To date, almost 400 years later, the same formula is still used. Modem improvements simply increase the quality of the optics now use, where modification minimized aberrations. We can now build larger telescopes with resolving power and brightness never taught possible in the time of Galileo, but the formula used in developing these modem instruments is the same as the earliest designs-bigger is better. The bigger is better formula is not without limitations.

For example, color aberration limits the brightness of a refractor telescope, which requires a focal ratio of f/I 5 to filter out secondary spectrum aberration. The required focal ratio limits the light collecting capabilities of refractors. Reflectors are not affected by secondary spectrum effect. Focal ratio in the range of ff2.5 is reasonable when requiring exit pupil close to 7 millimeters. However, any attempt to increase magnification within these reflector telescopes while maintaining brightness, will require increase in the aperture and the focal length in the same proportion. It is these design features that makes the phrase aEUR~bigger is better' so convincing.

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