Collimation Knob query

[Rob]

Managed to get first light with the 200P DS last night. did fight a little with the collimation, but I have to say when I nailed it the image was superb of M42.

My question is. I've not moved the secondary, just moved the primary collimation bolts... one has has to be tightened all the way up until you cant tighten it any more.. olny then could I move the other 2 to just bring it into position. Is this down to the secondary maybe being off?.. I would have thought there should be some slack in all 3 to allow adjustments. Dont get me wrong, I can unscrew with no issues. It will just loose collimation.

I did pop my laser in for a quick test.. now assuming that does not need collimation itself, it did show the red dot around 2" away from the center ring.

any thoughts?...

Thanks

Rob

[Doc]

It doesn't sound right Rob. If you haven't touched your centre secondary screw then it must be your primary. On mine all three adjusting primary knobs have loads of forward and backward travel.

Try screwing the knobs all the way back to take pressure of the springs and try adjusting again. You should get collimation pretty quick at least by a couple of turns.

[kniclander]

if the laser is collimated properly and the red dot is 2 (is that INCHES?) away from the centre spot then the 2ndary is miles out

[Doc]

if the laser is collimated properly and the red dot is 2 (is that INCHES?) away from the centre spot then the 2ndary is miles out

I agree with what you say but then why has the primary bolt gone dead tight?

I would take the primary back to as far as it will go and turn all three knobs one revolution to put some pressure on the springs. At the moment it sounds like your primary is tilted to one side.

[acey]

It's perfectly possible to need to tighten one primary bolt all the way in (or out) to achieve collimation - happens to me not infrequently, and if there isn't enough travel then I loosen all the bolts and start again.

But if the laser dot is way out of the centre ring then you aren't collimated. You need to adjust the secondary until the dot is inside the ring. Then readjust the primary.

[russ]

I would start the collimation process again. Do it the old fashioned way first and then check with the laser.

[kniclander]

I agree with what you say but then why has the primary bolt gone dead tight?

I would take the primary back to as far as it will go and turn all three knobs one revolution to put some pressure on the springs. At the moment it sounds like your primary is tilted to one side.

I see - if the secondary was centred correctly but the primary was seriously tilted, the laser dot could fall well away from the centre of the primary - fair point.

[Deneb]

Rob, When I received my 200P DS, since I did not know how much of a rough ride it had in the dispatch process, I done a collimation with a laser, I collimated the Secondary, then the Primary.

Regarding the primary knobs they had enough movement, the only time I have noticed they do not move anymore is when the locking screws have been tightened, which is a norm. As Russ has said your better off doing collimation from scratch.

PS. I looked at M42 last night using the 200P DS as well, i've never seen it that good.

Cheers

Nadeem.

[Cornelius Varley]

I see - if the secondary was centred correctly but the primary was seriously tilted, the laser dot could fall well away from the centre of the primary - fair point.

There is something not quite right there. If the secondary is correctly aligned it will fall on the centre of the primary regardless of whether the primary is tilted on not.

Peter

[kniclander]

um, it depends how the primary is tilted - if it was tilted around a central axis you would be correct but it wouldn't be it would be tilted about the axis of two of the collimation screws (I think)

but I am prepared to be wrong......

[themos]

Rotate the laser in the focuser and sample a few positions to eliminate laser collimation issues?

[acey]

Same thing has been said several times (including by me, but I'll say it again) - the scope is out of collimation.

First get the secondary properly aligned by centring the spot inside the ring on the primary. Then adjust the primary. If you happen not to have enough travel on one of the primary bolts, loosen all of them as far as they'll go, do an equal number of turns on each of them to take them all back in a bit, then fine-tune the primary (preferably using a cheshire, otherwise the laser if that's all you have).

Reason for taking the primary far back, other than convenience and not running out of travel, is that on fast scopes you can find some eyepieces not reaching focus if the primary is too far forward. Also you might not have a full image of the primary in the secondary. Probably not an issue on your scope but I noticed it with my 300P.

[Rob]

Thanks all. I will indeed loosen off all the screws on the primary and start again. The bolt that is full tightend loosens, so I know its not the thread (or at least I think so). Tonight will tell me I'm sure. Just got a little worried to hw much I could loosen the bolts off.

Maybe I'll do the other 2 right up also then run them all back an equal amount?.

Cheers

Rob

[russ]

Maybe I'll do the other 2 right up also then run them all back an equal amount?.

Yes, that's what you need to do. Tighten all three and then release of all three an equal amount. But you'll need to sort your secondary collimation before attempting the primary.

[Rob]

All done. I did indeed set the secondary by laser (which was a1 from when I last collimated that!).

racked in the remaining two knobs which was only around 1.5 to 2 full turns, then racked all three out 4 turns.. I only need to turn one knob a very small amount to snap the collimation in.

Here is how the collimation screws look now.

[russ]

Well done Rob......all sorted for an obs session, hopefully tonight. Scope looks the business.

Russ