ggkids

11 hours ago, vlaiv said:

It works for any mirror - if you tilt it, reflected rays will change direction.

In above image - incident rays 1, 2 and 3 are all the same - they don't change - but depending on tilt of the mirror - reflected rays go different ways (they all obey same rule - incident angle is the same as reflected angle).

Only difference between concave and flat mirror is that concave mirror converges rays - in case of telescope to a single point - but position of that point will depend on tilt of primary mirror.

When you change tilt of primary mirror - star position in the image changes. Simple as that.

Thing is - if you have one corner that star is particularly defocused at - this is due to tilt of primary and correct way to tilt back primary is such that star image moves towards the center.

If you've ever collimated reflector of any kind - you might have noticed that adjusting tilt of any component causes star image to shift at the eyepiece (or sensor). Same is here - star moving from bad corner to center is just indicator of good direction of tilt adjustment.

Thanks for your complete explanation, I misunderstood an important detail: the movement from the corner to the center is just an indication of the right correcting movement. 

When I read first I thought the star had to be placed there, right in the center of the fov.

Clear skies,

 Giovanni.

On 21/06/2018 at 16:32, vlaiv said:

No, I did not use collimator at all. I found this very informative blog post (let me see if I can find a link) that gave interesting instructions for collimating RC.

https://deepspaceplace.com/gso8rccollimate.php

 

 

Hello,

 I ran into this topic and I checked the link you suggested: very useful. I still don't understand what means: "Use the 3 sets of push/pull screws on the back of the scope to move the star from the bad corner toward the center of the field of view."

Is it meant to move the star from the corner to the center of the image using the collimation screw on the back of the focus? Why does this step work? 

I just want to be sure before acting and destroy what I have gotten so far 

Thanks in advance for your help!

Clear skies.