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TeleVue Travels (part 1)
Travels with a TeleVue 85 Apochromatic Refractor
By Antony McEwan
There are many TeleVue 85 refractors out there, and consequently there are many reviews of the TeleVue 85 out there too. They all praise the superb optics, outstanding workmanship and the versatility of the little APO. So what else is there left to say? Well, I thought in this ‘review’ I’d focus on the telescope’s ability to perform as a Travel-Scope; on its portability and ease of use in a holiday situation, when space and weight count and versatility is all-important.
The Telescope
The TeleVue 85 is an apochromatic doublet refractor of 85mm aperture and 600mm focal length. It has a super-smooth 2” rack and pinion focuser, weighs 8lb unloaded, and measures 21.5” in length. With a good 2” diagonal and a small finder added the weight increases to between 9lb and 10lb. The 2” focuser allows the use of a 2” diagonal, which means 2” barrel diameter eyepieces can be used. These provide wider fields of view than most 1.25” diameter eyepieces, so stunning wide field views can easily be obtained with the TeleVue 85. Mid-power views are also beautiful through this ‘scope, and by using short focal length eyepieces, or by adding a barlow lens to medium focal length ones, high power views can also be achieved which maintain the high levels of contrast and sharpness inherent to the TeleVue’s design. Being apochromatic, false colour around bright objects is not an issue. I have had this telescope for just over two years, since buying it second-hand, which in itself is quite a rarity as people tend to hang onto them! In fact, when I begin to wind down my visual observing in 60 or 70 years time, I’ll have to start thinking about who to pass this ‘scope on to…
The Trip
These events took place in September 2005, when I was on a 10-day holiday to the village of Frodsham in Cheshire, northwest England. I was staying on a holiday park about a mile and a half outside the village, in a static caravan. I have stayed, and observed from, there before and found the skies to be quite good, though there is some noticeable light pollution from the nearby villages and the city of Liverpool is not too far away.
Now I knew that there would not be much space to carry a load of astronomical gear in the back of a Ford Fiesta, so I had to travel light. An equatorial mount would be out of the question, so I decided to take my Tele-Optic Giro Mini alt-azimuth mount, and attach it to a borrowed tripod from a Synta EQ5 mount. The Giro Mini on EQ5 tripod is a lightweight set-up that moves very smoothly and carries the TeleVue 85 sufficiently well to allow moderately high magnifications to be used. I knew that I would be frustrated if I did not take a finder-scope with me, so I took the smallest and lightest that I own: an Orion 6x30 right-angled one that gives a correctly oriented view, much like in binoculars. This would attach to the clamshell ring that holds the ‘scope to the mount. As this is always at the balance point of the tube, the addition of a finder-scope would not affect the balance of the ‘scope, which is important when using an alt-azimuth mount.
For eyepieces I had to sit down and work out what magnifications I would be using, and which eyepieces to take that would be similar in weight and would take up as little space as possible. Having 25+ eyepieces didn’t make this easy, but I managed! I settled on the following selection:
Eyepiece...............................Magnification... Plus 2x Barlow
Meade 32mm Plossl..........................19x.................38x.........
TeleVue 21mm Plossl........................29x.................58x.........
TeleVue 10.5mm Plossl......................58x...............116x.........
Meade 6.7mm Ultra-wide angle.........90x................180x........
Celestron Ultima 2x Barlow....................................................
Note that magnification values have been rounded up to the nearest whole number for simplicity’s sake. This selection gave me a huge choice of magnifications, ranging from 19x (with a true field of view of 2.5 degrees) for glorious low power views, right up to 180x if needed. For reasons explained below, it was important that the eyepieces were all about the same weight, and I had also limited myself to a selection of eyepieces that would fit in the TeleVue carrying case- no additional cases! In the event, there was even room for my Ultra High Contrast and OIII filters, as you can see in the picture.
Some notes on the mount
The mount I used for this trip was a Tele-Optic Giro Mini mount. It is a lightweight yet beautifully engineered mount that attaches to any tripod with a 3/8” or M10 fitting. It simply screws on top of the tripod. On one side is a steering arm, on the other a Baader grab-arm with a locking knob. The TeleVue 85 has a clamshell ring that can be, and was, attached to a dovetail plate. The dovetail plate slots into the Baader grab-arm, and the locking knob is tightened. This holds everything in place.
The mount has two tension lock screws: one for the altitude axis and one for azimuth (left to right movement). To lock the telescope in place when it is pointing at something, the tension screws are tightened. To allow for panning the ‘scope around, they are loosened. Theoretically you can have them set halfway to allow a varying degree of friction control, but in my experience I have only been able to have them locked tight or completely open. This may be because the TeleVue 85 is at the upper limit of the mount’s capacity.
The picture below shows the various components used in mounting the telescope. The telescope tube is enclosed within the black Clamshell Ring, which screws to the long Dovetail Plate. That is held in the Baader Grab-Arm, and the Grab-arm attaches to the Giro Mini mount itself.
The beauty of an alt-azimuth mount for this type of observing is its simplicity. There is no need to polar-align it or calibrate anything mechanical, or align on multiple stars before being able to observe anything- you just extend the tripod legs, set it level, and attach the telescope. Easy. There are a couple of downsides though. As you will see, viewing near zenith can be tricky as it may require some repositioning of the tripod legs to allow clearance for the ‘scope body. It also reveals about the only shortcoming I can find with the TeleVue 85- the fact that the focuser is machined to be so smooth that there is not quite enough tension to keep the drawtube from slipping when the telescope is pointing at a high angle of elevation. There is a tension knob on the top of the focuser to allow more tension to be applied though, and this solves the problem quite well.
This mounting arrangement is also extremely sensitive to the weight distribution along the length of the telescope tube. If the telescope is too far forward in the grab-arm, it will be nose-heavy and tip downwards when left loose; if too far back, tail-heavy and it will rise. It is important to balance the tube within the grab-arm so that it will stay in any position without slipping in either direction. It only takes a minute to do, and as long as the different eyepieces used in a viewing session are of comparable weight it shouldn’t be a problem.
The final issue is the lack of motor-driven tracking. The only way to track with this set-up is by hand, requiring regular little nudges to the tube to bring the target into the field of view again after it drifts towards (or beyond) the edge. Anyone used to using a Dobsonian won’t have a problem with this, and using wide-angle eyepieces alleviates the situation, although the short focal length of the TeleVue 85 does give quite wide fields even with standard Plossl types so it’s not really a big deal.
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