Focal reducer

[Mark-V]

This may seem a stupid thing to ask but in VERY simplified terms - what does a focal reducer do and does it affect the magnification of a telescope if one is fitted ?

[Uranium235]

A focal reducer does exactly that - it reduces your focal length by whatever factor the reducer is rated at  (0.8x is the most common of these). The by-product of reducing your focal length is that you are also reducing focal ratio - and therefore increasing the photographic speed.

eg: f7.5 (80/600mm) reduced by 0.85x is f6.38 (80/510mm), which represents roughly a 30% increase in photographic speed.

Many reducers also act at a field flattener, so the corners of you image also improve dramatically. However, it is best advised to only buy a reducer/flatter made specifically for the telescope you are using as that will remove the guesswork and potential disappointment of it not working perfectly.

See here for reducer/scope combinations:

http://www.12dstring.me.uk/fov.htm