Coma Correction Skywatcher 300p

[Barry-W-Fenner]

Afternoon all,

I have recently purchased the attached coma corrector and 43mm extension ring for my 300p

I just wanted to clarify the current set up. I have a Baader 2" click lock inserted in to the CC, This in turn is attached to the focuser.

Is there a correct spacing i need to achieve with this setup? I can move the CC in and out of the focuser but i am unsure of its optimal position.

Also Does CC change the focal lengh of my scope?

Any help on the best way to utilise the CC appreciated.

Regards

Baz

[Captain Scarlet]

What I would do is this.

- collimate your scope.

- point it at Polaris (bright enough and doesn’t move)

- with a medium power eyepiece, deliberately mis-collimate the primary so the centre of your eyepiece view is in the “coma zone”. Also, use an eyepiece where you know where its focal plane is.

- adjust the CC distance to minimize the coma. For each new trial position of the CC, you’ll likely need to reposition the eyepiece in the CC to re-focus without changing the position of the CC. At that minimum coma, note where the “new coma-corrected focal distance” is (by knowing where the eyepiece focal plane is).

- (re-collimate the primary back to its original position)

- if the CC doesn’t have its own distance-adjusting mechanism (like the paracorr2’s “tunable top”), it’s a bit trickier. You need to be able to adjust focus from “outside” the CC, ie not change the CC position as you focus. You could focus roughly by sliding an eyepiece in and out then fine-tune using the actual focuser (which changes the CC distance but not too much).

hope that helps

Cheers Magnus

Edited August 17, 2023 by Captain Scarlet

[Louis D]

The GSO CC has a design distance of somewhere around 70mm to 75mm between the optics section and the eyepiece focal plane.  I use the original eyepiece holder and add a 25mm spacer ring (48mm thread) to mine to get it in the ballpark of the correct distance.  The design tolerates about 5mm of variance on either side of optimal spacing without changing correction all that much visually.  With the Clicklock instead of the original eyepiece holder, you'll need to measure the change in separation distance to figure out the best spacing ring length.

You'll probably want to remove the CC for high power work because it introduces some spherical aberration visible only at high powers.