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Which focal reducer best for astrphotography? 3.3 or 6.3?

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Which focal reducer would be better, a f3.3 or a f6.3? I have a CPC 925 and don't have a wedge yet, but plan to get one at some point.

I've learnt that the lower the f, the lower exposure time required when taking a photo. Why is it that celestron only sell a f6.3 and not a f3.3? I'm looking at the Meade f3.3.

What is the disadvantage of a 3.3 over a 6.3?



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Bucking the trend :), I've had great Watec 120n DSO performance with a 12" SCT using the F3.3 and the F6.3, the F3.3 images were always brighter and better focused. It's important to get the spacings correct in either case.

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