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Celestron C102HD

Well, I sold all of my scopes, and eyepieces in order to save money for a TEC Mak. The weather promptly cleared, and I am without a scope. I decided I needed a scope to keep me busy until I can afford the TEC. I have owned several scopes of different designs so the decision should have been easy, but it wasn't. After much agonizing I decided on the Celestron C102HD. The consensus seems to be that the optics are good for the price. I have decided that sharp images with refractors are for me. I relayed the news to the Mrs., and was advised Santa would be sure to deliver. I insisted that Santa include an upgraded diagonal, since Astronomics website states the scope comes with a prism type diagonal.

The scope arrived three days before Christmas, and it was clear. After much debate I insisted that the scope would be used, even if it required that I sleep outside that night with the scope. I promptly unpacked the box, everything comes in one box. The assembly went smoothly, and took about twenty minutes. The scope comes with a 6 x 30 finder, 20mm Plossel eyepiece, and a 90 degree Mirror Diagonal. I can only conclude that there are so many variations of this scope that the vendors are not sure what is packed in the box. Some version come with a 1.25" focuser, I wanted the 2" model, and got it. I have also seen the scope listed with two eyepieces, 25mm, and 10mm. I suggest that you ask questions about how the scope it equipped before you buy. I sat the mount in the garage, installed the rings, and mounted the tube. This is where I ran into the first problem.

The focuser needs immediate attention! The combination of the long tube, and marginal mount makes a bad focuser a exercise in frustration. The focuser requires a lot of effort to turn, and that causes the mount to vibrate wildly. I took the unit apart and discovered the problems were easy fixes. The first was the tensioning spring was not installed properly. The second problem I don't understand. When the scope is assembled the factory uses "grease" that has the consistency of dried playdo, and is sticky like glue. I had to use mineral spirts to get the stuff off of the focuser, and my hands. After the five minute repair job the focuser is acceptable for a scope in this price range. The scope has plenty of back focus, I haven't measured it, but I would say 5" or so. Don't count on it being very useable however, the draw tube has a lot of play with the focuser racked all the way out. Fortunately most eyepieces I have used focus with the draw tube rack in.

Now with the scope outside I worked on aligning the finder. A pleasant surprise for me is I really like the three-point bracket with the spring loaded pin. It makes aligning the finder easier than the six point brackets I am accustomed to. It may not be as sturdy, but so far it has held the alignment perfectly. The finder quality is certainly acceptable for a telescope in this price range.

First Light: I was looking forward to Jupiter, my favorite object, but it was still behind the trees. I settled on Saturn, then realized I only have a 20mm eyepiece, and no barlow. I run inside and place a wanted ad on Astromart. In five minutes I have purchased a barlow. Back outside, The view of Saturn is pretty good, but at 50x I can't make an optical quality statement. I did have one of the best views of M42 I have ever had, the contrast was amazing. I must admit that the first night with the scope was spent under the most transparent sky I have seen. After being inside for twenty minutes at the computer screen, the milky way was clearly visible, and bright upon stepping outside. I later learned from club members that the horsehead was amazing through an 18" Obsession at the dark sight, the best they have seen. I ended the first night with a good feeling about the scope, but reserving judgment until I can view the planets with more suitable magnification.

A week or so has passed since first light, I now have more eyepieces, and a barlow. Seeing has not been that good, but I have notice the sharpness and contrast are not at acceptable levels. I expected with this scope being a 102mm f10 scope, the images should be at least as good as the 80mm Megrez I owned, but they were not. I set out to isolate the problem(s).

I decided to take the scope apart, and see if there were any obvious problems, but there were none I could see. After a couple of days scratching my head I found the following problems; the tube has three baffles, the rear baffle was cutting into the light path. This should decrease color, and increase contrast, but I decided to locate the baffle in it's proper location. I also determined the focuser was not collimated with the tube. I decided to order an Orion Cheshire to collimate the focuser.. I wanted to test out the baffle relocation on Jupiter, and to my amazement the focuser now appears to be perfectly collimated. Evidently when I reinstalled the focuser I got lucky and accidentally aligned it.

After all is said and done the scope performs very well considering it's price. There is enough color to reduce low level details, but the images are sharp and contrasty. The planetary images rival a 6"f8 eq Starfinder I once owned, the newt was a little better in resolvable detail, the refractor is better at sharpness, and contrast. The scope does not compare well with the images I got with the 7" LX200, but that scope has it's own set of problems, mainly cool down time. It is probably not fair to compare those two however, considering the enormous price difference. In relation to the 80mm Megrez, the scopes are close surprisingly. The background was much darker in the Megrez, along with better contrast. The C102 makes up for that with the extra inch of light gathering power. This scope is much sharper than a 4.5" reflector that I once owned, especially on planetary detail.

I would recommend the C102 to a beginner, or someone looking for a second scope. There are some problems that need to be addressed however. It helps to be a tinkerer to get this scope to perform like it should, unless I got a bad sample. Be prepared to focus the image with the scope dancing around. Most people comment that the aluminum legs are the culprits for most of the mount problems, but with mine the culprit appears to be the backlash in the worm gears. There is a provision for adjusting the mesh, but so far I haven't been able to reduce the backlash to acceptable levels. I would also recommend that the flexible slow motion cables be replaced with rigid knobs. The flexible cables induces a vibration after adjustment that doesn't settle down until the cable quits bouncing around. It would be a good idea to check the baffles with exit pupil diameters to determine if they are cutting into the light path. The clear aperture on my scope was reduced to 95mm. Flocking paper may help to increase contrast, as the tube appears to reflect a lot of light. Another worthwhile investment would be the cheshire cross hair eyepiece to collimate the object, and focuser.

I hope I haven't been too critical on this scope. For the price it is an excellent deal. The images are good after any bugs are worked out, and it is light enough to be used often. I leave it next to my garage door, and is ready to use in two minutes or so. In the price range of less than $500.00 the choices are somewhat limited, and I would place this scope high on the list. I would certainly recommend this over the lower cost computerized scopes. The competition comes from 6" to 8" dobs which may be a better choice for some.

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