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Lawrence Sayre
Post Laureate
Reged: 10/16/04
Posts: 3677
Loc: N.E. Ohio
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Revisiting the furor that I caused awhile back with my thread about stars not being capable of being magnified by telescopes due to being only unresolved (as regards resolving the actual disk) point sources, I have had a new thought on this. Perhaps it would be most appropriate to say that stars can not be magnified, but they can certainly be amplified. Just as when a faint and distant radio signal when properly amplified becomes hearable, stars can be telescope amplified, making what was once invisible, suddenly become visible. You can't technically magnify it, but you can amplify it enough to make it visible. Just a fleeting thought that I figured I better enter here as a thread before it popped back out of my head and was lost forever. My flame suit is on for this one.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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flame? no i think id rather shoot you with a stream of frozen absolute zero hydrocarbons to freeze your body in a living state like han solo in star wars.
Just kidding, you are correct i think in your assessment. No matter how far i crank up mags on any star it never gets any larger, but it sure does get increasingly brighter.
Some stars that I barely see with averted vision during naked eye viewing are bright and distinct through the telescope.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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GlennLeDrew
professor emeritus
Reged: 06/18/08
Posts: 574
Loc: Ottawa, Ontario, Canada
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Magnify to the point where your eye can begin to resolve the Airy disk and diffraction fringes, and you'll be both magnifying AND amplifying a star's image. Before I don *my* flame-retardant cape, note that I said "image." 
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Luigi
Carpal Tunnel
Reged: 07/03/07
Posts: 1960
Loc: Massachusetts
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For a star, you only ever see the Airy disc in a telescope. At low power it's just too small for your eye to resolve. The airy disk is the image of the objective's diffracion patern, not the image of a star. The same amount of light is in that diffraction patern regardless of magnification. Also, a telescopes does not amplify in the strictly technical sense, which calls for an active device that adds power to a signal.
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17.5" f/5 Discovery Truss
IM715 7" f/15 MCT, Eon-120ED
Lunt 60mm single etalon HA
CG5A coffee grinder, Orion Skyview Alt-AZ
35,19,15 Pans.9 Nag. Meade 24.5 4kSWA, 4.7 5kUWA.
BO-TMB 7mm planetary.
Zeiss Diascope 85
Zeiss, Leica, Canon IS, Fujinon, Nikon binos
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 10920
Loc: Los Angeles
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No matter what the power, a star's image is a diffraction disc that is sized according to the optics of the scope.
Since changing magnification does not change the size or intensity of a star's image (only changing the size of a scope can do that), as magnification is increased, the light of the night sky is expanded and the background in the eyepiece gets dimmer. Hence, faint stars will be most visible at higher powers, not lower ones.
Any object with a size to it, though, gets dimmer and harder to see as the magnification goes up, so there is always an optimum balance between dimness and contrast with the sky on DSOs.
When the star image is magnified to the point where the actual spurious disc becomes visible to the eye, any increase in magnification will not aid resolution because no further improvement is possible. The point at which this occurs is somewhat subjective, though it is most often said to occur at around a 1mm exit pupil (usually 25x/inch).
Higher magnifications will make fainter stars more visible due to the darkening of the sky, but this appears to be an optimum high power for most extended objects.
Larger scopes can magnify to higher magnifications because the spurious disc (central part of the Airy disc) is smaller. Yet, the disc becomes visible just the same at about the 1mm exit pupil, just as in the small scope. Resolution is improved, though, due to the smaller size of the diffraction disc.
So there are a few good reasons to get a bigger scope:
--smaller stellar diffraction discs (improved resolution)
--higher magnifications at the same exit pupil (larger = more visible to our eye-brain combination)
--greater light grasp and brighter stellar images
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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