Celestron C9.25 Review

[Mr Spock]

Since I purchased my Celestron C9.25 OTA from FLO last November, the sky has not been kind. Either abundant cloud or poor seeing have given me little chance to assess its performance.

My Skywatcher 250P OTA had become a bit too bulky for me to lift with my worsening back condition. Given the C9.25's excellent reputation as a planetary imaging and visual scope, it's short tube and light weight was appealing.

The scope arrived in perfect collimation! Yay, no fiddling!

The OTA is kept in a porch, usually about 4-5° warmer than the outside. At this it is usable straight away, improving as it cools. Optimum performance takes about an hour of cooling. So far I've had no issues with dewing.

Mounted on an EQ-6 Pro, it is rock steady, even in strong winds. I suspect it would perform really well on a smaller mount such as an HEQ-5.

Tonight presented me with an opportunity to see what it could do. The sky was clear, the moon in a favourable position, and seeing was reasonable - a little boiling but with steadier moments.

Moon:

Most of the testing was done on Schiller. The northern peak was isolated in sunlight, and the central crater in the southern part easily visible. Also, this was a good chance to compare eyepieces, as I do seem to have collected a few...

13mm LVW, x181: A decent magnification on most nights, was to prove insufficient tonight. The image was sharp and contrasty but the central crater barely visible.

9mm NLV, 9mm Ortho, x261: Both sharp and contrasty. The NLV showing a little false colour, the ortho clean and bright. Both showing the central crater in detail.

7mm T6 Nagler, 7mm Ortho, x336: Good views from the Nagler with plenty of detail and contrast. An odd 'phasey' effect at times, probably due to its design. The ortho was restricted in field size by comparison, but really crisp and clear. The C9.25 was really in full flight at this magnification - very little reason to switch to a lower power. Everything was sharp and contrasty with very fine gradations on crater floors. Flawless.

6mm TMB II, x392: Starting to push the magnification now, the image was shockingly sharp and contrasty - most unexpected. The TMB fails a bit near the edges, but the centre has impressive sharpness. The Schiller peak was brilliant white, and the central crater sharp. I was later to study some very subtle detail inside Aristarchus with this combination.

4mm NLV, x588: Way too much magnification. Image was becoming a little dusky, but not that bad really. Contrast was a little soft and image quality not as good as x392.

Star Test:

For this I took a look at Castor. Views at x336 with the Ortho showed textbook diffraction rings. A most impressive performance.

Best view of the night:

...spending a couple of hours wandering up and down the moon's terminator at x392. A wealth of detail and easily the best lunar viewing I've had.

Conclusion:

The C9.25 I have is much better than I'd expected. Being mass produced it aught to be of average performance. What I've found is it is anything but average; the performance tonight gave me the impression these are high quality optics. Right now there is nothing that would prise this scope out of my hands.

[John]

Great review Mr Spock - thanks for posting it

I'd heard from several sources that the C9.25's were something a bit special and yours seems to underline those rumours. I believe their specification differs slightly from the other Celestron SCT's - is that correct ?

To be able to use 300x plus with ease under UK skies shows that the scope is a top performer.

If I were thinking of moving to a SCT, I think the C9.25 would be at the top of my list

Edited February 15, 2011 by John

[Mr Spock]

All SCTs have a f2 primary, the C9.25 is f2.3. I've also read extra effort is put into figuring the surfaces. Given my experience with an OMC-140 deluxe, better than 1/6th wave, I'd say the C9.25 I have is about 1/8th wave.

[Nexus 6]

Very decent report Mr Spock, I can agree with you on a few points for sure, I keep my 925 in the conservatory with a scope cover, once I know I can get out with it I usuallly leave it for around an hour before use, I do use a dew shield but must say although I can use a heater with it I have used it 2 or 3 times at most, the scope is 18 months old now so thats not bad going with the amount of damp nights we get. Views through the ep are fantastic, I only the other morning got my best view ever on Saturn, 13mm Nagler very pleasing

I remember reading somewhere before I had bought mine that the C9.25 is indeed even better than the 925 for its optics, wish I had it to post.I did consider selling my 925 and going for the C9.25 on an EQ6 as FLO had them at such a great price it was very tempting .

Glad you managed to give it a good test

Edited February 15, 2011 by Nexus 6

[Gadget]

Great write up Mr Spock and and will agree the C.9.25 is a great scope for punching out those high powers I also ordered a 6mm TMB 11 a while back and thought I may have been a bit optimistic and would not use it much but it gives some fantastic lunar viewing even at those magnifications and as for collimation although I check mine regularly it never needs touching they really are a great all round performer and a keeper if you get one

Kevin

[cgarry]

Great review. My C9.25 is in desperate need of collimation, possibly not unrelated to me fitting it with Bobs Knobs. I shall get that done as soon as I get the chance.

My one complaint about this scope is it does seem to be a bit of a cloud magnet...

Cheers,

Chris

[michael.h.f.wilkinson]

Nice review. The C9.25 was not available yet when I bought my C8, but I would have gone the extra mile to save up for it if it had been. As it is, I do not know whether I should put the C9.25 in the upgrade path (far future) or go directly for a C11.

[Mr Spock]

One thing I read was about someone who moved from C9.25 to a C11 but was considering moving back to a C9.25. I'll see if I can find the link when I get home (at work now - can't search for stuff). There is also a technical report (in german) which details a C9.25 with 1/7th wave optics - apparently 1/7th - 1/8th wave is typical of these.

Even slight miscollimation will ruin the image quality this scope is capable of.

[riklaunim]

All SCTs have the same optic. There is no magic in 9,25", but there are some myths. Also assuming PV wavefront error like 1/8 on the view it gives isn't accurate. Bad scopes can give "good" views also. But those SCTs tend to keep at least good level of quality.

One thing I read was about someone who moved from C9.25 to a C11 but was considering moving back to a C9.25.

I had C8, now C11 and the C11 is a big change over C8. Also the 9,25" is close to C8 so I can imagine why some people don't like C11 when the get one. It's getting quite big and heavy. Also it has to cool for a long time (or good cooler required), and things like focusing with a big 11" primary mirror can be very annoying.

[michael.h.f.wilkinson]

I had C8, now C11 and the C11 is a big change over C8. Also the 9,25" is close to C8 so I can imagine why some people don't like C11 when the get one. It's getting quite big and heavy. Also it has to cool for a long time (or good cooler required), and things like focusing with a big 11" primary mirror can be very annoying.

You can lock the mirror in some models and stick on a Crayford focuser.

[riklaunim]

EdgeHD and Meade ACF have mirror locks, but that's for imaging. Additional cryford (or motocryford) is a common solution (I have one), but still some focusing with the mirror has to be done. In the C11 turning the knob changes the focus slowly, but the field of view moves rather quickly so if you use a camera with small sensor - corrections have to be consistently made Smaller SCT are just far less demanding.

IMHO if you want a cool cat >= 10" - look at some open design with fixed primary ODK, TAL Klevtzow, RC, DK etc.

[michael.h.f.wilkinson]

EdgeHD and Meade ACF have mirror locks, but that's for imaging. Additional cryford (or motocryford) is a common solution (I have one), but still some focusing with the mirror has to be done. In the C11 turning the knob changes the focus slowly, but the field of view moves rather quickly so if you use a camera with small sensor - corrections have to be consistently made Smaller SCT are just far less demanding.

IMHO if you want a cool cat >= 10" - look at some open design with fixed primary ODK, TAL Klevtzow, RC, DK etc.

I am considering those as well.

[stevebb]

Great review, saw one of these at a shop in Sale, and was extremely tempted. Wish I had done now instead of taking the Solar route lol.

Thanks again Mr Spock :-)

Steve

[MarkSix]

Very nice review . I'm glad I made a good choice since this my first telescope. Sadly I haven't had the chance to try it out yet since my arm is broke :-(

Edited February 16, 2011 by MarkSix

[Merlin66]

I've used the 8" , 10" and still have the 12" Lx Meade.....

but I've got to say the C9.25 has won my heart....

The size v's weight is very good and sitting on the NEQ6 it just "looks right!"

I've had no issues with mirror flop etc using it for spectroscopy with 25-30 micron slits...it's a very good work horse...

If I didn't have the 12"Lx I'd be seriously interested in a C11... but that's another story......

[Mr Spock]

Re the 'Myths' page, and his views on the C9.25: "I like the C9.25. It’s a great telescope. Sometimes I wish I had one." - from that statement it's obvious he's never looked through one!

I prefer to believe my eyes and factual information rather than opinion.

Here's the test (in German) Ein göttliches Gerät - Astro-Foren.de - Die unabhängige Community

[Nexus 6]

Very nice review . I'm glad I made a good choice since this my first telescope. Sadly I haven't had the chance to try it out yet since my arm is broke :-(

thats very unfortunate Mark, I hope you are able to use it very soon

nice choice for your 1st scope

[riklaunim]

Re the 'Myths' page, and his views on the C9.25: "I like the C9.25. It’s a great telescope. Sometimes I wish I had one." - from that statement it's obvious he's never looked through one!

I prefer to believe my eyes and factual information rather than opinion.

Here's the test (in German) Ein göttliches Gerät - Astro-Foren.de - Die unabhängige Community

That guy knows a lot of SCTs and he surely looked throu someone 9,25" He started in the early days of orage (or even blue) Celestrons on the USA market.

[Westmoorland]

Nice report. Gives me hope for what I can do with mine, purchased last month with AVX mount, once I build my eyepiece collection.

[SthBohemia]

Tricky business comparing CAT's as quality control is the big issue. The secondary mirror should be very slightly aspherical which few are... In general CAT's have optics between 1/2 to 1/4 wave length correction. Not 'knocking' CAT's as a 9.25 Cel and a 10 LX200 are sittin' on the floor, biggest difference being the Meade is a LOT heavier than the Cel, as Meades have a considerably thicker lens and a bit heavier construction than the Celestrons.

Bottom line? A well made F10 Newt will outperform any CAT 🙂