Re: Telescope upgrade
- From: "Roger Hamlett" <rogerspamignored@xxxxxxxxxxxxxxxxxxx>
- Date: Mon, 30 Jan 2006 11:42:20 GMT
"McSlemon" <mcslemon@xxxxxxxxxxx> wrote in message
news:1138615620.513307.327080@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Hi
>
> I've been enjoying astronomy for quite some time now but am getting a
> little fed up with my equipment.. mainly because it wasn't treated as
> well as it should have been when I was a little younger - regrettably.
>
> For a while, I've been looking at the Celestron NexStar 130SLT:
>
> http://www.dhinds.co.uk/pages/fullProd.php?id=465
>
> Apart from taking a looking at celestial objects, I'd like to take a
> step into astrophotography. Now I realise that to take pictures of
> planets like Saturn, I'd only need a short exposure as its quite
> bright.
>
> Would this telescope be suitable for longer exposures as I'm under the
> impression that you would need a wedge to track objects across the sky.
>
> I guess my question is what do you think of the Celestron NexStat 130..
> and what should be my options in the long term for photography?
>
> Thanks for any help.
It doesn't need a wedge to track objects across the sky. However a wedge
would be needed for longer exposures. The problem is that with the Alt/Az
mount, though it can track anyway you want, the view seen through the
eyepiece (or camera), will rotate through the night.
Photography is a problem. Imaging for any length of time, requires a mount
that is really rigid, and it's ideally the axis used for tracking, wants
to be parallel to the axis of the Earth, to avoid this rotation. Now, the
'GEM' mount, avoids the need for a wedge (basically it has the ability
'built in' to it's base, to angle the axis the way required.
Alternatively, a wedge can be used, but this needs to be rigid, and easily
adjustable.
Generally, all telescopes of this sort, are sold with mounts that will
'do' for visual use, and will just about be able to cope with short
exposure imaging (a webcam on the planets), but will show problems for
longer exposures. Unfortunately, a mount that is really likely to track
well enough to image for any reasonable duration, is likely to cost as
much (more..), than this whole scope. It is possible to take some images,
with almost any scope combination, but unfortunately, with the more basic
mounts, it is a lot harder...
Seperately, there is the issue of keeping the scope pointing at the object
for longer times. With a really 'top end' mount, with very high quality
gearing, PEC, and the mount permanently fixed, and 'polar aligned', the
tracking may well be able to keep a star precisely positioned for a long
time. However for anything more reasonably priced, it becomes necessary to
'guide' the mount. Now there are a number of 'guide' solutions manual,
(using a crosshair eyepiece - this was the 'only' way for many years)
'self guide', (this is where part of the light feeding the camera, is used
electronically to generate the guide corrections - this is the Starlight
Express 'MX' series guiding), OAG, (here part of the main telescopes
light, is split off optically, to feed another camera - this is how the
internal guider on the SBIG cameras works, and many third party splitters
are sold), or a seperate 'guidescope'. All the 'OAG' type guiders, bring
wth them, the need for more backfocus in the scope itself. Now the reason
I 'raise' this here, is that the Newtonian telescope design, has as one of
it's 'limitations', a very limited range of backfocus, which may give
problems if you want to go for more than a very few seconds/minutes of
exposure.
OK, now the reason I am being 'verbose' about all this, is to try to give
some idea of the scale of problems involved for imaging. Far more money
can be wasted trying to take astromimages, than in almost any other area
of the hobby!.
In a sense, you need to think fairly deeply about your 'intentions' in
this regard. If you are happy to limit yourself to planetary images, then
these can be done with the NS130, though a fairly high magnification
Barlow type adapter will be needed, to get any sort of reasonable image
scale. You will find that at such a scale, aiming, and focussing will be
hard. Potentially, short exposures of the brightest objects (like the
Orion nebula), can also be taken by such a system, without the Barlow.
However if you really feel that longer exposures are somthing you want to
do, then wait, and start looking at what equipment people are using. A
mount like the Vixen GP-DX, is likely to be a better basis for imaging,
than the NS130. You also need to think about possible issues, like the
lack of backfocus on the Newtonian (this is one reason why SCT's are so
popular). Ideally, see if there is any form of local astronomical society
you can get to, and see how equipment performs, before spending any money.
Now as a 'guide', I wanted to set my niece up to do some limited imaging,
with a webcam. I ended up getting an Intes MN56 second hand, and a Vixen
GP (now the GP-E), with motor drives, by the same route. The total cost,
was about 25% more than the NS130, but I rate the Intes optics as being
some of the best for a reasonable price, and the tracking of the GP,
allows exposures over 30seconds, to be easily obtained. Now I'd consider
this a useable 'base' setup, without too many problems. Somewhat latter,
she switched to using a Starlight MX7 camera, and this has produced some
nice images.
Best Wishes
.
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