Hello all,I would appreciate any help in figuring the elliptical primary mirror for my Dall/Kirkham scope.I have figured parabolas in the past by reading about it.But this one is different,apparently it is figured to 70% of a parabola and I cannot find any literature on this subject that explains in laymans terms(thats me)how to approach that.I guess I should start with the design of the scope which was put together by someone else and this is what he came up with.I hope its right.

System...........F20

Primary dia..... 12.87"

Primary F/L..... 58.0"

System F/L...... 259.09"

Back F/L........ 8.0"

Distance secondary

from system focus 53.6175"

Distance secondary

from prime focus 12.0024"

Distance secondary

from primary.... 45.6175"

ROC of secondary 30.9284"

Primary conic... -0.7578

Secondary conic. 0.0

Extension factor 4.4671

Maybe someone with the expertise can double check the numbers on this design.I would greatly appreciate it.

Right now I have the mirror polished to a sphere with a ROC of 116" according to the focault test.I'm just a little confused about how to approach figuring it to only 70% of a parabola.I'm planning on using the everest stick pin method and will need to find the zones for an ellipse of -0.7578% of a parabola.Thats where I am confused.Also not sure if I start at the central zone during figuring and move away to what point like is done for a parabola?If anyone can help I would surely appreciate it.Thanks.-Joe-

System...........F20

Primary dia..... 12.87"

Primary F/L..... 58.0"

System F/L...... 259.09"

Back F/L........ 8.0"

Distance secondary

from system focus 53.6175"

Distance secondary

from prime focus 12.0024"

Distance secondary

from primary.... 45.6175"

ROC of secondary 30.9284"

Primary conic... -0.7578

Secondary conic. 0.0

Extension factor 4.4671

Maybe someone with the expertise can double check the numbers on this design.I would greatly appreciate it.

Right now I have the mirror polished to a sphere with a ROC of 116" according to the focault test.I'm just a little confused about how to approach figuring it to only 70% of a parabola.I'm planning on using the everest stick pin method and will need to find the zones for an ellipse of -0.7578% of a parabola.Thats where I am confused.Also not sure if I start at the central zone during figuring and move away to what point like is done for a parabola?If anyone can help I would surely appreciate it.Thanks.-Joe-