RESOLUTION OF A TELESCOPE Telescopes, Binoculars, Spotting Scopes, Microscopes, Riflescopes, Astronomical Accessories,Refractor,Reflector,Monoculars,Night Vision,Cassegrain,GPS,Optical Tubes,Digital Camera,Eyepiece,Filters,Barlow,Lenses,Diagonals,Prisms,Tripods,Mounts,Finder Scopes,BinoViewers,Optics,Astronomy,Astrophotography,Laser Range Finders,Rangefinders, Cheap
Secure website, verified, safe for online shopping
The World's Largest Selection of Optics for Astronomy, Sport, Science and Education
Shop By Price
Shop By Interests
Gift Certificate

 


RESOLUTION OF A TELESCOPE

  Scope City's Optics Crash Course
Tell Friend  

RESOLUTION OF A TELESCOPE

Whatever the quality of your own eyes, every telescope has a limit to the size of the details it can see. This is a physical limit imposed by the wave nature of light passing through our telescopes. That being said, it is rare that we get to experience the sharpest and smallest details our telescopes can give. The reason is that thick soup we call an atmosphere through which we must view. Our atmosphere is never stationary and the turbulence in the air actually modifies the light rays that pass through it, similar to a lens¡ªonly in this case the stack of lenses is many miles thick¡ª10 miles or so when we look straight up and nearly 100 miles thick when we look toward the horizon.

Our atmosphere usually limits what we can see, in the way of small details, and limits how much magnification we can use¡ªno matter what the size of the telescope! Yes, the big telescopes on remote mountaintops are limited by the atmosphere, too¡ªoften to the same limit as a 4¡± to 5¡± scope. [Of course, the images in big scopes will be brighter, even if the small details aren¡¯t any more visible].

Due to the wavelike nature of light and the infinitesimally small apparent size of stars (due to their distances), a good test of resolution for a telescope is the appearance of star images. With smaller telescopes, a star appears as a round disc with a visible size. This disc is not reality; it is an illusion. The actual stars are too distant and small to resolve into discs. Larger scopes will show these discs as smaller and brighter. The apparent star image¡¯s disc is called the Airy Disc. Smaller disc sizes improve resolution in both close star images and in extended objects like planets.

Astronomers usually talk about how close together two stars of a double star can be in seconds of arc and still be seen as two separate images. The ultimate limit, called Dawes Limit, can be expressed as 4.5/aperture of telescope in inches. This is where two star images will overlap to form a long oval with a wasp waist in the middle. In practice, the atmosphere must be exceptionally steady to see this, and a more practical limit, called the Rayleigh Limit is used: 5.45/aperture of telescope in inches. This second limit is easier to see, and the star images look like a figure 8 on its side.

In practice, doubling this separation limit will provide a better and more sensible viewing experience. If you want to be guaranteed you will see the double star as two separate stars, figure out what magnification will result in an 8¡¯ separation: divide 480 by the separation of the double star in seconds of arc. The star separation figure is usually listed in books, and in the hand controller of computerized telescopes. Even 20/40 vision will resolve this small a separation. There will be a little dark space between the two double stars.

The larger a scope, as you see from the formulas, the smaller the separation can be between two points and still see the two points as separate. This applies to extended objects like the Moon and planets as well. So, resolution-wise, though it may be tough on the pocketbook, there is still justification for the larger scope, even if all you do is observe the Moon and planets from your backyard.

<< Prev Table of Contents Next >>

CATADIOPTRICS TELESCOPE OTAS

   For More Telescope Selections, Click Here
Tell Friend  

(139 Items) 1 2 3 4 5 6 7 8 9 10  Next Gallery View Click here for List Display
Sort By: Price | New | Brand | Category | Name
TeleVue 76mm f/6.3 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser Ivory Tube
New
TeleVue 76mm f/6.3 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser Ivory Tube
Item No. 604-40010
Manuf. No. Televue WXF-3064

TeleVue WXF-3064 Telescope, 76mm f/6.3 APO Refractor Ivory Kit, with 20mm Plossl, New 10/1 Reduction Focuser, Soft Carry Case
MSRP: $2,590.00
Our Price: $1,995.00
Buy TeleVue 76mm f/6.3 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser Ivory Tube
You Save $595.00

TeleVue 76mm f/6.3 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser Green Tube
New
TeleVue 76mm f/6.3 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser Green Tube
Item No. 604-40000
Manuf. No. Televue GXF-3064

TeleVue GXF-3064 Telescope, 76mm f/6.3 APO Refractor Evergreen Kit, with 20mm Plossl, New 10/1 Reduction Focuser, Soft Carry Case
MSRP: $2,590.00
Our Price: $1,995.00
Buy TeleVue 76mm f/6.3 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser Green Tube
You Save $595.00

TeleVue 85mm f/7 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser, Ivory Tube
New
TeleVue 85mm f/7 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser, Ivory Tube
Item No. 604-30085
Manuf. No. Televue WXF-3371

TeleVue WXF-3371 Telescope, 85mm f/7 APO Refractor Ivory Kit, with 20mm Plossl, 2" Everbrite Diagonal, 1.25" Adapter, New 10/1 Reduction Focuser, Soft Carry Case
MSRP: $3,150.00
Our Price: $2,425.00
Buy TeleVue 85mm f/7 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser, Ivory Tube
You Save $725.00

TeleVue 85mm f/7 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser
New
TeleVue 85mm f/7 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser
Item No. 604-30080
Manuf. No. Televue GXF-3371

TeleVue GXF-3371 Telescope, 85mm f/7 APO Refractor Evergreen Kit, with 20mm Plossl, 2" Everbrite Diagonal, 1.25" Adapter, New 10/1 Reduction Focuser, Soft Carry Case
MSRP: $3,150.00
Our Price: $2,425.00
Buy TeleVue 85mm f/7 APO Refractor Telescope OTA with 20mm Plossl, 10/1 Reduction Focuser
You Save $725.00

Takahashi Epsilon 180ED f/2.8 Hyperbolic Flat-Field Astrograph OTA Telescope
New
Takahashi Epsilon 180ED f/2.8 Hyperbolic Flat-Field Astrograph OTA Telescope
Item No. 611-50601
Manuf. No. Takahashi TEK0180

Takahashi TEK0180 Reflector, Epsilon 180ED f/2.8 Hyperbolic Flat-Field Astrograph OTA Telescope
 
Our Price: $5,400.00
Buy Takahashi Epsilon 180ED f/2.8 Hyperbolic Flat-Field Astrograph OTA Telescope
 

Takahashi Mewlon-300CRS Dall-Kirkham OTA Telescope
Takahashi Mewlon-300CRS Dall-Kirkham OTA Telescope
Item No. 611-50551
Manuf. No. Takahashi TLK3502

Takahashi TLK3502 Telescope, Mewlon-300CRS Dall-Kirkham OTA
 
Our Price: $16,995.00
Buy Takahashi Mewlon-300CRS Dall-Kirkham OTA Telescope
 

Takahashi TOA-150F 5.9 inch f/7.33 Ortho-Apochromat Triplet Refractor OTA
Takahashi TOA-150F 5.9" f/7.33 Ortho-Apochromat Triplet Refractor OTA
Item No. 611-50301
Manuf. No. Takahashi TOK1501

Takahashi TOK1501 Telescope, TOA-150F 5.9" f/7.33 Ortho-Apochromat Triplet Refractor OTA
 
Our Price: $11,400.00
Buy Takahashi TOA-150F 5.9 inch f/7.33 Ortho-Apochromat Triplet Refractor OTA
 

Takahashi TOA-130NFB Refractor Telescope OTA
Takahashi TOA-130NFB Refractor Telescope OTA
Item No. 611-50251
Manuf. No. Takahashi TSA0131

Takahashi TSA0131 Telescope OTA, TOA-130NFB Refractor
 
Our Price: $7,200.00
Buy Takahashi TOA-130NFB Refractor Telescope OTA
 

Takahashi Triplet Refractor TOA-130S Kit, 5.1 inch Diameter, Ortho MC APO Telescope OTA w/ Lens Shade and 2.7 inch Focuser
Takahashi Triplet Refractor TOA-130S Kit, 5.1" Diameter, Ortho MC APO Telescope OTA w/ Lens Shade and 2.7" Focuser
Item No. 611-50201
Manuf. No. Takahashi TSA0130

Takahashi TSA0130, TOA-130S Kit, 5.1" Diameter, 1000mm f/7.7 Ortho MC APO Triplet Refractor Telescope Optical Tube with Lens Shade & 2.7" Focuser
 
Our Price: $6,500.00
Buy Takahashi Triplet Refractor TOA-130S Kit, 5.1 inch Diameter, Ortho MC APO Telescope OTA w/ Lens Shade and 2.7 inch Focuser
 

Takahashi FSQ-106ED Astrograph Telescope OTA
Takahashi FSQ-106ED Astrograph Telescope OTA
Item No. 611-50152
Manuf. No. Takahashi FSQ1016NU

Takahashi FSQ1016NU Refractor, FSQ-106ED Astrograph Telescope OTA
 
Our Price: $5,150.00
Buy Takahashi FSQ-106ED Astrograph Telescope OTA
 

Takahashi FSQ-106EDXIII F5 Astrograph Telescope OTA - Imaging Edition
Takahashi FSQ-106EDXIII F5 Astrograph Telescope OTA - Imaging Edition
Item No. 611-50151
Manuf. No. Takahashi FQK1061NUEX

Takahashi FQK1061NUEX Refractor, FSQ-106EDXIII F5 Astrograph Telescope OTA - Imaging Edition
 
Our Price: $5,150.00
Buy Takahashi FSQ-106EDXIII F5 Astrograph Telescope OTA - Imaging Edition
 

Takahashi TSA-120 4.7 inch f/7.5 Ortho-Apochromat triplet refractor OTA with 2.7 inch focuser
Takahashi TSA-120 4.7" f/7.5 Ortho-Apochromat triplet refractor OTA with 2.7" focuser
Item No. 611-50121
Manuf. No. Takahashi TSA0120

Takahashi TSA0120 Telescope, TSA-120 4.7" f/7.5 Ortho-Apochromat triplet refractor OTA with 2.7" focuser
 
Our Price: $4,695.00
Buy Takahashi TSA-120 4.7 inch f/7.5 Ortho-Apochromat triplet refractor OTA with 2.7 inch focuser
 

Takahashi TSA-102S Refractor Telescope OTA
Takahashi TSA-102S Refractor Telescope OTA
Item No. 611-50101
Manuf. No. Takahashi TSA0102

Takahashi TSA0102, Refractor Telescope TSA-102S OTA, Triplet APO
 
Our Price: $3,350.00
Buy Takahashi TSA-102S Refractor Telescope OTA
 

Takahashi Telescope Sky 90II - 3.5 inch f/5.6 Fluorite APO Refractor OTA
Takahashi Telescope Sky 90II - 3.5" f/5.6 Fluorite APO Refractor OTA
Item No. 611-50051
Manuf. No. Takahashi TSK9001

Takahashi TSK9001 Telescope, Sky 90II - 3.5" f/5.6 Fluorite APO Refractor OTA
 
Our Price: $2,400.00
Buy Takahashi Telescope Sky 90II - 3.5 inch f/5.6 Fluorite APO Refractor OTA
 

Takahashi FSQ-85EDX Astrograph Telescope Refractor OTA
Takahashi FSQ-85EDX Astrograph Telescope Refractor OTA
Item No. 611-50030
Manuf. No. Takahashi FQK0085

Takahashi FQK0085 Telescope, FSQ-85EDX Astrograph Refractor OTA
 
Our Price: $3,650.00
Buy Takahashi FSQ-85EDX Astrograph Telescope Refractor OTA
 

1 2 3 4 5 6 7 8 9 10  Next
 


Scope City 100% Satisfaction Guarantee

Scope City unconditionally guarantees that you will be 100% satisfied with your mail order purchase, or just
return the merchandise in original condition within 15 days for a Full Refund, less shipping and handling charges!