Author Topic: 6in Dall-Kirkham  (Read 134 times)


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6in Dall-Kirkham
« on: December 24, 2017, 09:10:15 PM »
I started grinding a brand new 6" mirror a week.  I'd got a borosilicate float glass disc some time ago with the intent of involving the substantial other in making a newtonian telescope since she showed interest after Stellafane 2016.  Long story short, I coarse ground it to an F4 with the intent of creating a small travel scope.  I've always wished to take a look at creating aCassegrain scope, so I figure why not give it a try.  I used a calculator "Initially composed by Jean Texereau.  Translated and modified by Will Remaklus.  JavaScript version by Tom???? Maru??ka 26-11-1999.  Removed bug in computing, additional 4 decimal places into output 4-8-2006."  And came up with the following.  Since it sits, the one thing which I am unsure of is if 8" of backfocus will probably be enough to utilize a star diagonal at the focuser.
I'm not brilliant with mathematics as the furthest I ever got in school (with mathematics) was 10th grade, but I try to learn/relearn since I go.  To cancel this lack in mathematics I do have an extensive background in mechanics and fabrication.  I am a backsmith by commerce with a few machine experience, and was a mechanic for General Motors in a past life - figuratively speaking.  I have so far built two telescopes, only 3" f10 in which I didn't make the optics, and yet another 6in F8, I just finished the optics on.
I intend on coring the primary 90% of the way before I go past 120gr.  I'm thinking 1.25" hole in the primary.  The secondary I plan on grinding from 3" rounds and also coring 80-90% of the way, and I'm thinking of slightly oversizing it to 1.5" to allow for some motion, and dealing with the small bit of additional light loss and diffraction.
I'll attach photos of the possible physical dimensions on the scope, as well as the calculations on the optics.  I'm planning to figure out the primary through traditional approaches using the Foucault knife-edge test.  The secodary I plan on testing by assessing the instrument with aFoucault knife-edge evaluation, and the mirror to the tool with a simple Fringe tester.  Then, assessing the entire system with autocollimation, and star testing.  I will silver the mirrors in store, so silvering the secondary for analyzing is a non issue.
We'll see what happens.  It may be a collapse, it may be a sucess.  However there's absolutely no way to know if I can or can't succeed if I don't try it.
I simply have to figure out if the rear focus is adequate before I could start on the secondary.
It would be wonderful to hear your thoughts on the subject.
Thank you,