|
Hi Dennis,
I also have a slightly different method to achieve better collimation after aligning with a cheshire eyepiece.
I focus on Jupiter or a really bright star such as Spica, Regulus or Alpha Centaurus and then wind my focuser ALL THE WAY OUT so that you get a classic target type picture in the eyepiece ( I use the LEAST magnifying and complicated one I have - 20mm plossl).
When I look at the "shadow" of the secondary ringed by light and bisected by the secondary spider vane shadows, I can see if the secondary is not exactly concentric within the circle of light that surrounds it.
What I do then is very slightly adjust the primary tilt on the screw to where the image needs to shift, this causes the picture to shift in the eyepiece, I jog it back with the slo-mo controls into the centre, check and repeat. Make sure you DONT adjust the primary tilt too much to make the image fall off the eyepiece's view, you only want to do LITTLE adjustments in any direction.
After a little practice with TINY adjustments, I can see if my secondary shadow and the light donut around it are concentric and then I return to the focus point and check it by eye.
Sometimes I wind the focuser all the way in to double check the circles that way as well and after a while, the whole process only takes me about 2 mins to fine tune after using my cheshire to get it initally all lined up.
Its surprising just how much difference a tiny adjustment makes on my F7.7 reflector, often being the difference between chromatic abberation (red or blue flaring at the limb) on the object or not.
See if this works for you, you will get what I mean when you wind the focuser all the way out and take a look, just be mindful not to lose the star by adjusting too much otherwise its a bugger to find it again with the mirror tilted too far off centre. In this case, I return the scope to the lit garage and realign using the cheshire and then start again (this saves time and swearing in the dark)
Cheers
Chris
|