Squaring a newtonian focuser - necessary ?

[Astroscot2]

Im currently doing a number of mods in my newtonian, one being focuser replacement and adding an inner strengthening ring. The new focuser required new holes to be made in the tube and the focuser base is on but not central over the tube hole. I assume this does not matter as long as the focuser is

perpendicular to the tube? On this point if the focuser is slightly out of alignment to the tube will this cause issues during collimation ?

Thanks

[Moonshane]

for visual it matters not a lot in truth. I have never even checked my focuser, just ensuring the collimation is correct at my usual point of focus (approx.). if imaging, it is worth getting it right as every little bit matters more when doing AP. the base not being central up and down the tube is better than across the tube as the former Is easier to adjust out with the central bolt.

[gaetgodi]

I just did that too. The focuser needs to be directly over the secondary or you will not be able to collimate properly.

[Astroscot2]

Well installing the focuser went well, I placed my 2" cats eye cheshire into the focuser and used the centre of the crosshairs and a clear ruler to determine the correct position on the inner tube opposite the focusser.(length of tube)  I then calculated the inner circumference using an IKea paper ruler using the centre of the crosshairs again on the catseye  and carefully taping the ruler to the inner tube.  Once I have the circumference I folded the paper ruler in half , retaped and marked the tube.  I was surprised to find the cross hairs pretty much bang on the right position and did not have to shim or adjust the focuser base.

As that went so well I started the flocking, that went well too with just a few fiddly bits to do around the focuser..  Id recently fitted a carbon fibe inner ring to strengthen the tube around the focser, a new CF double vaue spider needs to go on, the OO spider was slightly twisted and produced odd diff spikes,  ive also re-spotted the mirror - essential for correct collimation.

I hope to have the newt back on the mount for some galaxy imaging and im confident the above improvements wil make a diffeence , fingers crossed.

Mark

[Ajohn]

I doubt if you will have the problem but I came across 2 scopes where the entire mirror wasn't being used. One by design from Meade I suspect plus some one trying to collimate an offset 2ndry which can be tricky. The other one was down to the focus tube not being square to the tube. I fixed and checked it by removing the mirror and replacing it with a paper target. The 2ndry was fixed on this one so that aspect wasn't a problem and it did line up. I then literally bent the focuser to centre it on the target which just deformed the metal tube that the scope had or bent it back to where it should be. I found this was more effective than trying to judge that the entire main mirror was centred in the focus tube. The same sort of thing can be done by sticking a dot exactly on the centre of the main mirror but I didn't have any adjustment interaction problems by separating it out.

John

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