Laser collimation not all its cracked up to be...

[Jason D]

Jason - not coming to the UK any time soon....??

I would love to visit the UK in my lifetime but not anytime soon

[haitch]

I would love to visit the UK in my lifetime but not anytime soon

Hoping to visit my Uncle & Cousin in LA next year but will be unable to bring my scope so will be looking for someone out there to tap for a view of the Californian skies.

[daz]

I would love to visit the UK in my lifetime but not anytime soon

We could have a collection.....

[lancerde]

The scope has a lense at the bottom of the focuser tube. As mentioned you can't use the laser with it fitted so I took it out while using the laser. Its a real pig to collimate manually but I am new to this so I will have another go. Thanks for the replies and links.

I think I may get myself a Skywatcher 8'' Dob.

[daz]

Jason

Could I confirm that step 1 should be to ensure focuser alignment by using Vic's CDP procedure, and stacking P+3 by adjusting the focuser (i.e. by adding or removing shims as necessary)?

Once this is done, then move onto the secondary alignments as you outline in Telescope Reviews: Concise thread about autocollimators+improvements ?

Thanks

[Ford295]

My thoughts being very new to all this and liking gadgets and gizmos is this. I have a Skywatcher 200P and thought that things were not right from the off. I brought a laser collamater from Scopes and Skies and when I checked the secondary mirror seemed out. I adjusted it and then set everything to fire back through the target on the collamater and everything looked good to go. When I took it outside to wonder at the mysteries of the universe I could have have the same effect by squinting at the sky. A bit more reading lead me to check the collamation of the laser and it was way out, it was orbiting around the primary mirror like mad. I then went about setting up the laser to be accurate on every point and check the scope again.

In the end I went back to Skies and Scopes (just down the road) and asked them to set it up as is should be and after a bit of tweaking and adjusting it was perfectly setup (thanks Dave).

When I checked the laser at home with my newly set up scope everything lined up perfectly. I now only use mine to carry out the routine alignements from me having to move it around every time I want to view anything.

Moral of the story is, don't assume factory setting are perfect.

Don't blindly trust the laser and ask for help if you need it.

[Jason D]

Jason

Could I confirm that step 1 should be to ensure focuser alignment by using Vic's CDP procedure, and stacking P+3 by adjusting the focuser (i.e. by adding or removing shims as necessary)?

Once this is done, then move onto the secondary alignments as you outline in Telescope Reviews: Concise thread about autocollimators+improvements ?

Thanks

Step 1 (centering/rounding secondary mirror under the focuser) should be carried out by using a quality sight-tube. Step 2 (aligning the focuser axis to eliminate focal plane tilt) can be carried out by CDP with high precision. I would not attempt to shim the focuser using CDP -- CDP is just too sensitive for this task.

Jason

[Jason D]

Hoping to visit my Uncle & Cousin in LA next year but will be unable to bring my scope so will be looking for someone out there to tap for a view of the Californian skies.

California skies are better than UK in terms of seeing and transparency. But we have a bad LP problem around major metropolitan areas such as LA. I live in Northern California. I need to drive for 1 hour to get to decent dark skies.

Depending on which remote dark area you visit, be prepared to be visited by Raccoons, deer, bears, bobcats, boars, and/or coyotes – seen all in the wilderness. If you are lucky, you might be visited by a mountain lion – never seen one in the wild though I came close.

Jason

[daz]

Step 1 (centering/rounding secondary mirror under the focuser) should be carried out by using a quality sight-tube. Step 2 (aligning the focuser axis to eliminate focal plane tilt) can be carried out by CDP with high precision. I would not attempt to shim the focuser using CDP -- CDP is just too sensitive for this task.

Jason

Sorry Jason.... bit confused now....

I have the Blackcate XL, so have done the secondary centering and rounding, but if you don't shim the focuser, how do you align the axis?

Thanks

[Jason D]

There are two axes that need alignment.

The first is the focuser axis alignment. That can be done via CDP using Catseye INFINITY XL (or XLK) autocollimator. CDP fine adjustment is carried out via the secondary mirror three set screws.

The second is the primary axis alignment. You can use your Catseye Blackcat. Adjustments are carried out via the primary mirror 3 knobs.

You might have to reiterate between the above two alignments.

With respect to shimming (or squaring) the focuser, that is done once. The goal is to intercept the focuser axis with the OTA axis at 90 degrees. Squaring the focuser does not have to be precise. Reasonable effort for squaring the focuser is good enough. Focuser/primary axial alignment described in the last two paragraphs will compensate for any minor errors pertaining focuser squaring.

In addition to squaring the focuser, it is recommended to center the spider vanes. Again, this is done once.

So far, I have not mentioned centering/rounding the secondary under the focuser. That comes after you have squared the focuser and centered the spider vanes. This alignment needs to be touched once in a long while. You will need a sight-tube to complete this task. All 4 secondary mirror adjustment screws might be used.

I do not want to confuse you. Here is summary of the above:

1- Square the focuser – done once

2- Center the spider vanes – done once

3- Center/round the secondary under the focuser using a sight-tube – Repeated every long while

4- Align the focuser axis using CDP – Do it at the start of every observing session

5- Align the primary axis using Blackcat – Do it at the start of every observing session

One source of confusion is that there are two secondary mirror adjustments. The first is coarse adjustment involving centering/rounding the secondary under the focuser which might require the use of the center secondary bolt along with all 3 set screws. The second is fine adjustment involving CDP which uses only the 3 set screws.

Daz, let me know what is confusing and I’ll be happy to clarify.

Jason

[JB80]

Some good information here thanks guys.

I'm curious though about the barlowed laser, is it supposed to still be a fine point that returns back into the target area on the tool?

Because with mine the beam changes to a large fainter red disc and can't be seen back in the tool.

I have checked with both the x2 and x3 and they both do it.

Is that normal?

[haitch]

Some good information here thanks guys.

I'm curious though about the barlowed laser, is it supposed to still be a fine point that returns back into the target area on the tool?

Because with mine the beam changes to a large fainter red disc and can't be seen back in the tool.

I have checked with both the x2 and x3 and they both do it.

Is that normal?

Yes. You need to put a white paper mask over the face of the focuser inside the tube with a hole for the laser (I actually managed to make a mask that I can just pop on out of a white aerosol lid). Basically what you get back is a diffuse light with a circle in it from the shadow of the centre spot on the primary. This is what you are centering to the focus tube to align the primary mirror. Unfortunately that won't project through to the screen on the collimator and needs to be seen from the inside of the tube against the end of the focuser tube - not ideal for long Newts as it means some back & forth but well worth the effort when compared to normal laser collimation.

The advantage of this method is that it doesn't matter how well centred the laser is in the focuser - you can wiggle it to your hearts content and the spot reflected back will remain static.

[JB80]

Ahhhh.... I see, that makes sense.

Sounds a bit fiddly but I guess it's worth it.

Thanks for clarifying.

[Bart]

Have you read this? Might help.

Rear View Barlowed Laser Method

Bart

[haitch]

Have you read this? Might help.

Rear View Barlowed Laser Method

Bart

You can't see the ring on mine I guess the f/l of 1.6m is just too long to fit the doughnut in the view window.

[JB80]

Thanks again for the link, I'm going to try the barlowed laser tonight, I'm reasonably confident everything is pretty good as much as I can be not having a sight tube, it's just I can't ever seem to get a fully clear picture so I figure collimation is the first port of call.

When the pretty red chesire collimator comes back in stock I'm going to get one of those too and start over again.

[Jason D]

The advantage of this method is that it doesn't matter how well centred the laser is in the focuser - you can wiggle it to your hearts content and the spot reflected back will remain static.

Bear in mind that wiggling the barlowed laser setup will also wiggle the target location. Another thing to keep in mind that barlowed laser is only meant for aligning the primary mirror. It can't be used align the secondary mirror.

[Jason D]

You can't see the ring on mine I guess the f/l of 1.6m is just too long to fit the doughnut in the view window.

I use Glatter laser and TuBlug. The reflected shadow is sharp.

[Starlight 1]

Yes. You need to put a white paper mask over the face of the focuser inside the tube with a hole for the laser (I actually managed to make a mask that I can just pop on out of a white aerosol lid). Basically what you get back is a diffuse light with a circle in it from the shadow of the centre spot on the primary. This is what you are centering to the focus tube to align the primary mirror. Unfortunately that won't project through to the screen on the collimator and needs to be seen from the inside of the tube against the end of the focuser tube - not ideal for long Newts as it means some back & forth but well worth the effort when compared to normal laser collimation.

The advantage of this method is that it doesn't matter how well centred the laser is in the focuser - you can wiggle it to your hearts content and the spot reflected back will remain static.

i like this good post.I use two caps for seting up the centre spot .

[SteveA]

Jason - not coming to the UK any time soon....??

Are you thinking..."The 1st SGL Collimation Workshop" ?

[haitch]

I use Glatter laser and TuBlug. The reflected shadow is sharp.

Ooh I want one of those.

Same topic but another aspect (and something that has always played on my mind) - what does everyone think of self-centering collimators? Surely if you hold your EPs with a thumbscrew (whether or not on a compression ring) you are better off holding the collimating device (of whatever your preferred flavour) in the same manner so it gets the same offset as the EPs? (assuming a certain consistency of diamater)

[Starlight 1]

I was looking at a video today (he said that self-centering was the way to go and thumbscrew only put them off centre. Three video later in the seting up he was useing a self-centering with a barow with a thumbscrew and the laser in side of that.

I am lost.

[Jason D]

you are better off holding the collimating device (of whatever your preferred flavour) in the same manner so it gets the same offset as the EPs? (assuming a certain consistency of diamater)

I agree with your statement.

Interestingly, when you have a quality focuser and a quality laser collimator, self-centering becomes a moot point. I have a Moonlite focuser and a Glatter laser. My Glatter laser fits perfectly with no slop or wiggle. In addition, my eyepieces also fit nicely in the focuser with the compression ring.

Some confuse "consistency" with "accuracy." The fact a self-centered laser improves "consistency" does not necessarily translate to more "accuracy."

Jason

[Jason D]

Are you thinking..."The 1st SGL Collimation Workshop" ?

I am always available to assist to the best of my ability here in SGL and other forums.

Jason