Need help please to collimate new scope

[Shano592]

Hi All,

Well, it finally arrived, piggybacked in the container full of our business' stock.

A short-tube 6-inch Newtonian, on a surprisingly solid EQ mount. Granted, it is a simple Chinese one, but for the price, I just had to get it and have a crack.

Now, being new to this game, I was pretty chuffed to be able to assemble it all in about 20 minutes, with no spare parts.

Giving it a quick run outside the other night, Sirius and a couple of his mates were partly visible through the light cloud.

I was able ( I think ) to line up the secondary pretty well (I have no collimation gear as yet ... I wanted to see if the scope was worth the expenditure at this stage), but I am not so confident with the primary mirror.

At the moment, if I home in on a star, regardless of the eyepiece that I use, the image that I see has light tails off to the lower left. I don't know what this means, and I am hoping that it signifies that the primary is out of alignment, and can be brought into line fairly smartly.

Is anyone close by, on the Central Coast, that can possibly help me to right this, one day (night)?

Many thanks in advance. Any questions, please feel free ....

:help:

[rmcpb]

I'll be suprised if you don't get lots of good help from the Central Coast :)

Enjoy your scope.

[Kevnool]

Check this site out for basic collimation.

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

Cheers Kev.

[Shano592]

Thanks Kev,

That was an informative video.

I got it better centred on the secondary, but I still have tails on the stars. However, I am yet to tinker with the primary. The moon was quite sharp, though.

I think I need a laser collimator, to finish this properly.

**COUGH COUGH** Any volunteers?

[Kevnool]

Shane ive posted this before.

If you get a laser collimator it is only used to collimate the secondary mirror.

The cheshire will only collimate the primary mirror.

Make sure the mirror lock screws are loose ( for me i have thrown them away they are a pain and affect collimation ).

Make sure you have the primary mirror marked for centre (most newts have an annulus on the mirror).

1st put the laser in the focuser turn on and see where the returned beam is on the laser target then adjust the secondary to see the laser in the centre of the laser target.

Dont worry if the beam is not centred on the primary mirror as this is not an issue yet.

Turn the laser off and take it out then replace it with your cheshire now you will be able to adjust the primary mirror.

When you have adjusted the primary mirror and have the annulus in the centre of the crosshairs your nearlly but not quite there.

Take the cheshire out of the focuser then replace with the laser and repeat step 1 with the laser adjusting the secondary mirror until the beam again is centred.

Take the laser out and replace with the cheshire and adjust the primary mirror again.

You have to keep going back and forth with the laser and the cheshire and every time you keep doing this the adjusting will be getting finer and finer until you cant make any more adjustment.

The process of going back and forth between the laser and the cheshire may take up to 6 changes or more.

By doing it this way you will bring the collimation closer and closer until your scope is perfectly collimated.

Do not put the primary locking screws back in after its collimated or all your effort and time will be wasted as they will act as collimation screws.

This is the way my 16" becomes collimated every time i go observing and I hope this will help you out in the future.

Good luck and Cheers Kev.

[Kevnool]

Shane again look at the pic here and mark each collimation screw with numbers 1 - 2 - 3 then draw a pic near the focuser.

With the picture you can see that if i look in the cheshire and see the annulus in the top left then i know i have to adjust the screw that i marked number 1.

Its a time saver Cheers Kev.

[Chillie]

Kev,

Are you saying that I need to buy a cheshire collimating tool as well as a laser collimating tool?

I already have a laser collimating tool.

[Paddy]

You will be able to collimate both primary and secondary mirrors with a laser collimator.

[erick]

What is the focal length and how long is the tube? Perhaps a Jones-Bird design? can be difficult to collimate and performance not great.

Read here:-

http://www.iceinspace.com.au/forum/showthread.php?t=27116

[Kevnool]

It makes life easier for me as you see in my post and yes everyone should have a cheshire in there kit.

Cheers Kev.

[Screwdriverone]

Bugger Eric,

Wish I had read that before I bought the 5 inch SW135, would have saved me a LOT of time....

Still, you can only learn from mistakes. Its true that the inbuilt barlow/corrector is a pain,

FYI for any beginning amateurs wanting to buy a Skywatcher scope, ONLY BUY ONE with a P on the end, which indicates a Parabolic mirror, eg. Skywatcher 150 x 1000P EQ3-2 which would be the minimum I would get to start off.

Sorry if this is deemed off topic.

Chris

[Paddy]

I suppose this is a matter of preference, opinion and personal experience, but I find that I get excellent collimation using a laser only.

[Kevnool]

Hi Patrick i only posted my comments on my preferred way of collimation and if it helps anyone out then thats fine , But if my way is to complicated for anyone then anyone can post it here as well, even i would read it.

Cheers......Kev.

[Chillie]

Thanks Kev. My mate's collimator has finally turned up and to his dismay, it's a manual one (cheshire?). He thought he ordered a laser collimator. So we can share collimators.

I can't get a clear focus on anything but the moon, so maybe my collimation is out of wack.

[Kevnool]

Hope you found the information useful Henry, your symptoms are that your collimation is out and as you said share the collimators for now.

Cheers Kev.

[Jone5y]

If you plan on using a laser collimator only (which in my experience so far hasn't worked out too well) be sure to test the collimation or accuracy of the laser collimator itself or you'll be collimating to an angled laser.
To test the laser coll, cut a "V" into 2 pieces of timber and hold them in a vice, sit the collimator in the 'V' and aim it at a flat surface at least the focal distance of your primary away. Turn the laser collimator so it rotates inside you're 'V'. While turning the device, watch the path drawn by the laser on the surface it's pointed at. If the laser stays in the 1 point, all's well. If it traces a circle the collimator itself requires adjustment to make the beam rotate about a single point. On mine this is done via hex head screws on the coll. body.

You may have already done this, in which case I've just wasted my time.

Steve

[mswhin63]

Others may have done it but I didn't know many thanks. seems obvisious now but sometimes even techy's block the simplest thing.

Too much coffee :doh:

[Kevnool]

Or even you can find a metal lathe and manually spin it in there.

Theres lots of ways for different things.

Cheers Kev.

[Shano592]

Hi All.

I wouldn't be surprised if it is a Bird/Jones design.

It appears that, no matter what adjustments I make to the Primary, the aberrations are still present. On this scope, there are no correcting lenses, as the Celestrons and Meades had in the linked post.

I took out the mirror, and gave it a good clean, ala Mike Salway's little document. The mirror is shmick, but the light tails are still there. Being Chinese, I would suggest a round mirror. In actual fact, I asked this exact question before buying it, but you can't get a straight answer out the sales staff there (in China).

I can play with the collimating screws till the cows come home at the moment, but the quality of the image does not change. And not having a Crayford focusser on the OTA means that getting super-fine focus just isn't going to happen with this scope.

Please note : I still have not properly collimated this scope, to this point in time. I don't have the personal budget to buy any collimating device, for a scope that is going to sit in the corner, if it doesn't work well.

It's not a huge problem, as I really did only buy this scope, to test out the quality. I think I have my answer now. Hat rack ...

Now for the next question ... how likely is it, that I will find a parabolic, F/9 6-inch primary mirror? I know Bintel sell F/5 and F/8, but the scope's specs (assuming they are actually correct) are f=1400mm, d=150mm. To me, this says F/9.333^.

Does the f=1400mm refer to the focal length of the mirror only, and can this be changed easily? Or does changing the F/Ratio (currently F/9) affect all of the other components?

Not a fan of a total rebuild of this unit just yet. Maybe once the next scope comes along.

[Glenhuon]

I think you are correct. FL 1400mm, actual tube length ~700mm.
I had one of these too. Only way to get anywhere near colimation is to remove the barlow lens from the base of the focuser drawtube. On mine you had to reach inside the main tube and unscrew it (With tube horizontal, mirrors and dropped objects don't mix) . The mirror is spherical, not parabolic.

You can get colimation, but its a struggle. Without a Cheshire or better still a Laser Colimator, you'll be lucky to get close. Once its done, screw the barlow back in.
IMO, Hat Rack or Boat Anchor is their primary function. The OTA does well as an Umbrella Stand in your hallway :)

Bill

[mswhin63]

I have one of these scopes and it is frustrating to remove the lens. I checked my scope and the FL spec did not match the length of the tube I suspect the lens in mine was used to compensate for short tube to give better spec. Again another trap to get into buying cheaper scopes although wasn't really cheap. :screwy: (me)

Apart from that I hate having to take out the lens all the time to use my laser colliminator.

Hence I am looking at another scope.

[erick]

Sort-of yes - the corrector lens (a 2x barlow usually) allows the physical tube length to be around half the optical focal length.

My understanding is that the design achieves two things:-

1. Shorter tube length, hence more compact as well as less material used (= less cost)

2. Allows the use of a spherical mirror - cheaper to produce?

[Shano592]

Yeah, there is no way that my tube is 700mm. Actual length is 517mm, tip to tip. I reckon that it is about 350-355mm from primary to secondary, which with the barlow in the focuser (which was found easily enough), would give close to 1400mm, f/9 characteristics.

Now ... if I were to get an F/5 Bintel Parabolic primary ...theoretically, I should be able to modify this scope with minor minor adjustments, albeit halving any magnification in he process. I'm talking about adjusting the position of the secondary by a few mm, to accommodate for the new focal length.

This would then allow me to do away with the in-line barlow, and have a short-tube F/5 scope.

Any holes in my argument so far?

[Glenhuon]

Sounds good so far, but apart from the fun of doing the mods (which is something I like too). In money terms it would probably be a better option to look around for a good s/h 150 F5 to replace the OTA.

Just checked the lengths on my 150 F5 newt, centre of focuser to mirror 500mm, overall tube length 675mm. Looks like the tube is too short to accomodate a parabolic 150 F5 mirror.

Bill

[Shano592]

Yeah, I thought that, almost as soon as I posted.

Bunnings should have some good stormwater pipe that i can spray black inside. When I get the chance, I may take the spider off the top, take it on a roadtrip ...