Huygens eyepieces
From Scope F70076
Huygens eyepieces are the oldest design, and up to the middle of the 19. century all good telescopes had Huygens eyepieces. Some say that these are bad, and recommend not to buy telescopes which have Huygens eyepieces because these eyepieces have always a low quality. Of course, more expensive eyepieces are always better, but Huygens eyepieces are not necessarily bad when the focal ratio is small (like the almost 1/10 focal ratio which this scope has).
It seems that in spite that the eyepieces are Huygens, they are quality Huygens, the daytime images were very clear and sharp, and I never noticed any chromatic, spherical or other aberration at all. I'm very satisfied with these eyepieces. There might be some truth about the advice that Huygens eyepieces may have a low quality, so one should be careful while buying a telescope when it is known that the eyepieces are Huygens, as I have seen some cheap telescopes like these made by Bresser, where the eyepieces are whole plastic together with lenses.
There is only one problem which I noticed concerning the Huygens eyepieces -- the image tends to easily disappear when the eye is not in the correct position. It is completely possible to hold an eye in the right position by holding the eyebrow against the edge of the eyepiece. It needs to get used to, but I can now look through the eyepiece so that the image never disappears. So this is not exactly a problem, but rather a matter of convenience -- with better eyepieces one can take less care to look through the eyepiece in the right way, and this would certainly feel better. But I have read that there is such problem also with some other small telescopes, the eyepieces of which are said to be Kellner. So you should consider that the eyepieces of a cheap telescope could be inconvenient, no matter what type they are said to be, therefore the only thing which may guarantee you something, is that they are not made of plastic, then you see that some care has been taken at least to make them more durable with higher quality.
It is also not exactly certain that some low quality Kellner eyepieces with defective coating are necessarily better. Consider that a single good eyepiece costs much more than this telescope, so most certainly some bargain has been made to make the eyepieces cheaper, so it is not so bad when the only such thing is that the eyepieces have the Huygens design -- for some purposes there are Huygens eyepieces in some professional equipment even today.
The eyepieces consist of two lenses, but in more expensive eyepieces like Kellner and Plössi, these lenses consist of two or more lenses glued together, like achromatic objectives in refractors. There are two lenses instead of one to decrease the chromatic aberration in the eyepiece. The 4mm eyepiece can be opened, but the 12.5mm and 20mm eyepieces are glued and there are no obvious ways how to open them, thus they likely cannot be opened, but they seem to be at least watertight. In Huygens eyepieces, and also in Super Ramsden eyepieces, both lenses are simple, and the lenses also didn't seem to be coated.
Consider though that the difference between the eyepieces is big, good eyepieces would show the image a lot sharper and brighter. Unfortunately I have not much idea from what degree of quality the difference starts to become substantial, as I have never had a chance to compare my eyepieces with any other eyepieces. Thus what concerns the overall quality, the only thing which I can say is that these Huygens eyepieces are useful eyepieces, which produce an image without any noticeable transmogrifications or defects.
The telescope eyepieces also have another benefit. They can be used as magnifying glasses, in fact they are magnifying glasses in spite that they consist of two lens. As a magnifying glass, the 20mm eyepiece provides a 12.5 times magnification, 12.5mm eyepiece provides 20 times magnification and 4mm eyepiece should provide 62.5 times magnification, but cannot be used as it has to be so close to the object that it covers all light. Put the end of the eyepiece that goes to the focuser, close to the eye, and the viewed object close to the eyepiece. The 20mm and 12.5mm eyepieces can be very well used as a magnifying glasses, not worse at all than the cheaper jewelers magnifiers. With these also consider that their said magnification is never right, in fact what concerns magnifying glasses, their real magnification is mostly 3 times less than that said. So the 20mm eyepiece is certainly as powerful as the cheap 30x jewelers magnifier, maybe better. So if you need a powerful magnifying glass, having the telescope, you now have one.
