Vignetting is the darking of the edges of the field of view due to obstruction of light. It is typically caused by baffles in the optical system. These baffles reduce stray light (which is good) and sometimes stop light from the edges of the field of view (which is bad). The reduction in stray light is worth more than the appearance of darkening at the edges. Frequently the eye does not notice this. It is very noticable with film and CCD imaging.

Ralph Pass

Victor K wrote:

> 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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