Cleaning the Cat

[AMcD]

Since I have owned telescopes I have always adhered to the maxim ‘thou shalt not clean the optics unless it is absolutely necessary’.  This is definitely the best advice and it takes a very long time to reach the stage of ‘necessary’.  However, after owning my C8 for twenty years I decided this week that we had reached the point of ‘necessary’.  

The corrector plate was very dusty on the outside with some resin marks and, somehow, a spider had found its way inside the scope and spun a web on the back of the corrector plate.  The said spider had also, like a malicious burglar, pooped on the primary mirror.   

I should make clear that I only attempted this cleaning because my Cat is twenty years old and even then second hand.  Cleaning a newer, more expensive scope would be a very different proposition indeed. However, I found the following process, gleaned from various online sources, worked very well and resulted in a very clean, streak free corrector plate and primary mirror.

I first assembled distilled water, isopropyl alcohol, washing up liquid, pure cotton wool, latex gloves, an ultra-soft brush, a blower bulb and a Philips head screwdriver.  I then undertook the following staged process:

(1) I mixed a cleaning solution of 1/3 isopropyl alcohol, 2/3 distilled water and a drop of washing up liquid. In another bowl I poured only distilled water.

(2) Before removing the corrector plate I cleaned it on the outside by:

(a) using the bulb blower to blow loose dust and particles off the optical surface;

(b) using the soft brush then to gently dust further contaminants from the optical surface;

(c) wetting pure cotton wool in distilled water and dabbing (not rubbing or dragging) the wet cotton wool on the optical surface to wet it all over, discarding each piece of cotton wool as it became dirty;

(d) once wet all over, I dabbed the optical surface with clean cotton wool dipped in the cleaning solution, discarding the cotton wool and repeating until the cotton wool showed no visible signs of dirt;

(e) once the cotton wool showed no dirt I then gently dragged cotton wool dipped in the cleaning solution over the optical surface under its own weight (no pressing or rubbing) covering the whole of the surface;

(f) the next step is to dry the optical surface, again using cotton wool dragged gently under its own weight until a dry, streak free finish is achieved;

(g) finally, once the surface is fully dry the bulb blower is used to blow away any remaining cotton threads.

(3) I then removed the corrector plate retaining ring and then, taking care to mark (a) the orientation of the corrector by dabbing a spot of correction fluid at the edge of the plate and a corresponding dab on the plate holder and (b) the placement of the cork shims that ensure the corrector plate is centred, I removed the plate and set it on a towel (as I have a Fastar C8, I removed the secondary mirror and stored it during cleaning).

(4) I wiped down the inside of the telescope tube with a damp, clean cloth, taking care not to touch the primary mirror.

(5) The next stage is to very delicately clean the primary mirror using steps set out at (a) to (g) at stage (2) above in the same order as set out there.

(6) Finally, I cleaned the inside optical surface of the corrector plate, again using the steps (a) to (g) set out at stage (2) above in the same order as set out there.

(7) Once certain that the mirror and internal surfaces of the tube are dry, the corrector plate is then re-installed, with collimation to take place at the start of the next session.

To repeat, the maxim ‘thou shalt not clean the optics unless it is absolutely necessary’ should in my view always be followed, but once there is no option but to clean your Cat, I found that this method, delicately applied, worked very well indeed.

[Andy ES]

Thanks very much for the detailed description, glad it worked.

ill print this off and use it on mine in 2040! 😁

 

thanks

[Nigella Bryant]

I usually groom mine once a month, lol. Seriously though telescope cat has lots of dust on the corrected plate and I've ever only cleaned the mirror once in ten years. 

[Andy ES]

Tried to clean my CAT eyepieces today but didn’t go to well ! 😂

 

 

[Nigella Bryant]

35 minutes ago, Andy ES said:

Tried to clean my CAT eyepieces today but didn’t go to well ! 😂

 

 

That's so funny, thanks. Your cat is like my other cat, I'm always cleaning their eyepieces, lol.

[Andy ES]

Wow! proper show CAT ! Not like my old scabbers boy ! 😁

[saac]

3 hours ago, Andy ES said:

Thanks very much for the detailed description, glad it worked.

ill print this off and use it on mine in 2040! 😁

 

thanks

Alexa, set reminder,,,, 20 years  

Jim  

[Laurieast]

What about the Mak?

😆

[Nigella Bryant]

1 minute ago, Laurieast said:

What about the Mak?

😆

I think they have to be sent to a specialist cleaners, lol. 

[Andy ES]

40 minutes ago, saac said:

Alexa, set reminder,,,, 20 years  

Jim  

Lifting the CPC will keep me fit, so I should last another 20 years😁