Newtonian Collimation Query

[laser_jock99]

My new scope has a completely different mirror cell/collimation system to my existing Newtonian. There are six adjusting knobs on the primary cell. Three are directly resting on the mirror cell (the white ones) & three are sprung to the outer cell housing but tapped through the mirror cell itself (black knobs). As I see it the white knobs cam only move the mirror up and down within the tube tube. The black knobs seem to be the way to adjust the mirror angle- can anyone confirm this?

[Stephen]

The system is the same, it's still just a push/pull

The white ones are your locking bolts. They rest on the cell to stop it moving.

The black (sprung) ones are you adjusters. They thread into the cell to tilt it.

[laser_jock99]

The system is the same, it's still just a push/pull

The white ones are your locking bolts. They rest on the cell to stop it moving.

The black (sprung) ones are you adjusters. They thread into the cell to tilt it.

So in practice the white knobs should be slackened off if major adjustments are being made and not overtightend when being used at 'lock' the mirror position? The white srews look like they could mess up the collimation rather than hold it to me.

[Stephen]

So in practice the white knobs should be slackened off if major adjustments are being made and not overtightend when being used at 'lock' the mirror position? The white srews look like they could mess up the collimation rather than hold it to me.

That's about it. They shouldn't affect collimation as the adjustment bolts are threaded : they can only move by being tightened/released. Pressure from the locking bolts (which yes should only be minimal) should just hold it preventing minor shifts which would effect collimation.

It's a classic/standard collimation design to be fair.

Personally when I had one like that (looks like a GSO/Altair design?) I removed the locking bolts all together.

With strong enough springs under the adjustment bolts, you don't need locking bolts at all

[umadog]

I agree with Stephen. If the springs are strong enough you can chuck the locking bolts. More trouble than they're worth.

[John]

I agree with Stephen. If the springs are strong enough you can chuck the locking bolts. More trouble than they're worth.

I'm another one who did this with my 12" Meade Lightbridge, which has the same primary cell as your scope. I did this only after replacing the primary collimation springs though - the originals are just not up to the task of holding collimation. The primary mirror cell on these is also rather thin in my view - the locking screws can actually deform the cell if too tight.

Your scope is F/4 I believe so you are really going to need that primary cell to be rock solid.

[umadog]

Yes, you need it solid at f/4 but I think the locking screw situation can cut either way. The locking screws often move the cell when you tighten them so it can make precise collimation (which you want) harder. I think it's quite feasible for the springs to be sufficiently stiff that they allow for zero movement of the cell. The high-power primary tilt tolerances are tight at f/4 (0.32 mm) but they're of a similar magnitude to an f/5 (0.63 mm). So what goes for f/4 more or less also goes for f/5. It's not until f/6 that the primary alignment tolerances exceed 1mm.

[laser_jock99]

So it looks like to improve the cell I could fabricate a plate from INVAR 36 or stainless with some stronger springs and maybe metric fine pitch adjustment screws or even differential screw micrometer adjusters on two of the axes!