Celestron Omni XLT 150R Refractor
Posted 20 March 2009 - 07:41 PM
Is this the same optical tube as the Sky-Watcher 150mm?
Thanks for any insight.
Posted 20 March 2009 - 09:04 PM
Here are links to both the new Cel Omni XLT 150 R and SW 150. The SW 150 is based on the same F8 design as the F8 Cel C6R that has thousands of loyal fans, while the new Cel Omni XLT is a F5 design. In answer to your question "are they the same", it would appear that no, they are not the same.
I think you might expect the F5 150mm Omni XLT achro to have slightly more color than the ST120 you currently use even though it is also a F5 design. If that is not of concern, the Omni XLT 150 might be a nice scope for you. Hope this helps, and good luck!
Posted 21 March 2009 - 10:41 PM
The 150mm f/5 achro will likely show more chromatic aberration (CA), than the 120 f/5 achro because it is less corrected than the 120mm. (rule of thumb: a 120mm-4.724 inch-achro should have f/14.2 to provide minimal CA control, whereas a 150mm-5.9"-should have f/17.7)
However the larger aperture will also provide much better resolution, and 56% more light gathering power. If you do not look at brighter objects the 6" f/5 should provide superior views because of greater aperture.
Posted 22 March 2009 - 01:44 AM
Let us know how it does. I'm really curious about this one. With the shorter focal length and light weight it looks like it could be a nice addition to the 6" achromats. But the question is how much color. I noticed that the Celestron info states the color has been reduced (not an exact quote), so it will be interesting to see what you experience with it.
John in Oregon
Posted 31 March 2009 - 02:58 PM
I have now had 2 nights of observing with the OTA from a Celestron Omni XLT 6â€ f/5 Achromatic refractor, and give my impressions. (I only do impressions, not reviews My general reaction is that I am quite pleased with the scope.
First off, I Ieft the CG-4 GEM mount that comes with it with the dealer to sell, so I have no actual experience with that mount, but believe it to be inadequate.
My 1st night of observing was at a good dark sky site, with the scope mounted on a Orion SkyView Pro GEM, which handled the scope well. My 2nd night was in my light polluted back yard, 10 miles from a major city. The scope was mounted that time on a WO E-Z touch mount on a Oberwerk wooden tripod.
At the dark sky site, I was blown away by the dark skies, and spent the evening gawking unanalytically at familiar objects. The only scope related observations I made was that when I looked at Sirius at 21x, CA (chromatic aberration) was not noted, but then I wasnâ€™t looking for it either. Seeing was very unsteady, with neither my 6â€ achro nor the 12â€ dob next to me being able to resolve any detail on Saturn except the rings. SkyClock had seeing at that site as poor and transparency as below average, but the darkness of the sky trumped everything!
My second session at home was a done a bit more scientifically. I set up a Orion 6â€ f/5 Newt ( a StarBlast 6 on a Vixen Portamount) next to the achromat and observed the same objects using the same eyepiece in both. On the Pleiades, the refractor was noticeably better, with stars smaller and more symmetrical. The stars were not â€œpinpointsâ€ but nonetheless far more pleasing than in the newt. Brightness was the same. The refractor image looked a little sharper, doubtless due the newtâ€™s secondary.
I then focused on Sirius at 140x, and at that power CA was wicked! Flashes of fluorescent purple assailed my eyes and occasional shots of orange and red. I put on the aperture stop for the scope-which narrows the aperture to about 4.4â€- and that took away about half of it. I took the stop off, returned to full aperture and added the 2â€ Orion V-block filter and that removed most of the CA, but at 140x it was clearly still there. I should have done a comparative study at different powers, but did not.
As haze began to form I switched to the moon and Saturn-obviously not what this achromat is designed for!. I was amazed at how good the lunar views were through this scope. (Lunar observing has been my primary interest for many years) Detail was perhaps a tad sharper than in the 6â€ f/5 newt. (Incidentally the StarBlast 6 newt is a good performer and I have previously clearly seen portions of the Triesnecker rilles at 187x in the newt) The view through the achromat was good enough for me to spend some time sketching. I used about 140x for my sketch. I upped the power to 187x and still had a reasonably sharp view. I was very pleased to see how well the short tube achro did on the moon as I was not expecting much from it at that kind of thing at all.
While on the moon, CA was evident on the limb and then extending a bit into lighted areas next to the limb (Moon was 3.5 days old). Near the terminator I did not see that it was a problem. Nonetheless I tried the aperture stop (4.4â€) and half of the color on the limb disappeared. With the V-block filter color was hard to see. As has been my experience with the Orion 120mm f/8 achromat, CA seems a non issue to my eyes when you are near the terminator. I could not detect any increase in observable detail when using the filter, even though shadows were a little blacker.
I finally turned the achromat to Saturn and was again amazed at how good the view was. The rings were of course clear, and this time, with steadier skies, the dark line where the rings cross the planet was evident. A belt was seen in the Northern hemisphere. In the southern hemisphere immediately below the rings, a band of white was clearly observed, ending sharply at a darkened region that extended, it seemed, down to the southern pole.
Castor was easily and cleanly split at 94x
I did no star testing, and, in fact donâ€™t think I have ever been able to do that effectively with any scope. I did just get the disk pattern which seemed to be centered, but it was hard to be precise. I was pleased however to have the moon and Saturn to test this scope out on as I am more familiar with what can be seen on them.
A â€œcollimatingâ€ eyepiece comes with the scope, even though the scope does not have a collimatible lens. It did give a circular image. I also tried the old trick of putting a laser collimator into the draw tube and making sure the beam hit the lens near its center. If this scope were to be poorly collimated your only option would be to return it.
With a 2â€ diagonal put in as a replacement for the 1.25â€ diagonal it came with, I appeared to be getting about a 3.4 degree field of view with a 2â€ 36mm Baader Hyperion Aspheric eyepiece (claimed AFOV 72 degrees)I also noted the focuser had only about a 2.5" range, but I had no difficulty focusing any eyepiece, and none of my ep's (I tried out several 2" widefields with varying results) even came close to the maximum infocus or outfocus.
This scope is much better than I anticipated it would be on lunar and planetary, although I did not get it for that purpose. Its ability to give good lunar images augurs well for its ability to give good deep sky views in the cases when definition and contrast are important (e.g. M42) It appears it does very well what I wanted it for, which is wide field low power sweeps of the starry hosts, as a break from lunar observing.
Posted 31 March 2009 - 03:06 PM
Posted 31 March 2009 - 03:31 PM
However, I should note that while its operation during viewing was quite acceptable to me in terms of being able to move it up and down and focus it without shaking or other difficulty, the tripod with just the scope on it was just a bit too "tippy" for my comfort. The center of gravity is off to the side so the heavier the scope the more problem this is. I therefore put a 7 pound counterweight rig on the other side to balance the 16 pound OTA with its 2" diagonal rings and finder, and that restored my comfort level. Without some counterweight on the other side I fear bumping into it from the wrong side might knock it over.
I had a older never used counterweight
rig that I screwed into a spare dovetail bar and inserted it into the dovetail the scope came with-(I had to put the scope on a dovetail bar that I had added on the other side)
Posted 31 March 2009 - 03:34 PM
Posted 31 March 2009 - 04:55 PM
The CG-4 mount is a really fine mount, but I agree that it is not enough for this OTA.
Posted 31 March 2009 - 07:13 PM
Posted 01 April 2009 - 01:26 AM
Posted 01 April 2009 - 08:03 AM
Posted 01 April 2009 - 08:30 AM
Posted 05 April 2009 - 03:06 PM
I got this scope to replace my Orion 120mm ST. I plan to use it on a Giro III alt-az head mounted on a CG5 tripod fitted with an Orion Skyview mount extension. I have it duel-mounted with a Garrett Optical Signature 22x85 binocular as a platform for wide-field use. I replaced the original focuser on the 150mm with a 96mm GSO dual-speed Crayford focuser along with a 2" diagonal.
Due to weather so far I have only had one night of viewing, split into two sessions both after sunset and before sunrise. Both were from my urban backyard, about mag 4.5 limit with average seeing.
I compared the new 150mm with the 120ST, duel-mounted on the Giro III. Both scopes had a 2" diagonal. Eyepieces used were a Celestron Axiom LX 19mm (34x and 31.5x) and an Ethos 13mm (58x and 46x). I didn't use any higher power eyepieces this night.
The 150mm is the largest refractor I have ever looked through, and the short version is it was wonderful. Compared to the 120mm ST the increase in image brightness was striking. An increased image size and depth of magnitude reach with the 150mm were both notable and made for a more pleasing image.
Quick highlights starting with Canus Major revealed considerable CA on Sirus with both scopes, worse with the 150mm. CA was notable in the 150mm down to about mag 3 stars, but for me not really that objectionable. Stars were pinpont in the 150 below about mag 3. The wonderful color contrast of h3945 was equally fine in both scopes. Open clusters with the 150mm were fantastic. M41 and the Tau Canis Majoris Cluster NGC2362 were much better in the 150mm than the 120mm, larger, brighter, and with more stars. M46 and M47 in Puppis were visable in the same field of view with the Ethos in the 150mm, with the planetary NGC2438 just noted with averted vision. I couldn't see this with the 120mm.
For me touring Orion with the 150mm paid for the scope. M42 was just about as bright in the 150mm as with my Celestron C8 if memory serves. The trapezium showed four stars with the 120mm and five, A-E, but not F, in the 150mm using the Ethos. From a dark site with more power, I'm sure F would be no problem. The three belt stars were visable in the same field with the 19mm eyepice using the 150mm. But the deeper reach of the 150mm compared to the 120mm just added extra sparkle to a slow cruise of the constellation.
The entire Christmas Tree Cluster NGC2264 was framed nicely in the 150mm with the Ethos.
M35 in Gemini was magnificant in the 150mm and Ethos. This scope really shines with open clusters.
Viewing before sunrise showed M6 and M7 as real treats in the 150mm, again much brighter and more pleasing than with the 120mm. The globulars M13 and M22 were resolved much better with the 150mm than the 120mm with the Ethos, enough to make a quite satisfying view. M11 was a myrid of tiny sparks with the 150mm, simply better than what the 120mm could show.
For me the 150mm scope appears to really fit the bill as a compliment to a good pair of binoculars for wide-field and open cluster viewing. The scope weighs exactly 16 lb on my scales with rings and diagonal. The Giro III and CG5 tripod are rock steady with my set up. Can't wait for summer and a good dark sky.
Posted 05 April 2009 - 03:46 PM
Posted 05 April 2009 - 05:28 PM
I note in passing that the Celestron Omni XLT 6" f/5 appears to be about the only "traditional" 6" f/5 achromat available in the U.S. market. They have been offered abroad for some time.
Astrozap sells a 6" f/5, but this is a Petzval design, and they have listed it as being "sold out" for some time. It was also rather heavy and was listed at about 23 pounds, as compared to 16 pounds for the Celestron model. The other 6" "short tubes" I have seen advertised are really "shorter tubes" like either the Kunming type (f5.9) or the Antares and its look-a-likes at f/6.5. (Explore Scientific has announced plans for a 6" f6.5 ahcromat) Longer focal ratios than f/5 would aid in curtailing CA, but detract from the ability of the scope to give wide field views, which I believe to be its greatest asset!