Quote:
Originally Posted by simmo
Hello Knightrider
I've just experienced the same problem with my SW 10" dob's focuser.....
...Simmo  |
Your focuser didn't have the adjustment grubs and locking screws? It works the same way as the primary mirror adjusters.
I'm not deterred about quality by having this minor issue, it just meant something needed to be adjusted. I know this scope will serve me well in the years to come
Quote:
Originally Posted by Jason D
Knightrider,
I read your initial post and I have the impression most of your issues have to do with misunderstanding how certain collimation tools work. It is common for beginners to use laser collimators per given instructions to find out that the secondary mirror is not centered and rounded under the focuser and only part of the primary mirror reflection is visible. When that happens they get discouraged and assume the laser collimator is bad or assume they did not follow the instructions correctly. Bear in mind that the laser beam hits a tiny spot on the secondary mirror. Laser beams have no clue where the secondary mirror edge is located in reference to the focuser. Many assume that unless the secondary mirror is centered/rounded under the focuser they can never redirect the laser beam to the primary center and have the beam retrace its path all the way back. This is the wrong assumption.
Then you collimated with the Farpoint cheshire. Keep in mind that you can move your eye around until you can see the whole primary mirror and you assume the secondary mirror is collimated. But your eye axis is no longer in-line with the focuser axis.
Then you adjust your focuser by shifting the focuser axis to align it with your eye-axis. When that happens the laser agrees with the Cheshire.
I believe your collimation steps are not completely correct.
Check the attachment to explain what I meant.
Jason
|
That is very true.
I see what you mean also by the eye being off via the cheshire and then realigning the focuser to match when using the laser.
It was quite a challenge to be able to get all primary mirror clips to show through the cheshire, it was only a very minute window of opportunity i found to have them all in view equally.
Prior to changing the focuser alignment, I centred the secondary with the cheshire and aligned it with the primary. When I tested and adjusted the centred secondary with the laser, it decentered the secondary and I would no longer see the complete primary, but rather I would see the complete bottom clips and the matt black inner tube! The laser would've been useless to me completely if I didn't find what was happening.
Checking with the chesire, eye axial movement wouldn't go close to accepting this. Which has caused me to conclude even after having a straight laser it must be the focuser that is out, since it would not work any other way.
In saying all this, it seemed doing the cheshire collimation only prior to even adjusting the focuser alignment yielded good results at the eyepiece when observing.
Is it as simmo says and focuser alignment doesn't have to be that precise for it to even affect it after being collimated properly with just a cheshire?
Because if it wasn't for the laser, I wouldn't have even known.
I'm actually glad I've had this problem so early. It's given me some good practice (even if I was doing it wrong at the beginning
) and it's making collimation a breeze for future occasions