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View Full Version : Extra load on an LX200 (how much?)


Michael Kreuzer
November 24th 03, 06:31 AM
How much extra weight can I attach to an LX200 and still be in with a chance
at taking photographs? As a pre-emptive follow up question, is the 10"
better suited to photography (and can it take more weighty attachments) than
its larger brethren because it's on the same forks as a 12", or is that
missing something?

I'm envisaging a 4" guide scope (or smaller), plus cameras on the guidescope
& the SCT.

Regards,
Michael Kreuzer

ChrisH
November 24th 03, 03:58 PM
On Mon, 24 Nov 2003 06:31:26 GMT, "Michael Kreuzer"
> wrote:

>How much extra weight can I attach to an LX200 and still be in with a chance
>at taking photographs? As a pre-emptive follow up question, is the 10"
>better suited to photography (and can it take more weighty attachments) than
>its larger brethren because it's on the same forks as a 12", or is that
>missing something?
>
>I'm envisaging a 4" guide scope (or smaller), plus cameras on the guidescope
>& the SCT.
>
>Regards,
>Michael Kreuzer
>

There is no sudden cut-off, the more weight then the more flex you
get, so the tracking gradually degrades. The 12" is indeed on the same
fork as the 10" so it's already fully loaded.. You don't need such a
large aperture (i.e., heavy) guidescope, a small refractor (60/70mm)
is adequate for guiding with a CCD autoguider. Remember that whatever
extra weight you mount on the top of the OTA will need to be balanced
with counterweights underneath it. Accurate balance is the key to
success (that, and fixing the mirror flop if you're not using an
off-axis guider). Also, if putting extra weight on the forks then
reduce the slewing speed to 4deg/sec or less. Despite the mechanical
limitations of the Meade fork mount people have used the system to get
good results.

ChrisH

Chris L Peterson
November 24th 03, 05:38 PM
On Mon, 24 Nov 2003 06:31:26 GMT, "Michael Kreuzer"
> wrote:

>How much extra weight can I attach to an LX200 and still be in with a chance
>at taking photographs? As a pre-emptive follow up question, is the 10"
>better suited to photography (and can it take more weighty attachments) than
>its larger brethren because it's on the same forks as a 12", or is that
>missing something?
>
>I'm envisaging a 4" guide scope (or smaller), plus cameras on the guidescope
>& the SCT.

There is no simple answer to this. The more weight you add, the more problems
you introduce. I can give a reference point, though. I'm using a 12" LX00
classic, and have the following equipment: filter wheel, ST8i, 50mm dia
guidescope with ST237 guider using Losmandy mountings. There is also a RoboFocus
motor on the primary. This is all counterbalanced by a Losmandy 3D weight system
on the bottom of the scope, and I also have a couple of pounds on the east fork.
With this system, I don't have any problems with flexure, tracking error, or
resonance.

Film, with its lower sensitivity and lower resolution, is more tolerant of
tracking problems than CCDs. I don't think you will have any problems with
either a 12" or 10" LX200. You can save weight with a smaller guidescope- what
you are proposing using is larger than it needs to be.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Michael Kreuzer
November 24th 03, 11:12 PM
[good reply snipped]
> with counterweights underneath it. Accurate balance is the key to
> success (that, and fixing the mirror flop if you're not using an
> off-axis guider). Also, if putting extra weight on the forks then
> reduce the slewing speed to 4deg/sec or less. Despite the mechanical
> limitations of the Meade fork mount people have used the system to get
> good results.
>
> ChrisH

Many thanks for the info. I haven't yet properly considered off axis
guiders, that's the alternative, to be sure.

Regards, Michael

Michael Kreuzer
November 24th 03, 11:12 PM
> There is no simple answer to this. The more weight you add, the more
problems
> you introduce. I can give a reference point, though. I'm using a 12" LX00
> classic, and have the following equipment: filter wheel, ST8i, 50mm dia
> guidescope with ST237 guider using Losmandy mountings. There is also a
RoboFocus
> motor on the primary. This is all counterbalanced by a Losmandy 3D weight
system
> on the bottom of the scope, and I also have a couple of pounds on the east
fork.
> With this system, I don't have any problems with flexure, tracking error,
or
> resonance.
>

I suppose comparisons like this were what I was after really, many thanks
for that info.

> Film, with its lower sensitivity and lower resolution, is more tolerant of
> tracking problems than CCDs. I don't think you will have any problems with
> either a 12" or 10" LX200.

It's a choice, I think, between a 10" and a 14" scope, with the immobility
of the latter being a big consideration. Yet to read much about using the
latter photographically, either.

> You can save weight with a smaller guidescope- what
> you are proposing using is larger than it needs to be.

That's creeping aperture fever kicking in again. :-) OK, if I go the
guidescope route I'll limit myself to 60mm, there's a very nice Tak 60mm
that I can still also use visually.

Regards, Michael

ChrisH
November 25th 03, 09:14 AM
On Mon, 24 Nov 2003 23:12:28 GMT, "Michael Kreuzer"
> wrote:

>
>That's creeping aperture fever kicking in again. :-) OK, if I go the
>guidescope route I'll limit myself to 60mm, there's a very nice Tak 60mm
>that I can still also use visually.
>
>Regards, Michael
>

I recently started using a TV Pronto as a guidescope, good for guiding
prime-focus film through a 4" APO, but I would use a 2x barlow for
guiding an OTA of longer focal length. The Pronto is a nice rich-field
scope in it's own right, and it has a great 2" focusser. It's a wee
bit heavy but otherwise ideal. I'd thought of the Ranger as it's much
lighter but the focusser cannot be locked in position.

ChrisH

Michael Kreuzer
November 26th 03, 01:36 AM
I suppose I'm really just trying to have my SCT cake and eat it too (i.e.
also have a nice, small, wide field refractor), but there's no way my budget
will stretch as far as a second good mount. Using the refractor as a guide
scope makes buying it slightly more feasible because it'd save me some money
on the camera & off axis guider ...

The alternative (the much more expensive alternative) would be to get a
Losmandy G11 mount & Celestron 11" OTA with the option of interchanging the
scope with a refractor purchased in the future. It's _a lot_ more expensive
here though, and there's no celestron dealer in this country (Australia), so
for more money there's no service ...

On photography: Maybe I'll just go for an sbig camera with its own off axis
autoguider, not doing that could be a false economy. Shelve the refractor
plan for a few more years.

Thanks for your input, always nice to chat about scopes, Michael

> I recently started using a TV Pronto as a guidescope, good for guiding
> prime-focus film through a 4" APO, but I would use a 2x barlow for
> guiding an OTA of longer focal length. The Pronto is a nice rich-field
> scope in it's own right, and it has a great 2" focusser. It's a wee
> bit heavy but otherwise ideal. I'd thought of the Ranger as it's much
> lighter but the focusser cannot be locked in position.
>
> ChrisH