First Collimation

[JulianB]

Hi All,

Just performed my first ever collimation (of any scope) on my 250px truss tube dobsonian (black diamond) using a Hotech cross hair laser collimator. I have to say the Hotech is an incredible piece of kit, very easy to use and the whole process took less than 5 mins.

One thing bothering me though was adjusting the primary mirror, there are 3 large thumb screws and 3 smaller flat head screws. The manual says that for the 254mm 1200mm scope which I have, the large thumb screws are the locking screws and the flat head screws are the adjusting screws.

What I found though were that all the screws were loose, i.e all screws can be finger tightened and the thumb screws are the ones that make a real difference to the returning laser position, with the flat head screws only making minor movement changes. I assumed the manual was correct and tried to center the primary mirror with the flat head screws but the movement was so small it could not center it, so I used the thumb screws and centered it without problem, how can the manual be incorrect?

The other concern was once i'd centered it with the thumb screws, tightening the flat head screws then changed the laser position again so I had to pre empt where to place the dot slightly off center so that the flat head screws (now assuming they must be the locking screws and the manual has it in reverse) can be tightened again.

At the end of the day, I had no problem centering the primary but it concerns me that I got there by ignoring the instructions and that any tightening of the flat head screws to keep things in place ruins the allignment again

Cheers

Julian

[matt c]

Hi there Julian I had the exact same thing with my skyliner, I tightened the locking screws quite alot and hardly noticed any movement.

When I realised they were the locking screws (although the manual said otherwise) I actually started to worry that i might of bent the mirror cell because i did tighten them quite a bit. Maybe it's just a typing error:)

[John]

Sounds like the manual is incorrect - generally the larger screws are the collimation ones and the smaller are the locking screws. On the Orion Optics (UK) scopes the instruction is that the locking screws should be finger tight only to avoid either bending the cell (unlikely with OO scopes) or moving the collimation. I only used to use the locking screws on my Meade Lightbridge 12" when the scope was being transported - in general use I left them un-tightened and the scope still held it's collimation fairly well.

[Eyeball]

With most products now being made in China, something is lost in translation where manuals or instructions are concerned - it may be the case here!

[LukeSkywatcher]

I'm pretty sure the manual for the SkyWatcher Heritage has the same error in it. Also when i took my scope out of the box ALL the screws were loose and even the spider arm that holds the seconday mirror in place was loose. Maybe the makers/retailers leave the screws loose for transport reasons so that the mirror has a bit of give on it and wont smash if knocked about a bit?

Anyways.............collimation was pretty straight forward once i made myself a collimation cap.

As JFK once said "You have nothing to fear but fear itself".

[wulfrunian]

Sounds familiar - I haven't tackled collimation on my Skyliner 250 yet, but I also looked at the screws, and they appeared to be the other way round, as the supposed collimation screws are very loose and movement makes no difference!

[JulianB]

Ok thanks everyone this has reassured me no end, so I wont let this bother me and get on with enjoying the views, what a great forum

Happy New Year

Julian