Primary mirror scratch

[Forgey (Paula)]

I was given a 6" dob and the seconday mirror is chipped so ill need to replace that but thats no biggie. But i also noticed a scratch on the primary which is quite noticeable.
Would i need to replace the primary mirror aswell.
Pics attached.

[mill (Martin)]

Hi Paula you could first get a secondary and then see if the picture is good or not.
If not good you could always get a primary mirror.

Martin.

[mikerr (Michael)]

Paula, If it were me, I would paint the chips on the Secondary with Flat Black paint/Marking pen and ignore the little scratch on the Primary. Stick the whole thing back together and try it out.

You can always replace the secondary down the track and the lack of light gathering by the scratch will be a tiny percentage of the whole Primary surface.

I'll bet it is a whole lot better than this old thing......

http://invaderxan.livejournal.com/95262.html



Good luck

Michael.

[Rodstar (Rod)]

Paula, I would be unconcerned about the scratch on the primary. It is a much less significant issue than you might think.

The key issue with a primary is how well figured it is. A well figured mirror with a scratch will outperform a seemingly unblemished mirror, if the mirror is less well-figured. Your mirror could well be fantastic!

As for the secondary, it looks to me like you will lose about 10% of the light due to the missing coating. Again, it looks pretty dreadful, but in practice the difference will be barely discernible. It is often stated in astronomical lore than most people's eye's struggle to notice something less than 10% in difference. Remember, as a comparison, that a star which is only one magnitude brighter than another star is 151% brighter!

Like another has suggested, put it together, and give it a go!

[Forgey (Paula)]

Thanks for the advice guys. I'll see how she goes and go from there

[Forgey (Paula)]

Well I covered the seconday mirror chips with a black marker, put it all back together and took her outside.
The views of Jupiter were all good, saw the red bands and the 4 moons so it looks like its all good so far.
Can't notice the scratch or the chips on the mirrors looking at jupiter.
So once again thanks for your advice guys I will look at replacing the seconday mirror down the track but for now there's rush.

[Rodstar (Rod)]

Paula, that is great news! Glad to hear it works so well.

Clear skies.