Centre of the Universe

The focal ratio, or f-ratio as it is also known, is a very important number when we start talking about astro-photography.

The f-ratio is defined as the focal length of the telescope divided by the aperture of the telescope, and is known as the speed of the telescope. that is, a telescope with a f-ratio of f/4 is “faster” than a telescope with a f-ratio of f/8.

The “faster” the telescope, the brighter the image will be, which means that the length of exposures for photography don’t need to be as long to capture the same amount of light. The advantage of a “slower” telescope though is that images will have greater depth, meaning that sharpness over the whole image is better, so there is a little bit of a trade-off depending on what you are trying to do.

		public static double CalcFRatio(double FocalLen, double Aperture)
		{
			return FocalLen / Aperture;
		}

		public static double CalcFocalLen(double FRatio, double Aperture)
		{
			return FRatio * Aperture;
		}

		public static double CalcAperture(double FRatio, double FocalLen)
		{
			return FocalLen / FRatio;
		}

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