| Revision as of 07:34, 5 November 2011 edit24.205.64.27 (talk) without parallax correction, there is no way a finder scope can mark precisely where the main telescope is looking.← Previous edit | Latest revision as of 15:46, 9 June 2024 edit undoAssambrew (talk | contribs)Extended confirmed users1,363 edits →Function and Design | ||
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A '''finderscope''' is an accessory ] used in ] and ], typically a small auxiliary ]/] mounted parallelly on a larger astronomical telescope along the same ]. The finderscope usually has a much smaller ] than the main telescope, thus providing a larger ], useful for manually pointing (a.k.a. "slewing") the main telescope into a roughly correct direction that can easily place a desired astronomical object in view when zooming in. Some finderscopes have sophisticated ]s to more accurately aim the main telescope and/or even perform ]s. | ||
| ==Function and Design== | |||
| ⚫ | Finderscopes usually come with a designation of the form |
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| Finderscopes contain mechanisms to properly align them with the main telescope's line of sight. Accomplishing this alignment varies based on the design of the finderscope and its mount: usually on amateur telescopes it is done by three or six adjustment screws. | |||
| ⚫ | Finderscopes usually come with a designation of the form A×B, where A is the ] and B is the ] of the finderscope's ] in millimeters; for example, a 6×30 finderscope means a finderscope with a 30 mm objective and a magnification of 6×. This designation is in the same format used by most ].<ref>{{cite web|title=How to Select the Right Binocular|url=http://www.meade.com/support/selbinoc.html|publisher=Meade Instruments Corporation|accessdate=15 November 2013|archive-date=13 March 2014|archive-url=https://web.archive.org/web/20140313170729/http://www.meade.com/support/selbinoc.html|url-status=dead}}</ref> | ||
| ⚫ | A |
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| ⚫ | A 6×30 finderscope is typically considered the minimum useful size for a magnifying finderscope on an amateur telescope. An 8×50 or larger finderscope is preferred, which allows sighting of fainter objects.<ref>"The Backyard Astronomer's Guide", by ] and Alan Dyer.</ref> | ||
| Most finderscopes have one of three viewing orientations: | Most finderscopes have one of three viewing orientations: | ||
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| | Backwards (mirror-image) | | Backwards (mirror-image) | ||
| |- | |- | ||
| | RACI (Right-angle correct-image) | |||
| | Correct orientation | |||
| | 90 degrees | | 90 degrees | ||
| | Correct | | Correct | ||
| |} | |} | ||
| == Reflex Sights == | |||
| Telescopes also use finders based on the ]. This type of "finderscope" does not magnify the image at all, but instead puts a reticle generated by ] in the users field of view so that one can locate an object very quickly. The image seen through the finder is exactly the same as what can be seen with the naked eye with an illuminated crosshair seeming to float in space at ]. | |||
| ] such as the Telrad (pictured) are popular alternatives to traditional finderscopes, and are often used in conjunction with them.]] | |||
| Another type of finder commonly found on amateur telescopes is known as a ]. This non-magnifying ] (technically not a "scope") uses a type of ] to "reflect" a reticle generated by ] into the users field of view. The view of the sky seen through the sight is just what can be seen with the naked eye with an illuminated crosshair or dot seeming to float in space at ]. These crosshairs are generally illuminated by a small LED. Reflector sights are useful for locating bright objects visible to the naked eye such as stars and ]. Since the sight uses a beam splitter "window", instead of an optical telescope with the ability to ], objects dimmer than the naked eye limit can not be seen through it. Finding dim objects with a reflector sight is accomplished by using the object's known position relative to brighter objects as a reference and then slewing a known angular distance (or "]") from the bright object to the desired object. Many reflector sights have circles with a given angular dimension in order to facilitate this. Reflector sights are less useful in ] areas since the stars used to guide the observer to a dim object may also be invisible.<ref>Rod Mollise, The Urban Astronomer's Guide: A Walking Tour of the Cosmos for City Sky Watchers, Springer Science & Business Media - 2006, page 43</ref> | |||
| ==See also== | ==See also== | ||
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| <references/> | <references/> | ||
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Latest revision as of 15:46, 9 June 2024
A finderscope is an accessory sighting device used in astronomy and stargazing, typically a small auxiliary refracting telescope/monocular mounted parallelly on a larger astronomical telescope along the same line of sight. The finderscope usually has a much smaller magnification than the main telescope, thus providing a larger field of view, useful for manually pointing (a.k.a. "slewing") the main telescope into a roughly correct direction that can easily place a desired astronomical object in view when zooming in. Some finderscopes have sophisticated reticles to more accurately aim the main telescope and/or even perform stadiametric measurements.
Function and Design
Finderscopes contain mechanisms to properly align them with the main telescope's line of sight. Accomplishing this alignment varies based on the design of the finderscope and its mount: usually on amateur telescopes it is done by three or six adjustment screws.
Finderscopes usually come with a designation of the form A×B, where A is the magnification and B is the aperture of the finderscope's objective lens in millimeters; for example, a 6×30 finderscope means a finderscope with a 30 mm objective and a magnification of 6×. This designation is in the same format used by most binoculars.
A 6×30 finderscope is typically considered the minimum useful size for a magnifying finderscope on an amateur telescope. An 8×50 or larger finderscope is preferred, which allows sighting of fainter objects.
Most finderscopes have one of three viewing orientations:
| Type | Eyepiece mount | Image orientation |
|---|---|---|
| Standard | Straight through | Upside down and reversed (i.e. rotated 180 degrees) |
| Right-angle | 90 degrees | Backwards (mirror-image) |
| RACI (Right-angle correct-image) | 90 degrees | Correct |
Reflex Sights
Another type of finder commonly found on amateur telescopes is known as a reflector (reflex) sight. This non-magnifying sight (technically not a "scope") uses a type of beam splitter to "reflect" a reticle generated by collimating optics into the users field of view. The view of the sky seen through the sight is just what can be seen with the naked eye with an illuminated crosshair or dot seeming to float in space at infinity. These crosshairs are generally illuminated by a small LED. Reflector sights are useful for locating bright objects visible to the naked eye such as stars and planets. Since the sight uses a beam splitter "window", instead of an optical telescope with the ability to gather light, objects dimmer than the naked eye limit can not be seen through it. Finding dim objects with a reflector sight is accomplished by using the object's known position relative to brighter objects as a reference and then slewing a known angular distance (or "star hopping") from the bright object to the desired object. Many reflector sights have circles with a given angular dimension in order to facilitate this. Reflector sights are less useful in light polluted areas since the stars used to guide the observer to a dim object may also be invisible.
See also
References
- "How to Select the Right Binocular". Meade Instruments Corporation. Archived from the original on 13 March 2014. Retrieved 15 November 2013.
- "The Backyard Astronomer's Guide", by Terence Dickinson and Alan Dyer.
- Rod Mollise, The Urban Astronomer's Guide: A Walking Tour of the Cosmos for City Sky Watchers, Springer Science & Business Media - 2006, page 43