Celestron C9.25 V Explore Scientific AR152




I've had the AR152 up for sale since I got the C9.25 reasoning that The C9.25 should be able to do everything the Refractor can do and with more aperture.

But I never had the chance to put them head to head. The SCT can operate at F/10 with a focal length of 2350 mm - a nice long focal length for planets.

With the reducer lens it can operate at F/6.3 an effective focal length of 1480 mm - getting down to reasonably low power for wide field cruising.

I had over spent the scope budget last year and so decided to liquidate the Refractor - despite it not really having a good chance to prove itself.


Previously the AR152 outgunned my Astro-Tech AT8in - an 8" Imaging Newtonian - on a Jupiter shadow transit.

Although the Astro-Tech has an oversized secondary mirror I still thought the 8" of aperture would over rule the 6" Achromat.

But not so, it was a clear shut out for the refractor. Conditions were a little murky and I could not even detect the shadow with the Newt.

It was clear on the refractor and I switched back and forth twice to make sure conditions hadn't changed.


So, finally tonight - nice warm and dry conditions on a weekend night - when does that ever happen?

I started with the SCT on the CGEM mount. I aligned and looked at the Ring Nebula. The Moon was about 3/4 phase so the sky was a murky light grey.

The Ring didn't look good and I decided not to use it for comparison. I slewed over to M27 and even in the light sky it was easily visible.










I inserted my new Celestron UHC filter in the 2" diagonal and it did improve the image quite noticeably.

I soaked in the view with a 22mm Ultima LX eyepiece (67x). Then I set up the AR152 on the Alt Az - T-Mount.

I eyeballed where the SCT was pointing and just tried to angle the Refractor in the same position. It was mounted very low on the alt az and I had to do some driveway crawling to maneouvre it.


I looked again at M27 through the SCT and memorised the view. Then to the AR152. I moved the whole Eyepiece/Diagonal/Filter combination over to the refractor. I centred M27 and then changed to the Ultima LX 13 mm e.p. (76x) to better match the magnification.

I looked - and Wow! - the refractor put up a view every bit as bright and distinct as the SCT. But that just should not be so - the refractor was giving up 3 1/4

inches of aperture. I looked long and hard and tried to imprint the view.


I moved back to The SCT - switching the optical train over again and then dropping to the 22 mm again.

Nope, the view was not quite as good. It was just less distinct - perhaps less contrasty is the best description.

I took out the UHC filter on The SCT and the view was worse - looking very grey.


Debra arrived home and I asked her to look through both scopes.

She immediately voted for the refractor and said it just looked 'crisper' there.




I started to think of the possible reasons why the SCT was not clouting the Refractor with its greater light grasp and higher resolution.

I figured while using the F/6.3 Reducer, the SCT was using 2 lenses and 3 mirrors before the eyepiece:


the corrector

the primary mirror

the secondary mirror

the reducer lens

the diagonal


Whereas the refractor was using:


the objective lens

the diagonal


Since each time light is reflected or passes through a lens some if it is lost, it seems likely this must be a big factor?

But still - there's no way my C9.25 should be beat on deep sky by a 'big daft achro' as I have sometimes referred to it.


I've cancelled the sale (not kidding) of the achro pending a planetary shoot-out. There's just no way the Achro can win this one.

The C9.25 is legendary on planets and the Achro is going to have a blizzard of CA pouring out the eyepiece.

I'm thinking Jupiter here ....

But I would have dismissed any chance of it winning on deep sky - so who knows?


I tried the OIII filter but the sky was just too blown out by The Moon do find anything else worth comparing.


I did pull in Epsilon Lyra - The Double Double, and neither scope could cleanly split them - the stars appeared dazzling and a little spikey.

A clear tie on this object.










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