Celestron Astro FI-5 125 mm f/10 Schmidt-Cassegrain with a computerized altitude-azimuth single fork mount

A friend of mine wants to buy a telescope and begins observing in person. The area won't be among the most polluted in Italy, say the Milky Way is often visible by eyes and she already gets some traces of it while playing with modern smartphone and the apps they are equipped with.

She has spotted the above telescope.

Now, both me and my friend like amateur astronomy but we totally lack of knowledge on observational backyard astronomy and the related optics.

Would the linked telescope be a good starting point for a total beginner? Does it allow for the observation of nebulae and Andromeda while being OK for planetary seeing as well?

Alternatively feel free to signal if this can be a sort of overshooting. Though the budget is not an issue, considering that it just to begin is somehow mandatory.

What I began to consider is avoiding to invest some money in something that requires a very very dark environment in order to be used to see diffused objects. The telescope will stay, at least most of the times, in a dark extraurban area nevertheless close to several towns.

Would you suggest this scope or is there something making it not a good or reasonable choice for beginners?

  • PS beginning astrophotography is also considered, it can be as simple as having a smartphone mount. But playing with smartphones is how we became enthusiastic about astronomy and photography.
  • 2
    $\begingroup$ A 4 inch f10 seems a bit of overkill on the magnification, at the expense of field of view to me. You'll not reveal much detail on Mars or see much beyond the fact that Jupiter has moons and Saturn has a ring with it. A scope with a smaller F number 4 to 6 in that size will usually give you much wider starfields, and better views of big comets. 125mm is a starter scope. When I got mine, I preferred the larger field of view. Be sure to look carefully at eyepiece design. $\endgroup$ Feb 2, 2020 at 23:05
  • $\begingroup$ @Wayfaring Stranger thank you. $\endgroup$
    – Alchimista
    Feb 9, 2020 at 8:04

1 Answer 1


The Celestron SCTs at all apertures have been honed by 30 years of critical amateurs and a market-attentive manufacturer, so you will almost certainly get high-quality images from the OTA, the telescope itself. The Kellner-design eyepieces are another matter. Their apparent field diameter (AFOV, the size of the circle as you look through the eyepiece) is only about 55°, or roughly the diameter of the circle if you close your index finger to your thumb and hold it about 12.5 cm (5 in.) from your eye as you look at the sky. Moreover, these are mass-manufacture products sold as original equipment supplied to many telescope makers. Their quality assurance is not guaranteed. Most people find the star images are generally not as crisp as more modern designs. You would be wise to budget another €200 to €300 for two wider 70°–82° AFOV eyepieces to your budget. A good focal-length suggestion would be 25-30mm and 8-10mm. Quality wide-field eyepieces vastly improve the viewing experience. Objects stay in view longer, and generally are crisper and "deeper" (more pinpointy stars in the field than with mediocre optics). There are numerous telescope equipment retailers which you can locate with search terms such as "1.25 telescope eyepiece 82° 25mm". It is best to patronise a recognized astronomy-specialist than a drop-ship outfits like Amazon. Professional dealers will know most of the problems you encounter and have a vested interest in answering your queries promptly. Since you represent possible future business, they will go out of their way to give you info and service you don't get from sell-&-forget outfits.

The scope's 127mm aperture is a good starter choice. With the exception of M31 the Andromeda Galaxy, galaxies will not be impressive; "faint fuzzies" aptly summarises it. However, nearby star clusters and nebulae more than make up for it; you will find plenty of eye candy just roaming the Milky Way band. If your observing location is Italy, you may find that "rough air" (atmospheric turbulence) degrades image quality much more than any optical problems in the telescope or eyepieces. If you just can't get a good focus on any of the stars in a given field, it means the "seeing" is not great. In bad seeing, the moon will look like the seething shimmer of a distant village on a hot day. Except for really bright inner-city or moonlit skies, light pollution will be less of a problem in telescope fields compared with naked-eye impressions. You are effectively looking at a star cluster through a soda straw with a magnifying glass, so the inherent brightness of the stars will easily override the slight grayness of the background field. Yes, you do see a lot more under truly dark skies, but if you can see the MW visually where you live right now, your telescope will give you years of pleasure before you have to move on to that cabin in the woods. Finally, have a look at the amateur astronomy community www.cloudynights.com. Just about any telescope or astronomy info you need can be answered by the enthusiasts on that website. Moreover, there are four amateur astronomy forum/discussion groups in Italy. Check them out, you have a lot of friends out there you never knew you had.

  • $\begingroup$ Very nice and detailed, thanks. $\endgroup$
    – Alchimista
    Feb 3, 2020 at 16:30

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .