Focal reducer placement...

I have a 10" F/10 LX200 I've been using for visual observing for a
year now and I've just purchased the kit I need for imaging. (Thanks
for advice on the Digital SLR or cooled CCD thread folks! I bought an
SXV-H9, True Tech filter wheel, Orion 80ED and SXV auto-guider).

I'm keen to continue visual use and want a simple way to switch
between modes (i.e. I don't want to reconfigure the optical train each
time I switch between CCD and EPs).

I understand that SCT-focuser-filter wheel-CCD is the best
configuration but that's so long it prevents the OTA from swinging
through the forks (no imaging around Polaris and a heart attack if the
dec lock comes loose).

So I have chosen to mount SCT-focuser-2" diagonal-filter
wheel-CCD. I realise this is not the most stable configuration, but I
can easily swap the filter wheel and CCD for an eyepiece, and both
configurations swing through the forks. Ideal for now, except…

I also bought a Meade 0.63 focal reducer. If I mount it on the SCT
rear cell, besides being a pain to remove for visual work, it prevents
both configurations from swinging through the forks anyway! Not a
solution!

So my main question is can I mount the FR between filter wheel and CCD
or between diagonal and filter wheel? I assume I need adaptors as
there's no obvious way to make the connections with what I have.

In general, what is the best place to put a FR? Before or after the
filters? Close as possible to CCD or close as possible to rear cell?
Advice welcome – particularly from anyone else with a 10" LX200
Classic, 2" diagonal, Meade electric focuser, True Technologies filter
wheel and SXV-H9 CCD.

Cheers
Beats

"justbeats" wrote in message
m...
I have a 10" F/10 LX200 I've been using for visual observing for a
year now and I've just purchased the kit I need for imaging. (Thanks
for advice on the Digital SLR or cooled CCD thread folks! I bought an
SXV-H9, True Tech filter wheel, Orion 80ED and SXV auto-guider).

I'm keen to continue visual use and want a simple way to switch
between modes (i.e. I don't want to reconfigure the optical train each
time I switch between CCD and EPs).

I understand that SCT-focuser-filter wheel-CCD is the best
configuration but that's so long it prevents the OTA from swinging
through the forks (no imaging around Polaris and a heart attack if the
dec lock comes loose).

So I have chosen to mount SCT-focuser-2" diagonal-filter
wheel-CCD. I realise this is not the most stable configuration, but I
can easily swap the filter wheel and CCD for an eyepiece, and both
configurations swing through the forks. Ideal for now, except.

I also bought a Meade 0.63 focal reducer. If I mount it on the SCT
rear cell, besides being a pain to remove for visual work, it prevents
both configurations from swinging through the forks anyway! Not a
solution!

So my main question is can I mount the FR between filter wheel and CCD
or between diagonal and filter wheel? I assume I need adaptors as
there's no obvious way to make the connections with what I have.

In general, what is the best place to put a FR? Before or after the
filters? Close as possible to CCD or close as possible to rear cell?
Advice welcome - particularly from anyone else with a 10" LX200
Classic, 2" diagonal, Meade electric focuser, True Technologies filter
wheel and SXV-H9 CCD.
There is no 'best place'. The reduction from a FR, is dependant on the
spacing between it's optical centre, and the CCD plane. You can mount it
anywhere you like _provided this spacing is of the right order for the
compression required_. The standard F*.63 reducer requires a spacing of
about 3", from it's rear 'face', to the CCD. If you go much beyond this, the
reduction factor rapidly increases, and the distortions on the image, also
shoot up (it works quite acceptably with spacings perhaps up to about 20%
'long', but the effects become pretty uacceptable beyond this). Decrease the
distance, and the reduction factor goes down (though more slowly). Why
remove the reducer for visual work?. The F*.63 reducer works well with 1.25"
eyepieces, to give a field close to that available using 2" eyepieces, that
is flatter than the SCT otherwise manages. Now the problem is that with a
normal 2" diagonal, and filter wheel, the spacing will be more than the
design distance, and the results will probably not be acceptable. Given that
your diagonal, presumably has 2" SCT threads on the 'scope' end, you could
get the Ted Agos adapter, sold for the SBIG AO7 systems (He sells another
design for 'normal' use, but it is the AO7 version that would suit your
application). The SBIG cameras, when used with an AO7, have the camera, then
a filter wheel (about 1" thick - you want this to be as thin as possible -
hopefully yours is the 'thin' TT wheel?), then the AO7, which is effectively
a 'diagonal', which ends at the front with a 2" SCT thread. This combination
is too long to work properly with the standard F*.63 reducer. The Ted Agos
adapter, allows the optics from the reducer to be moved 'into' the nose of
the AO7 (in your case the diagonal), bringing the overall length, in line
with the design requirements. With this, you should be able operate with the
reducer, and simply replace the camera and wheel with an 1.25" adapter, and
eyepiece. If you get one that is about 1" to 1.5" long, there won't even be
much focus change.
Putting the reducer after the diagonal will result in a very small reduction
factor (probably only about *.8). If you want to do this, you would be
better off getting a shorter focal length reducer (like the Optic *.5 unit),
but this requires the spacing to the CCD, is exactly right (is is not as
forgiving as the *.63 unit).

Best Wishes

The focal reducer is best placed before the filter wheel as shown in the
following illustration:

http://www.astrovid.com/CustomWheel_...es/Config1.JPG

You don't want the filters up front as they will be reduced in effective
size by the focal reducer.

Del Johnson



"justbeats" wrote in message
m...
I have a 10" F/10 LX200 I've been using for visual observing for a
year now and I've just purchased the kit I need for imaging. (Thanks
for advice on the Digital SLR or cooled CCD thread folks! I bought an
SXV-H9, True Tech filter wheel, Orion 80ED and SXV auto-guider).

I'm keen to continue visual use and want a simple way to switch
between modes (i.e. I don't want to reconfigure the optical train each
time I switch between CCD and EPs).

I understand that SCT-focuser-filter wheel-CCD is the best
configuration but that's so long it prevents the OTA from swinging
through the forks (no imaging around Polaris and a heart attack if the
dec lock comes loose).

So I have chosen to mount SCT-focuser-2" diagonal-filter
wheel-CCD. I realise this is not the most stable configuration, but I
can easily swap the filter wheel and CCD for an eyepiece, and both
configurations swing through the forks. Ideal for now, except.

I also bought a Meade 0.63 focal reducer. If I mount it on the SCT
rear cell, besides being a pain to remove for visual work, it prevents
both configurations from swinging through the forks anyway! Not a
solution!

So my main question is can I mount the FR between filter wheel and CCD
or between diagonal and filter wheel? I assume I need adaptors as
there's no obvious way to make the connections with what I have.

In general, what is the best place to put a FR? Before or after the
filters? Close as possible to CCD or close as possible to rear cell?
Advice welcome - particularly from anyone else with a 10" LX200
Classic, 2" diagonal, Meade electric focuser, True Technologies filter
wheel and SXV-H9 CCD.

Cheers
Beats