Hi Doc G,

Thanks for the reply, looks as though I will purchase the 2" backplate along with the 2" to Schmidt adaptor, shame about the flip mirror though, only just bought that! Using a starlight Xpress ccd camera (no mechanicl shutter), the flip mirror is an excellent way to cut off the transmission of light reaching the ccd chip. In your opinion will there not be enough back focus available to continue using the flip mirror?

Best Regards,

Andy.

> -----Original Message-----
> Sent: 30 March 2000 15:31
> Subject: Re: [M]: 10" LX Backplate.
>
> "Heath, Andrew" wrote:
> >
> > I have been reading up on the NGF-s focussing unit on Doc G's website as I want to get one of these units soon. I have a question,
> > the standard backplate on the rear of the 10" has a clear aperture of 44mm, an optional one that can be purchased from JMI has a clear aperture of 50mm. This apparently is equal to around an extra 20% of light in the light path through the JMI adaptor. The question is, if you are wanting to use the Meade F6.3 focal reducer and flip mirror, how do you connect it all up?
> > Probably a stupid question, is it just a case of you can't use these items with it?
> >
> > TIA,
> >
> > Andy.
>
> These are excellent questions. I have been lucky to have a lot of stuff
> to add to the back plate over the years and am fascinated by the
> numerous combinations possible. It turns out that many combinations
> work very well. I use the JMI adapter plate because I feel it is the
> strongest way to attach the JMI focuser and that the slightly larger
> opening could not hurt. This is especially true when doing 35 mm film
> photography. (yes, film still exists!!)
>
> Since the nominal distance from the focal reducer to the focal plane
> should be a set and fixed at about 90 to 100 mm give or take a bit. It
> is installed on the output side of the JMI using a 2" to Schmidt
> adapter. The camera is then connected with a tube of the right length to
> give the proper reducer spacing. This could be a CCD camera or a film
> camera. There will be some vignetting with a 35 mm format when using a
> reducer that is of the Schmidt tube size of course.
>
> For no vignetting one has to consider the Lumicon giant OAG. In this
> case, the JMI cannot be used and another way to focus must be effected.
>
> Though I have several flip mirrors, I am now in the circle of those who
> strongly recommend not using a flip mirror because of the extra length
> of the optical path introduced by it. It is one of the greatest
> offenders in this respect. It is also an offender in maintaining
> rigidity of the whole system. A Van Slyke slider, which I have, is
> somewhat less offensive in both respects than most of the flip mirrors
> available.
>
> I suggest that for a film camera, finding and focusing be done on the
> camera view screen with the aid of a focus attachment. For the CCD
> camera, I suggest finding with an accurately collimated finder scope of
> medium power and final framing and focusing done using the imaging chip
> itself.
>
> As I say, there a dozen different ways to do this all. I am simply
> stating my preferences.
>
> Doc G <http://www.mailbag.com/users/ragreiner>
>
>

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