Limiting Magnitude introduction

This is the magnitude (or brightness) of the faintest star that can be seen with a telescope. The larger the number, the fainter the star that can be seen. An approximate formula for determining the visual limiting magnitude of a telescope is                                            9 + 5 log aperture (in inch).

This is the formula that we use with all of the telescopes we carry, so that our published specs will be consistent from aperture to aperture, from manufacturer to manufacturer.
 Some telescope makers may use other unspecified methods to determine the limiting magnitude, so their published figures may differ from ours.

Limiting Magnitude Calculator(click)

Telescope diameter and magnification

Light gathering capability of a circular telescope can be calculated as

Light gathering area calculation

Light gathering area,(LGA) is simply the area of the objective lens given by the formula for the area of a circle, A = pie* (D/2) 2 , where D is the diameter (37 mm) and therefore D/2 is the radius (r) of objective (18.5 mm)

A = 3.14 x 18.52 = 1075 mm2 (10.75 cm2 or 1.7 in2)

Light gathering power (LGP) is defined as the ratio of the light gathering area of one instrument to another. Light gathering power is often compared to the human eye, the pupil of which has a diameter of about 5 mm. Therefore the LGA of Galileo's telescope can be compared to the LGA of the eye by the ratio

 

Canceling like terms in the numerator and denominator leaves us with  

 which is the square of the diameter of the telescope objective (Do) divided by the square of the diameter of the pupil of the eye (Dp) or LGP = (Do/Dp) 2 . For Galileo's telescope the answer is

LGP = (37/5)2 = 54.8.

Therefore Galileo's telescope gathered about 55 times more light that the eye. 

Magnification can be defined as =is determined by dividing the focal length of the objective by the focal length of the eyepiece.

Focal ratio (f/n), or f-number, is the ratio of the focal length of the objective to its diameter, and the smaller the f-number, the greater the amount of light per unit area reaches the image plane of the telescope. For Galileo's telescope with a focal length of 980 mm and an objective lens with a diameter of 37 mm the focal ratio is 

Thanks  Telescope1609TM

Telescope Lens Features.

           In optics, an aperture is a hole or an opening through which light travels.So larger the aperture size more amount of light from a far object enters a lens. Powerful telescopes have large aperture lens.Telescopes gather many times the light of the unaided human eye, allowing us to see incredible views of the night sky. The following chart will describe the amount of light gathering.