reflector vs sct
prateek aindley
CELESTRON NEXSTAR SE 6.... please advice
difficult to make my mind.... i had a 6" newtoninan reflecotr
earlier.....
Robin Scagell
I did a search for BKP 150750 and came up with this page:
http://www.tejraj.com/reflectors-sk1507.html
150750 has to mean 150 mm aperture, 750 mm focal length, which is what
the specifications say, but immediately under the picture it says 1200
mm focal length, so we assume that this is an error. As shown, it is
not motorised, but the description below refers to the Go To SynScan
upgrade (which it further confuses by calling it SkyScan in the
heading).
If you are trying to choose between this and a NexStar 6SE, I assume
you are thinking of buying it with the SynScan upgrade. There is
little real point in having the telescope without any motors, as you
are losing the main advantage of having an equatorial mount.
So basically, the comparison is between a 150 mm f/5 Newtonian on
equatorial mount, with Go To, and a Schmidt Cassegrain f/10, of same
aperture, on Go To altazimuth mount.
Optically speaking, the Newtonian is best for viewing deep-sky
objects, while the SC is best for higher-power views, particularly
planets, because it has double the focal length and will give more
magnification with any given eyepiece. An f/5 telescope would have to
be of superlative optical quality to perform really well at high
magnification. I see that the Sky-Watcher comes with a variable Barlow
lens. I haven't seen one of these, and I assume that it has a variable
extension tube to give the different powers. I don't think this is a
Sky-Watcher product and can't vouch for its optical quality.
Personally I am not convinced that the package advertised, which has
lots of bits and pieces added to the basic Sky-Watcher package in
order to inflate the price, is ideal. You might be able to get the
instrument for less but without all the 'free' items that you might
not want. However, the basic NexStar package usually includes only one
eyepiece, so you would need to spend more in order to be able to
observe at higher magnification.
However, because the Newtonian is on an equatorial mount you should be
able to carry out long-exposure photography more readily than with the
NexStar, though you might need to add an autoguiding telescope on the
same mount for exposures longer than a minute or so. The NexStar is on
an altazimuth mount and any exposure longer than perhaps 20 seconds
will start to show unavoidable image rotation at the edge of the
field. However, it will be much better than the Sky-Watcher for
planetary and short-exposure imaging because of its longer focal
length.
So, briefly, the Sky-Watcher is best for observing the deep sky,
ideally from a dark location, and for astrophotography. The NexStar is
better for planetary and visual observing, though you are dependent on
having power to use it (either battery or an AC adaptor), whereas the
Sky-Watcher can still be used manually even without power. But both
telescopes will show all types of object, so you will still be able to
see the planets with the Sky-Watcher and deep-sky objects with the
NexStar. So decide what you want to observe and phoograph, bearing in
mind your location and the local light pollution.
Let us know how you get on.
Robin Scagell
Author, Stargazing with your Telescope
www.stargazing.org.uk
prateek aindley
thanks a lot for your prompt reply and facts... I do agree with you
that this dealer is giving more add-ons and a hyped price. the problem
in india is that all these telescopes from USA makers are expensive
here because of the duty and stuff... Also one is not allowed to ship
them online out of States. So prices are hiked or almost double
here... Regarding a few points please note the following
I stay in a appartment in Mumbai where transporting telescopes is an
issue... So getting an equatorial mount with a Newtoninan tube is a
bit of an issue.. I had one last time and it was problem storing and
transporting it... also back scatter of light is a problem.. as u know
in a city
Secondly regarding the Focal length although the SCT has f/10 one can
buy the focal reducer to F/6.3 i have not used it but hoping that
would solve the problem
would appreciate your views... so one can achieve two objectives with one scope
I am getting a cellestron powertank along with the nexstar 6 se... so
that solves my power problem...
regarding the extra lenses i am having a friend of mine get a
accessories set from states.. i am getting a set of lenses and
filters, a solar filter and an focal reducer from states... its quite
cheap there...
regarding photography the Nexstar 6se alt - az mount comes with an
equatorial wedge which helps in long time photography... so one can
align the telescope with EQ-N and go in for a equatorial mount on the
same alt-az mount....pls advice
please let me know how useful is the NEXIMAGE camera.....
so considering all these aspects i somehow am more inclined towards
the NEXSTAR 6 se.... thats why i want a neutral descison on this since
it is quite an investment from indian scenario point of view...
hoping to hear from you soon
Cheers
Prateek
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Robin Scagell
You're right, I had forgotten about the NexStar wedge -- oddly, their
publicity makes no mention of its availability, but bear in mind that
it is an extra, and even in the UK it costs about a third extra on top
of the price of the telescope. The NexStar 4 and 5 have built-in
wedges but the 6 is a larger instrument and requires a more beefy
setup. There is also the issue of balancing the instrument when you
have a weighty DSLR camera attached to the back, and there may be
problems with the size of the camera. I'm not sure about the 6SE, but
often you can't photograph objects high in the sky with a fork-type
mount as there is not enough clearance for the camera. With my Meade
LX90 I have extra weights on the front to compensate for the weight of
the camera.
The f/6.3 focal reducer is indeed an option, but my feeling is that
it's probably not worth getting until you have a lot of experienc with
using the telescope at f/10. You may decide that you don't need it,
particularly in city skies. I can't comment on the optical results,
not having used one, but photos taken with focal reducers look good.
The NexImage camera is well worth having. It is basically the same as
the famous Philips ToUcam webcam, which cost rather less, but even so
it is the best option for planetary imaging without going for one of
the more expensive webcam-based imaging devices. I still use my ToUcam
and it is very easy to use.
From your location, I think it is probably not worth trying to attempt
long-exposure photography, so the basic 6SE, with extra eyepieces and
NexImage, is probably a good solution. You can experiment with DSLR
cameras, and maybe get nice results with exposure times of many
seconds on the brighter objects.
All the best
Robin