Collimation for visual use only

[Knighty2112]

Hi all. After getting a second hand SW Explorer 200PDS OTA in excellent condition on Wednesday, and after getting a collimation cap and Premium Cheshire from FLO I set about checking the collimation. I also have a Seben laser colimator too (more later) that I can use too. So, after using the collimation cap & the new Cheshire to get the collimation as good as could do it by eye, I then put in the Seben laser colimator to see how close it was to the centre, and it was outside of the donut on the mirror by about 5mm or so. OK, the focuser slop doesn't help much here as depending on how you put the laser in you get a different result all the time (before you say it I also made sure my laser was collimated correctly itself, which it is), but it was always outside of the donut. So my question is if I splash out on a Hotech laser colimator (which self centres itself) for using the scope for purely visual observations am I going to notice a difference if my views if the collimation is slightly off by a small amount, as opposed to been spot on with a better laser colimator? With the brief views I've had of the Moon and Venus through the scope so far I'm pretty blown away by my views already, so would it only be nit picking or OCDish to want the collimation smack on with a laser, since visually with the Cheshire it seems spot on to me and the views are great too?

[alacant]

If you're satisfied with the views then leave it. I struggled with a laser too until I discovered that the Cheshire did all I needed, and with more accuracy:

• secondary centred in the focuser: old film canister with a hole
• secondary tilted and rotated until the primary donut is on the cross-hair intersection: Combination Cheshire sight tube (CCST)
• primary centred on the same cross-hair intersection: CCST
• done

If you now adjust the same setup by centring the laser onto the primary donut, it will not (never?) agree with the Cheshire. 

To answer your question, no. HTH.

[Knighty2112]

17 minutes ago, alacant said:

If you're satisfied with the views then leave it. I struggled with a laser too until I discovered that the Cheshire did all I needed, and with more accuracy:

• secondary centred in the focuser: old film canister with a hole
• secondary tilted and rotated until the primary donut is on the cross-hair intersection: Combination Cheshire sight tube (CCST)
• primary centred on the same cross-hair intersection: CCST
• done

If you now adjust the same setup by centring the laser onto the primary donut, it will not (never?) agree with the Cheshire. 

To answer your question, no. HTH.

Cheers! Yes, very happy with the views so far!  

[LukeSkywatcher]

Collimation needs only to be perfect for AP. For visual observing, close to perfect is good enough. Once its not out by miles.

[triton1]

One layer of masking tape around the laser barrel should take up the slop if you want to double check.

[Knighty2112]

41 minutes ago, LukeSkywatcher said:

Collimation needs only to be perfect for AP. For visual observing, close to perfect is good enough. Once its not out by miles.

Thanks. I thought as much that it would need to be perfect for AP. Cheers!  

[Knighty2112]

20 minutes ago, triton1 said:

One layer of masking tape around the laser barrel should take up the slop if you want to double check.

I'll try that later on and see how it goes. Cheers!  

[Stu]

I think it depends what your targets are. For Venus I doubt you would see dramatic differences, same as for deep sky stuff. For targets like Jupiter and Saturn though, the more subtle features may get lost if your collimation is off. Some of the trickier lunar targets would, I guess be the same.

When you say focuser slip, is that the laser moving within the focuser or the focuser itself flexing/wobbling?

[Knighty2112]

6 minutes ago, Stu said:

I think it depends what your targets are. For Venus I doubt you would see dramatic differences, same as for deep sky stuff. For targets like Jupiter and Saturn though, the more subtle features may get lost if your collimation is off. Some of the trickier lunar targets would, I guess be the same.

When you say focuser slip, is that the laser moving within the focuser or the focuser itself flexing/wobbling?

Not had chance to target Jupiter or Saturn yet, although I could make out the Rima Hyginus area much better with my Explore 200PDS than I could with my ST120 'frac. The slop comes not from play in the focuser itself, but the slight play due to the tolerance between the size of the laser colimator and the focuser opening itself. As Triton suggests this may be solvable with some tape around the laser colimator itself to make it a tighter fit. 

[Stu]

1 hour ago, Knighty2112 said:

Not had chance to target Jupiter or Saturn yet, although I could make out the Rima Hyginus area much better with my Explore 200PDS than I could with my ST120 'frac. The slop comes not from play in the focuser itself, but the slight play due to the tolerance between the size of the laser colimator and the focuser opening itself. As Triton suggests this may be solvable with some tape around the laser colimator itself to make it a tighter fit. 

Yep, the newt should have better resolution due to the aperture so no surprises there. Worth getting it as good as possible though so you see all there is to see.

Good that the focuser is fine, get the collimation tightened up in it and all should be well.

[John]

I could never get laser collimators that I tried to agree with my cheshire eyepiece. When I star tested, the cheshire was getting the right result each time so I gave up using laser collimators. I've tried low cost ones, the Baader one and a Hutech.

 

[Knighty2112]

14 minutes ago, John said:

I could never get laser collimators that I tried to agree with my cheshire eyepiece. When I star tested, the cheshire was getting the right result each time so I gave up using laser collimators. I've tried low cost ones, the Baader one and a Hutech.

 

So the Cheshire seems to be a better tool to get this collimation right. I've heard others say they could never achieve good results from a laser and switched back to a Cheshire. Might forget the laser and stick with the Cheshire then.  

[triton1]

I found also that once the tape was put on when rotating the laser in the focuser the spot should stay in the centre of the dounut if it doesn't it's normally the laser that needs recollimating not the scope.

[Mark at Beaufort]

A laser collimator will not sort out the secondary you really need a site tube for that. Over the years I have found that the Cheshire gives me the most accurate collimation. I did have a Hutech which was convenient but in the end I returned to a site cap and a quality cheshire.

[Mr Spock]

Using any sort of collimator, be it laser or Cheshire, should only be seen as a near enough start. The final collimation should be done using a star test.

Near enough isn't good enough for fine planetary detail. Less than perfect smears detail and reduces contrast.

It's not true that AP requires more precise collimation - both AP and visual should be collimated to the same standard