Re: [ATM] Schmidt corrector tools

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

On Tue, 24 Jan 2006, George Anderson wrote:

> I am about to finally start on my schmidt corrector for the 6" f/2
> camera that I am building.


Exciting project! System or mirror is F/2?


> The glass I have for the tools is 1/4" plate, is this too flexible?
> Would bonding two pieces together with either pitch or "crazy glue" to
> for 1/2" thick pieces make sense?


As a rule I do not bond two pieces for this. There is plenty of thicker
glass around if you need it, but I suspect you do not. If you calculate,
and maybe you already have, the corrector curve is not very deep. For
mine, I could almost get it with polishing (primary is 310 mm F/1.55,
corrector is 6 mm thick). The Schmidt curve I settled on is as follows:

http://www.canit.se/~dlwebb/catadioptric/310schmidt/schcorr.jpg).



> thinking of 220 grit for "hogging" (

This seems extreme. The corrector is not very thick and you are at
least a little bit dependent on the thickness to arrive at your
final configuration. I would check this glass to see that it is
reasonably flat on the two sides and decide if there is any reason
to hog out so much glass. I do not remember exactly how I decided
on this, but I am quite sure I ended up using 600 SiC (not larger
than 400) grit from the start. As you can see from the link above,
I remove 80 microns at the deepest point. This you can identify even
with a bad sherometer. If you already have glass that is reasonably
flat and does not contain deep pits and scratches, etc (probably not
if it comes from a scanner) I recommend you try considerably finer
grit than 220.


Dominic-Luc Webb

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