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淘豆网网友近日为您收集整理了关于OPTICS - TELESCOPE Plans - (eBook Astronomy Diy How To Build Construct pdf) (TEC@NZ)(1)的文档，希望对您的工作和学习有所帮助。以下是文档介绍：OPTICS - TELESCOPE Plans - (eBook Astronomy Diy How To Build Construct pdf) (TEC@NZ)(1) This is a .pdf version of the website any link on this page will start yourbrowser and take you to that site. If you wish to print a page select the pagenumber and print the one you want. Do not print the first three pages it willuse all your black ink!How to Build a Dobsonian Telescopehttp://flake/telescope/index.htm (1 of 4) [9/6/:04 AM]This manual was created using Acrobat 4.0 you need to downloa(来源：淘豆网[/p-6415014.html])d the latestfree reader to view this manual properly! Older readers will give you strangeresults.TABLE OF CONTENTSIntroduction and Photo pleted 'Scope&Not-too-tech advice&; Materials L Tool LSources ListOverview Drawing of Six-inch 'Scope with PlywoodCut PatternOverview Drawing of Eight-inch 'Scope withPlywood Cut PatternOverview Drawing of Ten-Inch 'Scope with PlywoodCut PatternSection &A&: Preparing the (来源：淘豆网[/p-6415014.html])Tube, Making &Spider&;Eyepiece TubeSection &B&; &Tailgate& (Mirror Cell) ConstructionSection &C&; Making the M Finishing T CareInstructionsFrequently Asked QuestionsHow to Build a Dobsonian Telescopehttp://flake/telescope/index.htm (2 of 4) [9/6/:04 AM]E-mail:Ray Cash-Le PennecTo my other WebPages:My Vanity PageMy Deep-Sky PageHow to Build a 13& Travel ScopeDobsonian EvolutionThe San Fr(来源：淘豆网[/p-6415014.html])ancisco Sidewalk AstronomersMy D PageThis site is a member of theAmateur Telescope Making Web RingPrevious 5 | Previous | Random | List | Next | Next 5Visitors since March 29, 1998How to Build a Dobsonian Telescopehttp://flake/telescope/index.htm (3 of 4) [9/6/:04 AM]Plans for Building a Dobsonian Telescopebrought to you by: The San Francisco Sidewalk AstronomersYes, it &looks like a cannon,& but the above is really a ten-inch (m(来源：淘豆网[/p-6415014.html])easured by the diameter of theobjective) Newtonian telescope that almost anybody can build. Here you will find plans to build thistelescope, or a smaller one--either a six-inch, or an eight-inch--of identical design. These plans are onlyslightly modified from the plans The Sidewalk Astronomers have been sending to interested parties for amere $2.00 via snail-mail. I have kept as close to this design as possible: One, because this is--handsdown--the (来源：淘豆网[/p-6415014.html])cheapest and easiest way to make and two, because I walk in the shadowof John Dobson, who invented many of these designs which have revolutionized amateur andprofessional astronomy alike... Besides, Los Angeles Sidewalk Astronomer, Pam Reid, did most of thework by writing and typing the procedures, as well as gathering the drawings--which, by the way, weredone by Earl Jungians (from photographs of John at work by Molly Lusignan)(来源：淘豆网[/p-6415014.html]). Most of my &work&consisted of scanning and re-typing Pam's work... though I do interject my two-cents here and there.In the category of &the left hand not knowing what the right hand is doing,& another Webpage, supportedby NASA's Telescopes in Education Project, also have these plans online. Here you will find theoriginal plans--images and text scanned together, without my minor meddling--which includes, by theway: the (来源：淘豆网[/p-6415014.html])Six-inch plans, the Sun Telescope construction tips page, a Links page, and a real person toE-mail your questions to. Regardless, it is a beautiful page, and I mespecially if you have any problems printing the plans from this page.If you would like to grind, polish and figure your own mirror, I suggest Victor's Telescope Making pageas well as the late Sam Brown's book , All About Telescopes, which may be ordered from Ori(来源：淘豆网[/p-6415014.html])onTelescope and Binocular Center.Dobsonian Telescope Planshttp://flake/telescope/Dobsonian%20Telescope%20Plans.htm (1 of 3) [9/6/:11 AM]--Ray Cash-Le PennecIntroductionThe plans you will find on these pages, are, by and large, the result of years of trial and error on the partof John Dobson, one of the founders of The San Francisco Sidewalk Astronomers and a prolifictelescope maker. John has, quite literally, helped thousands of people mak(来源：淘豆网[/p-6415014.html])e telescopes of this design!Only in the past few years mercial telescope manufacturers adopted the Dobsonian approach tomake affordable, alt-azimuth Newtonian telescopes... However, the three top manufacturers (henceforthreferred to as: &The Big Three&), Celestron, Meade, and Orion, continue to fall short mechanically of thesimple designs found on these pages. All of The Big Three, for example, use M a kind of coatedparticle board,(来源：淘豆网[/p-6415014.html]) which is heavy, not durable, not as strong or light as plywood, which, of course,we mend. All of The Big Three have undersized pivot bolts, do not use Teflon as bearing surfaces(there is no substitute!), and have shoddy mirror cells (tailgates). The list goes on... They do look&pretty,&
I'll give them that. If you happen to own you mightwell peruse these pages to find ways to tinker and fix up your mass-produced Dob: you can only improvewhat you got! It ain't rocket science!Dobsonian Telescope Planshttp://flake/telescope/Dobsonian%20Telescope%20Plans.htm (2 of 3) [9/6/:11 AM]The designs you find on these pages are also open to improvement by you: the builder. Not only will youdiscover the ins and outs of Newtonian / Dobsonian telescope design, but you are encouraged e upwith your own modifications. We include plans to make your own Primary Mirror Cell (we call it a&Tailgate&), Secondary Diagonal Mirror Holder and &Spider,& and Eyepiece Holder/Focuser. These areitems even the most seasoned TM (telescope-maker) usually buys from small telescope partmanufacturers: you may opt to do the same (although John's designs are perfectly functional--someingenious--and very inexpensive to fabricate). Contact your local astronomy club, there are usually atleast a handful of TM's that can help you out. Also, check my Sources page for materials and accessoriesyou will need, or, might want, to purchase.I think you will find these plans pretty clear, simple, and straightforward. If not, let me know.Have fun!Dobsonian Telescope Planshttp://flake/telescope/Dobsonian%20Telescope%20Plans.htm (3 of 3) [9/6/:11 AM]Some not-too-technical advice before you begin...This Webpage plete instructions for constructing a Sidewalk (Dobsonian) telescope using asix, eight, or ten inch (diameter) purchased objective mirror. If you are interested in grinding andpolishing your own mirror, we suggest you pick up John Dobson's video (listed under &Sources& below)as a start. Also, Victor's Telescope Making Page has step by step instructions for mirror making. AllAbout Telescopes, by Sam Brown (found at Orion Telescope and Binocular Center) also has goodinstructions on this art.How much is this going to cost? Well... an 8& f/7 mirror from Coulter with diagonal costs $219.95, plus$15.00 for shipping. If you can build an 8& scope for twice the cost of this, consider yourself lucky! Youcan buy a &Big Three& scope fo you can also buy used for less... Something else mustbe motivating you to &build your own.& This Webpage is for you... and your daughter and/or son!You will need to purchase one objective (&primary&) mirror and one diagonal flat, (&secondary) mirror,in order to build the telescope. Mirrors may be purchased from mail-order telescope supply houses.Coulter Optical is an excellent, dependable source for good-quality, inexpensive mirrors, so we haveincluded their address in the &Sources& list below. Orion Telescope and Binocular Center also sellmirrors, as well as alot of other stuff.REMEMBER! TELESCOPE MIRRORS ARE POWERFULCONCENTRATORS OF LIGHT.Sunlight reflected off the face of a telescope mirror can cause BLINDNESS or START AFIRE! Always handle your mirror indoors or in the shade! The telescopedescribed in these plans is for NIGHT USE ONLY. NEVER set up yourtelescope in a location where it may be reached by sunlight, and:NEVER LOOK AT THE SUN THROUGH YOUR TELESCOPE!The plywood cutout patterns on the next few pages are for the construction of telescopes with six, eight,and ten inch objective mirrors, but you can use the same design for smaller telescopes (4.5&, for example)or larger telescopes with objective mirrors of up to 15& in diameter. Just remember that the tube of yourtelescope needs to be at least 1-1/2& wider than the diameter of the objective mirror. Then increase (ordecrease) the tube box and rocker dimensions proportionately. THE DIAMETER OF YOUR TUBEDETERMINES ALL OTHER DIMENSIONS.Dobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (1 of 8) [9/6/:12 AM]For telescopes with mirror diameters 16& and larger, a different tube box design and mirror supportsystem is necessary. (Again, John Dobson's telescope-making videolisted in &Sources& shows theconstruction of a 16& telescope with this modified tube box and support system). A more popular methodof construction nowadays for large Dobs is the truss design, which allows the telescope to be &brokendown& for transport and storage. See my Vanity Page for examples I mendations, andresources.Objective and Diagonal MirrorsWhat we describe as a Sidewalk Telescope, or Dobsonian Telescope, is a simple Newtonian reflectingtelescope in a sturdy, wooden, alt-azimuth mount or rocker. The telescope consists of a concave (actuallyparabolic) objective (or Primary) mirror, which is mounted in the bottom of the tube. This objectivegathers light from the object under observation and brings
forming an image of theobject in what is called the focal plane or image plane, at the upper end of the tube.A small, flat, front-surface mirror called the diagonal (or secondary) mirror is mounted inside thetelescope tube near the front end. This mirror is mounted at a 45 degree angle to the tube's axishence itsname. It deflects light from the objective to the side of the tube where the image may be more easilyexamined with an eyepiece.The size of the diagonal mirror is dependent on the size and focal ratio of the objective mirror. So,when you order your mirrors, make sure to ask your supplier to tell you the correct size diagonal mirrorto order. Specify that you will be using a low-profile focuser. To determine more accurately the size ofthe diagonal, peruse the following email correspondence:@ (Paul Balzac) writes:&By the way, I tried to find the equation you mentioned in the archives, but&couldn't. Anyone help?The equation is found in Richard Berry's Build Your Own Telescope, pgs 26-28. However,there are a couple of errors on those pages: &E& on page 27 should be changed to &D& (this makesmore sense with the drawing). Also, in the final example he uses, the &6& and &8&switch them around, in other words.But to cut to the chase, the formula is:d = df +([D-df]/F) X LdeWhere &d& is the minor axis of the diagonal,&df& is the focal length of your primary multiplied by: the result of the amount of fullyilluminated field you want divided by 57.3 (radians in a degree). In other words,F X (x/57.3) where &F& is focal length and &x& is the amount of fully illuminated field youdesire. (&df,& is, in fact, the amount of fully illuminated field).Dobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (2 of 8) [9/6/:12 AM]&D& is the diameter of your primary,&F& is the focal length of your primary,&Lde& is the distance between the diagonal and the field stop of your eyepiece.A self-serving example: I recieved my 8& f/7.06 mirror from Coulter yesterday. mon ruleof thumb is to have a half (.5) degree of &fully illuminated field& for visual use. (But I will alsoplug in a .25 fully illuminated field, just to see how much smaller my diagonal will be...). Thetelescope will use a 10.5& outside diameter Sonotube, have a low profile focuser (say 2.125inches high), and I will add 3/4 of an inch to be sure all my eyepieces will focus witha variety of eyeballs: So my &Lde& will be: 8.125 inches: 5.25 (radius of 10& tube) + 2.125 + .75.&df& is then,for a .5 degree fully illuminated field: 56.5 X (.5/57.3) = .493for a .25degree fully illuminated field: 56.5 X (.25/57.3) = .247So lets plug these numbers in:The formula, again is: d = df +([D-df]/F) X Lde (be sure to multiply BEFORE you add).493 + .133 X 8.125 = 1.57 inches. So, a 1.57& minor axis diagonal will fully illuminate a half adegree at the eyepiece..247 + .137 X 8.125 = 1.36 inches. So, if I want only a .25 degree fully illuminated field toproduce more contrast on the s... I would go with a diagonal this size.Diagonal mirrors do e in the above sizes, but one can round off--in eitherdirection--your preference!--RayA Word About Focal Length and Focal RatioThe focal ratio of the mirror you select determines how long your telescope will be. A 10& objectivemirror with an f/7 focal ratio will give you a telescope with a 70& focal length. (Multiply the &f-number&by the diameter of the objective mirror to get the focal length.) Your tube will need to be cut to the lengthof the focal length, so you would have a 70& long tube. An 8& objective mirror with an f/7 focal ratiowould have a 56& focal length, and a 56& long tube.(John Dobson mends a focal ratio around f/6 or f/7)Dobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (3 of 8) [9/6/:12 AM]FOCAL RATIO (f-number) x MIRROR DIAMETER = FOCAL LENGTH = LENGTH OF TUBEWhen you get your mirror, the focal ratio may be exactly what you ordered, or it may be a little more, ora little less. So don't cut your tube till you receive your mirror. To measure your focal length exactly,have a friend help you: Take your mirror, a tape measure, and a piece of paper outside on any clear nightand catch the light of a bright star or the Moon with your mirror and reflect it back in that direction.Using that piece of paper find where the star, or Moon forms the smallest image. Measure that distanceas accurately as you can. (Instead of a piece of paper, it is often easier to reflect onto a fixed surface, suchas a garage door jamb or header). Write this measurement down! This determines the length of yourtelescope tube, as well as where you cut a hole for your focuser. The key thing to remember is that youwant this formed image (called the focal plane), to hover in the same plane as the field stop of youreyepiece. If you opt for mercial focuser, you will undoubtedly have to cut your focuser hole in adifferent place than these plans call for! Do you have your eyepiece(s) yet? If that's a &yes,& good: Lookinto your eyepiece and put your pinky finger in the other end--slowly and carefully--can you see whereyour es into a magnified focus? Usually there is a black ring (called a field stop) at this pointaround the in and usually this corresponds to where--on the outside of theeyepiece--the chrome barrel ends and the rest of the eyepiece body begins. This means this is where theeyepiece &bottoms out& when inserted into mercial focuser. But, you don't want mercialfocuser to bottom out when focusing! Individual eyes and eyepieces are different! Always allow at least3/4& &in travel& for mercial focuser, when doing the arithmetic to determine where to cut yourfocuser hole! More is said on this subject in &Section A& of these plans online.TUBE DIAMETERThe telescope tube should be about 2 inches wider in diameter than your objective:A ten-inch diameter objective mirror requires a twelve-inch diameter tube.An eight-inch diameter objective mirror requires a ten-inch diameter tube.A six-inch diameter objective mirror requires an eight inch diameter tube.Materials ListCardboard tube (&Sonotube&) (1):Construction, specifically concrete construction supply housesusually carry these tubes, which are used for forming concrete columns. Get the supply house tocut your tube rough, that is, longer than you need by, let's say, six inches or so. To &finish cut&your tube square: Tape several 8-1/2& x 11& pieces of paper together end for end--enough to wraparound the circumference of the tube, and do just that... Make theand mark the edge you want to cut. Proceed with a hand saw or Jigsaw...qExterior grade plywood: 4' x 8' x 3/4& thick. For an eight or ten inch telescope, one sheet will beplenty. An alternative to &exterior grade plywood& would be &shop grade&; not much moreexpensive, a MUCH smoother finish is possible.q(Optional) Six-Eight feet of Douglas Fir 2&X 2&: Cut these into small lengths and glue to insideof Rocker Box and Tube Box corners--this will strengthen these joints considerably.qPaint and painting supplies: Flat black any dark color is fine for the outsideqDobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (4 of 8) [9/6/:12 AM]播放器加载中，请稍候...
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OPTICS - TELESCOPE Plans - (eBook Astronomy Diy How To Build Construct pdf) (TEC@NZ)(1) This is a .pdf version of the website any link on this page will start yourbrowser and take you to that site. If you wish to print a page select the pagenumber and print the one you want. Do not print the first t...
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淘豆网网友近日为您收集整理了关于OPTICS - TELESCOPE Plans - (eBook Astronomy Diy How To Build Construct pdf) (TEC@NZ)的文档，希望对您的工作和学习有所帮助。以下是文档介绍：OPTICS - TELESCOPE Plans - (eBook Astronomy Diy How To Build Construct pdf) (TEC@NZ) This is a .pdf version of the website any link on this page will start yourbrowser and take you to that site. If you wish to print a page select the pagenumber and print the one you want. Do not print the first three pages it willuse all your black ink!How to Build a Dobsonian Telescopehttp://flake/telescope/index.htm (1 of 4) [9/6/:04 AM]This manual was created using Acrobat 4.0 you need to download t(来源：淘豆网[/p-6462155.html])he latestfree reader to view this manual properly! Older readers will give you strangeresults.TABLE OF CONTENTSIntroduction and Photo pleted 'Scope&Not-too-tech advice&; Materials L Tool LSources ListOverview Drawing of Six-inch 'Scope with PlywoodCut PatternOverview Drawing of Eight-inch 'Scope withPlywood Cut PatternOverview Drawing of Ten-Inch 'Scope with PlywoodCut PatternSection &A&: Preparing the Tub(来源：淘豆网[/p-6462155.html])e, Making &Spider&;Eyepiece TubeSection &B&; &Tailgate& (Mirror Cell) ConstructionSection &C&; Making the M Finishing T CareInstructionsFrequently Asked QuestionsHow to Build a Dobsonian Telescopehttp://flake/telescope/index.htm (2 of 4) [9/6/:04 AM]E-mail:Ray Cash-Le PennecTo my other WebPages:My Vanity PageMy Deep-Sky PageHow to Build a 13& Travel ScopeDobsonian EvolutionThe San Franc(来源：淘豆网[/p-6462155.html])isco Sidewalk AstronomersMy D PageThis site is a member of theAmateur Telescope Making Web RingPrevious 5 | Previous | Random | List | Next | Next 5Visitors since March 29, 1998How to Build a Dobsonian Telescopehttp://flake/telescope/index.htm (3 of 4) [9/6/:04 AM]Plans for Building a Dobsonian Telescopebrought to you by: The San Francisco Sidewalk AstronomersYes, it &looks like a cannon,& but the above is really a ten-inch (meas(来源：淘豆网[/p-6462155.html])ured by the diameter of theobjective) Newtonian telescope that almost anybody can build. Here you will find plans to build thistelescope, or a smaller one--either a six-inch, or an eight-inch--of identical design. These plans are onlyslightly modified from the plans The Sidewalk Astronomers have been sending to interested parties for amere $2.00 via snail-mail. I have kept as close to this design as possible: One, because this is--handsdown--the che(来源：淘豆网[/p-6462155.html])apest and easiest way to make and two, because I walk in the shadowof John Dobson, who invented many of these designs which have revolutionized amateur andprofessional astronomy alike... Besides, Los Angeles Sidewalk Astronomer, Pam Reid, did most of thework by writing and typing the procedures, as well as gathering the drawings--which, by the way, weredone by Earl Jungians (from photographs of John at work by Molly Lusignan). M(来源：淘豆网[/p-6462155.html])ost of my &work&consisted of scanning and re-typing Pam's work... though I do interject my two-cents here and there.In the category of &the left hand not knowing what the right hand is doing,& another Webpage, supportedby NASA's Telescopes in Education Project, also have these plans online. Here you will find theoriginal plans--images and text scanned together, without my minor meddling--which includes, by theway: the Six(来源：淘豆网[/p-6462155.html])-inch plans, the Sun Telescope construction tips page, a Links page, and a real person toE-mail your questions to. Regardless, it is a beautiful page, and I mespecially if you have any problems printing the plans from this page.If you would like to grind, polish and figure your own mirror, I suggest Victor's Telescope Making pageas well as the late Sam Brown's book , All About Telescopes, which may be ordered from OrionT(来源：淘豆网[/p-6462155.html])elescope and Binocular Center.Dobsonian Telescope Planshttp://flake/telescope/Dobsonian%20Telescope%20Plans.htm (1 of 3) [9/6/:11 AM]--Ray Cash-Le PennecIntroductionThe plans you will find on these pages, are, by and large, the result of years of trial and error on the partof John Dobson, one of the founders of The San Francisco Sidewalk Astronomers and a prolifictelescope maker. John has, quite literally, helped thousands of people make t(来源：淘豆网[/p-6462155.html])elescopes of this design!Only in the past few years mercial telescope manufacturers adopted the Dobsonian approach tomake affordable, alt-azimuth Newtonian telescopes... However, the three top manufacturers (henceforthreferred to as: &The Big Three&), Celestron, Meade, and Orion, continue to fall short mechanically of thesimple designs found on these pages. All of The Big Three, for example, use M a kind of coatedparticle board, wh(来源：淘豆网[/p-6462155.html])ich is heavy, not durable, not as strong or light as plywood, which, of course,we mend. All of The Big Three have undersized pivot bolts, do not use Teflon as bearing surfaces(there is no substitute!), and have shoddy mirror cells (tailgates). The list goes on... They do look&pretty,&
I'll give them that. If you happen to own you mightwell peruse these pages to find ways to tinker and fix up your mass-produced Dob: you can only improvewhat you got! It ain't rocket science!Dobsonian Telescope Planshttp://flake/telescope/Dobsonian%20Telescope%20Plans.htm (2 of 3) [9/6/:11 AM]The designs you find on these pages are also open to improvement by you: the builder. Not only will youdiscover the ins and outs of Newtonian / Dobsonian telescope design, but you are encouraged e upwith your own modifications. We include plans to make your own Primary Mirror Cell (we call it a&Tailgate&), Secondary Diagonal Mirror Holder and &Spider,& and Eyepiece Holder/Focuser. These areitems even the most seasoned TM (telescope-maker) usually buys from small telescope partmanufacturers: you may opt to do the same (although John's designs are perfectly functional--someingenious--and very inexpensive to fabricate). Contact your local astronomy club, there are usually atleast a handful of TM's that can help you out. Also, check my Sources page for materials and accessoriesyou will need, or, might want, to purchase.I think you will find these plans pretty clear, simple, and straightforward. If not, let me know.Have fun!Dobsonian Telescope Planshttp://flake/telescope/Dobsonian%20Telescope%20Plans.htm (3 of 3) [9/6/:11 AM]Some not-too-technical advice before you begin...This Webpage plete instructions for constructing a Sidewalk (Dobsonian) telescope using asix, eight, or ten inch (diameter) purchased objective mirror. If you are interested in grinding andpolishing your own mirror, we suggest you pick up John Dobson's video (listed under &Sources& below)as a start. Also, Victor's Telescope Making Page has step by step instructions for mirror making. AllAbout Telescopes, by Sam Brown (found at Orion Telescope and Binocular Center) also has goodinstructions on this art.How much is this going to cost? Well... an 8& f/7 mirror from Coulter with diagonal costs $219.95, plus$15.00 for shipping. If you can build an 8& scope for twice the cost of this, consider yourself lucky! Youcan buy a &Big Three& scope fo you can also buy used for less... Something else mustbe motivating you to &build your own.& This Webpage is for you... and your daughter and/or son!You will need to purchase one objective (&primary&) mirror and one diagonal flat, (&secondary) mirror,in order to build the telescope. Mirrors may be purchased from mail-order telescope supply houses.Coulter Optical is an excellent, dependable source for good-quality, inexpensive mirrors, so we haveincluded their address in the &Sources& list below. Orion Telescope and Binocular Center also sellmirrors, as well as alot of other stuff.REMEMBER! TELESCOPE MIRRORS ARE POWERFULCONCENTRATORS OF LIGHT.Sunlight reflected off the face of a telescope mirror can cause BLINDNESS or START AFIRE! Always handle your mirror indoors or in the shade! The telescopedescribed in these plans is for NIGHT USE ONLY. NEVER set up yourtelescope in a location where it may be reached by sunlight, and:NEVER LOOK AT THE SUN THROUGH YOUR TELESCOPE!The plywood cutout patterns on the next few pages are for the construction of telescopes with six, eight,and ten inch objective mirrors, but you can use the same design for smaller telescopes (4.5&, for example)or larger telescopes with objective mirrors of up to 15& in diameter. Just remember that the tube of yourtelescope needs to be at least 1-1/2& wider than the diameter of the objective mirror. Then increase (ordecrease) the tube box and rocker dimensions proportionately. THE DIAMETER OF YOUR TUBEDETERMINES ALL OTHER DIMENSIONS.Dobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (1 of 8) [9/6/:12 AM]For telescopes with mirror diameters 16& and larger, a different tube box design and mirror supportsystem is necessary. (Again, John Dobson's telescope-making videolisted in &Sources& shows theconstruction of a 16& telescope with this modified tube box and support system). A more popular methodof construction nowadays for large Dobs is the truss design, which allows the telescope to be &brokendown& for transport and storage. See my Vanity Page for examples I mendations, andresources.Objective and Diagonal MirrorsWhat we describe as a Sidewalk Telescope, or Dobsonian Telescope, is a simple Newtonian reflectingtelescope in a sturdy, wooden, alt-azimuth mount or rocker. The telescope consists of a concave (actuallyparabolic) objective (or Primary) mirror, which is mounted in the bottom of the tube. This objectivegathers light from the object under observation and brings
forming an image of theobject in what is called the focal plane or image plane, at the upper end of the tube.A small, flat, front-surface mirror called the diagonal (or secondary) mirror is mounted inside thetelescope tube near the front end. This mirror is mounted at a 45 degree angle to the tube's axishence itsname. It deflects light from the objective to the side of the tube where the image may be more easilyexamined with an eyepiece.The size of the diagonal mirror is dependent on the size and focal ratio of the objective mirror. So,when you order your mirrors, make sure to ask your supplier to tell you the correct size diagonal mirrorto order. Specify that you will be using a low-profile focuser. To determine more accurately the size ofthe diagonal, peruse the following email correspondence:@ (Paul Balzac) writes:&By the way, I tried to find the equation you mentioned in the archives, but&couldn't. Anyone help?The equation is found in Richard Berry's Build Your Own Telescope, pgs 26-28. However,there are a couple of errors on those pages: &E& on page 27 should be changed to &D& (this makesmore sense with the drawing). Also, in the final example he uses, the &6& and &8&switch them around, in other words.But to cut to the chase, the formula is:d = df +([D-df]/F) X LdeWhere &d& is the minor axis of the diagonal,&df& is the focal length of your primary multiplied by: the result of the amount of fullyilluminated field you want divided by 57.3 (radians in a degree). In other words,F X (x/57.3) where &F& is focal length and &x& is the amount of fully illuminated field youdesire. (&df,& is, in fact, the amount of fully illuminated field).Dobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (2 of 8) [9/6/:12 AM]&D& is the diameter of your primary,&F& is the focal length of your primary,&Lde& is the distance between the diagonal and the field stop of your eyepiece.A self-serving example: I recieved my 8& f/7.06 mirror from Coulter yesterday. mon ruleof thumb is to have a half (.5) degree of &fully illuminated field& for visual use. (But I will alsoplug in a .25 fully illuminated field, just to see how much smaller my diagonal will be...). Thetelescope will use a 10.5& outside diameter Sonotube, have a low profile focuser (say 2.125inches high), and I will add 3/4 of an inch to be sure all my eyepieces will focus witha variety of eyeballs: So my &Lde& will be: 8.125 inches: 5.25 (radius of 10& tube) + 2.125 + .75.&df& is then,for a .5 degree fully illuminated field: 56.5 X (.5/57.3) = .493for a .25degree fully illuminated field: 56.5 X (.25/57.3) = .247So lets plug these numbers in:The formula, again is: d = df +([D-df]/F) X Lde (be sure to multiply BEFORE you add).493 + .133 X 8.125 = 1.57 inches. So, a 1.57& minor axis diagonal will fully illuminate a half adegree at the eyepiece..247 + .137 X 8.125 = 1.36 inches. So, if I want only a .25 degree fully illuminated field toproduce more contrast on the s... I would go with a diagonal this size.Diagonal mirrors do e in the above sizes, but one can round off--in eitherdirection--your preference!--RayA Word About Focal Length and Focal RatioThe focal ratio of the mirror you select determines how long your telescope will be. A 10& objectivemirror with an f/7 focal ratio will give you a telescope with a 70& focal length. (Multiply the &f-number&by the diameter of the objective mirror to get the focal length.) Your tube will need to be cut to the lengthof the focal length, so you would have a 70& long tube. An 8& objective mirror with an f/7 focal ratiowould have a 56& focal length, and a 56& long tube.(John Dobson mends a focal ratio around f/6 or f/7)Dobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (3 of 8) [9/6/:12 AM]FOCAL RATIO (f-number) x MIRROR DIAMETER = FOCAL LENGTH = LENGTH OF TUBEWhen you get your mirror, the focal ratio may be exactly what you ordered, or it may be a little more, ora little less. So don't cut your tube till you receive your mirror. To measure your focal length exactly,have a friend help you: Take your mirror, a tape measure, and a piece of paper outside on any clear nightand catch the light of a bright star or the Moon with your mirror and reflect it back in that direction.Using that piece of paper find where the star, or Moon forms the smallest image. Measure that distanceas accurately as you can. (Instead of a piece of paper, it is often easier to reflect onto a fixed surface, suchas a garage door jamb or header). Write this measurement down! This determines the length of yourtelescope tube, as well as where you cut a hole for your focuser. The key thing to remember is that youwant this formed image (called the focal plane), to hover in the same plane as the field stop of youreyepiece. If you opt for mercial focuser, you will undoubtedly have to cut your focuser hole in adifferent place than these plans call for! Do you have your eyepiece(s) yet? If that's a &yes,& good: Lookinto your eyepiece and put your pinky finger in the other end--slowly and carefully--can you see whereyour es into a magnified focus? Usually there is a black ring (called a field stop) at this pointaround the in and usually this corresponds to where--on the outside of theeyepiece--the chrome barrel ends and the rest of the eyepiece body begins. This means this is where theeyepiece &bottoms out& when inserted into mercial focuser. But, you don't want mercialfocuser to bottom out when focusing! Individual eyes and eyepieces are different! Always allow at least3/4& &in travel& for mercial focuser, when doing the arithmetic to determine where to cut yourfocuser hole! More is said on this subject in &Section A& of these plans online.TUBE DIAMETERThe telescope tube should be about 2 inches wider in diameter than your objective:A ten-inch diameter objective mirror requires a twelve-inch diameter tube.An eight-inch diameter objective mirror requires a ten-inch diameter tube.A six-inch diameter objective mirror requires an eight inch diameter tube.Materials ListCardboard tube (&Sonotube&) (1):Construction, specifically concrete construction supply housesusually carry these tubes, which are used for forming concrete columns. Get the supply house tocut your tube rough, that is, longer than you need by, let's say, six inches or so. To &finish cut&your tube square: Tape several 8-1/2& x 11& pieces of paper together end for end--enough to wraparound the circumference of the tube, and do just that... Make theand mark the edge you want to cut. Proceed with a hand saw or Jigsaw...qExterior grade plywood: 4' x 8' x 3/4& thick. For an eight or ten inch telescope, one sheet will beplenty. An alternative to &exterior grade plywood& would be &shop grade&; not much moreexpensive, a MUCH smoother finish is possible.q(Optional) Six-Eight feet of Douglas Fir 2&X 2&: Cut these into small lengths and glue to insideof Rocker Box and Tube Box corners--this will strengthen these joints considerably.qPaint and painting supplies: Flat black any dark color is fine for the outsideqDobsonian P Sourceshttp://flake/telescope/Dobsonian%20P%20Sources.htm (4 of 8) [9/6/:12 AM]播放器加载中，请稍候...
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