Author Topic: Reducing down my data, the bad and the good.  (Read 203 times)

Tim Jauregui

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Reducing down my data, the bad and the good.
« on: December 29, 2017, 03:49:17 AM »
Maybe it doesn't happen very often, when someone posts their data on a bad mirror.
I was looking for a program to plug-in my data for KE readings. I don't really want to get into a discussion on how accurate they are or not. I just wanted something to give me a general idea, if the mirror is good or bad. So, I downloaded Figure XP. No pros or cons on it, I just read a lengthy post earlier.
This is more about my discovery on the data on the 8" f/3.1 primary that is in my Gregorian. I had believed that the mirror was good. Tom Waineo took the mirror back to his shop back in '69, to put some final touches on it. He tested 8 zones and recorded the readings for me. He said, "reduced a .020 focus shift down to about .004. The mirror is very slightly overcorrected, but only by about 1/8 wave." So, I believed the mirror was good. But after re-assembling the optics last year, I found it gives "soft" images. I felt the error was initially do to culmination or the secondary. I figured and null tested the secondary. Plugging in the data into Figure XP I get:

8" f/3 primary:

PV wavefront 1.42 wave
Transverse error 13.23
Encircled Energy ratio .087
Strehl .016
surface error 82.7

This is a very bad mirror! I thought I'd fess up on it.

However,  when I plug in the data from my 10" f/7 newt, I get:

PV wave front 1/27.52
Transverse error .538
Encircled Energy ratio .996
Strehl .996
surface RMS error 2.9

I knew from using the 10" for many, many years, that it was a very good mirror. So, maybe a little bragging on this one.

I'm in the process of making a 4-1/4" f/13 newt, so I'll see what numbers it can generate as I complete it. I'm also going to pull the 6" f/9.6 mirror out of another newt and test it too. No zone readings were ever taken. The guys in the DAS back in the '60s said it was good enough. It gives great views too, and IMO, it has an excellent mirror. Well we shall see.

Any and all comments welcome, but I cannot debate.



contreleri

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Re: Reducing down my data, the bad and the good.
« Reply #1 on: January 03, 2018, 11:03:54 PM »
Quote
What conic are you using for this test?

charnhoupito

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Re: Reducing down my data, the bad and the good.
« Reply #2 on: January 04, 2018, 10:27:07 AM »
Quote
However,   when I plug in the data from my 10" f/7 newt, I get:

PV wave front 1/27.52
Transverse error .538
Encircled Energy ratio .996
Strehl .996
surface RMS error 2.9

I knew from using the 10" for many, many years, that it was a very good mirror. So, maybe a little bragging on this one.

Any and all comments welcome, but I cannot debate.

Ok, Strehl .996 is impossible. I believe you it is a very good mirror, but any mirror above Strehl 0.90 is a very good mirror! The main part of the impossibility is for a simple one-dimensional Foucault test to guarantee such numbers. Just reading the errors in the shadows, the mask opening, placements, makes for several thousands inch error in the lateral motion readings, not to mention unmeasured astigmatism, so, no its not a real measurement or result.

I doubt I could even see a 1/27 pvw by star test, a very sensitive test! What does it look like by star test?

Maybe try averaging several readings and reductions, by rotating the mirror, taking the mask off and on, etc. And do your best not to be biased in the shadow measures, if you have an idea of what they "should" be

bersrorexnutg

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Re: Reducing down my data, the bad and the good.
« Reply #3 on: January 05, 2018, 03:41:52 PM »
Quote
Ok, Strehl .996 is impossible.
Maybe you could read the first post again? Specifically "I don't really want to get into a discussion on how accurate they are or not. I just wanted something to give me a general idea, if the mirror is good or bad".

​Dave

John Sanchez

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Re: Reducing down my data, the bad and the good.
« Reply #4 on: January 08, 2018, 12:07:26 AM »
Use ML conditions for establishing tolerances for each zone. Take measurements and simply 'zero' them for minimal transverse error.
The ML will represent a rating of around 1/10th wave @ .97 strehl. Also establishes the tornado curve +-.
 You can do this all with a pencil and a piece of scratch paper. I do not favor how XP optimizes the raw data, for it's not conservative enough as set up with default.
Anything over 6-8" aperture, you won't see 1/27th in a startest. Practically everyone does it wrong by intra-extra images where they -should- be paying attention to the -IN- focus pattern. A good benchtest done right where 'atmospherics' can be controlled/minimized will tell you everything you need to know without taking it outside; IE startest won't tell you anything you don't already know.

ryepittimy

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Re: Reducing down my data, the bad and the good.
« Reply #5 on: January 11, 2018, 09:27:02 AM »
Quote
Quote
Ok, Strehl .996 is impossible.
Maybe you could read the first post again? Specifically "I don't really want to get into a discussion on how accurate they are or not. I just wanted something to give me a general idea, if the mirror is good or bad".

​Dave
How can you get a general idea if its good or bad with 0.996? Well if you believe its true, then your mirror is perfect, thread finished Anyway, my comments were regarding the second mirror, the regular parabola. Not sure what the first set were for, the primary alone or the whole system?

Jody Mukherjee

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Re: Reducing down my data, the bad and the good.
« Reply #6 on: January 11, 2018, 03:35:59 PM »
<< This is more about my discovery on the data on the 8" f/3.1 primary that is in my Gregorian. I had believed that the mirror was good. >>I don't see any data for this mirror. What am I missing?

dan

inlaylale

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Re: Reducing down my data, the bad and the good.
« Reply #7 on: January 12, 2018, 08:25:37 AM »
Quote
<p class="citation">QuoteI figured and null tested the secondary. Plugging in the data into Figure XP I get:
PV wavefront 1.42 wave
Transverse error 13.23
Encircled Energy ratio .087
Strehl .016
surface error 82.7

What conic are you using for this test?[/quote]
Conic is -1

compstifcolpai

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Re: Reducing down my data, the bad and the good.
« Reply #8 on: January 12, 2018, 09:34:10 AM »
Quote
Quote
However,   when I plug in the data from my 10" f/7 newt, I get:

PV wave front 1/27.52
Transverse error .538
Encircled Energy ratio .996
Strehl .996
surface RMS error 2.9

I knew from using the 10" for many, many years, that it was a very good mirror. So, maybe a little bragging on this one.

Any and all comments welcome, but I cannot debate.

Ok, Strehl .996 is impossible. I believe you it is a very good mirror, but any mirror above Strehl 0.90 is a very good mirror! The main part of the impossibility is for a simple one-dimensional Foucault test to guarantee such numbers. Just reading the errors in the shadows, the mask opening, placements, makes for several thousands inch error in the lateral motion readings, not to mention unmeasured astigmatism, so, no its not a real measurement or result.

I doubt I could even see a 1/27 pvw by star test, a very sensitive test! What does it look like by star test?

Maybe try averaging several readings and reductions, by rotating the mirror, taking the mask off and on, etc. And do your best not to be biased in the shadow measures, if you have an idea of what they "should" be
I understand that .996 is impossible, but I'm only saying what the program says.

Back then, back about '75, I did take several tests, even rotating the mirror 180. I understand the bias, and taking measurements from scratch each time. I also understand about human error, but it seems it would average out (?).

The star test is very good.

grountentaybrig

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Re: Reducing down my data, the bad and the good.
« Reply #9 on: January 13, 2018, 01:12:45 PM »
Quote
Quote
Ok, Strehl .996 is impossible.
Maybe you could read the first post again? Specifically "I don't really want to get into a discussion on how accurate they are or not. I just wanted something to give me a general idea, if the mirror is good or bad".

​Dave
Thanks Dave, but I know I am an amateur compared to you guys. Do I think the mirror is .996? NO! But I do think the mirror is very good.

Jason Hillyer

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Re: Reducing down my data, the bad and the good.
« Reply #10 on: January 15, 2018, 02:56:19 PM »
Quote
Quote

Quote
Ok, Strehl .996 is impossible.
Maybe you could read the first post again? Specifically "I don't really want to get into a discussion on how accurate they are or not. I just wanted something to give me a general idea, if the mirror is good or bad".

​Dave
How can you get a general idea if its good or bad with 0.996? Well if you believe its true, then your mirror is perfect, thread finished Anyway, my comments were regarding the second mirror, the regular parabola. Not sure what the first set were for, the primary alone or the whole system?
For clarification, the 8" primary of the Gregorian - the data is just of that mirror not the whole system.

I don't agree that my 10" mirror is perfect. I will accept very good.
I agree the 8" mirror isn't good. I didn't think it would be sobad.

I guess the program puzzled me, I didn't think my average readings were that good, to give such results on the 10".
I felt something may be wrong with the primary on the 8", but I didn't think the data would give such badnumbers.
Then the opposite on the 10", the program gave better results than what I thought they would be. I will try and post a pic of the Figure XP pages.

So, do I just take Figure XP as just a tool to see if the mirror is good or bad? and ignore it's results? Or not use it at all?

anficonco

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Re: Reducing down my data, the bad and the good.
« Reply #11 on: January 15, 2018, 10:03:19 PM »
Quote
&lt;&lt; This is more about my discovery on the data on the 8" f/3.1 primary that is in my Gregorian. I had believed that the mirror was good. &gt;&gt;I don't see any data for this mirror. What am I missing?

dan

I did not post the data from either mirror, just the results of the program. I will get the original hand written sheet on the 8" that was sent to me and get it up.

I have used Millies-Lacroix for both mirrors. I will try and get everything up to you guys to see.
-not sure if that's going to help.

cludertypos

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Re: Reducing down my data, the bad and the good.
« Reply #12 on: January 25, 2018, 04:32:22 PM »
Quote
I understand that .996 is impossible, but I'm only saying what the program says.
Back then, back about '75, I did take several tests, even rotating the mirror 180. I understand the bias, and taking measurements from scratch each time. I also understand about human error, but it seems it would average out (?).

The star test is very good.
Yeah that's a common issue with Foucault and reduction programs, people often take them as biblical quotations  It would be really nice to try take some star test images with your phone, on the brightest star you can get, at the highest elevation, to minimize seeing. Sirius is good for me, but I think you'd be better off with Capella or such.

If you measured that f/3 by itself, then you need to have the program adjust to find the best conic fit. -1 works only for a perfect parabola, so I'm not surprised the Strehl is off, if there is a significant correction difference at this f/ratio.

ertafsurpnant

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Re: Reducing down my data, the bad and the good.
« Reply #13 on: January 25, 2018, 11:39:16 PM »
Quote
Quote
I understand that .996 is impossible, but I'm only saying what the program says.
Back then, back about '75, I did take several tests, even rotating the mirror 180. I understand the bias, and taking measurements from scratch each time. I also understand about human error, but it seems it would average out (?).

The star test is very good.
Yeah that's a common issue with Foucault and reduction programs, people often take them as biblical quotations  It would be really nice to try take some star test images with your phone, on the brightest star you can get, at the highest elevation, to minimize seeing. Sirius is good for me, but I think you'd be better off with Capella or such.

If you measured that f/3 by itself, then you need to have the program adjust to find the best conic fit. -1 works only for a perfect parabola, so I'm not surprised the Strehl is off, if there is a significant correction difference at this f/ratio.
But in the Gregorian, it's suppose to have a parabola for the primary, and an ellipse for the secondary.

longtichaten

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Re: Reducing down my data, the bad and the good.
« Reply #14 on: January 26, 2018, 01:02:26 AM »
Quote
<p class="citation">QuoteI figured and null tested the secondary. Plugging in the data into Figure XP I get:
PV wavefront 1.42 wave
Transverse error 13.23
Encircled Energy ratio .087
Strehl .016
surface error 82.7

What conic are you using for this test?[/quote]
Mark, that is the primary, not the secondary.

"I figured and null tested the secondary. Plugging in the data into Figure XP I get:8" f/3 primary:
PV wavefront 1.42 wave
Transverse error 13.23
Encircled Energy ratio .087
Strehl .016
surface error 82.7"

Dave