The Firing Line Forums - View Single Post - Why the loooooooong scope body on target scopes?

mikikanazawa · November 24, 2004, 12:38 AM

I can't answer the question exactly-precisely, but I am a telescope nut.

Magnification is a function of the focal length of the objective (front lens) and eyepiece lens. The focal length is the distance between the lens and the point in space where the lens focuses its image when pointed at something at a distance of "infinity" (over 100 feet). So if you have an objective lens with a focal length of 100mm and an eyepiece lens with a focal length of 50mm, you have a magnification of 2x, objective of 400mm and eyepiece of 18mm you have a mag power of 22.222x, and so on.

So, more magnification means longer focal length of objective, shorter focal length of eyepiece. High-mag scopes could be put in a short package, but to do so would require an eyepiece with an extremely short focal length, which adversely effects image brightness and contrast. It also tends to amplify flaws in the scope, such as aberrant light in the tube.

November 24, 2004, 12:38 AM	#3
mikikanazawa Senior Member Join Date: September 26, 2004 Posts: 449	I can't answer the question exactly-precisely, but I am a telescope nut. Magnification is a function of the focal length of the objective (front lens) and eyepiece lens. The focal length is the distance between the lens and the point in space where the lens focuses its image when pointed at something at a distance of "infinity" (over 100 feet). So if you have an objective lens with a focal length of 100mm and an eyepiece lens with a focal length of 50mm, you have a magnification of 2x, objective of 400mm and eyepiece of 18mm you have a mag power of 22.222x, and so on. So, more magnification means longer focal length of objective, shorter focal length of eyepiece. High-mag scopes could be put in a short package, but to do so would require an eyepiece with an extremely short focal length, which adversely effects image brightness and contrast. It also tends to amplify flaws in the scope, such as aberrant light in the tube.