1. Look at the magnification
Many parents think that the higher the magnification of the telescope, the better the observation effect, but in fact, the magnification is inversely proportional to the size of the field of view.
The lower the magnification, the larger the range seen, and the image will be brighter and more stable; the higher the magnification, the narrower the range seen, and the brightness of the image will be lower.
Also, high magnifications require high stability, and if you can't hold the telescope steady (or use a tripod) for long periods of time, the image will shake violently, causing eyestrain or nausea.
Therefore, a portable telescope under 10 times is the best choice for children.
2. Look at the weight
Since children observe by hand, the weight of the telescope should not be too heavy, otherwise it will be difficult to carry it, and the imaging effect will be unstable. For binoculars used by children aged 5 to 10, it is best to control the weight under 500 grams.
3. Look at the objective lens
Generally speaking, the larger the aperture of the objective lens, the larger the light-passing area, which helps the human eye to distinguish details and the higher the resolution. However, the large objective lens will increase the weight of the telescope, which is not conducive to children's use. In recent years, with the development of telescope manufacturing technology, many small objective lenses around 20mm can also provide good imaging effects.
4. Optical coating
If the lens of the telescope is not coated, 50% of the light passing through the objective lens will be scattered and cannot reach the human eye.
The best way is to multi-coat the mirror surface, so that the light transmission rate can reach 90~95%.
5. Exit pupil diameter & exit pupil distance
The exit pupil of the telescope can intuitively represent the amount of light entering the human eye. Only when the exit pupil matches the human eye pupil can a complete and bright image be seen. The matching here includes size and position, that is, exit pupil diameter and exit pupil distance. If the diameter of the exit pupil of the telescope is smaller than the pupil of the human eye, the image seen by the human eye will be blocked by the frame.
Generally speaking, the diameter of the pupil of a person under the sun is about 2-3 mm. Children's pupils are larger than adults. The diameter of the exit pupil of children's telescopes is preferably not less than 2.5 mm.
6. Look at the price
The quality of optical products is bound to be limited by price, so we do not recommend using telescopes that are too cheap.
But Similarly, we don't recommend high-priced telescopes that are several hundreds and thousands dollars. After all, children's usage needs have not reached the professional level, or they will be more distressed if they are damaged.