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ATM 13" SCT update
This is just an update on my 13" SCT project to those few that might
be interested. First I will list the specs for the optics assuming
perfect optics. Yeah sure <G>
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Clear Aperature 13.1"
Focal Lenght 157.2"
Secondary dia. (for 1.5" field) 3.2"
Focal ratio 12.00
Primary Radius 58.50"
Primary Aspheric Deformation 0.00000 (spherical)
Secondary Radius -16.287"
Secondary Aspheric Deformation -0.585258 (elliptical)
Primary to Secondary Distance -22.62"
Schmidt Corrector (n=1.523)-
strenght 0.812051 (compared to a true Schmidt)
Schmidt Corrector Thickness 0.38"
Primary to Corrector Distance 25.60"
Secondary to Focal Plane Distance 35.62"
Primary to Focal Plane Distance 13.00"
Spericcal Aberration 0.000000
Coma 0.000000
Astigmatism 0.000448
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I have completed the primary and have perforated it with a 2.75"
hole. The perforation even with the plug left in did give me
some problems with the correcting. It was mostly
my boo-boo , long story.
The hole was core drilled with a hole saw. The teeth were ground off
and and some slits ground in the saw for the 80 grit.
The core drilling was done on a mill- drill at 120 rpm.
The corrector plate was cut from a piece 1/2" thick white crytal glass.
First the glass was checked with cross polarizers for strain.
It just had a little shadow on one side so I cut around that side.
The 13.75" dia. glass plate was biscuit cut with a homemade trepanning
cutter on my mill-drill at about 30 rpm. This took about 40 min.
Unlike plate glass this glass is neither flat or parallel.
My plan is to grind one side mechanical flat then( have) the other
side blanchard ground parallel and to the correct thickness.
I am going to make the vacuum pan from a surplus 1.25" thick steel disk.
My metal dealer wanted $180.00 for a piece of 16"x16"x1.5" aluminum
plate. The steel is a bit heavy but for $20 yeah well <G>
That its for now :-)
Bob Pfaff