collimating troubles

[Jarrod]

hi, i need advice regarding the collimation of my telescope. the telescope has a 127mm objective mirror with 1000mm focal length (f=8), but the tube is only 45cm long. inside the focuser is a lens/s to compensate for the short tube. this is making visual collimation very difficult, as the view is being alltered by the lens/s. i've marked the exact centre of the objective and i've tried collimating while the focuser is removed, but i still can't get everything lined up. any idea's?

thanks, jarrod.

[astro_nutt]

Hi Jarrod..
It seems the brand of scope has fitted a 2x barlow lens into the focuser..which means you need to have the focuser installed and correctly aligned to be pointing directly on the opposite side of the focuser..if possible remove the barlow lens assembly from the focuser being careful to record the proceedure..re-install the focuser then try to collimate.
BTW..what type of collimation tool(s) are you using?...
Cheers!

[Jarrod]

i would rather aviod removing the lenses unless it turns out to be the only way to get the job done.



i'm not using any collimation tools, just my eyes. i was thinking of buying a laser collimator, but would it work properly on such a telescope?

jarrod

[Chr]

Hey Jarrod,

I have a telescope thats designed the same way. I found with mine, that the lens in the focuser can just be screwed out from the bottom (though I did completely remove the focuser to discover this). I have used a laser collimator in attempt to align mine. though have found it to be nigh impossible with that silly lens still in. So best way I found, is to remove the lens, collimate, put it back in again.
Unfortunatly the scope wont focus without this lens :(

[Jarrod]

the lens will screw out from the bottom, but first i need to buy that laser collimator.

thank, jarrod.

[astro_nutt]

Hi Jarrod...
Many people have various methods in regards to collimating their scope..many of them use a Cheshire Crosshair type collimation tool which allows you to look through a tiny hole at the top of the collimator in order to align/adjust the secondary mirror to the primary mirror as part of the mechanical alignment...you can achieve a high level of collimation this way which can be confirmed and maintained by using a Laser collimator.
Just a few helpful hints to make collimation easier...
Allow yourself plenty of time.
Find a nice quiet room..no pets..children..just yourself.
Have the optical tube fixed in a horizontal position.
Place a lamp with a light coloured shade about a metre or two in front of the scope. This will provide filtered light needed.
Make sure the surroundings in the room are safe and the area clean.
Check that the tools and equipment needed are in good order and clean. Secure tools that may be use to adjust the secondary mirror with a small strap attached to your wrist...even though the optical tube will be horizontal when you adjust..it only takes on slip and the secondary/primary mirror will cop it!
Record the number of turns for each screw..eg top screw 1/8th left etc..just in case you need to reverse an adjustment.
Never force a screw that is too tight.
Be very careful when tightening any of the adjustment screws..
Have a ball of Blutack on a stick to pick up any bits that may fall on the inside of the optical tube under the seconday mirror after you adjust it..just gently dab it so the dirt won't fall on the primary mirror.
Have frequent breaks during the proceedure.
When purchasing any type of collimator, ask for a demo and also have the collimator checked to make sure it itself is properly collimated!!
Cheers!

[Jarrod]

good news! i got everything lined up visually, although it's not perfect. i'll have to test the scope outside on a star. any advice regarding fine tuning?

thanks everyone for all your ideas and opinions, you've made it alot easier.

jarrod.

[Gargoyle_Steve]

Best advice Jarrod is that you want to get it as close to perfect as you can - every step closer will improve your viewing dramatically when it comes to finer details. Without knowing what you've used in terms of tools to line it up it's difficult to give more accurate advice.

[astro_nutt]

Well done Jarrod..as for fine tuning..I use the laser collimator to return it's beam back to it's source after adjusting the seconday to the primary whereas the laser shines on the centre mark on the primary when the focuser is turned fully in then fully out without movement...from there you adjust the primary to return the laser beam to it's source..that pretty close to near perfect.
Cheers!

[tjquoll]

Hi Jarrod,

I had to do an initial adjustment of the secondary with the lens removed from the focuser. I set the secondary using a collimation cap made from an old film canister. Once that was setup I aligned the primary with a laser then put the lens back in the focuser and fine tuned by star testing. As I'd never collimated a scope before, there was a fair bit of trail and error, but I think I've got it as good as I can get with the quality of the optics in this model. Basically that means there is still a slight touch of coma when focused. However if the seeing is good, I can just see the bands on Jupiter and I've been able to take some cool photographs of the moon and some of the brighter clusters. Not too bad for light polluted inner city Melbourne,

Given the vibration from the fairly dodgy tripod and the rough focuser on this scope, it can be really improved by adding some sort of fine focus control. I added a motor to the focuser but it involved a bit of surgery and I probably invalidated the warranty at the same time. You could try fitting a larger knob to one of the focus controllers - say a plastic vegemite jar lid drilled out to snuggly fit around one of the existing knobs.