small chips

[Jooster]

I picked up a new Bintel 12 inch dob about 2 weeks ago. Unfortunetly I havnt had a chance to really use it yet. The other night I was playing around with my collminating eye piece and noticed that are small chips on the edge of the primary mirror. I had a look down the opening and instead of the mirror having a clean sharpo edge there are these slight irregularities.

I called in and asked them and they said that it would not denegrade the image. I was wondering if other people have seen this and if it indeed would not cause problems. Thanks for anyones help

[Tilt]

How does the surface of the mirror look (other than the edges).

Michael

[AlexN]

if its only the edges... dont worry about it... if the rest of the surface shows irregularities, scratches or chips, then depending on the severity (post pics?) it may cause you grief...

If its just the very outer edges of the mirror, it will be sweet, no EP going to give you a field so wide that the outer rim of the mirror is going to be used...

[miketheobscure]

If I bought a scope new & it had any defects at all -- even cosmetic ones -- I'd go & get it exchanged. If you pay full boat price why not get what you paid for?

My two cents - Mike

[AlexN]

Fair and valid call... If my C11 had have shown up with even a hairline scratch in the tube, I'd have set it right back..

[Garyh]

Done quiet a bit of reading about the effects of chips and scratches on mirrors and lens and unless you have a lots of chips or scratches there would be very little image degradation. Remember your secondary and spider vanes have the same effect as huge gashes in your mirror, so a few little edge chips are no prob. As long as the rest of the surface looks good.
cheers

[monoxide]

you could probably draw a big smiley face on your mirror and still not notice the difference.

my 12" has lots of tiny holes eaten through the coatings all over the surface and it hasnt made any major difference at the eyepiece
(2 big pine tree's that belch pollen everywhere and the salt air)

[Jooster]

Thanks for all the comments. seeing it only on the edges, i dont think it will make to much difference. The overall mirror surface looks good. I did a newton test under mono chromatic light and the rings looked good and tight. I guess when you pay the price for a 12 inch ( 900 bucks) you would not expect a mirror worth a couple of thousand. When I get a half decent night of seeing I will report back.

[Max Vondel]

The best way to test your optics is with a star test. Identical images are best in and out of focus. Check online references, I got a great text from Bintel on testing a whole range of optical systems. Can't seem to locate it now. Maybe some other member can mention the book that space forgot.
:D :) :D

[monoxide]

probably this one:
http://www.willbell.com/TM/tm5.htm

[Ian Robinson]

Tell them you want it replaced and send it back (the mirror that is) at their cost . Even if they tell you it wont effect performance.

Even pinhole sized defects in the coating can effect the diffraction limited performance of a mirror.

Should not have sent it to you in that condition without asking you first. BAD QC.

[Jooster]

The mirror surface looks good. The guys at bintel want me to photograph the mirror and send them a photo. Any comments