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Mircea Pteancu

20 Iun 2008 22:50


Mariri extreme

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Sunt nitel ametiti si va invit si pe voi sa luati o ''priza ''! Iata povestit mai jos, pe ATM Email List, 
cum au facut Mel Bartels si Judy Dethloff  observatii cu mariri de pana la 6000x prin telescoape de 50cm si 40 cm cu ocazia Oregon Star Party din 1997.Eu unul,am ajuns pana la 800x cu telescopul meu Dobson de 16 cm (primul Dobsonian din Romania ),etajand  doua lentile Barlow.''Limita Tasco'' despre care se vorbeste in gluma  ,inseamna de 10x diametrul in mm. Deci am ajuns pana la jumatatea ''limitei Tasco''.O limita in general fantezista ,dar de unii,uneori, si cu instrumente exceptionale,atinsa.Voi pana la ce mariri extreme ati ajuns?Mircea

>>>>
> 
>
>
> Well, nights of 1000x are mighty rare, but we remember them forever.
>
> Here's an experience of ours from the 1997 Oregon Star Party (note the
> comment about what become the inspiration for the flex rocker design)...
>
> "No one can capture all the action at a big star party, so I will restrict
> my comments to my experiences.  Thursday night highlight was our M57 Ring
> Nebula circus.  It started innocently enough, with the nightly trek to the
> chuck wagon for our after midnight star burgers and hot chocolate and 
> triple
> mochas.  Upon our return, Judy Dethloff put her wonderful 16" f/4 on the
> Ring, ran up the power to 500x, and started getting excited about seeing 
> the
> central star.   Hmm, on second thought, maybe it was those triple mochas.
> Nah, that couldn't be it because seeing the central star in the Ring 
> Nebula
> is always more energizing than even a double-triple mocha, right?.  By the
> way, her scope, built by her husband Chuck Dethloff, was my favorite scope
> at the star party.  Short enough to forgo a ladder, it had fantastic 
> optics,
> and was a joy to maneuver around the sky.   The eventual dust in the
> bearings gave it a zippy sound as it was aimed, a sound louder than my
> computerized 20" dob made while slewing.  (You see, the original 
> incarnation
> of my scope had rather loud motors for which I took a lot of heat, but now
> is genuinely hard to hear).
>
> Speaking of my scope, I was so impressed with how easy the central star 
> was
> in Judy's 16" that I put my 20" on the Ring.  The central star was right
> there at 700x, but the inside of the Ring was too bright for my taste, so
> after everyone got a look, I tripled the power with my trusty barlow and
> took a gander at 2000x (100x per inch of aperture).   This did lower the
> brightness in the middle of the Ring.  Incredibly, the central star shone
> forth as a little pinpoint of light, all who looked agreed that it could 
> be
> held steady.  By now, everyone within ear shot was on the Ring, taking
> advantage of the exceptional seeing and transparency.  I determined to go
> higher in power, but had some difficulty in procuring another barlow, 
> since
> they were all in use.  At 6000x (300x per inch of aperture!) I was able to
> focus the star just outside the Ring to an acceptable little dot.  Even 
> with
> a completely motorized and computerized scope, it was difficult to find 
> the
> center of the Ring because the field of view at 6000x was a tiny fraction 
> of
> the Ring, indeed, the thickness of the Ring's rim was greater than the 
> field
> of view.  Unable to find the exact center of the Ring, we gave up.  I 
> think
> I made the comment, "Let's go back down to that low 2000 power" a little 
> too
> loudly, because the peanut gallery reacted with kibitzing like "You've
> exceeded even the Tasco limit!"
>
> Tracking scopes like mine and Howard Banich's 20" on an equatorial 
> platform
> really shined.  Howard had a similar fantastic view of the Ring at
> 1200-1500x, I am told.  The object floating in the middle of the field of
> view even at the highest powers meant leisurely inspection by a whole line
> of people.  With the motorized focus, no one had to touch the scope to get
> their best view.
>
> Later that night, we went through a similar episode with Saturn.  Judy
> started off by exclaiming how wonderful Saturn looked in her 16" at 500x.
> It was very impressive indeed, even unbelievable considering the f/4 speed
> of the primary.  I put my computerized 20" on Saturn at 700x and enjoyed
> seeing the Cassini Division so wide that I could drive a truck down it, 
> and
> found Encke's Division obvious.  During moments of exceptional seeing, the
> rings broke up into many ringlets.  A couple of experienced observers even
> mentioned the word, "spokes".
>
> Friday night we enjoyed awesome views of the Orion Nebula and found the
> Horsehead visible without filters in even small scopes.  The lessons that 
> I
> learned once again is how decisive the atmospheric transparency and seeing
> is to a scope's performance, and that extremely high power can be employed
> on small objects to good effect.
>
> The other scope that really caught my attention was Dan Gray's 
> computerized
> 14". Dan has come up with the most nifty over-under drive plate, where the
> altitude drive sits on top of a thin flexible plate and the azimuth drive
> sits underneath the same plate.   This is a design that ought to be widely
> copied."
>
>
> Mel Bartels