Center dot accuracy

[Dave_D]

So, I noticed my mirror had got a lot of air-born particles on it from the guy a couple of houses away who insists on burning 'stuff' in his back yard in the middle of my observing sessions. Took out the mirror to clean i off and thought while i'm at it i'll check out the center dotting template i made on a piece of acetate and found this... (most of the muck is on the acetate btw)

I'm not sure if this is the original dot placed there by Orion Optics but either way, it's certainly a couple of millimetres out. How much of an effect will this have on overall collimation? i'm sure it will  definitely affect laser collimation.

[dobbie]

Hi Dave , if your happy with the scopes image it produces then I would leave it alone , if your developing " ocd " about it then there's a guy called Dion heap ( who has got ocd.. ) on astronomy shed that has a excellent video on how to remedy this .. Luckily mine was spot on .

[Dave_D]

Hi Dave , if your happy with the scopes image it produces then I would leave it alone , if your developing " ocd " about it then there's a guy called Dion heap ( who has got ocd.. ) on astronomy shed that has a excellent video on how to remedy this .. Luckily mine was spot on .

Hi Dobbie, yeah i guess i've got ocd lol and have seen the videos. What will be bugging me now is that i *know* the dot isn't central. I don't have any qualms about respotting, the only problem i'm having is finding somewhere that sells the triangular dots on their own.

[Moonshane]

I use the circular hole reinfocers from staples - about £2 for 100. if you send me a SAE I'll send you a few.

[laser_jock99]

If you're having collimation issues then it's one thing that needs checking - I wouldn't assume automatically that the factory puts them right place.

As an aside the physical centre of a mirror may not always be the position of the optical axis. In optics we call this a centration error- where the generated curve in the glass surface is not central. 

[Dave_D]

If you're having collimation issues then it's one thing that needs checking - I wouldn't assume automatically that the factory puts them right place.

As an aside the physical centre of a mirror may not always be the position of the optical axis. In optics we call this a centration error- where the generated curve in the glass surface is not central. 

centration error, that's a new one on me...  just to add to the confusion   i think before i start messing round with it i'll email orion optics with the mirror serial number and see if they have any record of it. 

[brantuk]

So long as you get the red cross pattern on the primary you'll know you're hitting dead center. The only problem will be if the ring covers the dead center of the mirror. In theory you don't really need the ring at all if you're good at "seeing" the center.