Telescope Accessories

Introduction | LED Red + White Flashlight (Adjustable Brightness) | Crosshair eyepiece, 12.5 mm focal length, illuminated | 12V / 7 Ah Rechargeable Power Tank | SkyWire Serial Accessory | Telrad Finder | Baader Laser-Colli Mark III (Laser Collimator) | Variable Polarizing Filter (Gray Filter) | Sun Filter | Links

On this page, I present an overview of my telescope accessories. Details and experiences are/will be reported on extra pages that I mention at the end of the descriptions of the respective accessories.



As with all hobbies, you are not done with astronomy when you buy a telescope with perhaps two kit eyepieces. Unfortunately, this is only the beginning of a series of further investments. These do not only apply to larger and larger telescopes, but also to better eyepieces, which can be even more expensive than beginners' telescopes, as well as a wide range of accessories that improve the observation experience or make it possible at all.

In the following I present the most important accessories (except eyepieces), which I acquired over time. This includes things such as devices that

In the following, I list the accessories that acquired over time (the order of which is historical...).


LED Red + White Flashlight (Adjustable Brightness)

Flashlight with box, side view

Side view: You can see three screws that need to be loosened to open the case for changing the 9 V battery

White light

Flashlight with box, top view

Top view: On the top you can see the red-white switch (left) and the control for setting brightness and turning the light on or off (center)

Red light

I use this lamp (from Sky-Watcher) to read star charts and astronomy books or do other things at the telescope without losing my dark adaptation. Unfortunately, the red light illuminates everything rather unevenly. Annoying is also that you have to unscrew the lamp for changing the battery (9V block battery; I am curious how long this will work...).



Crosshair eyepiece, 12.5 mm focal length, illuminated

Package content, batteries already installed in the illumination device

Above: Illumination device with batteries and brightness control / on/off switch screwed in

Middle right: double cross hairs, not illuminated

Bottom right: double cross hairs, illuminated

I bought the crosshair eyepiece (12.5 mm focal length; by Seben) for two purposes:

However, I have the impression that the focal length of the eyepiece is a bit short (or the magnification is too high...) for the second purpose. After experiencing some difficulties, I once again returned to the 32mm eyepiece for the alignment...

I am curious, how long the two small batteries will last...



12V / 7 Ah Rechargeable Power Tank

The 12 V cable for charging via car battery and for supplying the GoTo mount is stored in a timber (with caption); initially, I thought it would be missing (in the instructions it is listed, but not where it is ...)

I bought the Sky-Watcher 12V / 7Ah Power Tank with red / white light and a rechargeable lead acid battery, because the 8 AA batteries, with which I had initially supplied the Star Discovery mount, had been used up very quickly. So I hoped that with this device power will last longer. However, I read that even the Power Tank is drained in only one night. In my eyes, this is not a problem, because you can recharge the Power Tank over night (if you do not forget this...). At the moment, I can only tell that the power did not exhaust in one session...

Main technical data:



SkyWire Serial Accessory

Originally, I intended to use the Star Discovery GoTo mount only with the SynScan hand box, even though I knew that controlling the telescope using astronomy software applications such as Stellarium is possible with the Star Discovery mount. However, an RS232 to USB adapter is required to connect the hand box to the computer, but it is not guaranteed that such an adapter will work on the Apple Macintosh. So I did my first attempts on using GoTo with the SynScan hand box. This succeeded fairly well, but I'm not a friend of this kind of interaction and find hand boxes rather counter intuitive - quite in contrast to controlling telescopes using astronomy apps.

Southern Stars SkyWire Serial Accessory

Ditto connected to iPad and hand box


Ditto, detail



I accidentally came across SouthernStars' SkyFi WiFi device (built for Simulation Curriculum, the developers of the Starry Night and SkySafari astronomy applications), which seemed too expensive for me. But then I discovered that there is also a wired solution for the iPad from SouthernStars, the considerably cheaper SkyWire (unfortunately it does not work with the MacBook ...). This device is available in two versions, a cheaper one for the old 30-pin connector and a slightly more expensive one for the Lightning connector. Since my iPad sports a Lightning connection, I would have needed an adapter for the cheaper version. But this combination would be priced similarly to the Lightning version - and would include a potentially wobbly adapter. So I finally decided to buy the Lightning version of the SkyWire device, because I was curious to learn how controlling a telescope using an astronomy app works.

One advantage of the SkyWire compared to the SkyFi is that it does not need any power supply. Its drawback is that it is connected to the iPad by cable. This means that it can not be positioned at will, and in the dark it is also a potential stumbling block.

So far, I have only had a few experiences with SkyWire, but I can already report that the setup is hassle-free and controlling the telescope works well. Furthermore, if the deviations from the target are not too large, the position can be corrected so that the observed object is actually approached and not a point in its vicinity. Sometimes, however, the deviation was too large. Then, however, I mostly managed to steadily approach the target and kept updating the position in the SkySafari app (command "Align").

Note: The SkyFi and SkyWire telescope control accessories are now owned and supported by Simulation Curriculum Corporation. Contact Simulation Curriculum for technical support on these products (from:



Telrad Finder

Base from above and already mounted on the telescope tube

Finder (without base) from the side. You can see the little feet for mounting the finder to the base as well as the main switch (left).

Finder (without base) seen more from above

Rear view of the finder; you can see the three collimation screws at the back and the main switch on the side (also regulates brightness of the LED/rings)


Telrad finder with LED switched on; regrettably, the rings on the mirror are blurred

Telrad finder opened; battery holder on the right (2 AA cells)

I purchased the Telrad finder for my GSD 680 telescope, because I prefer a red dot finder to a (magnifying) viewfinder. The Telrad finder projects three rings (corresponding to a visual angle of 0.5°, 2°, and 4°) on a mirror, which serve to target celestial objects. However, I have not yet resolved the assembly of the viewfinder at the GSO 680 telescope satisfyingly.



Baader Laser-Colli Mark III (Laser Collimator)

To adjust misaligned telescopes correctly, a collimator is used. A collimator using a laser beam is also referred to as a laser collimator. In the case of a Newtonian reflecting telescope, the primary and the secondary mirror must be adjusted so that they are mutually centered as well as centered on their optical axes. Since I was not satisfied with the performance of my telescopes, I decided to buy a laser collimator to improve the adjustment of my telescopes.

The Laser-Colli Mark III with package and instructions

Laser-Colli Mark III in "off" state

Laser-Colli Mark III in "on" state: Laser beam made visible

Baader Planetarium offers a laser collimator, called Laser-Colli Mark III, which differs from other collimators by having a vertically mounted transparent disc with a central hole and a grid of crosses to show the position of the the laser dot. Thus, one can observe the adjustment process when adjusting the primary mirror. Moreover, the device has a particularly large cut-out, which also reduces its weight.

Since this collimator was selected in a comparative test by the magazine Night at Sky in 2010 as the winner, I decided for it. It is a little more expensive (85 EUR) than other devices (but there are also much more expensive devices ...), but Baader is considered to be a renowned manufacturer of astronomical products, and therefore, I hope that the device was adjusted properly at the factory (you can re-adjust it).



Variable Polarizing Filter (Gray Filter)


The variable polarizing filter from above...

...consists of two filters that can be turned two adjust the brightness

Filter taken our of the package

Filter at eyepiece

Ditto, more oblique view

Filter at eyepiece

Ditto, more oblique view


The moon, as well as the planets, can be very bright - sometimes too bright - so that it is advisable to dampen the light. In addition, details of the moon or of planets can be overshadowed by areas that are too bright. Remedy is provided by gray filters of different densities or by variable polarization filters, which allow to adjust the brightness within certain limits (the filters are screwed into the eyepiece). I have decided for the latter, even though damping the light is sometimes a bit "fiddly".



Sun Filter

EMC Sun Filter SF 100, Order Number 600-105

In order to be able to watch the Mercury transit in May 2016, I acquired a euro EMC solar filter for my Sky-Watcher Heritage 100P Dobsonian telescope, namely the type SF 100 filter (order no. 600-105, size 5: for tubes with a diameter from 103 to 131 mm). These filters utilize the Baader Planetarium Astro Solar film of density 5 (ND5), which is suitable for both visual observation and projection photography.

Packaging of the filter from above

Filter from below

Filter from above

EMC Sun Filter SF 100, Order Number 600-109

Initially, I had purchased a solar filter from the same series for my GSO GSD 680 8" Dobsonian telescope (order no. 600-109, size 9: for tubes with a diameter from 219 to 283 mm).


Packaging of the filter from above


Ditto from below


Filter from below - note the 4 additional slots (from size 9 on)


Filter from above - note the 4 additional slots (from size 9 on)

But I had to order also the smaller filter, because, due to a surgery, I was no longer able to carry the heavy 8" telescope. So I had to resort to my smallest telescope, the Heritage 100P, for the observation of the Mercury transit in May 2016.





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