Can't collimate primary after putting it back. Stupid laser...

[bambuko]

A Cheshire is next to useless for collimating in the dark though...

that's not entirely true

I use it quite happily at night with my little red light torch

...I've never had a Cheshire...

that probably explains your comment above

if you prefer using laser for collimation that's fine, but there is nothing wrong with "combination sight tube" often referred to as simply "Cheshire"

[Jannis]

So i've tried the barlowed laser right now, but with little luck. As in, when i had it spot on with that, i put in the camera, and tried on an out of focus star. Then i didn't get a perfectly round circle with the 3 mirror clips showing again. What am i doing wrong? Or is it the secondary that have for some reason come out of collimation?

I tried to adjust the primary now and got it to be more or less perfectly round, with the secondary's shadow dead center. This is how a stack of 10x 6 sec exposures look now (no tracking, it's polaris):

https://www.dropbox.com/s/3s3p4j74bc0krhd/darncollimation.jpg

Rather odd looking stars? They all have the same shape, so it dosn't seem to be due to no tracking.

And, i do use the MPCC when i take these images, in case it matters.

[Jannis]

I think maybe i did somethign wrong, and i gave the barlowed laser another go. This time with more success, but still odd stars.

This is how a stack and a single star looks like now. full res: https://www.dropbox.com/s/tjqkmlvk9nvbffy/afterbarlowedlaser-center2.jpg

Attached is how a stacked video of how a slightly out of focus star looks when in center of the frame. Looks quite OK?

But why are the star shapes so darn odd, and not round? They all look like saturn, lol.. >_<

[Jannis]

I feel like i'm spamming down this thread now, but... Sorry ^^;

Here's how a long exposure look. The odd star shape is gone. No idea what caused it in the first place, but it's gone at least. I still have ugly stars in the corners though.

crop from center, and added each corner. 600s exposure.

[astronymonkey]

Stick some blutac in the grub screw holes to hold them in place then hold this in with electricians tape. This will help it stay collimated.

Cheers

[Jannis]

An update here now, as i'm still having some issues, but i belive i'm down to the cause; scope flexing...?

I've now made a collimation cap, and when using it i could clearly see all the 3 clips holding the primary, and the secondary looked centerd too, as shown in the manual that it's supposed to be if it's properly adjusted. But when i asked my wife, she said that one of the clips looked slightly larger - indicating the secondary was slightly off.

So I then used the (now collimated properly) laser to asjust secondary so that it was hitting dead center on the primary. When i started, it was hitting on the outer part of the center ring.

After doing all this, i flipped the scope 180 degrees, and guess what, the laser was now lighting up teh center ring again. Still on the inner side of it, but it's not where it was. I thought about focuser slack/flexing, but no matetr how much i moved on the focuser, the laser staied put.

So i thought i hadn't tightend the primary locking screws enough, and retightend then rather hard - but still with no difference.

then i noticed that once i loosend the opper scope bracked, the laser woudl also move a bit. So i was though maybe i had just tightend the scope brackets too much, and loosend them, and tightend them only enough so teh scope wouldn't move around - stil no difference.

I run out of options, and ended up collimating it with the scope pointing stright up to prevent any kind of flexing.

So now i'm kind of out of ideas, if it's flexing. Because then it means i simply can't have a perfectly collimated scope all over the sky...?

Also, is there any otehr explorer 200 PDS users here that can confirm that it is actually flex causing this? (insert the laser, lock focuser, check laser position, flip 180 degreed and recheck laser position)

[lensman57]

So i took out my primary for cleaning on my 200PDS. Everything went pretty fine, untill i had reassembled everything, and only had to collimate it again.

I had waited with cleaning it untill i got my laser, to be sure it would be easy - big misstake not testing the laser first...

It's not so much that i don't understand how to do it, as i only need to do the primary, but aperantly my laser is rather off by a lot. if i turn it around, it's clearly making about a 0.5cm diameter circle on the primary.

Either way i gave it a try, but i ended up way off. I managed to get it better by using live-view on a star, but still far from good.

I'm currently doing some imaging, and i can clearly see the stars around, especially in the corners, are a complete mess.

Just to make matters even better, the adjustment screws on the laser are sealed, so it's none-adjustable.

It's doing very well as a cat toy though, so not a total waste, lol.. Anyway..

So what options do i have now to get it accurately done? Is it best to do it on a star, to make a cap for it and do it visually, or get a proper 2" laser collimator (wich isnt sealed, if it should need to be adjusted)?

You need to collimate the laser as most of these are not centerd by default at the factory, search the web for a  tutorial on how to do this but in short you need to have a flat and level surface, a V groove, I have some steel ones from my model engineering hobby ( they are really very expensive ) and  mine  are accurate to within 0.01 of a mm and then you need to rotate the laser in situ on the V bed and if it is collimated you have a pinpoint light at a distant wall and if not then the laser will project a circle on to the wall as it rotates, adjust the collimating grub screws until you get a pin point of light on the wall as the laser is rotated on the V bed.

Regards,

A.G

[Jannis]

Thanks for the reply, but the laser is no longer the issue.

I belive it's mostly down to flexing, if you read my last post. If it is indeed flex, it probably explains why i still had odd looking stars after collimating it "properly" with the scope in a horizonal position, as when it was flipped around to image a night sky target, the collimation would be quite off. I ended up collimating it vertically, as i'm guessing this will give me the overall best collimation. I wonder in what position it's facory collimated?

I haven't yet been able to try it, as it's snowing outside, and it's said to be clouded for over a week at least. But i'm very curious to see if it's made any difference.

[Jannis]

Finally i got this thing done. Made a collimation cap, and after an hours work i had resenterd, re-rotated, and re-adjusted the secondary (so it all 3 adjustment screws were equally far inside (withing 0,2mm)), then i proceeded to the barlowed laser collimation method to focus only on teh primary, and got it spot on.

Went outside, did a star test, and looks pretty good to me. It's not 100% in the corners, but it's as good as, or better, then it have ever been, so i'm happy.

So now i know, drop these fancy annoying lasers, and just use a cap with a small hole, and get the job done good right away. Could have saved so much time had i only knew. And the worst part, is that it was way easier then the laser alone... :-/

[lensman57]

Finally i got this thing done. Made a collimation cap, and after an hours work i had resenterd, re-rotated, and re-adjusted the secondary (so it all 3 adjustment screws were equally far inside (withing 0,2mm)), then i proceeded to the barlowed laser collimation method to focus only on teh primary, and got it spot on.

Went outside, did a star test, and looks pretty good to me. It's not 100% in the corners, but it's as good as, or better, then it have ever been, so i'm happy.

So now i know, drop these fancy annoying lasers, and just use a cap with a small hole, and get the job done good right away. Could have saved so much time had i only knew. And the worst part, is that it was way easier then the laser alone... :-/

Looks very good, perhaps you ought to write all the steps necessary to do this so some other people with similar problems could benefit from it.

Regards,

A.G

[Charic]

That backs up what I try to tell everyone, use a 35mm film cassette or make your own cap, by drilling a 0.5 - 1mm hole in the dust cap. I only use my laser to adjust the primary, when there is no-one else to help me., because of the distance between the adjusters and having an eye on the eyepiece. My laser needed collimating from new . I used the you tube method and made a 'V' support from PVC tubing. Works fine for me.