Subject: [interferometry] Digest Number 1582 From: interferometry@yahoogroups.com Date: 9/18/2010, 4:06 AM
 To: interferometry@yahoogroups.com

interferometry

# Messages In This Digest (8 Messages)

1a.
Re: Al Mirror & Bath From: Stephen Koehler
2a.
Re: Analysis of secondary igram From: atmpob
2b.
Re: Analysis of secondary igram From: Martti Koskimo
2c.
Re: Analysis of secondary igram From: Martti Koskimo
2d.
Re: Analysis of secondary igram From: Mark Whitaker
2e.
Re: Analysis of secondary igram From: atmpob
2f.
Re: Analysis of secondary igram From: atmpob
2g.
Re: Analysis of secondary igram From: Martti Koskimo

# Messages

1a.

## Re: Al Mirror & Bath

### Posted by: "Stephen Koehler" s.c.koehler@gmail.com steve_koehler

#### Fri Sep 17, 2010 8:36 am (PDT)

Bruce,

Your contrast calculations are misleading since you don't take the third
> beam into account.
> It makes a much larger difference to the fringe contrast than the
> amplitude mismatch of the 2 beams you consider.
>

I believe you, but I need to look up what the third beam is. I also need to
remind myself what a Twyman-Green interferometer is, and how it precludes
the third beam.

> Your calculation of the fringe contrast for 2 beam interference seems
> somewhat astray.
>

That's entirely possible. I did it off-the-cuff.

One thing I did differently was to define contrast as (Imax - Imin)/Imax. I
believe this is approximately Weber contrast, whereas you used Michelson
contrast. I think we have some other differences, however.

> For an aluminised mirror with R= 0.9 (intensity) the corresponding
> amplitude reflection coefficient is ~ 0.948
> For an uncoated glass surface with an intensity reflection coefficient
> of 0.04 the corresponding amplitude reflection coefficient is 0.2
>

Agreed.

> Intensity at the fringe maxima, I2 ~ (0.948 + 0.2)*(0.948 + 0.2) ~ 1.319
> Intensity at the fringe minima I1 ~ (0.948 - 0.2)*(0.948 - 0.2) ~ 0.560
>

Sure. I was leaving one beam at intensity 1 and the other beam at intensity
r.

What I did wrong was to calculate the contrast ratio in amplitude (hence,
the need for the abs() functions), then square that to get contrast in
intensity. That doesn't work, because (a+b)^2 is not the same as a^2+b^2.

And the corresponding contrast is (I2-I1)/(I2+I1) ~0.4
>

Once corrected, I get this value, too.

For a beam intensity ratio of r the contrast is
>
> 2*SQRT(r)/(1+r)
>

I agree.

--
Steve Koehler
2a.

## Re: Analysis of secondary igram

### Posted by: "atmpob" atmpob@yahoo.com atmpob

#### Fri Sep 17, 2010 2:23 pm (PDT)

Thinking out loud here.

I suppose it should be negative. I use the ROC and desired conic to compute the Artificial Null. I think that and Z8 is the only place it gets used in calculations. Making it negative would change the sign of the artificial null and the computed Z8 term from what I tried (keeping it positive.)

Perhaps it is correct to make it negative or may not matter because if we get a calculated conic or Z8 term with the sign wrong we just reverse the fringes.

Since we do that it probably does not matter until someone has an optic whose concic is really positive with they thought it was negative.

Comments welcome.

Dale Eason

--- In interferometry@yahoogroups.com, "Martti Koskimo" <martti.koskimo@...> wrote:
>
> Mark,
>
>
>
> To make it clear:
>
>
>
> The radius of Cass secondary should be Negative in OpenFringe.
>
>
>
>
>
> Martti
>

2b.

## Re: Analysis of secondary igram

### Posted by: "Martti Koskimo" martti.koskimo@kolumbus.fi optifigure

#### Fri Sep 17, 2010 3:44 pm (PDT)

Dale,

I generated artificial correct igrams from ZEMAX. These was analysed in
OFringe. By trial and error it was quite easy to find correct input to
OFringe. I used all possible combinations and correct input for Cass mirror
was only possible if both radius and conic constant is same sign. Both
should be negative and also if both are positive you get the right answer.
And highs are high and lows are low correctly. As mentioned the conic
constant should be half of its real value.

Theoretically reasoning this would have been impossible to me.

Just in completing a Cass secondary (D=156 k=-2.065). I test it also in the
whole telescope using auto collimation when it is ready (according to
contact testing). I inform if there is any difference in test results.

Martti Koskimo

-----Original Message-----
From: interferometry@yahoogroups.com [mailto:interferometry@yahoogroups.com]
On Behalf Of atmpob
Sent: 18. syyskuuta 2010 0:24
To: interferometry@yahoogroups.com
Subject: [interferometry] Re: Analysis of secondary igram

Thinking out loud here.

I suppose it should be negative. I use the ROC and desired conic to compute
the Artificial Null. I think that and Z8 is the only place it gets used in
calculations. Making it negative would change the sign of the artificial
null and the computed Z8 term from what I tried (keeping it positive.)

Perhaps it is correct to make it negative or may not matter because if we
get a calculated conic or Z8 term with the sign wrong we just reverse the
fringes.

Since we do that it probably does not matter until someone has an optic
whose concic is really positive with they thought it was negative.

Comments welcome.

Dale Eason

--- In interferometry@yahoogroups.com
<mailto:interferometry%40yahoogroups.com> , "Martti Koskimo"
<martti.koskimo@...> wrote:
>
> Mark,
>
>
>
> To make it clear:
>
>
>
> The radius of Cass secondary should be Negative in OpenFringe.
>
>
>
>
>
> Martti
>

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2c.

## Re: Analysis of secondary igram

### Posted by: "Martti Koskimo" martti.koskimo@kolumbus.fi optifigure

#### Fri Sep 17, 2010 5:44 pm (PDT)

Martti Koskimo wrote:

The conic constant in testing Cass mirror in OpenFringe should be half of
its real value.

This is not exactly true. If in Analysing the Double Pass (mirror /test
parameters) is on, then the half of the conic constant value should be used.
After analysing clicking Double Pass on/off has no effect. It has effect
only before analysing. Not understanding this was my error.

The surface error you get is only half of its real value. I was getting
always Strehl ratio 0.99 and 0.98 and it was too good to be true.

So it is better to check that Double Pass is off and use the real conic
constant.

Excuse me this disturbance

Martti Koskimo

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2d.

## Re: Analysis of secondary igram

### Posted by: "Mark Whitaker" tnut55@yahoo.com tnut55

#### Fri Sep 17, 2010 6:37 pm (PDT)

Yes, this is what I am finding.

Mark

________________________________
From: Martti Koskimo <martti.koskimo@kolumbus.fi>
To: interferometry@yahoogroups.com
Sent: Fri, September 17, 2010 7:44:44 PM
Subject: RE: [interferometry] Re: Analysis of secondary igram

Martti Koskimo wrote:

The conic constant in testing Cass mirror in OpenFringe should be half of its
real value.

This is not exactly true. If in Analysing the DoublePass(mirror /test
parameters) is on, then the half of the conic constant value should be used.
After analysing clicking DoublePasson/off has no effect. It has effect only
before analysing. Not understanding this was my error.
The surface error you get is only half of its real value. I was getting always
Strehl ratio 0.99 and 0.98 and it was too good to be true.

So it is better to check that DoublePassis off and use the real conic constant.

Excuse me this disturbance

Martti Koskimo

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2e.

## Re: Analysis of secondary igram

### Posted by: "atmpob" atmpob@yahoo.com atmpob

#### Fri Sep 17, 2010 7:31 pm (PDT)

I like Martti's experimental approach.

You and Martti are using OpenFringe where I'm no expert. What version of OpenFringe are you using? There was a version where double pass was not used correctly by OpenFringe. I hope you are using the version I posted several months ago in the files section. But that does not assure there is still not a bug.

I worry when you say that the conic needs to be set to 1/2 the actual value. That was not my intention. But we are getting into the area of the analysis math that I am just a follower of others who I hope have a better understanding of what is needed.

I hope Steve and Mike can help out here. Maybe I still have some bugs in this area.

Dale Eason

--- In interferometry@yahoogroups.com, Mark Whitaker <tnut55@...> wrote:
>
> Yes, this is what I am finding.
>
> Mark
>
>
>
>
>
> ________________________________
> From: Martti Koskimo <martti.koskimo@...>
> To: interferometry@yahoogroups.com
> Sent: Fri, September 17, 2010 7:44:44 PM
> Subject: RE: [interferometry] Re: Analysis of secondary igram
>
>
> Martti Koskimo wrote:
>
> The conic constant in testing Cass mirror in OpenFringe should be half of its
> real value.
>
>
>
> This is not exactly true. If in Analysing the DoublePass(mirror /test
> parameters) is on, then the half of the conic constant value should be used.
> After analysing clicking DoublePasson/off has no effect. It has effect only
> before analysing. Not understanding this was my error.
> The surface error you get is only half of its real value. I was getting always
> Strehl ratio 0.99 and 0.98 and it was too good to be true.
>
>
> So it is better to check that DoublePassis off and use the real conic constant.
>
> Excuse me this disturbance
>
> Martti Koskimo
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> =======
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> lÃ¶ytynyt.
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>

2f.

## Re: Analysis of secondary igram

### Posted by: "atmpob" atmpob@yahoo.com atmpob

#### Fri Sep 17, 2010 7:38 pm (PDT)

Can you post the simulated igram into the Photo section along with the parametes like roc, actual cc, and wavelength. I might be able to use that to help me test OpenFringe better.

Dale Eason

--- In interferometry@yahoogroups.com, "Martti Koskimo" <martti.koskimo@...> wrote:
>
> Dale,
>
>
>
>
>
> I generated artificial correct igrams from ZEMAX. These was analysed in
> OFringe. By trial and error it was quite easy to find correct input to
> OFringe. I used all possible combinations and correct input for Cass mirror
> was only possible if both radius and conic constant is same sign. Both
> should be negative and also if both are positive you get the right answer.
> And highs are high and lows are low correctly. As mentioned the conic
> constant should be half of its real value.
>
>
>
> Theoretically reasoning this would have been impossible to me.
>
>
>
> Just in completing a Cass secondary (D=156 k=-2.065). I test it also in the
> whole telescope using auto collimation when it is ready (according to
> contact testing). I inform if there is any difference in test results.
>
>
>
>
>
> Martti Koskimo
>
>
>
>
>
>
>
> -----Original Message-----
> From: interferometry@yahoogroups.com [mailto:interferometry@yahoogroups.com]
> On Behalf Of atmpob
> Sent: 18. syyskuuta 2010 0:24
> To: interferometry@yahoogroups.com
> Subject: [interferometry] Re: Analysis of secondary igram
>
>
>
>
>
> Thinking out loud here.
>
> I suppose it should be negative. I use the ROC and desired conic to compute
> the Artificial Null. I think that and Z8 is the only place it gets used in
> calculations. Making it negative would change the sign of the artificial
> null and the computed Z8 term from what I tried (keeping it positive.)
>
> Perhaps it is correct to make it negative or may not matter because if we
> get a calculated conic or Z8 term with the sign wrong we just reverse the
> fringes.
>
> Since we do that it probably does not matter until someone has an optic
> whose concic is really positive with they thought it was negative.
>
> Comments welcome.
>
> Dale Eason
>
> --- In interferometry@yahoogroups.com
> <mailto:interferometry%40yahoogroups.com> , "Martti Koskimo"
> <martti.koskimo@> wrote:
> >
> > Mark,
> >
> >
> >
> > To make it clear:
> >
> >
> >
> > The radius of Cass secondary should be Negative in OpenFringe.
> >
> >
> >
> >
> >
> > Martti
> >
>
>
>
>
>
>
>
>
> =======
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> ei löytynyt.
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> =======
>
>
>
>
>
> =======
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>

2g.

## Re: Analysis of secondary igram

### Posted by: "Martti Koskimo" martti.koskimo@kolumbus.fi optifigure

#### Sat Sep 18, 2010 4:03 am (PDT)

Dale wrote:

<Can you post the simulated igram into the Photo section along with the
parametes like roc, actual cc, and wavelength. I might be able to use that
to help me test OpenFringe better <

Sure, I will post several igrams from low to high asphericity (For curiosity
I put there also Texereau’s Cass mirror).These are useful in learning to use
analyse programs. You know the result you have to get. It is also useful for
the program user to experiment how critical accurate edge detection is and
get feeling to these tolerances too. The same igrams can be used to test
concave mirrors. The igram is the same but ‘inverted’.

As you mentioned they are good also for testing analyse programs and how
well the zernikes fit and thus find the tolerances and to test modelling
accuracy.

It is good to have ‘perfect interferogram’ (and to analyse this also) from
the mirror you are just making and also VISUALLY compare them to real life.
>From experience I have learned not to trust only numbers and computer
output. Not to mention typing errors I do. For the same reason in every
testing I make also artificial perfect igram from intermediate stage
corrected mirror.

I have been eager to test Mike’s RFringe. I have the R running but
unfortunately at point to read interferogram RFringe is not accepting any of
my igram files. I have been unable to convert them to acceptable format.

Martti Koskimo

-----Original Message-----
From: interferometry@yahoogroups.com [mailto:interferometry@yahoogroups.com]
On Behalf Of atmpob
Sent: 18. syyskuuta 2010 5:39
To: interferometry@yahoogroups.com
Subject: [interferometry] Re: Analysis of secondary igram

Can you post the simulated igram into the Photo section along with the
parametes like roc, actual cc, and wavelength. I might be able to use that
to help me test OpenFringe better.

Dale Eason

--- In interferometry@yahoogroups.com
<mailto:interferometry%40yahoogroups.com> , "Martti Koskimo"
<martti.koskimo@...> wrote:
>
> Dale,
>
>
>
>
>
> I generated artificial correct igrams from ZEMAX. These was analysed in
> OFringe. By trial and error it was quite easy to find correct input to
> OFringe. I used all possible combinations and correct input for Cass
mirror
> was only possible if both radius and conic constant is same sign. Both
> should be negative and also if both are positive you get the right answer.
> And highs are high and lows are low correctly. As mentioned the conic
> constant should be half of its real value.
>
>
>
> Theoretically reasoning this would have been impossible to me.
>
>
>
> Just in completing a Cass secondary (D=156 k=-2.065). I test it also in
the
> whole telescope using auto collimation when it is ready (according to
> contact testing). I inform if there is any difference in test results.
>
>
>
>
>
> Martti Koskimo
>
>
>
>

=======
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