Tell me in terms of focal lenght. I am tryin to make a truss tube dobsonian design.
215088
As the focal length was not mentioned it's impossible to measure the distance between primary mirror and diagonal. I calculated that it should be more than a meter if the f ratio is high enough.\nI don't need be an Indian to see Indian movies. DVDs are released worldwide. However, I am neither from S.P.A.C.E nor from Galileo. I run an astronomy organization myself. I'm associated with many other international organizations.
17452
commmon one is Convex lens\n(with different angles, to magnify upto diff levels)\nbut for higher levels, it depends upto the magnifying object and distance also
86695
Thats a hard one. the 5 ft dish is C-Band, the mini dish is K or KU band. The parabolics are different. You might be able to do it, and use the mini-dish lmb, but you will probably have to adjust the mounting point in order to get the best focal point...There is a listserve that you can probably join and ask some questions. I believe you can email listserve@scte.org. Good luck, hope it helps
547678
I haven't seen the movie, but I've seen some stills from it.  The telescope design is called a Dobsonian named after John Dobson who popularized it.\n\nA local astronomy club may be able to point you to some Amateur Telescope Makers (ATM) if you want to build your own.  Dobsonians are also sold commercially at near the same cost as building your own, if you shop around.\n\nFor more information and additional links see:\nhttp://en.wikipedia.org/wiki/Dobsonian
120025
a double convex lens will magnify, i can't remember which ones reduce size, but i'm guessing some sort of concave lens, and lenses REFRACT light, while mirrors REFLECT light.
160702
The focal length of an optical system is a measure of how strongly it focuses or diverges light. A system with a shorter focal length has greater optical power than one with a long focal length.\n\nContents [hide]\n1 Thin lens approximation \n2 General optical systems \n3 See also \n4 References \n \n\n\n[edit]\nThin lens approximation\nFor a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens. For a converging lens (e.g., a convex lens), the focal length is positive, and is the distance at which a beam of collimated light will be focused to a single spot. For a diverging lens (e.g., a concave lens), the focal length is negative, and is the distance to the point from which a collimated beam appears to be diverging after passing through the lens.\n\n[edit]\nGeneral optical systems\nFor a thick lens (one which has a non-negligible thickness), or an imaging system consisting of several lenses and/or mirrors (e.g., a photographic lens or a telescope), the focal length is often called the effective focal length (EFL), to distinguish it from other commonly-used parameters:\n\nFront focal length (FFL) or Front focal distance (FFD) is the distance from the front focal point of the system to the vertex of the first optical surface. \nBack focal length (BFL) or Back focal distance (BFD) is the distance from the vertex of the last optical surface of the system to the rear focal point. \nFor an optical system in air, the effective focal length gives the distance from the front and rear principal planes to the corresponding focal points. If the surrounding medium is not air, then the distance is multiplied by the refractive index of the medium. Some authors call this distance the front (rear) focal length, distinguishing it from the front (rear) focal distance, defined above.\n\nIn general, the focal length or EFL is the value that describes the ability of the optical system to focus light, and is the value used to calculate the magnification of the system. The other parameters are used in determining where an image will be formed for a given object position.\n\nFor the case of a lens of thickness d in air, and surfaces with radii of curvature R1 and R2, the effective focal length f is given by:\n\n \nwhere n is the refractive index of the lens medium. The quantity 1/f is also known as the optical power of the lens.\n\nThe corresponding front focal distance is:\n\n \nand the back focal distance:\n\n \nIn the most common sign convention, the value of R1 will be positive if the first lens surface is convex, and negative if it is concave. The value of R2 is negative if the second surface is concave, and positive if convex. Note that sign conventions vary between different authors, however.\n\nFor a spherically curved mirror, the focal length is equal to half the radius of curvature of the mirror. The focal length is positive for a concave mirror, and negative for a convex mirror.\n\n[edit]\nSee also\nDepth-of-field \nDioptre \nFocus (optics) \nNormal lens \nTelephoto lens \nWide-angle lens \n[edit]\nReferences\nGrievenkamp, John E. (2004). Field Guide to Geometrical Optics, SPIE Field Guides vol. FG01, SPIE. ISBN 0819452947. \nHecht, Eugene (2001). Optics, 4th ed., Pearson Education. ISBN 0805385665. \nRetrieved from "http://en.wikipedia.org/wiki/Focal_length"
409021
Because the focal point is half the distance of the radius of curvature, the focal point is 4 cm.\n\n1/f = [1/d(image)]  + [(1/d(object)]\n\n1/4 = 1/17 + 1/d(image)\n\n1/d(image) = 1/4 - 1/17 = 17/68 - 4/68 = 13/68\n\nd(image) = 68/13 = 5.23 cm
370895
Absolutely nothing is better than attending a star party and actually trying out a handful of different scopes.\n\nAnyone who brings one is there to share and would be happy to tell you about their scope and its strengths and weaknesses.\n\nWhen buying something that enables you to see, it is best to go and try them first rather than trying to visualize from a text description in a magazine or website.\n\nGo to your local community college and ask when the next one is or maybe some libraries around would have a community board.
495748
I would recommend a Meade ETX-90.  That's about the lowest price scope you can buy with good optics.  Don't waste your money on a $49.95 cheap 60mm scope - a good pair of binoculars are much better, you don't have to set anything up, and they go with you in your car's glove compartment.\n\nThe Meade ETX-90 is a Matsukov Cassegrain ("Mak-Cass") telescope.  It comes with Autostar (computer guided "GOTO" feature that lets you view 1000s of celestial objects with the push of a button).  It also comes with a very sturdy tripod, motor drives, and push-button focus.\n\nRetail price about $750.00 with everything included.  As I said, if that's too much money, binoculars are a better option.  A good pair (10 x 25) will run about $60 to $100.  With good binoculars you will be able to see craters on the moon, the Andromeda Galaxy, and star clusters.  You wil also be able to make out Saturn's rings and Jupiter's main moons and equatorial bands.\n\nThe nice thing about a telescope with a motor drive is you can stay focused on an object without constantly having to adjust the telescope.  The art of astronomy is not something you can pick up in a day.  Most people looking into a astronomical telescope for the first time won't be able to make out even one tenth as much as somebody with experience.  So, if you plan to spend some time with your new toy, it's well worth it to get something that will hold your interest.\n\nThe other nice feature about this particular telescope is that it doesn't flip things upside down (like most reflector scopes do), which means you can also look at land objects.  It does flip them horizontally, like a mirror image, but that's not a big deal.\n\nOne last thing:  For astronomy, magnification is the least concern.  You want light gathering ability.  No matter how powerfully you magnify a star, it's not going to get any bigger.  You want to see as big a field of the sky as you can.  Magnifying it just narrows the field to a few stars, which is highly uninteresting.  By the same token, if you view the Moon, magnification helps somewhat, but it just makes things bigger and fuzzier, not any clearer.  A tiny detail in sharp focus is much better than that same detail made large and fuzzy.
328581
A 5" scope should be more than enough.  There are hobbyists on the net that talk of watching Jovian transits with 4"\n\nThe site link below has an uncrippled shareware program JupSat95 that calculates a lot of info about Jupiter include satellite transit information,\n\n"When a satellite is transiting Jupiter, (passing in front of Jupiter's disk), then it's numerical information is printed in Yellow."\n\nhttp://indigo.ie/~gnugent/JupSat95/
365370
They both have objective lenses (what your looking at), and they both have ocular lenses (the ones near the eye)\n\nThe primary difference is the focal length- a telescope for all practical purposes has an infinite focal length.   A Microscope has a very finite focal length, usually measured in millimeteres
198390
You need a parabolic 5-inch reflector which you can get from headlight (but not a sealed beam) or a large flashlight. Or you can use a 5-inch convex lens like the ones used for close-up work (try a hobby shop). You will also need a very small source of light. A flashlight bulb should do. The light source should be positioned at the focal point of the reflector or lens. Since the lens/reflector will not be perfect and the light source will not be a true point, the beam will not be perfectly parallel.\nThe sun IS a near-perfect parallel light source in the context of a 5-inch viewing field. Maybe that's what you meant. I can't see it being used by your construction.
12425
The James Webb Space Telescope is being built to replace Hubble. The Webb Telescope will be a large, infrared space telescope designed to provide even clearer pictures of our Universe than those received from Hubble. It's going to have a mirror that is about 2 1/2 times the diameter of the Hubble Mirror. ( The Hubble's mirror is 94[?] inches in diameter I believe, and the Webb Telescope mirror will be made up of 18 diagonal mirror pieces that will be about 250 inches in diameter.) It's also going to be about a million miles away from the bright Earth and have a Sunshade the size of a Tennis Court! The telescope's name sake, James Webb, was NASA's second Administrator years ago.\n   With telescopes, it's not really a question of "power." With my telescope the "power" depends on the eyepiece I use. It is actually more about how much light you can "gather." Think of it as being in a completely dark room with a magnifying glass and a flashlight. The powerful magnifying glass is really useless in the dark, but the flashlight could help you see anything and everything in the room, right? Well, space is about the darkest "room" you will ever find especially for looking deeper and deeper into the Cosmos. The bigger the mirror you have to detect the faintest stars and galaxies, the better.  These telescopes really aren't made to see really bright things- that's why you have never seen a Hubble photograph of the Moon. From Hubble's orbit just above the Earth, the Moon is just too bright.\n This may not be the most satisfying answer to your great question- I get that question all the time when I bring my telescope out- but I think you can see the advantage of having a flashlight in that dark room especially if you don't know where all the furniture is!!!
22622
Simple: http://www.life.uiuc.edu/hughes/boast/sciencelessons/telescopes.htm\nAdvanced: http://www.funsci.com/fun3_en/tele/tele.htm
99586
easy. For a basic refractor just reflects light through lense then bends by way of mirror into eyepiece which also has lense. Focusing lense. Hope helps.
99960
First, the type of telescope you want depends mainly on what kind of observing you want to do. If you're mostly interested in deep space, get yourself what's called a REFLECTOR. I have an 8" Meade reflector and under good "seeing" conditions can observe just about every star in our galaxy visible from the Northern Hemisphere, plus structures beyond the Milky Way up to about 10-billion light years. Just be sure and buy a reflector system that has a clock drive. This makes it possible to stay locked on to some object without having to constantly move the 'scope tube to compensate for Earth's rotation.\n\nIf you're into Solar System observing, then a refractor will do nicely. They don't gather as much light as a reflector, but the resolution is much better--plus images aren't inverted as with most reflectors.\n\nCelestron Inc puts out the Cadillac of telescopes, but Meade provides very good products at less cost. Do NOT buy any telescope from retail stores like K-Mart, Sears, etc.,. Most of the stuff is cheap junk. Either buy mail order from Celestron or Meade, or visit a store that sells nothing but astronomy-related things.\n\nGod is spelled B-I-G B-A-N-G\nPBrax@netscape.com
117380
Focal length.\nThe distance from the lens to a point at which the light going through the lens will converge into a sigle point.\n\nAfter the light enters a lens straight on, the light is bent, causing the light to focus toward a signle point. After that point the image is turned upside down.