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Aperture Fever

Started by brucesdad13, 07/02/2015 08:28PM
Posted 07/02/2015 08:28PM | Edited 07/02/2015 08:30PM Opening Post
Well, this gripping telescope fever has taken hold so deeply and with such force that I basically feel like I will move anything in the way of getting towards a big scope. I can't explain why it's so quickly ballooned. December 25th 2014 I was gifted a Celestron PowerSeeker 70AZ. Within a few weeks a used Celestron C8 SCT. Then cameras and astrophotography galore. Then some fixer-uppers including a Criterion RV-6. And now.... drum roll...

... I've purchased a 46" wide x 36" deep x 34" high 220v kiln for $100 made up of 200 fire bricks and weighing over 500lbs. I just need to find a friend with a flat bed to help me bring it home. I've also found several sheets of plate glass 46" x 75" x 5/8"... where is this all leading... I'm thinking something like this: http://wonderfuluniverse.com/telescope_page1.htm but the string telescope version.

In the beginning I'm going to take a mirror making workshop with a guy from the club. Wondering what a good size to start is. He's trying to keep me realistic and starting without something too insane. I thought I had found a 14" plate glass blank but it was sold. Pyrex seems too pricey as does Zerodur (sp?).

Anyone else go bananas like this? I feel like I have to go forward with this even if it takes years and it probably will. I've just finished reading Starlight Detectives and so I know all the trials and tribulations of say the 100" Mt. Wilson among dozens of others. At least by the time I finish the 40" mirror I will have had time to remove trees and dig a seriously stable base for a pier to hold everything.

~ Charlie Stevenson

8" f/5.7 String Telescope - 1st Scope Build; 2nd Place Stellafane 2016 Optical Award for Newtonians 12.5" and Smaller
10" f/4.5 Newtonian (June 2015) mirror refigured by Optic Wave Labs P-V WaveFront 1/14.24, Strehl Ratio 0.993 (Aug '15)
Criterion RV-6 seems to be circa 1973 (June 2015) [For Sale]
Celestron C8-A XLT (January 2015) [For Sale]
Celestron PowerSeeker 70AZ (Christmas 2014)
Aldrich Astronomical Society member since 2015
http://astro.charleskelleystevenson.com/
Posted 07/02/2015 10:01PM | Edited 07/03/2015 10:32AM #1
Per the biggest scope you presently have, my later-production Meade 10" Starfinder came with a 2.3" diagonal which effectively made it a 9" f/5 with the focal plane 10" (edit: this should be 11" distance rather than 10") from the secondary as it was set-up. A 2.6" diagonal is the minimum size necessary with such a set-up (a 2.6" diagonal was in in the original early 1990's 10" Starfinders) so I replaced the stock diagonal with same; the 2.6" here provides full illumination on-axis with an unnoticeable 1/2 magnitude fall-off at the very edge of a low-power 2" barrel eyepiece or corners of full-frame 35mm film. A larger diagonal in this case wouldn't really benefit light-wise photographically or visually, but would detrimentally increase the central obstruction for planetary or Lunar observing (high-resolution planetary viewing really demands a tracking mount or platform). While my scope's original Meade mirror had a good figure with slight astigmatism and performed well, it now has a Swayze-figured primary and Antares 1/30th wave 2.6" secondary; that extra light in the airy disk really shines on all objects, making faint deep-sky clearer as well. I've self-made several mirrors in the past and suggest your 10" would be a good starter size; perhaps eventually re-figure it yourself if a re-figure is warranted after star-testing when it returns from the coater. The grinding is not that skill-demanding (just lot of work) but figuring a really large mirror I do not recommend for the very first attempt. And BTW, any mirror 6" or larger gathers plenty of light un-coated for night-time Star-testing or even viewing the Moon and Saturn to check it's figure before coating, likewise for mirrors with deteriorated coatings.