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May 07 2012

Celestron NexStar 5Se – a 125mm reflecting telescope

CelestronNexStar5SEThis is a brief overview of my shiny new purchase: a Celestron NexStar 5SE telescope. As an experiment I have also embedded a video review (here), I should also point out that so far cloud cover has meant the only celestial object I have observed is the sun (using the appropriate safety measures).

I bought my ‘scope from Sherwood’s, who I am happy to recommend for their good prices, and quick and efficient service. My purchase list was as follows:

  • Celestron NexStar 5SE (with mains adaptor)
  • SLA AstroPower station 12v 7Ah battery pack
  • Piggyback mount for my Canon 400D SLR
  • Universal camera adaptor and T-mount for similar
  • Moon filter
  • Baader solar filter film

The mount is powered, the add-on battery pack seemed like the best option for providing that power conveniently. I have a Canon 400D SLR camera which I wanted to use with the telescope, the piggyback mount lets me put the camera on top of the optical tube and simply use it to point the camera at the sky. The T-mount assembly allows me to use the telescope as a camera lens, albeit without auto-focus and aperture.

The solar filter is essential if you want to look at the sun, and I got the impression a moon filter was useful for dimming the brightness of the moon, photographers will know that when photographing the moon the exposure time is as if for a rock sitting in full sun, which is exactly what it is!

The 5SE is a Schmidt-Cassegrain telescope with a 125mm (5 inch) primary mirror, a focal length of 1250mm and an overall F/ratio of 10. “Schmidt-Cassegrain” means that the open end of the tube has a corrector plate (Schmidt’s contribution) and light is focussed by a large concave primary mirror and a smaller convex secondary mirror in the centre of the corrector plate. The image is viewed through an eyepiece in the back of the optical tube, behind the primary mirror. In practical terms it also means the telescope has a very short tube length making it more portable than similarly specified telescopes. The whole assembly is easy to pick up and carry in its deployed state, and the optical tube in particular was well-packed on delivery forming the basis of a useful carrycase.

The telescope is supplied with a 25mm focal length eyepiece which gives a magnification of x50, the maximum useful magnification of the telescope should be x300 with appropriate eyepiece. Focus is achieved by turning a knob on the back plane of the telescope tube, which moves the primary mirror. The eyepiece is attached to a periscope (Star Diagonal in Celestron’s parlance) to give a more comfortable viewing position. The finderscope is a Celestron Star Pointer, which is a non-magnifying window with an LED spot projected to the middle for guiding, it took me a little while to get the hang of this but I can see the benefit of a low magnification finderscope.

The telescope is on a computerized alt-azimuth mount which also includes an equatorial wedge (like the equatorial platform), meaning that the rotational motion of the mount can be made co-axial with that of the earth – allowing un-rotated tracking of objects through the sky for astrophotographic purposes. The controller is a handset device on a cord, in night time operation the telescope can be aligned to the night sky by pointing it to three different stars, after which it will goto any one of a huge catalogue of celestial objects selected using the handset.

The optical tube feels nice and chunky, although the finderscope is a bit plasticky. The piggyback mount attaches using the same mounting holes as the finderscope, the finderscope then bolts back on top, I did a bit of tweaky of the screws along with adjustments on the finderscope to get it aligned. I have achieved fine views of my neighbours chimney pot!

There is a battery compartment in the mount which takes 8xAA batteries, reading on the internet I understand the lifetime for this set is about 30 minutes in operation, which is why I got both a mains adaptor and a 3rd party battery pack. I suspect I’ll mainly use the add-on battery pack for the convenience of fewer trailing leads. The mount doesn’t operate without power, which is a bit of a drawback, the telescope can be tilted but not rotated. The mount sits on top of a nice chunky tripod, to which it is attached by three screws, so in principle you could make yourself a “manualised” version by sitting the scope on a turntable. I have the slightly spurious desire to see a graduated scale on the mount movements. I’m used to using research grade optical equipment and whilst the optics have that feel about them the mount, although functional, does not.

The telescope comes with TheSkyX (First Light edition) planetarium software, and also an application called “NexRemote” which seems to allow you to control the telescope using a virtual version of the handset on screen – this seems a bit pointless to me! Other telescope control software is available, and it appears there is an interface standard. The programmer in me is hankering to write my own controller software!

Overall I’m pleased with my new purchase but desperate for a slightly less cloudy night to try it out properly – no doubt more blog posts to follow once I’ve done this! Even at £650 for the telescope it is cheaper than many lenses for my Canon SLR, although it is a little chastening that John Hadley’s 1721 reflecting telescope had a larger primary mirror.

Update:

After a few weeks of twilight use I thought it might be useful to add a couple of further comments which don’t really make a full new blog post:

1. You can get and set the telescope azimuth and altitude directly using the appropriate entries in the Utilities menu, without alignment these values are based on an assumed initial position of 0,0. During the hours of daylight, when only a very limited number of celestial bodies may be visible, you can carry out a “single body” alignment using the “Solar System Align” option in Alignment. This allows you to enable tracking, and to Goto specified absolute coordinates – useful if you want to survey heights of neighbouring obstructions.

2. The 5SE does not support autoguiding whilst the 6SE and 8SE do. The NexStar range does seem a bit confusing in terms of the facilities available across the range, the 5SE for another example is the only one to have a built-in equatorial wedge.

Here is a video tour, which covers much of what I’ve written above but includes the sound of me tripping over the cat’s water bowl:

 

7 comments

4 pings

  1. ALAN WRIGHT

    Dear Ian, Many thanks for your helpful and informative video and review of the 5SE. I intend upgrading from my Celestron 130EQ to either the 5SE (my preferred choice) or if I save a bit longer (!) the 6SE. Living in Sudbury Suffolk gives me an opportunity to quickly drive out into darker sky territory, though in practice our heavily light polluted back garden is my usual location for the few hours I usually have for observing. Having owned the 5SE for a few weeks, have you been impressed with the quality of the optics? My primary objective with a new scope is achieving much clearer resolution of bright light sources, free of the collimation probs I have with my Newtonian. Do you think that, given my strictly ‘amateur’ level of star gazing, there would be much advantage in spending extra on the 6SE? (which I realise has greater light gathering capabilities). Many thanks, Alan Wright

    1. Ian

      I should point out this is the first telescope I’ve owned, and I’ve had just two viewing nights so far – I have also inspected neighbour’s chimney pots and pigeons.

      I’m happy with the quality of the optics, but I’ve got nothing to compare it with.

      The 5SE has an equatorial wedge, whilst the 6SE doesn’t but I suspect aligning it in equatorial mode will be challenging/impossible.

      The bigger aperture of the 6SE gives you a theoretical improvement in resolution as well as light gathering.

      I’m wondering whether “tube only” is an option for you

  2. ALAN WRIGHT

    Many thanks for your prompt and helpful reply. I think I need the GoTo mount in order to reduce the considerabl time it take me to line up the 130 on anything other than the moon!! Perhaps the extra £200 cost of the 6SE might be better spent on the 5SE plus upgraded eyepieces. It is so difficult making a decision without being able to see any of these scopes in action.
    Thanks again,

    Best wishes,

    Alan W

  3. kishore

    Dear Ian,

    I have question on 5Se. Do you know the actual focal lengths of the primary (focusing) and secondary (defocusing) mirrors? I would like to see if the secondary focal length can be changed so as to get a different f# system.

    Thanks
    Kishore

    1. Ian

      Hi Kishore,

      The technical specifications only list the overall focal length.

      The HyperStar imagers which replace the secondary(?) mirror with a camera adaptor claim to give f/2 as opposed to f/10 on a conventional Schmidt-Cassegrain:
      http://www.hyperstarimaging.com/what.php

      The system isn’t compatible with the 5SE (I think the secondary mirror is too small), but the figures they talk about suggest the primary mirror is f/2 which would be 625mm for the primary on the 5SE. This is confirmed here:

      http://en.wikipedia.org/wiki/Schmidt%E2%80%93Cassegrain_telescope

      best regards

      Ian

  4. Ian D

    Hi Ian,

    Thanks for this very interesting piece. It has made me finally decide to get one of these scopes from Sherwoods.

    Would you be able to tell me what the scope is like for collimation, i.e does it need collimation and if so how frequent and how easy is it?

    Also, i understand you get a 25mm eyepiece with the scope, if you were wanting to add one more eyepiece for the moment which one would you go for. Maybe a 10mm?

    Thanks again
    Ian D

    1. Ian

      Hi Ian,

      I’ve not needed to do any collimation – I believe this is as a result of the very short tube length of the Schmidt-Cassegrain design compared to a Newtonian.

      I got a 12.5mm eyepiece and a x3 Barlow however, I’ve discussed this with a number of people who suggested a zoom eyepiece instead and, on reflection, I think I agree with them so this is probably going to be my next purchase and if I’d known then what I know now it would be my first purchase.

      I’m not getting to much viewing in – small child means I need the hours of darkness for sleeping!

      best regards

      Ian

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