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focal reducer..?

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A focal reducer reduces the focal length of the telescope so, as you say, it therefore reduces the magnification for any given eyepiece. This does give you a wider field of view and also makes faint objects like nebulae and galaxies a bit brighter and clearer - which you wouldn't get with a wider field eyepiece.

Just as an example my scope has a focal length of 2800 mm. Even with a 40 mm eyepiece the lowest magnification I can achieve is 70x (i.e. 2800/40) This is just too much for many faint deep sky objects. Remember that the more an object is magnified the fainter it gets. So I use a focal reducer to reduce the focal length. Its also useful for photography when you want to get more of a large DSO in the frame. Hope this helps.

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It effectively reduces the focal length of the telescope ie a f10 SCT with a x0.63 reducer becomes a f6.3. ( effective focal length changes from 2000mm to 1260mm on an 8"sct)

It doesn't always affect the FOV with visual observing... as you say you can change to a lower power eyepiece and get the same result......

Probably more important for imaging and field of view.

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