![]() If you're not interested in learning the fundamentals of observing with a telescope or fiddling with camera settings, but simply want a great piece of technology that will give you beautiful captures of deep-sky objects, this could be the telescope for you, provided the price tag doesn't put you off. Telescopes for photographing the MoonĪt its core, the Unistella eVsccope eQuinox is a cool piece of kit that effortlessly produces images of the night sky and sends them to your smartphone or tablet. So if you have a 100mm refractor with a focal length of 900mm, its f-ratio is said to be f/9.Īdding a 2x Barlow lens increases the effective focal length to 1,800mm and doubles the f-ratio to f/18, but there is a limit to how much focal length is useful. The f-ratio is defined by dividing your telescope’s focal length by its aperture, using the same units. ![]() So f-ratio is a key value that will help you choose which telescope to use for a specific type of astronomical target. When choosing a telescope for astrophotography - or, indeed, for visual observing - it pays to consider the focal ratio of the instruments available.įocal ratio (f-ratio) gives an indication of the ‘speed’ of an optical system: the time it takes your telescope to deliver a set amount of light.Īs the f-ratio goes up, so the image scale increases: the object appears larger and consequently dimmer. The PrimaLuceLab Airy APO 65F’s 420mm focal length makes it a relatively fast (f/6.5) instrument.
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