Author Topic: Outer zones too high?  (Read 192 times)

Adam Washington

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Outer zones too high?
« on: January 03, 2018, 08:42:06 AM »
I'm having a senior moment....figuring/testing my 12" mirror, I'm thinking my outer zones are too high, IE they need to be worked down?

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ropnolini

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Re: Outer zones too high?
« Reply #1 on: January 12, 2018, 06:45:53 AM »
its focusing too long if your readings are accurate, so you need to remove correction 3-7 most in the outer zones.

you would easily confirm that with a ronchi grating. you ctr bands would be really skinny and the outer zone bands be really fat maybe curve too much

Elroy Stockton

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Re: Outer zones too high?
« Reply #2 on: January 12, 2018, 09:28:58 PM »
Thanks, I did see that in the Ronchi test. I get confused by the % Zonal Correction numbers, I always want to equate overcorrection to "over-worked" in my head, as if I had worked the zone "down" too much.
I finally understand overcorrection means too much curvature, basically.....correct? Also, focusing too long outside of focus = too short inside, right? I'm getting dense in my old age.....

soecolerfe

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Re: Outer zones too high?
« Reply #3 on: January 13, 2018, 07:25:20 AM »
Quote
I always want to equate overcorrection to "over-worked" in my head, as if I had worked the zone "down" too much.
well in the outer zones that's true, its too flat, focusing longer.

in the center, overcorrection is too deep, focusing shorter.

and the .7 zone is where they match a sphere, and overcorrection changes from deeper in the center to flatter in the outer zones.

Chris Mancia

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Re: Outer zones too high?
« Reply #4 on: January 13, 2018, 11:14:16 PM »
So Figure XP is telling me the outer zones are too flat? Thanks for your help!

John Sanchez

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Re: Outer zones too high?
« Reply #5 on: January 18, 2018, 03:18:26 AM »
Heresa Ronchi, outside of focus, 85 LPI

wagishohots

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Re: Outer zones too high?
« Reply #6 on: January 18, 2018, 10:54:39 AM »
yeah, the lines are hooking too much, looking at your ronchi I'd deepen the ctr a little so the lines curve gently.

tot would lower you outer zones but also raise your ctr, so you'd have to be mindful of that.

but you know a hill is easier to deal with....https://www.youtube....h?v=Vr5c3NL9yR4


David Reynolds

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Re: Outer zones too high?
« Reply #7 on: January 25, 2018, 05:52:27 PM »
here's ideal and .4~ over

your so close...


swarfestmatvo

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Re: Outer zones too high?
« Reply #8 on: January 26, 2018, 12:02:41 AM »
OK, Thanks. I'm going to live dangerously and put it on the machine for 10 moreminutes, 7.5" star lap, COC, 7 RPM, stroke about an inch over each edge, eccentric 20 RPM.
Worked good to deepen center smoothly before, fingers crossed.

John Fimbres

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Re: Outer zones too high?
« Reply #9 on: January 30, 2018, 03:19:58 AM »
do you ever use polishsim?

https://www.youtube....h?v=cs-g3MT-AFM

acbanlota

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Re: Outer zones too high?
« Reply #10 on: January 30, 2018, 10:10:53 AM »
Yes, I have used it, pretty neat!

renjaysunsdis

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Re: Outer zones too high?
« Reply #11 on: January 30, 2018, 11:28:34 PM »
Polsim shows my plan of attack looks good!

Leon Vale

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Re: Outer zones too high?
« Reply #12 on: January 31, 2018, 01:19:42 PM »
I'm slowly working a 10", and I'm dealing with the remnants of a really bad TDE. I find that the dark Ronchi bands generally look good, but on closer inspection, the bright lines, curving out to the edge [outside focus] show a tiny hook. Even with a diffraction edge.... Foucault also confirms that there's a narrow TDE. (Also inside focus, there's the opposite "pinch' in the dark lines).

Does anybody see that same effect on the ronchigram photo in post #6.

Or because I'm dealing with a TDE, I'm seeing it everywhere?

Gary Eldridge

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Re: Outer zones too high?
« Reply #13 on: February 02, 2018, 05:50:33 PM »
his is longer focusing, not tde, but similar effect - a tde is a overcorrection cause its not really turned down just a qick flattening of the radius

the ronchi can give you a diffraction effect and my you think you have a tde.

a ke diffraction will tell you if it is a tde