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Celestron 150mm

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Date: NA
Price: above $599
Design: 150mm achromatic refractor operating at f/8
Description: Large 150mm achromatic refractor that ships with a 25mm Plossl eyepiece, 2x Barlow lens, 9x50 finder, mirror diagonal, and a CG5 equatorial mount with an aluminum tripod.

The Review

I acquired this telescope as a loaner to test some filters I was developing to reduce the intrusion of chromatic aberration.

Rules are being broken here. A 6 inch refractor should be f/18-f/20 to decrease the chromatic aberration to acceptability and f/8 is too short. Of course  a f/18 6 inch refractor would require an extremely sturdy mount which translates to high price. The mount and tripod proved to be very wobbly. A good portion of the fault goes to the light aluminum legs. Replacing the aluminum tripod with oak removed most of the problem. To make the telescope comfortable you should have the equatorial head that is 6 feet or slightly higher. This makes it an enormous telescope.

Optically, this telescope is good not great. Globular star cluster are viewed in glory. Planets and high definition objects suffer as a result the chromatic aberration.

As an optical engineer I developed a filter that maintains high transmission in most of the visible spectrum and still maintains some natural color rendition by permitting some of the blue through.

In a direct comparison to my 5 inch Intes Micro MakNewt the CR150 took second place except light gathering power. The MN56 has world class optics and is difficult to overcome. The CR150 is a surprisingly good telescope for viewing globular star cluster and in this regard more enjoyable than the MN56. For lunar, planetary, and double stars it is the MN56 all the way. As an aside, the MN56 is on the order of 2 to 3 times more expensive when properly equipped.

With the chromacor from Aries the CR150 could be elevated to a much better performing telescope. In some ways I regard the CR150 as somewhat inferior to its little brother the C102HD.

As a conclusion the CR150 is not a perfect scope, but it has its place. It handles deep sky objects well. If you can't handle blue halos around bright objects then go to something else

Submitted by Al Misiuk - AlMisiuk@email.msn.com - Seattle, Washington


The Review

Being a user of 6" and 9" APO scopes, I had the use of a CR 150 Refractor for a month. Now it is true that these scopes have a lot of bad samples out there. The optics on this scope were more than just good, they were very good. The objective lens was very smooth and the coatings were smooth and even on all surfaces with the biggest surprise of no dust between the lensís. As for the issue of false color,  this scope seemís to be better then most of the oneís Iíve read about in most reviews. For the optics testing on this scope I had removed the observatoryís 6" f/8 APO and mounted the 6"  f/8 CR150 in its place ( being the Director I get to do these things ) to see what kind of remark I would get from the planetary observers. I also made sure that the observers using the 9" APO and the 12" SCT would also get a look through the CR150 so that I could also get their remarks about the scope. My fun with the scope would come later when I would take the scope home and give it a good workout. Onto the testing of the optics.

With no full Moon a good test for false color on the outer edges would have to wait. The next best object would have to be Jupiter and some bright stars. With the reviews that Iíve read itís been said that this scope starts to breakdown somewhere between 300 and 350 power so I knew that the planetary observers would not be too happy. I had each observer write down what they had seen as far as sharpness and contrast went, and their thoughts on the amount of false color. John was the youngest with an eye for contrast so he would be the first to use the scope. He was very surprised at the contrast and sharpness of detail that could be seen at a power range of between 171x to 425x using orthoís and Siebert Optics 7mm and 10mm eyepieces. As for the issue of the amount of false color,  he wrote in his observations that it was not as bad as most of the reviews that he had read on this scope. He had seen more of a faint yellow at low power ( 171x ) and at high power ( 425x ) more of a faint violet color when using the orthoís. When using Siebert Optics eyepieces the amount of color was fainter at low powers and the same at higher powers. Breakdown started at around 450x compared to the 300 to 350x range that most reviews had stated. In focus and out focus images of stars were the same.  First magnitude and brighter star came to a good sharp focus and not fuzzy ones like some reviews had stated. The other three planetary observerís reports were very much the same as what John had stated. Next came deep sky observing with the scope and the two observers using the 12" scope would do the next testing of the scope on nebulas, globular clusters and large star fields. All were amazed at how well this scope worked on M13 with the Siebert 7mm eyepiece working at 171x power, and then using the 8.8mmUWA Meade with a 2x TV POWERMATE with a power of 272. The cluster was fully resolved to the core with dark lanes run through. Next would be the Veil nebula, to see how well this 6" refractor would do on this what some would call hard for a 6" scope to do object. These two guys were amazed at the sharpness and how well it snapped into focus (  UHC and OIII filters were used ). This scope is a very good deep sky scope, with good contrast and very nice optics, is all that the two could say in amazement.

My turn on the scope would come two days later. Using the scope in my backyard with no one around is the why I like to test eyepieces and telescopes. I had set the scope on my G11 mount. I wanted a good stabilized platform to work with, and I must say that with an 80mm Burgess scope sitting on top of the 6",  this setup was no lightweight, being somewhere around 24lb. The first thing that I did was to take off the focuser and place a custom made 2" B&D focuser ( available through burgessoptical.com ) on the scope. The stock focuser on this scope was very smooth, but Iím spoiled on using nothing but the best focusers and they get no better than a B&D focuser. Jupiter was going to be my first object, and I wanted to compere my views to Johns to see how close my observation would be to his. I must say that I was very amazed at the contrast and sharpness that I could see. At 240x six belts and some festoons could be seen. At 350x more belts and zones with greater festooning could be observed with ease. As for false color I was amazed to see that it was not bad at all and must say that the view was the same as what John had seen. On the limb of the full Moon, there is more of a yellow than violet color. Even though there was color to be seen, it was not taking away from the sharpness or contrast in the view.

Either this scope has great optics compered to others that have gotten bad reviews, or the reviewers are one sided to comparing this scope to APOís ( which is not the thing to do ), or there are a lot of bad CR150's out there. If you buy from a dealer that you know has a good return policy if you get a bad one, then these scopes are worth looking into. The one that Iíve tested is a very good sample that I was able to do some serious observing with. Yes there is false color, but if your use to seeing no color at all, then the smallest amount of color can turn some totally off and give bad review ratingís to this scope. Iíve seen two other CR150's and they both had very good optics. The scope in this review I ended up buying and will use it a lot, and Iím an APO  user. As for the amount of useable power, 425x is great for a classical refractor working at f/8.

Review by Don Regan Director of the Deep Sky Observatory located in upstate New York. Using 6" f/8 custom made Refractors for Planetary observing, and a 12"SCT for super novae research.

Submitted by Don Regan - deepsky@scsinter.net - New York

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