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Date: 16 May 2007 09:04:02
From: canopus56
Subject: Meade LX200 - How to use with a DSI? Backfocus
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For this summer, I have the opportunity to use a publically available
LX200 Classic version. I would like to expand to some imaging. I have
a Meade DSI but am unsure how back focus works on a Meade LX2000 in
terms of aligning an object to a chip using a flip mirror.
My usual scopes are a 10" GEM mounted newt and a 5 1/4" refractor. For
those scopes I have backfocus and target centering problems reasonably
worked out - I have a flip mirror, a parfocal eyepiece set up, and for
the newt, a low-profile focuser. This makes getting the image on the
small DSI chip a _relatively_ easy task. A separate off-axis 70mm
refractor is used for alignment and guiding.
Looking at the Meade LX200 - and one equipped with an autofocus
controller - it is unclear to me how there is enough back focus room
on these SCTs. How much backfocus room is there? Is there enough room
to accomodate a flip mirror, a parfocal ep and a camera. Most pictures
that I see of LX200s and most people I have seen using them seem to
just stick the camera directly into the visual back with no flip-
mirror or parfocal e.p.
That setup seems like it would make targeting the feature onto a small
DSI chip quite difficult - that is aligning the feature by using the
camera view.
In reading the LX200GPS manual, there appears to be separate primary
mirror lock and adjust knob. In the LX200 classic manual, there is no
primary mirror lock knob. The scope I will be using an LX200
classic.
Specifically, what is the backfocus distance on an LX200 classic?
- Clear Skies - Canopus56
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Date: 18 May 2007 14:53:36
From: RMOLLISE
Subject: Re: Meade LX200 - How to use with a DSI? Backfocus
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On May 17, 2:13 pm, canopus56 <canopu...@yahoo.com > wrote:
> On May 17, 7:29 am, RMOLLISE <rmoll...@hotmail.com> wrote:
>
> Rod wrote:
> > Why do you need a flip mirror? The go-to on the Classic is usually
> > good enough to easily put DSOs on the DSI chip (especially if you'll
> > be shooting at f/6.3 or f/3.3 as most DSI users do).
>
> Rod, I'll give centering using live camera mode as a digital ep on
> faint fuzzies some more practice, but _easily_ isn't the adjective I'd
> use. -:) Even at f/6.3 the detector array only covers about 11 x 8
> arcmins.
>
> So from other group replies, it seems that there is no theoretical
> backfocus limit on the SCTs; there is only a physical interference
> limit between the focuser tube assembly and the bottom bracket of the
> fork. You can hang a filter wheel and/or other gear off the focuser
> ring - but at some point, a not well planned slew potentially could
> loop off the assembly.
>
> - Canopus56
Nope...not hardly. There is plenty of backfocus on an SCT due to the
moving mirror focusing. But it ain't limitless. As you'll see if you
combine an f/6.3 reducer-corrector with a flip mirror. ;-)
I'm not sure what you mean by using the camera as a "digital
eyepiece"--it's not really well suited for that. If you want that,
think about a Stellacam or Malincam.
I've never had any problem getting objects on that small chip with the
ASGT mount from Celestron, which is in the same accuracy leage with
the LX200 Classic.
Unk Rod
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Date: 17 May 2007 12:13:55
From: canopus56
Subject: Re: Meade LX200 - How to use with a DSI? Backfocus
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On May 17, 7:29 am, RMOLLISE <rmoll...@hotmail.com > wrote:
Rod wrote:
> Why do you need a flip mirror? The go-to on the Classic is usually
> good enough to easily put DSOs on the DSI chip (especially if you'll
> be shooting at f/6.3 or f/3.3 as most DSI users do).
Rod, I'll give centering using live camera mode as a digital ep on
faint fuzzies some more practice, but _easily_ isn't the adjective I'd
use. -:) Even at f/6.3 the detector array only covers about 11 x 8
arcmins.
So from other group replies, it seems that there is no theoretical
backfocus limit on the SCTs; there is only a physical interference
limit between the focuser tube assembly and the bottom bracket of the
fork. You can hang a filter wheel and/or other gear off the focuser
ring - but at some point, a not well planned slew potentially could
loop off the assembly.
- Canopus56
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Date: 17 May 2007 06:29:03
From: RMOLLISE
Subject: Re: Meade LX200 - How to use with a DSI? Backfocus
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On May 16, 11:04 am, canopus56 <canopu...@yahoo.com > wrote:
> For this summer, I have the opportunity to use a publically available
> LX200 Classic version. I would like to expand to some imaging. I have
> a Meade DSI but am unsure how back focus works on a Meade LX2000 in
> terms of aligning an object to a chip using a flip mirror.
>
> My usual scopes are a 10" GEM mounted newt and a 5 1/4" refractor. For
> those scopes I have backfocus and target centering problems reasonably
> worked out - I have a flip mirror, a parfocal eyepiece set up, and for
> the newt, a low-profile focuser. This makes getting the image on the
> small DSI chip a _relatively_ easy task. A separate off-axis 70mm
> refractor is used for alignment and guiding.
>
> Looking at the Meade LX200 - and one equipped with an autofocus
> controller - it is unclear to me how there is enough back focus room
> on these SCTs. How much backfocus room is there? Is there enough room
> to accomodate a flip mirror, a parfocal ep and a camera. Most pictures
> that I see of LX200s and most people I have seen using them seem to
> just stick the camera directly into the visual back with no flip-
> mirror or parfocal e.p.
>
> That setup seems like it would make targeting the feature onto a small
> DSI chip quite difficult - that is aligning the feature by using the
> camera view.
>
> In reading the LX200GPS manual, there appears to be separate primary
> mirror lock and adjust knob. In the LX200 classic manual, there is no
> primary mirror lock knob. The scope I will be using an LX200
> classic.
>
> Specifically, what is the backfocus distance on an LX200 classic?
>
> - Clear Skies - Canopus56
Hi:
Why do you need a flip mirror? The go-to on the Classic is usually
good enough to easily put DSOs on the DSI chip (especially if you'll
be shooting at f/6.3 or f/3.3 as most DSI users do).
The only problem you'll have is if you use a flip mirror in
conjunction with a 3.3 or 6.3 reducer. If you do indeed intend to
image with the DSI at f/10, you should have enough backfocus with a
flip mirror in place.
I'd forget flip mirrors. You don't need 'em for deep sky imaging. They
do work well for hight mag planetary imaging, and I do use the Meade
flip mirror to help for that.
Unk Rod
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