First things first.... Specs on this package from Orion:

• APO refractor, fully multi-coated doublet in which one element is ED glass
• 100mm aperture, 900mm focal length (F/9)
• Mount: Sky View Pro GEM
• Tripod: Steel
• Eyepieces: 25mm & 10mm Sirius plossl
• Focuser: 2" Crayford
• Diagonal: 2" 90 degree Mirror Star
• Finderscope: 6x30 straight through
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I purchased this telescope early in March of 2005, so that gives you an idea on how long I've been using it.... a few days short of a year as of this writing.  I also have an Orion XT8 Sky Quest dob that I have been using for 4 years now. You will see me compare the two in parts of this article.

Let's start with the Sky View Pro mount. I want to start out by saying that when I first received this telescope I had problems with the mount. It was tight and hard to move in Right Ascension. I called Orion's tech support and asked for instructions on how to adjust the tension. They talked to me for a minute or two, then didn't offer any help in what to adjust... they just decided to overnight me a new mount and a return label (pre-paid) to send back the other mount. (And it really did arrive the next day.) It's not that the mount couldn't be adjusted.... it's just that they felt there must be something wrong and wanted me to have a nice working mount without any problems. It surprised me that they didn't want the defected mount back first to try to fix, then send out a new one if they couldn't fix it. That's what I call excellent Customer Service! I should add here that if you do need to make any adjustments on this mount after owning it for some time, there is an excellent web site to help you along. The web site is called Andy's Shot Glass. There is a lot of other great information at Andy's site, much of it in the form of movies, so you get a good visual idea on how to follow Andy's instructions.

First of all this mount is plenty rigid for a 4" refracting telescope. While looking through the telescope I gave the mount a few hard smacks with the palm of my hand. The telescope steadied itself in about 2 seconds. Nice! The legs are heavy tube steel, not aluminum. The EQ mount seems solid and well made. All the parts move nice and smooth on the new one Orion sent out. When you want to slew in any direction the whole mount just seems to smoothly float to where you want it to go. Lock it back down, and it's ready for the drive motors to start tracking again. The drives are optional, but I recommend that you get these. The dual axis drives are around $90. Why have a nice GEM mount and not be able to track an object? I am not sure why, but Orion does not include a polar alignment scope with this mount. You can purchase one for about $50 from Orion, and I recommend that you do. The only thing I don't like (and this would be true for any type or brand of EQ mount) is that when looking at different objects, the telescope can end up in some pretty weird positions. I'm going to have to get used to being somewhat of a contortionist. Once this mount is set up and polar aligned, and the drive motors engaged, it tracks very well. I followed Jupiter for 15 minutes before it even started to drift from the center of the field of view. I have attached my camera to the eyepiece and taken a series of 15-second photos (that's the time limit on my current camera). I stacked a total of 20 minutes of exposures and hardly had to do any adjustments to get them to line up. I'm impressed with the way this mount tracks.

The Optical Tube Assembly (OTA) comes with a 6x30 straight through finderscope. I felt that I needed to change this to a right angle type more so than I did with my XT8 telescope (which I have owned for 4 years now). The reason is that with the EQ mount getting into some weird positions, a right angle finder would be much easier to look through. The focuser is a Crayford type, which is very smooth. I really like this one. The drawback to this focuser is that with a heavy eyepiece or a camera mounted to the eyepiece, the extra weight could make the focuser slip out of focus from the weight. There is a set screw you can use to tighten it down if it becomes a problem, then you have to loosen the set screw again when you want to move the focuser, but for the most part it really doesn't move to easily out of place.

This is an APO (apochromatic) refractor telescope. The optics in an APO are much better than an achromatic refractor. The light in an APO focuses the incoming light more at the same point. This is unlike an achromat's wider light spread, which results in more false color (chromatic aberration, or CA). Think of light going through a prism..... the tighter the light beam forms together, the whiter the light is. Spread the light out and you see more colors. The optics in this scope is a doublet type, both with fully multi-coated glass, and one element is ED (Extra-low Dispersion) glass. When the focus is slightly off you can sometimes see a slight bit of CA on very bright objects, but it disappears as soon as the telescope snaps into perfect focus.

When it comes down to observing this telescope is a real planet killer! While the planets (and the moon) are not as bright as they are in my XT8, they are much sharper. I can pick out more detail in this telescope when it is side by side with the XT8. Don't get me wrong.... the XT8 picks out a lot of detail... it's just that the apo optics are sharper when it comes to very fine detail. The moon, in a 40mm eyepiece (22x in the 100ED, 30x in the XT8)) looks almost 3-D in appearance, which is just my mind playing tricks on me because of the extra sharpness in the view. I see detail in craters and other lunar features that is crisper in the 100ED than it is in the XT8 at both low and high powers. Jupiter's bands are much more distinct in the 100ED, as is the Great Red Spot. With a 7mm Nagler eyepiece (128x in the 100ED, 171x in the XT8)) under excellent viewing conditions I can see some of the festoons in Jupiter's bands. In Saturn's rings the Cassini Division stands out better, Saturn itself shows more color variation than I see in my XT8. Again, with a 7mm Nagler eyepiece, and again under excellent viewing conditions, I can see more of an olive green color by Saturn's pole than I can with the same eyepiece in the XT8. The features on Mars show up a bit better too. However, when it comes to observing deep space objects (DSO's) the XT8 wins in almost any category. The larger aperture of the XT8 collects so much more light, which you desperately need for this type of observing. The only types of DSO that looks better in the 100ED refractor are open clusters. I don't know exactly what it is, but with open clusters the stars look more like jewels in a box. The contrast is so much better that even though I can't see as many stars in an open cluster because of the smaller aperture, the ones I do see just stand out sharper on a darker background. Besides.... I just love open clusters!

My XT8 will still get used a lot, but this telescope will be used often too. Would I recommend the Orion SVP 100ED telescope to a friend? In a heartbeat!