A cheap telescope can discourage anyone from pursuing the astronomy hobby. Usually the effect of lowering the price of a scope is associated with compromising its performance. In many cases the vendor includes additional features that intend to attract the buyer and have no real value.
The point is that if the main features of the scope such as the quality of the objective and the focusing mechanism are acceptable we can deal with the rest and make improvements.
All the tips and modifications described here are common knowledge to experienced amateurs. A fresh user may find this information helpful in evaluating and using her/his own instrument.
I also demonstrate how to make a finderscope out of a small set of binoculars and how to use discarded lenses to make your own eyepiece. Some of these modifications are shown in the photo.
Step 1: My Bresser Junior 70/700 EQ-Sky
I bought this small scope as a department store offer of LIDL in Athens a few years ago for 70 Euros (the current internet value is about 150Euros). I found a lot of reviews and modifications for it, coming from Germany, Austria and England although for a different equatorial mount with a counterweight. This scope has been included in a comparison test for 70mm refractives in the BBC edition "Sky at Night " November 2010.
I summarize how I feel about it:
1. Light weight, it will go anywhere, the biggest advantage.
2. The objective is good. I tested the field of view with a Celestron 8-24mm zoom eyepiece and the result was about 90%.
3. The 20mm and 12mm eyepieces are usable.
4. The focusing mechanism is acceptable.
5. The tripod works both as an Alt-Az and Equatorial. This is useful as well as instructive..
1. The viewfinder is not too secure on its holder but this can be dealt with. The viewfinder's lenses are plastic and diffuse light.
2. The 4mm eyepiece is inevitably of very low quality with plenty of distortion and chromatic aberrations. This was included in order to advertise 175x magnification. A 2x Barlow lens for use with the 12mm eyepiece would be preferable but I suspect that at this low price the Barlow would not be good either.
3. The tripod tries to do it all but there is a cost. It is too light and unstable. Even a weak breeze will make the scope tremble. The guiding system that supports the scope is well designed and well made. The main source of instability are the legs of the tripod. Hanging a weight makes the whole system more stable.
4. The set included also an orthoscopic tube with a plastic lens in order to turn it into a spotting scope. To be discarded. I use a 45 degree prism instead.
WHAT YOU CAN DO WITH IT
You may use a scope of this size and type to observe the planets (zones on Jupiter and satellites, the phases of Venus, Saturn, Mars), the moon, nebulas, clusters and double stars.
The theoretical minimum feature size that a 70mm objective lens can resolve is ~2 arcsec. To compare with, the apparent size of Saturn is 15-20 arcsec. Saturn with this scope appears as an oval shape , no chance of seeing more features.
I also have resolved double stars distant 8-10 arcsec apart, provided their magnitude is high enough. For example Mizar A (magnitude 2.25) and Mizar B (magnitude 4.0) in Ursus Major , distant 14.5 arcsec is an easy target. Everybody's favourite Albireo in Cygnus (35 arcsec) is even easier to resolve in its two colourful components.