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Posts Made By: joseph bobick

May 2, 2010 09:46 PM Forum: Telescope Making

bonding plate glass for mirror blank.

Posted By joseph bobick

Hello all,
I'm planning to make a 16" mirror for a dob and was wondering why I couldn't bond two pieces of 3/4" plate glass together for the blank.I can't find much discussion anywhere regarding this idea and I'm afraid it's probably because it's not a real good idea for some reason.Possibly because of the thermal properties of the glass? could anybody out there shed some light on this Idea.(No pun intended). Thank's.

November 7, 2010 10:54 AM Forum: Telescope Making

Figuring Dall/Kirkham primary.

Posted By joseph bobick

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.
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-

September 12, 2012 09:57 PM Forum: Telescope Making

Folded Newtonian

Posted By joseph bobick

Hello all,
I need a little help.I'm constructing a 16" truss style Dob.Primary dia. is 15.88" clear aperture.Focal ratio is 6.07.Focal length is 96.31".I'm a little concerned about truss length and stability.I saw some examples of folded newtonians and thought I might try that with mine.I was considering the single larger secondary design.I was curious as to how much shorter my truss poles would be using this design and trying to keep the secondary obstruction to a minimum.I'm good at building the scopes but not so much with the optical design.Can anybody help me with the numbers for this.Just need to try to take as much length away from truss tubes as possible and still get a decent image.Need secondary diameter,distance from primary,tilt angle etc.Thanks. -Joe-

November 13, 2010 04:22 PM Forum: Telescope Making

Figuring Dall/Kirkham primary.

Posted By joseph bobick

Thanks for your help fellas.-Joe-

March 13, 2010 05:41 PM Forum: Polls

Health Care

Posted By joseph bobick

I agree this country was not founded on greed.But put your ideology aside long enough to see how much money the government has thrown at the so called unfortunate.It does not help it only makes them more dependent.I know, I see it every day all around me.The media is waging a psycological war on any one that is not mentally strong enough to resist it.Just look what's happening to the youth.That's the war that needs to end.Just remember this:If you give a man a fish,you feed him for a day.If you teach him how to fish,you feed him for a lifetime.The successful people in this country contribute enough.It's just not being used properly.