Collimation: Secondary placement/travel

[Raglan]

Hello everyone. I am wondering whether anyone could point me in the right direction on a collimation issue I am experiencing with my SW Explorer 150P. Very likely (almost inevitable) this is user error, but having read as much as I can, including Astrobaby's guide, I cannot for the life of me figure out what I am doing wrong in relation to secondary mirror placement. I am very much a novice so take what is said below with a pinch of salt.

The issue is this: I cannot centre the secondary under either a collimation cap or cheshire combi tool's crosshairs, as there is not enough travel in the centre screw of the secondary mirror to bring it far enough to the right (as you look down the tube - i.e. to 3 O'clock). I have obstructed the primary as recommended with a piece of brown card, and placed a sheet of white paper opposite the focus tube.

The secondary is pretty much screwed into holder (i.e. there is probably the best part of 3mm or so between the secondary holder and the spider), and the mirror still on my view needs to come further over to the right hand side (considerably so when looking through the sight tube).  It feels to me that the focuser has been installed too high on the OTA or alternative is considerably out of collimation itself.

Some pictures below  and attached to illustrate.  I am wondering what on earth I have done:

1. View through the collimation cap;

2.  View through sight tube (sight tube pulled back somewhat to expose all of the secondary).

Any responses greatly appreciated. 

 

 

 

[Boki Aristarh]

Dear Raglan,

I had similar problem with TAL-150P reflector.

It was problem with spider wines which was mounted 180 degrees contrary  relative to secondary cage. Probably someone removed wanes and mounted again wrong (maybe even in factory).

First off all try to retract 3 collimation screw maximum inside, and then move back central screw until you have contact between secondary and spider holder. After that check if secondary is enough "to the right side".

Note that you have to look only at "silvered" part of mirror, not complete secondary mirror.

If there is not enough space, than you can see if there any possibility to change focuser position left to right on telescope tube (some telescopes have this option).

And on the end check if maybe spider wanes are mounted wrong (it would be useful to take pictures of wanes also).

Some of those 3 reasons must be at the root of your problem.

Anyway, be patient and you will solve this minor problem.

 

[Dan_Paris]

I vaguely remember a thread on CN discussing a similar issue. The spider had been mounted into the tube backwards. Maybe you could post a picture ?

 

 

[Raglan]

@Boki Aristarh @Dan_Paris - thank you both. The spider is installed correctly (as if  flipped the collimation screws (I replaced with bob's knobs) lock up before exiting the holder). 

It appears the focuser is at fault and having adjusted it using the grub screws, as per @Boki Aristarh's suggestion, I can now centre the entire secondary mirror under the focuser easily, and with some space for the collimation screws on the secondary to easily adjust tilt. It looks as if the focuser needed to be lifted away from the OTC slightly on one side to centre it. 

The sight tube cross hairs hit the middle of the untitled secondary, and after tilting slightly I can see all three mirror clips without needing to retract the sight tube at all.

Thanks again.

[Spile]

I am glad to read that you have resolved your placement. For future reference, you may wish to use this guide https://astro.catshill.com/collimation-guide/