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Highest theoretical magnification?
What does a highest theoretical mag. of 720X mean? What would one be able
to see with a telescope with that level of magnification? Chuck |
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Highland wrote:
What does a highest theoretical mag. of 720X mean? What would one be able to see with a telescope with that level of magnification? Chuck Talk about excellent questions............. |
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Divide the focal length of your primary lens (or mirror) by the focal length
of your highest powered eyepiece, for example a typical 6 inch reflector might have a focal length of 900mm and come with three eyepieces, 6mm, 12mm and 25mm. This would give you a highest theoretical magnification of 150X (900 / 6). Get a 2X barlow lens and now your highest theoretical magnification is 300X, but ( and this is a huge BUT), there are several practical factors that make the theoretical maximum of any scope "practically" un-attainable. 1. atmospheric seeing (the steadiness of the air column you are looking through) 2. the resolving power of your telescope (mostly a function of the aperture). 3. the quality of the optics in your telescope. 4. the collimation of your scope. With the example above, of 300x, Jupiter would look about 5 times bigger in your telescope than the moon looks with the naked eye, but it would be very "shaky" most of the time (because of poor atmospheric seeing) and possibly grainy looking if you are using a small aperture scope (less than 4 inches). IP "Highland" wrote in message news:Y2%Lc.142980$a24.46611@attbi_s03... What does a highest theoretical mag. of 720X mean? What would one be able to see with a telescope with that level of magnification? Chuck |
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In article Y2%Lc.142980$a24.46611@attbi_s03,
"Highland" wrote: What does a highest theoretical mag. of 720X mean? What would one be able to see with a telescope with that level of magnification? Chuck The following formulas should help: ta = Telescope Aperture in millimeters Minimum useful magnification = ta * 0.13 Maximum useful magnification = ta * 2.00 Magnification for Best Visual Acuity = ta * 0.25 Dawes Limit can be calculated = 115.8/ta (answer in arc seconds) Hope this helps, tom |
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Excellent. Thank you all.
Chuck "tom" wrote in message ... In article Y2%Lc.142980$a24.46611@attbi_s03, "Highland" wrote: What does a highest theoretical mag. of 720X mean? What would one be able to see with a telescope with that level of magnification? Chuck The following formulas should help: ta = Telescope Aperture in millimeters Minimum useful magnification = ta * 0.13 Maximum useful magnification = ta * 2.00 Magnification for Best Visual Acuity = ta * 0.25 Dawes Limit can be calculated = 115.8/ta (answer in arc seconds) Hope this helps, tom |
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"Highland" wrote in message news:Y2%Lc.142980$a24.46611@attbi_s03... What does a highest theoretical mag. of 720X mean? What would one be able to see with a telescope with that level of magnification? Chuck Almost certainly, that the scope is crap!... 'Highest magnification' claims, are common on cheap 'department store' scopes, and rare on better kit. To really have a useable magnification this high, would require around a 14" aperture. All you will see at this magnification, is probably the optical defects of the scope, and the atmospheric blur, showing very large... If the scope is 14" in aperture, then the claim is 'reasonable', and for bright objects (the planets), on nights of very good seeing, a magnification at this sort of level, might be used to show as much as possible, in the odd moments of good seeing. Best Wishes |
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I know people in this group are very able but to answer the question from a
novice like myself [who is aware that some of us know very little!] the theoretical bit applies to max magnification but it means very little when applied to smaller telescopes and so the number is meaningless! Keith |
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Hello,
To know the real magnification for any scope, multiply 50 by inch of apperture (primary mirror), so for 3 inch, the maximum available is 150x, but it's in the very best air condition, that mean, perfect darkness, perfect seeing, no atmospheric turbulence, etc... The real practical maximum, is more like 30x to 40x by inch. This equation is true for all kind of scope. And if you whan know what is your magnification, you take focal lenght (not the diameter lenght, usualy, it's write on the scope, like D=xxxmm F=xxxmm, the F is the Focal lenght), divide by the ocular focal (usually, the number is write in mm and it's write on the ocular), i.e. if F=800, and you use your 25mm ocular, the magnification will be 800/25 = 32x. I hope this little information help you! Clear sky Eric "Keithbcook" a écrit dans le message de ... I know people in this group are very able but to answer the question from a novice like myself [who is aware that some of us know very little!] the theoretical bit applies to max magnification but it means very little when applied to smaller telescopes and so the number is meaningless! Keith --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.737 / Virus Database: 485 - Release Date: 2004-07-29 |
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Keithbcook wrote:
I know people in this group are very able but to answer the question from a novice like myself [who is aware that some of us know very little!] the theoretical bit applies to max magnification but it means very little when applied to smaller telescopes and so the number is meaningless! Generally, the maximum power that a telescope is capable of is often quoted to be around 50x per inch of aperture (2x per millimeter of aperture). The aperture of the telescope is the diameter of the main lens or mirror. If the telescope is 3 inches in aperture, the maximum power will be around 150x or so. This is not exactly a hard and fast rule, but more of a general "rule of thumb" kind of guide for how much power might be employed. However, for larger telescopes, the Earth's atmosphere comes into play, as it frequently will disturb the path of incoming light, causing the variable blurring known as "seeing" and preventing the full magnification of a telescope from being used all the time. Usually, most observers will only be using half to perhaps 2/3rds of that maximum power, and for fainter and larger objects, the power used might be less than 1/4 of the maximum. I hope this helps a little. Clear skies to you. -- David W. Knisely Prairie Astronomy Club: http://www.prairieastronomyclub.org Hyde Memorial Observatory: http://www.hydeobservatory.info/ ********************************************** * Attend the 11th Annual NEBRASKA STAR PARTY * * July 18-23, 2004, Merritt Reservoir * * http://www.NebraskaStarParty.org * ********************************************** |
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