Barlowed laser collimation problem

[Warped Drive]

As I have had hardly any decent view of the stars for nearly four weeks now I've been mucking around with trying out different mods and things and thought I'd give the old laser collimator a go again as I had, had no success with it before, if I used it and checked it with my collimation cap it was like looking at the Olympic flag, circles all over the place and when I redo it by sight and put the laser in its all over the place. I've checked the laser and it's actually straight as a die but it appears that every time I put it in the focuser it points somewhere different. I have discovered when I was measuring up for a tripod table I am building for my scope ( Heritage 130p) that when I put and EP or the laser into the focuser there is a certain amount of deflection about 1mm with the standard 25mm EP that came with it but it's about 3-4mm when I put in the BST EP and Barlow this alone must be affecting collimation. I tried the method where you put the laser in a Barlow to diffuse it and use the reflected shadow of the centre spot to alien the primary but instead of getting a diffused blob of light, I know lasers don't produce a perfect circular dot of light, I am getting a jagged streak of laser light . I am assuming this must be something to do with the quality of the Barlow as even visually it seems to degrade the view or could it be the laser perhaps it's lens might be faulty or need cleaning, has anyone else had a similar problem?

[Coastliner]

Some have got around the slop problem by winding a strip of masking tape around the laser before dropping it into the eyepiece holder.

[Warped Drive]

I have tried that and the funny thing is even just one layer makes it too tight to fit. I measured the diameter of the laser and the bore of the focuser with a digital callipers and there is only about 0.3 of a mm in the difference but it still wobbles a lot. The other problem is that the piece of plastic that the focuser is mounted on is a bit too flimsy and physically bends down with the weight of the laser or an eyepiece.

[Warped Drive]

These are two pic of the laser, first with out the Barlow the second with the Barlow. It is a bit more of a rough line with jagged edges than the photo shows. The couple of pics i have seen online of a Barlowed laser seem to be larger and more  round.

[John]

My laser collimator produces something similar when barlowed. Mines a low cost collimator presumably with a cheap laser in it. As long as you can diffuse the laser spot enough to cover the central spot of the primary mirror that should be enough for barlowed laser collimation.

I don't think it's the barlow lens but the cheap laser beam thats to blame here.

[Dave In Vermont]

I use the Orion LaserMate Deluxe Laser Collimator. They guarantee they are collimated (mine was), and will remain so. Nice, tight red dot .Works great on my 200mm F/4 Newt. That and the following instructions should de-mystify collimation for most folks:

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

I actually enjoy collimating my scope. Perhaps I should see a doctor...

Dave

[John]

Despite my post above, I actually use a cheshire eyepiece for collimation 99% of the time. I find it more intuative and accurate than laser collimators. I've tried a few lasers including the Baader and Hutech ones but I've not found any particularly satisfactory.

[Warped Drive]

I agree totally with the Cheshire route as I think my secondary is what is out of whack. The trouble is that even when I look trough the 35mm film can collimation cap I made there is so much space around the secondary it is very hard to judge if it is correctly aligned. The longer tube of a Cheshire should correct that, but I am worried that the poor design of the focuser on the Heritage 130p might make perfect or near perfect collimation impossible as even the weight of a Cheshire will probably make it bend down. It's something I never really noticed before but now I that have it's really alarming how much it bends down when it put a BST Starguider into it. Although it still seems to give pin sharp views of the moon and Jupiter. Maybe if these clouds finally clear off and I can see some stars I'll forget about it.

[Warped Drive]

Astro Baby's guide was what I use for my first time collimating the scope. It's funny that in all the other guides and articles about it I've read since, hers is one of the few that mention the off set of one of the circles in fast scopes, even the collimation section in the manual for mine shows all concentric circles. This must really confuse beginners. I know I would have been if I hadn't read about it.

[Scooot]

The Howie glatter works very well. I use it all the time. I can re-clamp it, rotate it and it's in the same spot. I bought it to replace a hotech which seemed to move when I re-clamped it.

[Charic]

Place some paper or card (cereal package )  inside the telescope between the secondary and the primary, in such a way as to block the view of the primary mirror. Also place something similar, maybe a different colour just to the left of the secondary mirror, (inside the telescope ) this will give some colour definition around the secondary mirror when viewed from the focuser.

Now first looking down the focuser, check to see if the secondary is concentric to the outline of the focuser tube your looking through. Regardless of how much space there is around the secondary, it should be equal  all around, and the mirror should look as circular as possible, not elliptical, inserting the 35mm cap you made to better align your eye to the focuser axis.

When this is done, you can next use the laser to align the secondary to the primary. Small, little, as required adjustments to the secondary  are all that's required.

As for the Laser fitting, pop the laser into the focuser and place a finger on the end of the laser, to ensure, as best as possible, the laser is fully seated, then GENTLY tighten the focuser screws to hold the laser in place. They just need to be nipped. If you over do it, you will misalign the laser due to the slop inherent in some focuser's?

As for the two images you supply, they look ok, but the first is a bit too rectangular for my liking ? Mine is a perfect dot and does not wiggle off centre even at 18 feet away, and rectangular if I slap a Barlow on the end?

But this is the advantage of a Laser, it can be Barlowed to good effect.

During secondary  mirror alignment, you should chase the single laser spot inside the circle/primary spot. But  when using the Barlow-Laser  on the primary , there is no spot! what you should  have now is a shadow, reflected  from the primary spot, visible on the Laser target face, align  this around the hole in the target face of the laser.

Also don't concern yourself with the secondary mirror offset on your telescope, ignore that feature, also double check the focuser assembly if you feel there is any weakness or anything is loose. Is  it possible to shim the focuser if there is an issue.

I have all the ' tools' and can  collimate this f/6 scope quite well using anyone of them, but if there was an order, then the Cheshire Tool should be the first. I use a long reach version ( for me offers a tighter, more accurate view ~ which can be withdrawn to offer a wider view if required?) I use the Barlowed Laser for when I'm ready to view for a quick and final check.

Start over again, its just technique . You will get there. Although, if that spot remains rectangular before the fitting of the Barlow, something may need adjusting/replacing?

[Warped Drive]

I am afraid the photos aren't the best I was holding the laser by hand at about roughly the focal length 650mm and obviously there was movement as the laser does produce a single point dot. In the the second one of the laser in the Barlow the phone's camera has captured more light as to the naked eye it's more of an elongated streak with jagged edges. I have a piece of brown cardboard made up that I can fit in, in front of the secondary to block out the primary reflection and I use half an A4 sheet of white paper opposite the focuser and this give a good contrasting image the trouble is that the Heritage has no draw tube and even looking through the 35mm film can cap you are staring at the secondary in wide open space so I think a Cheshire or a longer tube of some sort would be need to get a more accurate picture. The image of the brown cardboard in the secondary does appear to be circular and not elliptical against the white background.

[Charic]

Sorry......forgot about the short focuser on the 130P.

Your scope, being so small, and easy to adjust, have you tried working in reverse?

Put the eyepiece into the focuser, then adjusting the focus collar, defocus on a bright Star ( Polaris is stable, but not the brightest!) and check the Airy disk ( page 9 user manual ). If its out of alignment, then you need to follow those instructions again! If the disk looks concentric, then laser alignment wont improve the situation, and therefore not required?

So in principle, reset the scope to what looks right to your understanding, using the collimation cap, then check the Airy and see what the result is.

Unless there is something clearly wrong, or missing? there isnt much else to try, that you haven't already.

Good luck

[Warped Drive]

I've just taken these photos with my phone the first is the view through the TS Optic collimation cap i got with the scope very hard to see throgh even with the naked eye, the second is with the 35mm film can cap and the thrird is my kit for isolating the secondary. The camera view through the 35mm cap is better than with the naked eye.

It seems to be compressing the view so you can see the rim of the film can.

[Charic]

......there is a little program available that you can overlay onto your images to check the alignment!

Can I find it just now........No!

Still looking. It may be of some or little help?

[Charic]

....its called    AlsCollAid. Check here,  http://stargazerslounge.com/topic/136286-als-collaid-sct-collimating-assistant/

Just remember to square the Phone/Camera for the initial image.

[Warped Drive]

Cool I'll give that a shot

[Warped Drive]

OK here is the result looks preety close to me. I can't vouch for the 35mm film can being a perfect circle so that may account for  the outer ring not matching on the righthand side.

[Charic]

..........yep, looks good to me so far,  the secondary is centred and concentric. Next  though, you  may have to adjust the secondary by the slightest amount,  correcting  the tilt  when you align  to the primary, looking for those mirror clips!   

[Charic]

.......I've also noted in the user manual, page 10,  that it suggests loosening the adjusting screws a few turns?

I would prefer to ensure that after the locking screws are loosened, you actually tighten the Adjusting screws to just finger tight? This action alone  should ensure that the mirror as flat to the surface to which it is mounted. Having a flat mirror to start with can only aid the alignment in my books, unless proven different?

If the mirror clips are  all visible, just re tighten the locknut's ( carefully ~ as over-tightening can upset the alignment again!) If adjustments are required to see the clips, then unscrew the adjusters slightly. Its a minuscule amount of adjusting, no more than the maximum thickness of the securing washers behind that adjuster ( if built the same as my Skyliner?)

[Warped Drive]

Whoops got the order wrong, the first and last are of it after optical collimation, the photo may not be clear enough but all circles are concentric and if i pop the laser in as in pics 2 & 3 the dot is hitting the doughnut on the primary and as you can see missing the target on lthe aser. If I adjust to suit the laser,  when I look through the cap all or most of the circles are out of whack.

[Charic]

.........looking better. Slightly adjust the secondary tilt ( the three adjusting bolts) until the laser is inside the primary doughnut,  then secure (tighten gently) the secondary. Make sure the laser spot  is still inside the doughnut!

 Now looking at pic 3, you just need to chase that laser dot into that hole on the laser target? Slight adjustments on the primary mirror till that laser spots goes back into the hole. Then that's you done! Your so close looking at these pics. 

[Warped Drive]

I probably should have done this with the last post, seems to be showing it slightly out. But it also seems to show the secondary as being closer to the opposite side of the OTA which its not I have measured it with my digtal claippers and its preety much bang on it the centre, or is that part of the off set illusion that fast scope give.

[Dave In Vermont]

If you have a fast scope - F4 or F5 or so - the offset above is typical. Regards the secondary, it is almost there.

The laser image above tells me to adjust the primary-mirror. Then check secondary again.

You're almost home!

Dave

p.s. I use both a Cheshire and a laser. It's nice when they agree.

[Warped Drive]

Ok I adjusted the secondary till the laser dot was in the centre of the doughnut and then adjusted the primary till the laser dot disappeared in to the hole. I put the 35mm Colli cap back in and this is what i have the reflection of the primary is no longer concentric in the secondary and the centre dot seems way off too.

I may have also been wrong about the scondary being dead centre as the pic shows the centre adjusting screw is dead centre but the secondary mirror is glued on off centre, bias to the opposite side of the OTA from the focuser, is that the way it should be?