No subject
Thu Feb 4 12:37:29 PST 2010
g from the following.
=20
1. Air turbulence
2. Tube current
3. Spherical aberration
4. Rough surfaces
5. Zonal aberrations
6. Turned edges
7. Astigmatism=20
8. Pinched optics
=20
Hope you enjoyed=2C Roger
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The moon and stars to govern the night..... Psalm 136:9
Hotmail: Trusted email with Microsoft=92s powerful SPAM protection. Sign up=
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Roger=2C<BR>
 =3B<BR>
Cool story!<BR>
 =3B<BR>
I met my friend Tony Labude at my very first Okie-Tex star party. He later =
said I was the only one that would take the time to show him =3Bstuff i=
n my old home-built 16" f/6.4. He said I didn't have an "attitude" and open=
ed his eyes to a lot of objects =3Bhe didn't even know were out there.<=
BR>
 =3B<BR>
I not only showed him some "tourist" objects=2C but as I did my deep sky se=
arching=2C I showed him every one and what to look for. We became buds afte=
r that and the next year=2C he had an 8" scope=2C which I seem to remember =
was a Coulter. He was the one person I always looked forward to seeing at e=
ach Okie-Tex.<BR>
 =3B<BR>
All it takes is a kind word and a little effort and you never know what wil=
l happen. That was 17 years ago and he is now one of our =3BObserver's =
Challenge participants.<BR>
 =3B<BR>
Fred<BR>
<BR> =3B<BR>
<HR id=3DstopSpelling>
From: drivester at hotmail.com<BR>To: lvas at lvlug.org=3B trenglish at gtcc.edu=3B =
dolive at gardner-webb.edu=3B jdire at gardner-webb.edu=3B reskridge1 at carolina.rr=
.com<BR>Date: Thu=2C 18 Feb 2010 03:39:28 +0000<BR>Subject: Re: [LVAS] Star=
Testing a Telescope<BR><BR>
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Fred=2C <BR> =3B<BR>You make a good point. <BR> =3B<BR>I remember r=
eading an article in S&=3BT many years ago. It said that if the image sn=
apped into focus this was a good =3Bindicator that the optics were =
=3BOK. =3BI have had scopes in the past that have had problems and they=
would just=2C "kinda" roll into focus. Never really getting there. <BR>&nb=
sp=3B<BR>I must confess something. =3BEvery scope that I have ever look=
ed through at a star party or elsewhere I perform a star test. The owner of=
the 4-inch Takahashi =3Bfluorite did not even know that I had performe=
d the test. I did tell him=2C but he already knew that it was "textbook" op=
tics. The same for the 5-inch Astro-Physics.<BR> =3B<BR>My Vixen would =
rate as an A(--). The =3B10-inch =3Bf/4.5 would be B+. Pretty much =
all commercial optics other than the "very" premium =3Bhigh end refract=
ors will have some problem. =3BI think that all will =3Bagree with =
me on this one. <BR> =3B<BR>A quote from Meade Instruments in the late =
80's and also early 90's=2C advertised my 10-inch DS-10A. <STRONG>"The prim=
ary mirrors included with the Models 826C=2C 1060=2C and 1266 are virtually=
 =3Bas fine as be manufactured. It is impossible from a practical point=
of view=2C and without great expense=2C to manufacture the 10-inch and 16-=
inch short focus (DS-10A and DS-16A) to the same level of accuracy. But tha=
t is precisely =3Bthe point of the Deep-Space telescopes. The DS-10A an=
d the DS-16A are primarily designed for deep-space observations of galaxies=
=2C nebulosities=2C and extended stellar objects. In these cases it is esse=
ntially meaningless for an astronomical mirror to be of research-grade accu=
racy=2C since mirrors =3Bof lower optical accuracy perform fully as wel=
l=2C and for much less cost. =3B</STRONG><BR><STRONG></STRONG> =3B<=
BR><STRONG>However=2C on one special night I was able to use 500x on Saturn=
without any breakup =3B =3Bwith a view that rivaled any photo that=
I had ever seen. =3BA friend was observing with me also. He has one of=
the best 14.5 mirrors that I have ever encountered. He was able to use alm=
ost 600x with =3Bimages that could =3Bnot be imagined. =3BThis =
was one night only =3Bin my 30+ =3Byears of observing =2C and never=
to be repeated. The year was 1992.  =3BI am glad that I had a witness.=
When I see Bob=2C the owner of the 14.5-inch=2C we always talk about that =
night.</STRONG><BR><STRONG></STRONG> =3B<BR><STRONG>When I first met Bo=
b =3Bat an observing session one night I did a star test on his scope. =
We had never met before. I asked for several of his EP's=2C and then conclu=
ded that I had never seen an f/4.5 mirror this good. =3BI told him. He =
was surprised that someone in the crowd would be able to test his mirror. H=
e thought that I was just another casual observer. =3BHe was already aw=
are of this fact. He did not know me at the time nor did I know him. Some o=
f the expert mirror makers in Charlotte had helped him make the mirror seve=
ral years earlier=2C and like the Komorowski scope=2C all test revealed tha=
t =3Bit was =3Bbeyond superb. =3B =3B</STRONG><BR><STRONG><=
/STRONG> =3B<BR><STRONG>Bob and I became friends that night and spent m=
any=2C many nights observing together=2C often till 2 AM or later on work n=
ights. Bob has since moved to Charlotte and I seldom get to see him anymore=
. =3B =3B =3B</STRONG><BR><STRONG></STRONG> =3B<BR><STRONG>=
Roger =3B =3B =3B =3B</STRONG><BR><STRONG></STRONG> =3B=
<BR><STRONG></STRONG> =3B<BR><STRONG></STRONG> =3B<BR><STRONG> =
=3B =3B =3B =3B =3B =3B</STRONG><BR><BR><FONT face=3DAr=
ial> =3B<BR><FONT size=3D4></FONT> =3B</FONT><BR><FONT face=3DArial=
></FONT> =3B<BR><FONT face=3DArial></FONT> =3B<BR><FONT face=3DAria=
l></FONT> =3B<BR><FONT face=3DArial></FONT> =3B<BR><FONT face=3DAri=
al></FONT> =3B<BR><FONT face=3DArial></FONT> =3B<BR><FONT face=3DAr=
ial> =3B<BR><BR> =3B<BR></FONT><EM><FONT face=3DArial><STRONG> =
=3B =3B =3B </STRONG></FONT>The moon and stars to govern the night.=
.... =3B =3B Psalm 136:9</EM><BR><BR><BR><BR> =3B<BR>
<HR id=3DecxstopSpelling>
From: rayworth1969 at hotmail.com<BR>To: lvas at lvlug.org<BR>Date: Wed=2C 17 Feb=
2010 20:00:27 -0600<BR>Subject: Re: [LVAS] Star Testing a Telescope<BR><BR=
>
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All=2C<BR> =3B<BR>I've used everything from an =3Boatmeal box with =
a light inside and a pinhole on =3Bthe side=2C to the old reliable insu=
lator on a telephone pole=2C to Polaris with a Ronchi grating. I prefer the=
Ronchi grating on a bright star=2C and not usually Polaris as it's kind of=
dim. In some ways=2C maybe you don't want to star test your optics either.=
If you suspect something major wrong=2C sure. However=2C if you are happy =
and just curious=2C it may not be wise to dash your hopes and dreams by fin=
ding your optics are astigmatic=2C over/under corrected=2C have a turned do=
wn edge. Sometimes it's better to let sleeping dogs =3Blay/lie=2C whate=
ver...<BR> =3B<BR>Fred<BR><BR> =3B<BR>
<HR id=3DecxecxstopSpelling>
From: drivester at hotmail.com<BR>To: lvas at lvlug.org<BR>Date: Wed=2C 17 Feb 20=
10 13:45:09 +0000<BR>Subject: [LVAS] Star Testing a Telescope<BR><BR>
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All=2C<BR> =3B<BR>Hey guys=2C just some good information. I am sure man=
y are aware of the following information=2C but it is still some good readi=
ng.  =3B<BR> =3B<BR>Do you know how to star test your telescope? Ha=
ve you ever collimated your scope in the daytime using an artificial star?&=
nbsp=3B<BR> =3B<BR>1. <STRONG>Artificial star:</STRONG> Any very shiny =
well polished sphere. I use a =3Bround brass cabinet knob that I sit on=
the top of a =3Bhollow metal tube. =3BSome people use an insulator=
on a utility pole at a distance=2C or the corner of a chromed auto bumper.=
There is a formula for the distance=2C but hey don't worry about this.&nbs=
p=3BJust make sure that the =3Bsphere is at least a few hundred feet aw=
ay and you can focus on it. =3BA larger scope requires =3Ba greater=
distance.  =3B<BR> =3B<BR>During the early mornings when the wind =
is calm and the sun is shinning very brightly. =3BSit your =3Bscope=
is in the shade=2C to avoid heat on the OT. Observe =3Bthe disc at ver=
y high magnification. Look for the <STRONG>airy disc</STRONG>. Are they of =
the same brightness all around the star? Now de-focus your scope. =3BAr=
e the rings on the inside of focus exactly the same as the outside? Very fe=
w scopes will pass this test. <STRONG>Probably the most sensitive =3Bte=
st of all. </STRONG>I have seen "textbook" images =3Bin only one scope =
that I =3Bhave ever tested=2C =3Ba Takahashi 4-inch refractor=2C an=
d I think it was a 5-inch Astro-Physics refractor. =3BOf course we all =
know that these are high resolution=2C very high quality =3Bscopes=2C a=
nd cost as much as a very good used car. I attempted to do a test on a Ques=
tar one night=2C but the seeing was not good enough.  =3B =3B =
=3B =3B =3B =3B<BR> =3B<BR>Are you familiar with the <STRON=
G>"airy disc"</STRONG> named after 19th century scientist Sir George Airy. =
This is a critical test of your scope. Have you ever observed the airy disc=
 =3Bin your scope?<BR>No=2C this is not the out of focus diffraction ri=
ngs=2C <STRONG>but the very faint ring or rings surrounding the perfect in =
focus star at very high magnification. =3BThis can be almost impossible=
for a larger scope as =3Bit =3Brequires at least 30x per inch of a=
perture. =3BIf this test is performed at night "almost" perfect seeing =
is required.</STRONG><BR><STRONG></STRONG> =3B<BR><STRONG>I had an exce=
llent quality 80 mm f/15 Japanese refractor quite a few years ago. I notice=
d when working on double stars =3Bthat the airy disc was brighter on on=
e side as compared to the =3Bother (180=B0). However=2C it was =3Bv=
ery slight and I could not see the miscollimation while observing or defocu=
sing on a star. =3BA precise adjustment of the =3Baperture resolved=
this problem. I am somewhat afraid to mess with the adjustments on a refra=
ctor. I would never=2C let me repeat=2C never =3Btouch =3Ban Astro-=
Physics=2C Tak=2C or any other $5=2C000 (+) OTA. This is not a job for the =
amateur=2C wanting to learn. =3B =3B</STRONG><BR><STRONG></STRONG>&=
nbsp=3B<BR><STRONG>I also had an ETX 90 with superb optics. When comparing =
to a $5=2C000 90 mm Questar the images were not much different. The ETX was=
a =3B1996 model=2C the first year that they were introduced. I am not =
sure how well the mirrors are in the newer=2C made in China ETX's. The same=
problem as the 80 mm. At very high magnification the airy disc was brighte=
r on one side=2C again=2C exactly 180=B0.</STRONG><BR><STRONG></STRONG>&nbs=
p=3B<BR><STRONG> =3BI could move the test star very slightly from the c=
enter and could find perfect collimation within the scope. Being a =3BM=
aksutov-Cassegrain scope without those primary adjustments screws (Laura&nb=
sp=3Bwas talking about this =3Bin an e-mail a couple of days ago=2C reg=
arding a certain =3B100 mm Newtonian) I could not put the scope in perf=
ect collimation. It was so slight that the performance of the scope was not=
really compromised. A great little scope indeed=2C that would split double=
stars far beyond its limits=2C so this would indicate the miscollimation w=
as not that great. </STRONG><BR> =3B<BR><STRONG>A good book that I woul=
d like to recommend that will explain everything above and much more.</STRO=
NG><BR><STRONG></STRONG> =3B<BR><STRONG><FONT size=3D3><EM>Star Testing=
Astronomical Telescopes </EM>by Harold Richard Suiter. This guy is really =
a genius at optics. He is an experimental physicist.</FONT></STRONG><BR><ST=
RONG><FONT size=3D3></FONT></STRONG> =3B<BR>From pictures in this book =
you can determine if your star image is suffering from the following.<BR>&n=
bsp=3B<BR>1. Air turbulence<BR>2. Tube current<BR>3. Spherical aberration<B=
R>4. Rough surfaces<BR>5. Zonal aberrations<BR>6. Turned edges<BR>7. Astigm=
atism <BR>8. Pinched optics<BR> =3B<BR>Hope you enjoyed=2C Roger<BR>&nb=
sp=3B<BR> =3B<BR> =3B<BR><BR><FONT face=3DArial> =3B<BR><FONT s=
ize=3D4></FONT> =3B</FONT><BR><FONT face=3DArial></FONT> =3B<BR><FO=
NT face=3DArial></FONT> =3B<BR><FONT face=3DArial></FONT> =3B<BR><F=
ONT face=3DArial></FONT> =3B<BR><FONT face=3DArial></FONT> =3B<BR><=
FONT face=3DArial></FONT> =3B<BR><FONT face=3DArial> =3B<BR><BR>&nb=
sp=3B<BR></FONT><EM><FONT face=3DArial><STRONG> =3B =3B =3B </S=
TRONG></FONT>The moon and stars to govern the night..... =3B =3B Ps=
alm 136:9</EM><BR><BR><BR><BR><BR>
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