Sky-Watcher Star Travel 102

To understand this telescope, you will need to understand certain terms that astronomers use. I will try and expain things as we go along, but this is a fairly long review. Stay with me, OK ?

*** Background :
I have always been into astronomy, and have owned various telescopes over the years, since about the age of 11. A few years ago, I got back into photography as a major hobby, this time, combined with photography.
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...expensive scope I could afford, a huge reflector by Helios on massive mount and tripod. Unfortunately, I am physically disabled, and this combination was just too much for me to handle, so I sold it and looked out for a much smaller lighter scope.

After visitng several local astronomers, I was convinced I had found the right scope in the Skywatcher Startravel 102mm F5 Short Tube. I can use this for astronomy and also for "terrestrial" ... more

To understand this telescope, you will need to understand certain terms that astronomers use. I will try and expain things as we go along, but this is a fairly long review. Stay with me, OK ?

*** Background :
I have always been into astronomy, and have owned various telescopes over the years, since about the age of 11. A few years ago, I got back into photography as a major hobby, this time, combined with photography.

I started off with the biggest and most expensive scope I could afford, a huge reflector by Helios on massive mount and tripod. Unfortunately, I am physically disabled, and this combination was just too much for me to handle, so I sold it and looked out for a much smaller lighter scope.

After visitng several local astronomers, I was convinced I had found the right scope in the Skywatcher Startravel 102mm F5 Short Tube. I can use this for astronomy and also for "terrestrial" use, eg : bird watching & wildlife.

OK, so what does all this 102mm, F5 and short tube stuff mean ? There is a lot of explaining before I review the actual scope, so if you are interested, here we go -

*** The Technical Stuff, what does it all mean ?

1) 102mm lens :

The 102mm size is the diameter of the main lens at the front of the telescope, in old money, about 4.5 inches. Generally, good quality astronomical refractors are available from 70mm up thru 90mm then 102mm, up to (usually) a maximum size of 150mm.

2) F5 :

The "F5" part of the description is the "Focal Ratio", and is the ratio of the focal length (more or less the length of the scopes tube) to the diameter of the lens - in this case, 500mm focal length with a 102mm lens, gives 4.9, so we round it up to F5. This is considered to be a "fast" ratio, as it gathers more light than longer focal ratio scopes of, for example, F8 or F10 with the same size lens. The main advantage for having an F5 is that it uses a shorter exposure time on a camera than if a higher F ratio scope were used. This gives more stable images for planets, and more light gathering for deep space objects such as galaxies with longer exposures.

3) Short Tube :

The "short tube" refractors are just that, short tubes. The other type of refractors have considerably longer tubes, giving "slower" F ratios of F8 to F10 (for example).

Right, got all that ? I'll be asking questions later....

*** Buying one, options and availability :

I bought this scope as a Optical Tube Assembly (OTA), as I already had an existing mount and tripod. If you decide to buy one of these, do make sure that you get the bigger mount (EQ3) and the dual motor drives fitted by the shop which enable automated star tracking. The standard offering is an EQ1 mount which really is not good enough for this scope.

*Star Tracking ?

If you set a telescope on a standard camera tripod, and look at the stars at a reasonable magnification of say 50x, you will notice that the star moves out of your field of view (FOV) very quickly. So you need a special mount on top of the tripod, which is capable of tracking the stars movement. Most mounts that do this are known as German Equatorial Mounts (GEM's) or EQs. The EQ range of mounts come in several sizes, from EQ1, thru EQ2, 3, 3-2, 5, HE5 all the way up to 6 (a monster at over £700 just for the mount !).

These EQ mounts have slow motion controls which enable you to move the telescope along the arc of the stars movement and track it thru the night sky. An optional but fairly essential extra, especially if you are using a camera, is a set of motorised drives, which automate the tracking. If these drives are fitted, you can centre the scope on a star, leave it running, and come back half an hour later with the star still centred.

The EQ3-2 is about right for this telescope, but the EQ1, which is offered in a lot of instances, is a little too flimsy for the scope, especially if you then add a camera on the end of it.

*** So, after all the lecturing - the review :

* Ease of use :

Very light in weight - even when attached to my EQ3-2 mount and sitting on the tripod, the total weight is about 17KG, easily manoeuverable, even by my disabled self. It takes about 15 minutes for the optics to cool down, so while it is doing that, I do the Polar Alignment and levelling of the tripod, so that the mount will track accurately. It takes a little practise, but once you have the hang of the setup it can be done in about 10-15 minutes.

* Supplied accessories : A 45 degree erecting prism, and eyepieces including a 10mm and 25mm wide angle, all with 1-1/4" fitting. This is the current standard size for the eyepiece barrel diameter. These will give magnifications of 50x and 20x respectively (work it out by focal length divided by focal length of the eyepiece). Due to my photographic requirements, I changed these for a for a set of 2" eyepieces to get a wider field of view. The supplied eyepieces offer around 50 degrees of vision, my new 2" system offers 80 degrees. I also changed the diagonal from the 45 degree prism to a 2" mirror.

The 45 degree prism has one distinct advantage : it enables the scope to be used as an "ordinary" telescope, as opposed to an "astronomical" telescope. The "astronomical" scope inverts the image and swaps left and right, but if the "erecting prism" is used, the image appears to be the "right way up". The replacement 2" mirror simply swaps left and right, so I still have my "right way up" image. This is important as I also use the scope for bird watching.

This has gone on quite a while now hasn't it ? Are you still with me ?? I hope so - nearly done.

*** Views through the scope :

With the originally supplied items, the system offers 50x or 20x magnification. This is plenty for the moon, which appears very sharp and contrasty. Crater definition is superb. Planets photographed successfully include Jupiter and four of its moons, Saturn with its glorious ring structure, Venus, with a cresent shape just like our moon, and, pushing the limit : Mars and Neptune.

You can add more eyepieces, or something called a Barlow Lens, which effectively doubles or triples the magnification. However, the maximum "useable" magnification is governed by a rule of thumb : "2x the lens diameter in mm", so the effective maximum for this scope would be 2 x 102 = about 200x - but even at this theoretical maximum level, the scope shows stability and clarity that I was not expecting. On this basis, I would not be surprised to be able to use the scope at up to maybe even 300x !

Galaxies and globular clusters are visible at good resolution, but a star map is an essential if you want to fully explore the night sky. M42 in Orion was wonderful during the winter, but is just below the horizon now. M31 Andromeda galaxy will be visible soon, and that can be an impressive sight too....

Overall, this scope never ceases to amaze me. You would need to be an astronomer to understand the significance of resolving the Trapezium in M42 - it has done it. And to see the dust lanes in M31 - it has done it....

Now I have the new 2" eyepiece system, I can take this little scope to much greater depths of space, and not once have I regretted buying my short tube 102mm F5 !

* Problems ?

The only down side to the scope is the build quality. Made in China by the Synta company, this scope is sold under many different badged brand names. The internals of the scope tube could have been finished off a little better, with some gaps in the baffles being filled in, and a little more internal blackening to avoid light reflections causing ghost images at the eyepiece. The focusser was a little floppy too. However, it was a simple matter for me to strip the scope down and perform a few mods to fix these problems, but if you felt that this was beyond your ability, your local astro clubs would be happy to help. The scope is now as good as it gets !
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Well, the marathon is over, I think I came in about 3rd ..... Hope this has been useful, please feel free to comment !!

*Specs :

Overall length (excluding any mirrors or eyepieces, focusser fully closed) : 500mm
Largest Diameter : 115mm
Weight (just the scope) : 10kg approx
Weight on the EQ3-2 mount, with dual motors fitted : 17KG approx.
Supplied : scope, tube mounting rings, 10mm eyepiece, 25mm eyepiece. 

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