我用Orion的XT１０i 快半年了， 比较满意， 之前我一直是玩折射镜的。 现在加上一个跟踪平台， 更是如虎添翼， 在３００倍的情况下也不用每３０秒去动一下望远镜了。
下面是我刚刚拿到XT１０i时候在CN上发的评测。 当时肯定是有点兴奋了， 后来的使用中， 也有了新的感触， 不过总的来说还是物超所值的。
Being a refractor guy, I'd say I was really impressed with what I saw last night.
I asked some questions about what is the best complementary scope for my 5" refractor on the forums some time ago. I went to star parties to observe and gathered suggestion from the experienced, too. I finally joined with an Orion XT10 intelliscope due to the very convenience of a dropby at the local orion store in Cupertino, CA, where I can check the scope before I buy.
Collimation is no problem as I have laser collimator for rough collimation and Catseye tool set for fine collimation. The collimation was pretty close to perfection according to the auto-collimator before I moved the scope outside the room. At 10:00 pm, I set up the scope in a badly light-polluted patio. Even without a telrad, the stock RACI finder did a decent job to find the object, thanks to some skills I learned from the star parties. Sirius was the first victim , and unsurprisingly I saw so called annoying spikes. But I thought the opposite and found the spikes were actually aesthetically "good-looking" since I've learned to live with that after viewing so many terrific astrophotos taken by scopes with spikes, such as HST. Sirius looked kinda loose compared to the embedded memory I have from viewing it through my Tak FS128. M42 got the second view as it would soon disappear behind a tall building. I was not surprised to see a well resolved nebula, as I did a couple of times on the star parties with the same type of scope. A quick check on Trapezium with nagler 9mm T6 at 133x revealed that the seeing was not bad even if the mirror was still warm, because I could catch a glimpse of the F star, while E star was a piece of cake.
The unexpectedly view of Trapezium F star had me thinking of viewing Saturn regardless of the still hot mirror. I quickly centered Saturn in the nagler zoom 3-6mm EP and recalled what some experienced observers said about the mechanics of this type of Dobs. To foucs at above 200X and keep centering the object was really a challenge for me, since I've been spoiled by the tracking capability of the GEM mounts in the past 2 years. As a side note, the new Crayford style focuser which is similar to what is found on the Orion ED series refrector is really nice, although I was a bit spoiled by the moonlite focuser and FT focuser I've used before. After fiddling with the focuser at high mags, I quickly found that the "best view region" in the EP was rather narror where Saturn looked really sharp as long as the air became steady. I recalled that many reflector users mentioned that for such a fast newt scope (f/4.7), the "diffraction limited region" is rather small. I suspect what I saw echoed with what I read on the forums. As the mirror cooled down (with a fan blowing air) after about 45 minutes, I caught some really sharp views of Saturn at 300X in the center 20 degree region through the nagler zoom 3-6mm. Cassini division, C ring and the belts on the surfact, even the shadow of the ring were really sharp. I knew what I would expect from a 5" refractor under most common seeing conditions, however, I was really impressed by the view from a 10" newt which I bought for viewing DSOs. I spent almost one hour viewing Saturn, learning to nudge the Dob at the high mag. I remember in a recent thread on the forum, people have been discussing if a fast newt can deliver decent planetary view. Now I totally believe what those mirror gurus say about that.
To confirm the thought on "best view region", I targeted Procyon that was fairly high in the sky. At 300X through the nagler zoom EP set at 4mm, I found the diffracted star image looked really good within the central 30% of the field of view, which corresponds about 15 degrees. The intra-focus and extra-focus images looked almost the same, without signs of turned edge or apparent zones. When the star image lied in the center of the FOV, the concentric rings were really nice, thanks to the very good collimation and the steady air. As the image drifted towards the edge of the FOV, I could see squeezed rings at one side, which indicates the coma became really bad. Note that I am no optical expert and the test was also brief. I think I'll do a more thorough test tonight when an excellent seeing is highly possible. Since undercorrection is a common problem in this type of Dobs, I'll mainly focus on checking SA.
As time passed midnight, I got no time for a thorough test of the "push-to" function. I then packed up and went back to the room, sitting there and enjoying the wonderful views of Saturn in my head.
I was very happy with the XT10i's debut last night, and I found that
1). The optics are really good
2). Excellent seeing and accurate collimation are the major factors that determine the sharp views of Saturn
3). XT10i is really fast, even my plossl-like nagler zoom EP performs poorly at the edge
4). A fast newt can deliver decent planetary view as long as 1)~3) are satisfied
5). Most importantly, "Aperture Rules!!". I've been viewing Saturn using 5 different scopes, including a 5" apo, a 5" achro, a 6" mark-newt, 8" newt and XT10i. XT10i is the winner, or I should say it has the most potential to deliver the best view given the right conditions.
6). I become a mirror lover
I'm a little concerned on the "diffraction limited region" as I mentioned above. Can anyone guide me to a thread or some link which tells how to calculate the size the of region (actually size and FOV in a EP) for a newt of any f ratio? I have read some and just cannot find them since the searching fucntion is under recovery. Or maybe a simple answer for "Is what I found normal?" is better.
Thanks! |
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