Re: [ATM] What the schmidt?

[Dominic-Luc Webb <dlwebb@canit.se>]

Me too! I never really mastered OsloLT, the spot diagrams looking
prettty bad for a design I expect to prove exceptional (310 mm
F/1.55 primary with standard Schmidt corrector). For current
discussion, the spots I got were different, but not much. On the
other hand, what certainly matters is the thickness at any given
distance from center. The surface of any glass you obtain from any
source is going to have deviations from flat, so I have always
wondered what the most straightforward way is to get the effect of
the Schmidt curve (the right thickness at any give point). Two
halves of a Schmidt curve start looking easier than an optical
flat and a full Schmidt curve, so I really do wonder how people
prefer working the second surface these days and which of these
was easier to make with precision.

Along same discussion, has anyone else compared common low iron
plate glass to BK7, etc. I have not seen much info on subject of
choice of glass for this surface to cover entire UBVRI.

Dominic-Luc Webb


On Sat, 17 Feb 2007, Jarvis Krumbein wrote:

> George, are you putting the correction on both (1/2 & 1/2) sides of the
> corrector?  If you are, do you have to adjust the sagitta depth to
> account for the glass removed from the first side?  While I'm not working
> on a Schmidt this is a question I've always been curious about.
>
> Jarvis Krumbein
>
> On Sat, 17 Feb 2007 04:29:16 +0000 (GMT) tillerman1@videotron.ca writes:
> > The vacuum pan is complete and the rim was greased, boiled distilled
> > water added to the pan and the 6.125" corrector blank gently
> > pressed
> > in place so as to remove almost all bubbles.
> > I sucked the pan down to the required sagitta and left it alone,
> > after
> > 6 hours it had lost half the sagitta. Sucked it down again and left
> > it
> > for another 8 hours, lost about 1/8 the sagitta. Sucked down again
> > and
> > left it for 10 hours with no loss.
> > Spent a little over an hour tonight with 400 grit cautiously
> > grinding
> > the tool profile into the corrector blank. There is about a 1"
> > diameter spot in the middle that isn't ground yet and the tool has
> > changed to try to match the original deeper sagitta of the vacuum
> > pan.
> > I'll regrind the tool tomorrow night after the kiddies are in bed
> > and
> > then go back to grinding the corrector and do a few more passes (I
> > hope).
> > I think this is the most time consuming part of the grinding, once
> > I
> > get past this it should go pretty fast (comparitively) through the
> > other grits and then comes the hours of polishing.
> > Many thanks to Bob Pfaff and Dave Rowe for the documentation and
> > knowlege they have put on line on various sites.
> >
> > George Anderson
> > Montreal Canada
> >
> > Clear skies and good health
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
> >
>
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