyepiece.To do this took about 2mm of shim under the side faceing the primary. Finaly aligned everything looked good so i proceeded to the primary mirror and a few turns and mister black dot was perfect in the middle.Feeling pretty proud for doing such a good job on just my 5th try i eagerly waited for saturn.
Saturn arose and what a shocker all i could see was about 1/2 of saturn,no rings but lots of blurry fuzz around the bottom. Came back in here and found Andys site with video. seems like what i had printed out neglected to explain clearly that after adjusting secondary to middle of viewfinder to align secondary with primary and then set the tip.I was under the impression of stright line bounce and not realizeing the primary is just a tip to align it to the secondary for even bounce.

looks like its Back for another day of frustration tomorrow.I wonder how many trys it will take or if the screws will wear out first.

[astronut (John)]

Watch Andys video a few times, it's the most common sense approach to collimation. It will eventually all make sense

[laika (Brenton)]

Hookedonsaturn,
Not sure where you live but if you have a good telescope shop near by with friendly staff go an ask to be shown what it is ment to look like.
The weekend just gone I visited Bintel in Melbourne (1.5 hours from home) to pick up more goodies including their lazer collimator. I asked how it should be used and 20 mins later I had been shown what a baddly collimated scope looks like what to adjust and when and then what it looks like when the job is done. Thanks guys what a great help.
I now have the cheshire eye piece and the lazer collimator and both are prized pieces of equipment in my tool box.
The advice above is good, watch the video several time to get the idea of what it should look like. From the video instructions after you first adjust your secondary the view through the focuser tube may not show the primary and secondary perfectly alinged. Make sure your secondary miror is central in the focusor and then adjust the tilt screws on the secondary to put the primary centre dot in the centre of the secondary miror, dont worry if the whole picture does not look central. Once that is done then adjust the primary miror screws to bring everything into alingnment.
MOST IMPORTANT WATCH THE VIDEO SEVERAL TIMES.
I had problems trying to collimate but when you are shown what to look for you think to yourself how easy is that.
The tools mentioned above are a great help. Last night was the first night that I was able to get out with my scope due to rain and cloudy nights and what a difference a propperly alinged scope makes.
I hope my ramblings may be of some help, take it one step at a time and above all just have fun.

[Mr. Subatomic]

Hey guys,

I too have a Dob (10") and I just know that the time is approaching (probably very soon) when I will have to collimate my mirrors. I'm a complete newb at it, never done it before, but this video sounds fantastic! Could anyone give me a link to where I could find it?

Also, how often should a telescope be collimated, or is something that is to be done when it NEEDS to be done?

Cheers.

[erick (Eric)]

I think this one:-

http://www.andysshotglass.com/introduction.html

See "Collimating a Newtonian Telescope" on the right hand side.

It's a big download and the site is Flash intensive.

Collimating - how often? Depends: Type and size of scope; truss versus solid tube; whether it is moved around? transported? But generally it should be checked everytime before use. Probably secondary mirror tilt and primary mirror tilt need to be tweaked.

Also search for "barlowed-laser" for a more accurate technique for primary mirror tilt.

With the right tools and an understanding of what is happening, there is nothing to it for observing use. I suspect for astrophotography, much greater accuracy (and therefore the very best tools) is required.

[hookedonsaturn]

Watched andys video several times and followed it right to the t. everything seems right.I do have 1 question . If after collimination i line up on a radio tower about 3 km away and get clear image on small parts like wires and bolts would that be classified as set or do i have to wait till dark to check with stars

[laika (Brenton)]

Hookedonsaturn,
Good to hear that every thing is ok. I would also to a star test when you are next out before you start any serious observations, doesnt take long and it just tweeks the primary mirror into exelent alignment.

[hookedonsaturn]

Here we go again back to square 1.Set up tonight for a look at saturn and what i figured was going to be just a tweak here and there.What a shocker i had exactly the same image i had last night.For some reason i am getting the impression that this scope is just utter junk.The way it came out after being set up in shop as display model.The secondary mirror when you looked through viewfinder was way off center.Is this normal? when you set it to be centered the secondary is just about back to the spider leaving very minimal adjustment movement on the adjusting screws.Looking through the viewfinder you are actualy looking more towards the spider side unless you shim the primary side.Is this normal? I guess what i am trying to find out is if anyone else with newtonians has had any of these problems colliminating .
It just doesnt seem to matter how close i follow the instructions in here and Andys i always come back to the same crap image.Even though i have made up my mind on a 12 inch dob I would still like to get this one properly colliminated so when i sell it to some newbie he/shewill not have these same frustrations.

[erick (Eric)]

I could only comment that Saturn is quite low down now, so looking at Saturn isn't a great test - that's a lot of atmosphere to look through. How does Jupiter look when it is high in the sky - around 10-11pm? Are you seeing some surface details at high magnification - a bit of banding should be seen if seeing is OK. How do stars look with the star test as you wind the focusser in and out around the focus point? Are you resolving the double stars at Alpha Centauri?

Beyond that, it sounds like there is something very wrong with the mounting of the focusser. How does it look when you work your way around looking at it from every angle? Does it look "square" to the OTA? Take a couple of photos and post them here - maybe someone can spot the problem.

[hookedonsaturn]

thank you for your help. I am going through andys tutorial again and double checking everything. I will if skys stay clear check with Alpha Centauri tonight and if i still have problems post some pics.

[rmcpb (Rob)]

Do you still have the shims under the focuser? If so then they may need removing, as you installed them very early. Try aligning everything as per instructions and take it out and look at some stars up high to see if they come to a pinpoint. Then go a bit either side of focus at about 200x and see if the fuzzy circles are indeed circular. If so then all should be OK, otherwise its back to the drawing board.

Planets are unforgiving as far as getting to see details. For the past couple of weeks the seeing here has been shocking and I can barely get the equatorial belts on Jupiter! I showed Saturn to some kids the night before last and could only just get the rings to seperate from the planet, its too low for any serious observing. With the seeing this bad its low power work at present here.

Another point would be to ensure your mirrors are at ambient temperature by putting your scope outside for at least an hour before observing and using any fans that are installed. If you have a warm mirror then your images will be distorted by the air currents.

BTW if you were getting detail on wires about 3km away it must have been in pretty good alignment so all is not lost.

Cheers

[hookedonsaturn]

Watched andys video again over and over about 4 times for each step.I did take the shims out from under focuser but something just doesnt look right after adjusting primary.I have included some photos.I dont know how much you can tell from them as they were taken with web cam.The first 2 steps centering and aligning the secondary liik quite good i feel but when i adjust the primary to bring view into center of viewfinder it shows the primary and secondary are no longer concentric.I hope someone can tell me where i am going wrong because i feel like i'm chaseing my tail

[duncan]

Just re-tweak the secondary again, then primary,then secondary etc. until perfect circles. Not hard and you will get used to it. Once you've got it right it wont need much in the future.
Cheers,
Duncan
Ps. Keep your adjustments small and remember which one was last. That way if it goes the wrong way you can undo the mistake.

[hookedonsaturn]

Thanks guys checked Alpha Centauri tonight and can tell it is a double but still a bit fuzzy.will tweak it a bit tomorrow.with any luck i'll get it right,the atmosphere will clear and i can spend the weekend up among the stars where nobody can find me

[hookedonsaturn]

It looks like my choice to join Iceinspace was a smart move. I would like to thank all involved for the help in collimination of my 8" newtonian.With your advice and a bit of tinkering i did find the problem.It seems when i centered the secondary under the viewfinder i was not level so when i adjusted the tilt the front side of the viewfinder was showing up in the mirror.I did some carefull measurments and found that with the spring behind the secondary i could not draw it back enough to center.That done the colimination seems to be as spot on as i will ever get with this scope.
I truly wish i had joined here before purchaseing my scope.Different choices would have been made.
Now i can get some decent viewing if the dam skys clear.Since you guys know everything about astrono0my can someone tell me where the "clear sky switch" is?

for iceinspace

[erick (Eric)]

Originally Posted by hookedonsaturn

....Since you guys know everything about astrono0my can someone tell me where the "clear sky switch" is?

I know it's on the same board as the one that switches the Moon off, but haven't located the switchboard as yet - obviously "secret astronomers' business" that I'm not privy to

Glad to hear that you think you've beaten it into submission finally!