The C9.25 is the second newest entry in Celestron’s line of Schmidt-Cassegrain telescopes and probably their least often purchased telescope, right after the gigantic C14.
The C9.25 was introduced in the 1990s as a telescope that came in a low cost bundle with Losmandy’s GM-8 mount, which was the new back in the day. The bundle was marketed by Celestron.
The C9.25 has always advertised its Starbright coating and water-white corrector-glass – and most of the ones around today are newer models with StarBright XLT coatings.
Only a handful of C9.25s have ever been sold on a fork mounting, like the ultra rare Ultima 9.25 (of which maybe 300 were made), the CPC 9.25, and the currently available NexStar Evolution 9.25 (which is technically a 1-armed fork mount). None have been hugely popular.
Optics Of Celestron C9.25
The C9.25 uses an f/2.3 primary mirror and a secondary mirror that amplifies the focal ratio by about 4.33 as opposed to the normal f/2 + 5x combination in most SCTs. This results in the tube being a little longer proportionally than other SCT optical tubes. However, the main difference is that the primary mirror is slightly easier to make to high tolerances and collimation is made easier by the longer focal ratio primary, resulting in better images on average with C9.25s compared to other SCTs of similar apertures. As I’ve heard from one source, the slight change to the optical design was supposedly done to better illuminate full-frame cameras and reduce vignetting problems seen in the C8, but as to how this change affects the edge-of-field illumination I have no idea.
The C9.25 is also just the right size to make it practical for planetary use. Your average air cell is about 10 inches wide, so a scope at or above 10” of aperture is looking through more than one column of turbulent air and is thus more affected by atmospheric seeing – another reason, I suspect, why many people rate the planetary views with the C9.25 as equal or better than larger, equally good quality SCTs.
Unfortunately, increasing the length of the tube makes the C9.25 a heavy and rather unwieldy scope compared to a C8 – 20 pounds for the C9.25 versus 12.5 pounds for the C8. You’re nearing the weight of Celestron’s C11, which as specified by the manufacturer clocks in at 27.5 pounds. In practice, all three scopes are a couple of pounds heavier than advertised – and that’s before you even add accessories. The tube length is only 2 inches shorter than a C11, despite being a full five inches longer than the C8. So if you want better portability for your given aperture you’re better off with going with a C8 or C11.
The main advantage over the C9.25 over the C8 or C11 is that it grants you about 33% more light-gathering ability over the C8, but the 2350mm focal length is not going to box you in when viewing deep-sky objects. The C9.25 is the largest SCT I would really recommend as an only telescope; anything bigger is going to have a focal length of at least 2500mm which is really too claustrophobic for deep-sky use, even when coupled with an f/6.3 reducer, so you’ll definitely want a fast Newtonian, refractor, or even a smaller SCT for low-power wide-field views – you may even want this with a C9.25.
There is an EdgeHD version of the C9.25 which has improved cooling, better edge-of-field correction for astrophotography, and mirror support knobs to prevent image shift and mirror flop. However, until recently there was no 0.7x reducer available for the Edge 9.25 due to the complications of designing it combined with low demand, so you may be hard-pressed to find any actual users of these scopes since most astrophotographers use reducers with their SCTs.
The C9.25 XLT optical tube comes with a 6×30 finderscope, 1.25” visual back, 1.25” prism star diagonal, and 25mm (94x) E-Lux Plossl eyepiece – if you buy the Advanced VX, CGEM, CGX, CGX-L, or CGE Pro kits where the C9.25 is bundled with one of these mounts you will get the same accessories. The 6×30 is fine for aligning a GoTo mount, but if you plan on using the scope manually something like a 9×50 or Telrad is preferable – additionally, the 6×30 can be uncomfortable to use even for aligning the mount. The 1.25” visual back, prism diagonal, and 25mm Plossl are all fine but the field of view is rather narrow with 1.25” eyepieces and you will really want a 2” diagonal and low-power eyepieces for most use.
If you buy the EdgeHD version of the C9.25 you will get a 2” prism star diagonal, 9×50 finderscope, and a 23mm (102x) Luminos eyepiece – these are excellent.
Like all industry-standard Schmidt-Cassegrain telescopes the C9.25 will accept a reducer-corrector, T-adapter, and other Celestron or third-party supplied accessories attached to the back.
The C9.25 is spec’d at about 20 pounds. In actuality it weighs a few more pounds than that, and once you add heavy eyepieces, a finderscope, and a dew shield you are probably going to end up with a scope nearing thirty pounds.
If you’re looking for a lightweight setup, Celestron’s Advanced VX (or an older, used CG5) will work just fine for visual use and planetary/lunar astrophotography – if you’re buying the OTA separately, you’ll want the version with the Vixen/CG5-style dovetail (the Advanced VX bundled C9.25 comes with one, of course). Beware that the Orion Sirius/Skywatcher HEQ5 has 1.75” tripod legs versus the VX’s 2” legs and really can’t support the weight of the C9.25 adequately.
For deep-sky astrophotography, I have seen people getting away with Atlas/EQ6-class mounts but only after modifications to the mount like belt-tuning, and even with good autoguiding you’ll have to discard some frames. You need a mount with at LEAST the capacity of 50 pounds, preferably more if you can get it. With an EQ6 mount or heavier, you’ll, of course, want the CGE/Losmandy-style dovetail.
You could put the C9.25 on one of the various manual alt-azimuth mounts like the Explore Scientific Twilight II, but I find that tracking with a focal length above 2000mm by hand is rather tedious and annoying even at low magnification.
If either the C8 or C11 interest you but you want decent aperture without a claustrophobic field of view, the Celestron C9.25 is an all-around excellent choice. It may be little much for a beginner to handle, but on a mount like the Advanced VX, I would not consider the C9.25 unwieldy by any stretch. I highly recommend it.