Hi, I've been looking through the archivesall right, wise move <g>
and saw that buying ratherNick:
than making the secondary was an easier option. I've got the
catalogues for Ealing and for Newport, and it looks like Ealing is
the cheaper company. Ealing claims lambda/8 for their mirrors, while
Newport has lambda/10. I wasn't quite sure how to take these numbers
really - are they more than suitable, is it unimportant as long as
the variation is less than the variation in the primary? They also
quoted a surface quality in terms of scratch-dig, the ealing being
60-40 and the newport being 15-5. I figured from the blurb that lower
the numbers the better, but other than that it was pretty vague.
Anybody want to explain these numbers?Nik
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I'm not familiar with Ealing, and Newport has good and bad opinions,
depending on whom you speak to. That aside, 1/8th wave is NOT more
than suitable, but will work
well. A 1/10th wave or better is what you want, try to get certification
of flatness(ie a print of the interferometric fringe patterns if they can
provide that.
I feel it is better to spring with the extra bucks for a better diagonal
Re: Scratch/dig numbers
They have to do with the defect size and number in relation to the
size of the part.
The first number is for scratches, the second for digs, (i.e.
pits)
Commercial surfaces are typically called out at 80-50, which, especially
for larger optics, allows for some pretty big stuff..
60-40 Good commercial surface
40-20 Starting to be a true optical surface
20-10 High quality non-laser surface
10-5 Laser Quality -For the most part, defect free
0-0 In some ones dream <g>
The above are IMHO format
There are specific formulae for figuring size and count of these defects.
If it was truly 1/10 wave edge to edge, and 15-5 surface call out, it
should be a fine diagonal
--
Bill & Tracy Marriott
Woodacre, Ca. USA
btk@pacbell.net
http://www.starlightoptical.com
Telescope/Optical Stuff
And now, P1800 Volvos
http://www.starlightoptical.com/volvos.htm