Sorry, I don't know what vignetting is, can you tell
me ?
Tks.

> The problem is that it is a lot easier to shoot
> without a focal reducer
> especially when you have to use a filter wheel. Also
> I would think that there
> should be more vignetting with the focal reducer.
> Bob
>
> "Michael A. Covington" wrote:
>
> > Tom, I think several published tests, and well as
> optical calculations, have
> > shown that the f/10 telescope with f/6.3 reducer
> actually works better than
> > the f/6.3 telescope by itself. The reason is
> field flattening done by the
> > reducer lens, which is actually a 4-element
> system. Also, the central
> > obstruction is a little smaller.
> >
> > Visually, most eyepieces are a good bit sharper
> with an f/10 telescope than
> > with an f/6.3 telescope.
> >
> > So although neither one is a really bad choice, I
> think the f/10 is
> > preferable. It can do everything the f/6.3 can
> do, and more.
>
>


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