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6 f/15 = 8 f/? equivalent classic achro

Started by pkelly, 12/05/2006 06:02PM
Posted 12/05/2006 06:02PM | Edited 12/05/2006 06:09PM Opening Post
Here's one for the numbers and program-runners...I really love my D&G 6" f/15 all ways...and its permanently set up and all comfy it its own little roll-off house. Now, if I wanted to step up to an 8", and maintain the same level of "color correction" (yes, I follow all the achro/apo stuff)...I guess I should better say "color performance", what would be the equivalent f/ratio...and likely tube length? I've had several chances at 8" f/12, but timing/$$/experience wasn't right, I like the "kinda almost apo" wink performance I get (yea, I know a color bloom is in there), I liked the light quality vs quantity. What would I need to do to have both at an 8" level? :S cwy shocked 8O

No..there's no way I could ever fabricate a folded refractor.

FWIW I'm a purely old-skool visual observer, have absolutely NO, NEVER any inclination for photography or imaging, love doubles and the like.

Thanks for your calculations smile

8" f/12 D&G classic refractor
Astro-Physics 1200 DA equatorial mount
BlueStar Observatory (roll off) by Backyard Observatories of Lodi, Ohio
Previous telescopes A-Z...Astro-Physics to Zeiss
Posted 12/05/2006 08:08PM #1
For the same level of color correction, you'd need to go to f/20 on the 8". That's getting a bit on the long side, and would be very tough to mount properly in a straight through version.

Clear skies, Alan
Posted 12/05/2006 09:21PM | Edited 12/05/2006 09:21PM #2
Hi Pat,

Not a direct answer, but I went from a 6" F/15 D&G to an 8" F/12 D&G and did not find the color in the larger scope to be any problem. I did not have them side by side to compare, but the color in the 8" was just a bit more pronounced than the 6". Much less than I expected. A fellow out here added a Chromacor to his 8" D&G and never looked back. He said the 8" gave views similar in detail to a 16" Newtonian he owned.

I still envy your observatory. By the way, I went from the 8" D&G to a 10" Mak-Cass.

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lthaxton's attachment for post 109736