[ATM] Re: ATM zones

["Bob Walker" <tac@i1.net>]

wait for equilibrium before testing mirror--sounds right, but for us
impatient types, is there an alternative?  Reasoning that the evidence for
the effectiveness of fans for keeping mirrors at equilibrium temperature
during observing is now overwhelming, would the same thing work for
figuring?  During figuring my 16" f/5.4, I set it on the test stand
immediately after figuring (and washing!) and set a 20" window fan blowing
across it at a medium gale.  I found after something like 15 minutes of
this, the figure seemed the same as it was if I waited another couple of
hours, or overnight.  Has anyone else tried this?  or am I the only one
whose motto is "Patience is a wast of time"?
I still haven't gotten my scope completed enough to do careful star testing,
but during Mars' apparition last fall, it looked mighty good -- still
uncoated. I've left further testing until I get the structure more
complete -- also waiting for some semblance of clear skies!!

----- Original Message -----
From: <atm-request@atmlist.net>
To: <atm@atmlist.net>
Sent: Friday, December 10, 2004 7:14 PM
Subject: ATM Digest, Vol 12, Issue 10


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> When replying, please edit your Subject line so it is more specific
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>
> Today's Topics:
>
>    1. cutting tube in the first generation
>       (Ina Ron Lippard Renaissance Reproductions)
>    2. RE: Ray tracer for cheap? (Julio Sanchez)
>    3. Cassegrain Secondary testing (Mike Lockwood)
>    4. Re: FW: Oslo short (Woodchuck)
>    5. Re: Square over Round Truss Tube (Bob May)
>    6. Re: Set of specs. (Bob May)
>    7. re Oslo (Ellen Mackenzie)
>    8. Telescope Optics Workshop (Richard Schwartz)
>    9. Re: ANY LENS IN DIGITAL PHOTOCOPY MACHINE ? (Dave Smith)
>   10. Re: Square over Round Truss Tube (Arjan te Marvelde)
>   11. Re: Ray tracer for cheap? (vladimir sacek)
>   12. zones (David  Williams)
>   13. zones 1 (David  Williams)
>   14. Re: zones (Jerry B. Hillman)
>   15. OT: Question for David Williams (GARY FUCHS)
>   16. Re: Re: Ray tracer for cheap? (Guy Brandenburg)
>   17. Re: zones (Guy Brandenburg)
>   18. Re: Waineo/Jones null test question (Hiroyuki HIKITA)
>   19. Re: Re: Holographic Foucault null test (Mauritz Andersson)
>   20. Re: Holographic Foucault null test (Mauritz Andersson)
>   21. Re: zones 1 (Bob May)
>   22. Re: zones (Bob May)
>   23. Re: zones (Jim Burrows)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 09 Dec 2004 07:15:24 -0500
> From: Ina Ron Lippard Renaissance Reproductions
> <renrepro@surfglobal.net>
> Subject: [ATM] cutting tube in the first generation
> To: atm@atmlist.net
> Message-ID: <41B841DC.6040404@surfglobal.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>     If you don't have a cut-off saw but do have a bench and circular
> saw,try this: Start by taking a block of squared wood and drive a 1 1/4"
>   bright finish nail 1/2" into it.Clip off the head and file it to a
> point.The nail point should be on center to your tube.Rig up the skill
> saw with a barn door arrangement(I'd get a good ball bearing door hinge
> at a salvage yard for about $10) that acts like a chop saw.Screw the
> assembly to the bench.A rail installed at the proper angle to the blade
> is screwed to the bench.A wood clamp can act as an adjustable
> stop.Scratch a mark along the side of the workpiece on the first
> end.With a prick punch,lightly mark this line.After some trial and
> adjustment,cut the first tube.If it looks to long either use some shim
> stock inserted between block and workpiece or us a a light tap of the
> mallet on the stop.After all pieces are cut and marked flip the pieces
> and trim side 2 using the marks and block to line up both ends.If you
> took the time to make your 'surface gage' it will keep your angles
> aligned to one another.I'm taking up valuable space here to make a point
> of value.That being,you can do some very close work with the simple
> tools of doing everything the same way based upon a flat plane.A simple
> bench vise can be made from 3 screws and a block of hardwood.The jaw is
> shaped the same as the tube.It has a 1/4-20 long bolt that is threaded
> thru the block you screw down on the bench using the other 2 screws.By
> turning the bolt,the jaw closes on the tube,firmly holding it near the
> saw.If you take your time making this jig,you should be able to hold a
> tolerance of +/- .010 or less.Not everyone has a table saw or chop saw.
> regards,Ron
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 9 Dec 2004 08:56:30 -0600
> From: "Julio Sanchez" <jsanchez@skipanon.com>
> Subject: [ATM] RE: Ray tracer for cheap?
> To: <atm@atmlist.net>
> Message-ID: <NNELKFNKFMLCIKADIHGAEECGCMAA.jsanchez@skipanon.com>
> Content-Type: text/plain; charset="us-ascii"
>
> First of all, thanks to Jim, Vlad, and many others who have taken part in
> the "Small Ritchie-Chretien" discussion topic. I am very glad I brought
this
> up.
>
> Can anyone recommend a good ray tracer that does not break the bank? I use
> DBOptic and like it very much but would often like to have a "second
> opinion" before committing to a design. For example, my trace of a 6" f:6
RC
> in DBOptic reports a flat field and all other aberrations much below the
> tolerance. Is the software "smoking" something?
>
> Thanks,
>
> Julio
>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Thu, 09 Dec 2004 10:01:30 -0600
> From: Mike Lockwood <melockwo@uiuc.edu>
> Subject: [ATM] Cassegrain Secondary testing
> To: M/S Heald <maheald@octa4.net.au>
> Cc: atm@atmlist.net
> Message-ID: <41B876DA.3050208@uiuc.edu>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> Mike,
>
> M/S Heald wrote:
> > Hello!  I am figuring a secondary for my 11 inch classical cassegrain.
The
> > primary is a parabola.  I am using a star or petal lap on the secondary
> > after obtaining a sphere.  The star test of the system (after 1 ½ hours
of
> > figuring) shows a prominent ring outside of focus, which indicates
> > overcorrection, if I am interpreting it correctly.  According to my
basic
> > ray tracing program, overcorrection by star test in the classical
cassegrain
> > system indicates that the secondary is undercorrected, that is, I
haven't
> > gone far enough from the sphere to the desired hyperbola shape.
> >     Is this a correct interpretation of the star test with respect to
the
> > secondary correction?  Thank you and bet regards.
>
> Sounds like you've got the star test interpretation right.  It was
> wise to ray-trace it and ask for verification.
>
> If you have good seeing and frequent clear skies where you live, and
> you practice a lot, figuring using star testing is a valuable skill to
> develop.  Suiter's book is the bible on this.  Don't let me discourage
> you if you want to learn how to do this well.  You can also do a null
> test with a ronchi grating and a fairly bright star, which allows you
> to see zones directly, although how clearly you see them depends on
> the seeing conditions.
>
> Also, if you just want the scope finished, to use and enjoy, then you
> are probably using the fastest technique to get "done".  If this is
> the case, stop reading here and enjoy your scope.
>
> I'm more of a perfectionist when it comes to optics, and where I live,
> (in the cloudy, unstable, light-polluted midwest) the simplest method
> that can give excellent results (in my opinion) is the "test plate"
> method.  You polish out the concave tool for the secondary mirror,
> figure it to a sphere or hyperbola (using the Focault test), and then
> match the two pieces using interference testing.
>
> I'm using that method right now on two classical Cassegrains, a 16.25"
> and a 12.5", both about F/12.5.  Here's a link to the 16.25" page:
>
http://bi-staff.beckman.uiuc.edu/~melockwo/telescopes/16in_CUAS_cass/16in_CU
AS_cass.html
>
> There's a section on the 5" secondary work that is updated frequently
> (and will probably be updated again tomorrow - I went from 18 fringes
> of relative concavity on the secondary to 12 last night in about 1 hr
> of work.  Turntables are great!)  There's also a section about my
> interference tester.  Texereau covers the test plate method in his book.
>
> To me, the work of polishing a hindle sphere is more than the work of
> the test plate method, since the sphere must be larger than the mirror
> and you have to perforate it.
>
> It's nice to see some people working on Cassegrains and Dall-Kirkhams
> lately on the list.  Interference testing is fun!
>
> Mike Lockwood
>
>
>
> ------------------------------
>
> Message: 4
> Date: Thu, 9 Dec 2004 11:16:14 -0500 (EST)
> From: Woodchuck <djv@bedford.net>
> Subject: Re: [ATM] FW: Oslo short
> To: Ellen Mackenzie <mackenzieconsulting@sympatico.ca>
> Cc: atm <atm@atmlist.net>
> Message-ID: <Pine.BSO.4.44.0412091048140.32584-100000@pollux.chuck>
> Content-Type: TEXT/PLAIN; charset=US-ASCII
>
> On Thu, 9 Dec 2004, Ellen Mackenzie wrote:
>
> >
> > Richard:
> >     A bit of a flaw is the understatement of the day - - - when using
the
> > sliders to optimize it has the bad habit of changing the values by -1000
o
> > plus 500  -- -whatever, and the spot diagram isn't scaled so you have to
go
> > to another graphics screen to get a scale of your spot size. The program
has
> > a tendency to have sort of a nervous breakdown if you are evaluating
more
> > than two surfaces - - - it is as if the premium program can't quite make
it
> > past the Edu program - - - I can't trust the output and am feeling
ripped
> > off.
> > I think it's time Oslo took a good look at some of their
> > programming, this isn't the first time you and I have had this
discussion
> > about various peculiarities in program results.
>
> Just a note of sympathy -- I don't have Oslo (no windows), but have
> written more code than is good for me, none of it optical (alas).
> It sounds a lot like the design is weird, i.e. that the surface of
> the cost fuction is weird, namely something like a shallow valley
> with steep walls, and that Mr OSLO is not doing a very good job of
> recognizing this situation -- hence large yet ineffective steps
> down the valley, unwillingness to climb the walls, etc.  You're
> hundred percent right -- this is a programming fault, and I've seen
> such pathologic functions exhibited in optical literature from at
> least 35 years ago.  If the lens design tickles the fault, the
> program should have a way of saying that it's "ticklish" there...
> that it doesn't like high-curvature low-power elements, or whatever
> its problem is.  Maybe it's paying too much attention to a focal
> length constraint when bending the corrector(s)?  This might cause
> huge steps.  Does it control focal length by bending (not good?)
> or by scaling (good? I dunno)?
>
> This OSLO program cannot bend more than one element at a time?  Good
> grief, if that is so.  I've seen non-linear constrained optimization
> programs that dealt with a hundred parameters at once.  (in aerodynamic
> modelling, when tweaking).  Perhaps I'm missing something.
>
> I would think you could essentially give a lens design program
> three chunks of glass labelled "Crown", "Flint" and "Crown" and
> say Object at Infinity, Focal length 100, Aperture f:4, FOV 40,
> and it would hand you back a Cooke Triplet.  Not so?  (I'm being
> flippant and facetious, of course, but nonetheless...).
>
> This is what open source is good for... you/we could gut the pgm
> a little and beat the truth out of the optimization routine.  I've
> found programs to be much more cooperative if they can see the
> programmer's scalpel or even the dreaded boning knife...these
> sealed packages have a certain arrogance...  This gets me about that
> PLOP, too... I *know* I've played cards (029) with his grandfather,
> NASTRANS, but he won't play with me now...
>
> Dave
> --
>         In each of us, there burns a soul of a woodchuck.
>         In every generation a few are chosen to prove it.
>
>
>
> ------------------------------
>
> Message: 5
> Date: Thu, 9 Dec 2004 10:29:22 -0800
> From: "Bob May" <bobmay@nethere.com>
> Subject: Re: [ATM] Square over Round Truss Tube
> To: <atm@atmlist.net>
> Message-ID: <003901c4de1d$01955c00$1600a8c0@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Make up a measuring jig that will measure the tubes length just by putting
> in the jig and file the long ones til they all match.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
>
>
>
> ------------------------------
>
> Message: 6
> Date: Thu, 9 Dec 2004 10:32:19 -0800
> From: "Bob May" <bobmay@nethere.com>
> Subject: Re: [ATM] Set of specs.
> To: <atm@atmlist.net>
> Message-ID: <004001c4de1d$6af86ca0$1600a8c0@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Most of us pick up a piece of paper to find where the light is coming back
> to and it got mentioned.  The unfortunate thing is that the reason for the
> piece of paper didn't get explained properly and the poor guy is now
trying
> to do the test with the paper instead of his eye.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
>
>
>
> ------------------------------
>
> Message: 7
> Date: Thu, 9 Dec 2004 14:07:42 -0500
> From: "Ellen Mackenzie" <mackenzieconsulting@sympatico.ca>
> Subject: [ATM] re Oslo
> To: "atm" <atm@atmlist.net>
> Message-ID: <00e401c4de22$5f5b74a0$0d02a8c0@mackenzio2mm5r>
> Content-Type: text/plain; charset="us-ascii"
>
> My version of OSLO Premium is 6.2.4
>
>
>
>
> ------------------------------
>
> Message: 8
> Date: Thu, 9 Dec 2004 11:40:11 -0800
> From: "Richard Schwartz" <richas@earthlink.net>
> Subject: [ATM] Telescope Optics Workshop
> To: <atm@atmlist.net>
> Message-ID: <003101c4de26$e5dd8500$88a4b2d1@starzv2zzychda>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Will there be a Bellingham workshop in April, or are the workshops
permanently dead?
>
> If there will be a workshop, is any help needed to set it up?
>
> If permanently dead, might another group continue the workshops at a new
location?
>
> .. . Richard
>
> ------------------------------
>
> Message: 9
> Date: Thu, 9 Dec 2004 12:27:58 -0800 (PST)
> From: Dave Smith <smithersscope@yahoo.com>
> Subject: Re: [ATM] ANY LENS IN DIGITAL PHOTOCOPY MACHINE ?
> To: Lee Chin Huat <lee@nakano-const.com>, ATMLIST <atm@atmlist.net>
> Message-ID: <20041209202758.6708.qmail@web51804.mail.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> Hello Lee,
> I recently made 2 copy scopes from salvaged lenses.
> One larger one from an old Pitney-Bowes copier and one
> from a newer 'cheesy' copy machine. In my stastical
> analyses (n=2), the newer machines have smaller
> lenses. ;O)
> I think it's highly likely that even the newest
> machines still use a lens to capture the scanned image
> before digitizing (especially if the unit is capable
> of capturing large format images, such as legal size
> documents). This is not true for FAX machines, as I
> recently tore into one and found a laser and a very
> nice first surface mirror. I'm afraid if your copy
> machine maker has gone laser/mirror/digital you'll be
> out of luck for finding a lens assembly.
> If there is a lens, be prepared for some color in your
> images; mine both have coatings that tint the final
> image green and orange.
> Even if you don't find a lens set in your salvaging
> efforts, no doubt you will find a trove of useful
> shafts, screws, hardware etc.
> The pointer to Surplus shed is a good one, too.
>
> HTH,
> Dumpster Dave
> --- Lee Chin Huat <lee@nakano-const.com> wrote:
>
> > Hi All Atmer,
> >
> > I understand that some of you have savaged lens from
> > photocopy machine
> > to make copy scope. However todays machine are
> > mostly digital do they
> > have any lens worth savaging for copyscope ?
> >
> > Thanks
> >
> > LEE CHIN HUAT
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
>
>
>
>
> __________________________________
> Do you Yahoo!?
> Jazz up your holiday email with celebrity designs. Learn more.
> http://celebrity.mail.yahoo.com
>
>
> ------------------------------
>
> Message: 10
> Date: Thu, 9 Dec 2004 22:12:01 +0100
> From: "Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>
> Subject: Re: [ATM] Square over Round Truss Tube
> To: <atm@atmlist.net>
> Message-ID: <001501c4de33$b9e816b0$0301a8c0@Acer>
> Content-Type: text/plain; charset="iso-8859-1"
>
> > From: "Lee Chin Huat" <lee@nakano-const.com> wrote:
> ...
> > Why do people prefer round truss tube over square truss tube ? Is it not
> easier to use square tube to connect to the mirror box and the secondary
> cage ?
>
> Stiffness is determined by tube diameter in bending direction.
> Round tubes are lighter than square, with equal wall thickness.
> You can also choose U or I profiles, which are even lighter.
> Weight ratio is approximately (thin wall)  4 : PI : 3.
>
> In truss structures, the tubes are usually overdimensioned, but the extra
> stiffness and weight decreases vibrations.
>
> I used 10mm cross section U profiles on my 250mm F6.3 scope, carrying a
> 500gr secondary cage. Plenty stiff when clamped tightly, and they fold
> together as a compact package inside a PVC pipe for transportation.
>
> /Arjan
>
>
>
> ------------------------------
>
> Message: 11
> Date: Fri, 10 Dec 2004 17:41:26 -0500
> From: vladimir sacek <vladis.2@juno.com>
> Subject: [ATM] Re: Ray tracer for cheap?
> To: atm@atmlist.net
> Message-ID: <20041210.174126.3268.0.vladis.2@juno.com>
> Content-Type: text/plain; charset=us-ascii
>
> Julio Sanchez wrote:
>
> >Can anyone recommend a good ray tracer that does not break the bank? I
> use
> DBOptic and like it very much but would often like to have a "second
> opinion" before committing to a design.<
>
> You can try ATMOS demo version:
>
> http://web.tiscali.it/ATMOS/
>
> Vlad
>
>
> ------------------------------
>
> Message: 12
> Date: Thu, 9 Dec 2004 18:55:12 -0500
> From: "David  Williams" <dwilliams1128@earthlink.net>
> Subject: [ATM] zones
> To: "ATM" <atm@atmlist.net>
> Message-ID: <001001c4de4a$872c7380$cbc9e504@yourm5d4u9r2uv>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hello
>
> When I take the zone measurements on my 20", do I null both portions of
the sides of the mask?  Like if it's the outer edge on the right, do I do
the left too?  But when I try to do this (my knife is on the right and moves
to the left by the way), and move the knife to the left, the right opening
in the mask starts to go black before the left one.  And the measurement on
the micrometer that this happens is .61"  I hope this helps both you and me.
>
> David
>
> ------------------------------
>
> Message: 13
> Date: Thu, 9 Dec 2004 18:57:20 -0500
> From: "David  Williams" <dwilliams1128@earthlink.net>
> Subject: [ATM] zones 1
> To: "ATM" <atm@atmlist.net>
> Message-ID: <001b01c4de4a$d55218d0$cbc9e504@yourm5d4u9r2uv>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hello
>
> My mask has 5 zones including the big one in the center.  The one in the
center is about 4 or 5 inches wide.  It's a couder mask.  So do I do both
sides of the null?
>
> Thanks
> David
>
> ------------------------------
>
> Message: 14
> Date: Thu, 9 Dec 2004 18:48:53 -0600
> From: "Jerry B. Hillman" <JBHillman@ev1.net>
> Subject: Re: [ATM] zones
> To: "David  Williams" <dwilliams1128@earthlink.net>, "ATM"
> <atm@atmlist.net>
> Message-ID: <003301c4de52$069aa860$ff67fea9@ev1.net>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi David,
> Now we are making progress.
>
> >When I take the zone measurements on my 20", do I null both portions of
the
> sides of the mask?  Like >if it's the outer edge on the right, do I do the
> left too?
>
> The mask openings are treated as pairs.  Both must null at the same time
to
> be at ROC.
>
>
> >But when I try to do this (my knife is on the right and moves to the left
> by the way), and move the knife >to the left, the right opening in the
mask
> starts to go black before the left one.  And the measurement on >the
> micrometer that this happens is .61"
>
> Since the opening on the same side of your mask as  the knife edge is
> getting darker before the opening on the opposite side of the mask, your
> knife edge is inside of the ROC for that zone (Zone one)  Move the knife
> edge back a little and try again.  Keep moving it back until as you move
the
> KE into the light cone, both mask openings null at the same time.  If you
> overshoot and the mask opening on the opposite side of the mirror from the
> KE gets dark first, then move the KE a little closer to the mirror.
>
> Make sure, when you have found the point for zone one that both sides go
> null at the same time, that you have enough movement in your micrometer to
> move at least an additional .5" away from the mirror.  That will allow you
> room to measure the rest of your zones. Also, you do not have to take a
> measurement for the center zone.  I usually find the center zone ROC and
set
> my micrometer to zero for that point.  It helps me understand the readings
> for the rest of the zones.  For a 20" mirror, I would recommend at least
> eight zones, not counting the center zone. It will give you a more
accurate
> measurement of the surface of the mirror than just four zones not counting
> the center zone which is in the shadow of the secondary anyway.
>
> I hope you realize that the surface of your mirror has to be accurate to
> plus or minus 2 microns between any two given points on the surface.  A
> micron is one millionth of a meter.  About 1/1000th the thickness of a
human
> hair.  That is why you must test your mirror.  So that you know how to
work
> on it to make it a parabolic surface.
>
> Clear skies, Jerry
>
>
>
> ------------------------------
>
> Message: 15
> Date: Thu, 9 Dec 2004 20:05:23 -0500
> From: GARY FUCHS <gary@rcn.com>
> Subject: [ATM] OT: Question for David Williams
> To: atm@atmlist.net
> Message-ID: <8971ffec.ac4023af.8206c00@ms02.mrf.mail.rcn.net>
> Content-Type: text/plain; charset=us-ascii
>
> Hello David,
>
> I sent you an answer yesterday (off list) to your previous
> question. Did you receive it?
>
> Thank you,
>
> Gary Fuchs
>
> -Apologies to list participants-
>
>
> ------------------------------
>
> Message: 16
> Date: Thu, 9 Dec 2004 17:16:56 -0800 (PST)
> From: Guy Brandenburg <gfbrandenburg@yahoo.com>
> Subject: Re: [ATM] Re: Ray tracer for cheap?
> To: vladimir sacek <vladis.2@juno.com>, atm@atmlist.net
> Message-ID: <20041210011656.56328.qmail@web40510.mail.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> I like OSLO edu (used to be OSLO LT), myself.
> Guy B
> --- vladimir sacek <vladis.2@juno.com> wrote:
>
> > Julio Sanchez wrote:
> >
> > >Can anyone recommend a good ray tracer that does
> > not break the bank? I
> > use
> > DBOptic and like it very much but would often like
> > to have a "second
> > opinion" before committing to a design.<
> >
> > You can try ATMOS demo version:
> >
> > http://web.tiscali.it/ATMOS/
> >
> > Vlad
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
>
>
> =====
> Guy  Brandenburg
> Washington, DC
> My home page:
> http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
>
>
> ------------------------------
>
> Message: 17
> Date: Thu, 9 Dec 2004 17:20:13 -0800 (PST)
> From: Guy Brandenburg <gfbrandenburg@yahoo.com>
> Subject: Re: [ATM] zones
> To: "Jerry B. Hillman" <JBHillman@ev1.net>, David Williams
> <dwilliams1128@earthlink.net>, ATM <atm@atmlist.net>
> Message-ID: <20041210012014.91405.qmail@web40528.mail.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> Everything Jerry said is correct. (Great job, Jerry!)
> Please allow me to add one more point. With plate
> glass, you really have to wait a very long time after
> doing any polishing or figuring before you can take
> any reliable measurements. It is simply amazing how
> much the figure will change from the heat of the
> polishing motion. Waiting overnight is best; or at
> least, wait a couple of hours. Otherwise, your time is
> wasted.
>
> Guy
> --- "Jerry B. Hillman" <JBHillman@ev1.net> wrote:
>
> > Hi David,
> > Now we are making progress.
> >
> > >When I take the zone measurements on my 20", do I
> > null both portions of the
> > sides of the mask?  Like >if it's the outer edge on
> > the right, do I do the
> > left too?
> >
> > The mask openings are treated as pairs.  Both must
> > null at the same time to
> > be at ROC.
> >
> >
> > >But when I try to do this (my knife is on the right
> > and moves to the left
> > by the way), and move the knife >to the left, the
> > right opening in the mask
> > starts to go black before the left one.  And the
> > measurement on >the
> > micrometer that this happens is .61"
> >
> > Since the opening on the same side of your mask as
> > the knife edge is
> > getting darker before the opening on the opposite
> > side of the mask, your
> > knife edge is inside of the ROC for that zone (Zone
> > one)  Move the knife
> > edge back a little and try again.  Keep moving it
> > back until as you move the
> > KE into the light cone, both mask openings null at
> > the same time.  If you
> > overshoot and the mask opening on the opposite side
> > of the mirror from the
> > KE gets dark first, then move the KE a little closer
> > to the mirror.
> >
> > Make sure, when you have found the point for zone
> > one that both sides go
> > null at the same time, that you have enough movement
> > in your micrometer to
> > move at least an additional .5" away from the
> > mirror.  That will allow you
> > room to measure the rest of your zones. Also, you do
> > not have to take a
> > measurement for the center zone.  I usually find the
> > center zone ROC and set
> > my micrometer to zero for that point.  It helps me
> > understand the readings
> > for the rest of the zones.  For a 20" mirror, I
> > would recommend at least
> > eight zones, not counting the center zone. It will
> > give you a more accurate
> > measurement of the surface of the mirror than just
> > four zones not counting
> > the center zone which is in the shadow of the
> > secondary anyway.
> >
> > I hope you realize that the surface of your mirror
> > has to be accurate to
> > plus or minus 2 microns between any two given points
> > on the surface.  A
> > micron is one millionth of a meter.  About 1/1000th
> > the thickness of a human
> > hair.  That is why you must test your mirror.  So
> > that you know how to work
> > on it to make it a parabolic surface.
> >
> > Clear skies, Jerry
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
>
>
> =====
> Guy  Brandenburg
> Washington, DC
> My home page:
> http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
>
>
> ------------------------------
>
> Message: 18
> Date: Fri, 10 Dec 2004 18:58:41 +0900
> From: Hiroyuki HIKITA <hikita@tkb.att.ne.jp>
> Subject: Re: [ATM] Waineo/Jones null test question
> To: atm@atmlist.net
> Message-ID: <41B97351.9070403@tkb.att.ne.jp>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hi all.
>
> Here is what I tried. The program seems to run.
> But since I don't have a printer connected,
> I haven't compaired the results with the
> original program. :(
>
> 1) Download free pascal from http://www.freepascal.org/ and install.
> 2) modify waineo96.pas and change places that look like
>           "writeln(lst," to "writeln("
>     and
>           "writeln(lst);" to "writeln;"
> 3) open a command prompt. (cmd.exe)
> 4) c:\"where free pascal lives"\bin\win32\ppc386.exe waineo96.pas
>
> I've repackaged and put the results here
> -> http://rakuen.yi.org/~hikita/waineo96.zip
>
> # H.Hikita
>
>
>
> ------------------------------
>
> Message: 19
> Date: Fri, 10 Dec 2004 16:33:59 +0100
> From: Mauritz Andersson <mauritz@physi.uni-heidelberg.de>
> Subject: Re: [ATM] Re: Holographic Foucault null test
> To: ATM@atmlist.net
> Message-ID: <1102692838.6888.251.camel@atomp.physi.uni-heidelberg.de>
> Content-Type: text/plain
>
> Paul,
> Very good references that explain more about holographic null testing as
> done by the pros.
> I hope that I did not give the impression of inventing holography... nor
> the use of CGH for testing aspheric mirrors. I'm simply trying, together
> with the great people on this list, to adapt it to something simple that
> can be used in an amateur workshop.
>
> Regards,
> Mauritz
>
>
> On Tue, 2004-12-07 at 17:34, IAPDK@ADMIN.DRAKE.EDU wrote:
> > It is a simplified version of a well-documented technique.  In the
> > usual form the CGH (computer-generated hologram) is projected onto the
> > mirror using additional optics.  But this way none of that is needed.
> >
> > A little web-reading on the subject:
> >
> >
http://www.optics.arizona.edu/jcwyant/pdf/Published_Papers/Computer_Generate
d_Holograms/cgh_test.pdf
> >
> >
http://www.opticsexpress.org/view_file.cfm?doc=%24%29%3C7%2DJ0%20%20%0A&id=%
24%2A%2C%3B%2FJ%20%20%20%0A
> >
>
> > http://ej.iop.org/links/q53/XirTYnW05XL9pbHnsbBJ8A/jdv5i11p1982.pdf
> I could not access this one. What's the reference?
>
>
>
> >
> >
http://www.optics.arizona.edu/jcwyant/pdf/Meeting_papers/Use%20of%20computer
%20generated%20holograms%20for%20testing%20aspheric%20surfaces.pdf
> >
> > And here is how to make a diffraction-limited mirror without grinding
> > and polishing, just cast it and correct it with a CGH:
> >   http://www.usafa.af.mil/dfp/research/lorc/tele.htm
> >
>
> Now, that's cool! Can it be adapted to amateur use, do you think?
>
> > Paul Kline
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
>
>
>
> ------------------------------
>
> Message: 20
> Date: Fri, 10 Dec 2004 16:48:04 +0100
> From: Mauritz Andersson <mauritz@physi.uni-heidelberg.de>
> Subject: Re: [ATM] Holographic Foucault null test
> To: atm@atmlist.net
> Message-ID: <1102693684.6887.267.camel@atomp.physi.uni-heidelberg.de>
> Content-Type: text/plain
>
> Mark,
> That's a good idea. Earlier, I have been in contact with a company
> that does computer cutout of graphics and they indicated that the
> eps file format might work for them. If enough people is interested
> I can explore that option a bit more, send me a mail. (Just to stress:
> I'm not interested in making money on this.) Anyone can also on their
> own check with their local graphic shops if they can use the EPS format.
> If you or someone knows the AutoCad file format maybe a conversion of
> the code can be made to produce such a file.
>
> The code on the web is php and if someone want a copy I'm happy to
> provide it.
>
> Mauritz
>
>
> On Wed, 2004-12-08 at 02:51, Mark Holm wrote:
> > If you could get the mask layout into an AutoCad file, somebody with one
> > of those X-Y laser cutting rigs could cut out a precise mask from thick
> > paper or thin plastic in no time.  there are guys that do contract laser
> > cutting for model plane parts.  Something like this should be fairly
> > straightforward for them.
> > --
> > Mark Holm
> > mdholm@telerama.com
>
>
>
> ------------------------------
>
> Message: 21
> Date: Fri, 10 Dec 2004 10:51:45 -0800
> From: "Bob May" <bobmay@nethere.com>
> Subject: Re: [ATM] zones 1
> To: <atm@atmlist.net>
> Message-ID: <004401c4dee9$4c9388e0$1600a8c0@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Don't understand the question.
> The Foucault test is the comparison of the two sides of a zone to get them
> to be the same level of gray for a reading of where that zone's relative
ROC
> is.
> For the first timer, making a set of 5 masks, each one with one zone on
it,
> will allow for the easier reading of the zones rather than the all-in-one
> mask that you normally see in the literature.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
>
>
>
> ------------------------------
>
> Message: 22
> Date: Fri, 10 Dec 2004 10:55:47 -0800
> From: "Bob May" <bobmay@nethere.com>
> Subject: Re: [ATM] zones
> To: <atm@atmlist.net>
> Message-ID: <004d01c4dee9$dc5c4fc0$1600a8c0@amd>
> Content-Type: text/plain; charset="iso-8859-1"
>
> One thing that I will note is that the mask opening may exibit a dark side
> and a bright side on each of the openings.  When this happens, make the
> effect the same for both sides or you aren't at the right ROC point.  I'll
> also note that when this effect gets fairly strong, you are definitely not
> using enough zones.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
>
>
>
> ------------------------------
>
> Message: 23
> Date: Fri, 10 Dec 2004 16:34:06 -0800
> From: Jim Burrows <burrjaw@earthlink.net>
> Subject: Re: [ATM] zones
> To: atm@atmlist.net
> Message-ID: <6.0.1.1.2.20041209165429.02cc1eb0@pop.earthlink.net>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
>
> At 2004-12-09 18:55 -0500, David  Williams wrote:
>
> >But when I try to do this (my knife is on the right and moves to the left
> >by the way), and move the knife to the left, the right opening in the
mask
> >starts to go black before the left one.  And the measurement on the
> >micrometer that this happens is .61"  I hope this helps both you and me.
>
> That says for this zone, the KE is too close to the mirror.  What you want
> is the (longitudinal) position of the KE that makes the two holes for the
> zone equally gray.
>
> W. J. Smith, "Modern Optical Engineering", p. 108, has several comments
> about using the eye as a comparison photometer in the Foucault test.
> 1)  The fields that we're trying to match should be bright.  Smith says >
> 10 millilamberts (whatever that is).
> 2)  The background (the mask) should be lighted, i.e., turn on the room
lights.
> 3)  "... the precision of the setting is increased by making a series of
> readings.  In half the readings, the brightness of the variable area is
> raised until an apparent match is obtained; in the other half of the
> readings, the brightness is lowered to obtain the apparent match.  The
> average is then much more accurate than either set."
>
>          -- Jim Burrows
>          -- mailto://burrjaw@earthlink.net
>          -- http://home.earthlink.net/~burrjaw
>          -- Seattle N47.4723 W122.3662 (WGS84)
>
>
>
> ------------------------------
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
> End of ATM Digest, Vol 12, Issue 10
> ***********************************
>

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