兩位大APO折射鏡用家的對話 - 免疫力低下者勿讀!

[社長]

去年APM的負責人Markus Ludes告訴我他有一位美國的用戶可以把一台APM-TMB 304 f7.5 APO折射鏡名額可以讓出來，而剛巧我在內地有一位用戶正在物色這個級數的APO折射鏡，最後這台由Thomas Back生前設計，但從未投產的特大口徑APO折射鏡，最終落戶中國 - 列序號001，亦是全國最大口徑的APO折射鏡，跟之前APM生產的304 f12APO主要分別是，這台f7.5的折射鏡採用了兩片Super ED玻璃，以取得最高的修正度。

由於LZOS造工要求極高，一片OK4 Super ED玻璃要約一年時間鑄造、回火、檢定、打磨拋光測試及組裝，再加上期間發生意外要重頭再來，鏡組預計2011年3月完成。

這個世界上大口徑APO折射鏡用戶不多，所以很多天文圈內對於APO折射鏡、反射鏡、折反射鏡的意見其實不是十分完整，甚至有不少以訛傳訛的成份。至少，甚少人用過150以上口徑的頂級APO折射鏡做過長期觀測，尚未到大氣視寧度極限下測試APO折射鏡的終極性能。

我其實跟那位美國用戶是認識的，也在08年美國Lunt Solar Party碰過面，所以不時交換心得，至少我擁有一台APM-TMB 203 f7 APO折射鏡，算是大口徑APO折射鏡的入門級別吧。

以下有兩段很值得細味的對話，免疫力低下者勿讀：

我的問題一：你如何看APO折射鏡及反射鏡的分別? 能以較大口徑的反射鏡取代APO嗎?

他的回應：Your question is not an easy one to answer. There is no question that it is easier and cheaper to have larger aperture with reflecting telescopes, or some adaptation or design using mirrors. And certainly, for imaging, there are telescope systems being designed to provide cheap but very efficient imaging results. But, your question focuses on the visual experience of a telescope. I think that aperture does play some role in visual also..... as far as being able to see detail. But.... for me, a large refractor 8" and larger provides a more exciting visual experience. I have seen it time and time again at Starizona (local astronomy store where they have public viewing Monday, Wednesday, Friday and Saturday) when I had my 10" APM/TMB APO out for the public. The professional astronomers couldn't stop playing with the scope. They were so excited, and remarked quite often they had not seen the detail and resolution on the objects we were viewing. The level of excitement and interest was obvious. They work with big reflectors every day of the week. It was the big refractor that generated excitement. Visual experience is a combination of a number of things. I believe that the feeling one is peering directly into deep space rather than looking through a mirror is one aspect of the experience. I think that looking through a refractor, or spyglass, generates that feeling more than a reflector. Sometimes a reflector feels more like a picture to me.... hard to describe.... There is more excitement generated from looking through a large refractor. You can see it in the kids and professional's eyes. I watched David Levy just fascinated for hours looking through my scope. Of course, I have never had the chance to look through the 10" in really dark skies yet, and would be quite excited to see it's potential. What I can say, is that I had the chance to view Mars through a 7" Astro-physics scope and the 10" TMB APO during some of Mar's oppositions, and it was a mesmerizing experience, one I will always remember. The 10" when seeing was good, was remarkable.... , and the image scale so large and detailed. With binoviewers, the planets do take on a 3D effect, especially the roundness of the planet. I'm sure you have experienced that with your 8" TMB. The contrast always seems better in a well made APO.... somewhat like a TV, one with a washed out picture vs one with good contrast. The washed out picture might have as much detail, maybe even more, but it is not as enjoyable to view..... Certainly, large reflectors will always be available, and they can always be installed. The era of the large APO is a rare and beautiful happening. Markus has made large APO's a reality. Large APO's will always be rarer, and generate more excitement. They can be moved from site to site, and will always generate excitement, to the young and old. The wow factor. I think someday, LZOS may choose not to produce such large refractor lenses, and the ones they have made will be so so rare.... Other than APM, only TEC is still making 7" scopes (for a reasonable price), but 8" seems to be their limit. I think what Markus has accomplished with the big refractors is amazing.... I am biased, because I really like APO's. And for imaging in dark sites, they should be able to provide astounding images, so clear with great contrast.... Maybe not as deep as the larger reflecting scopes, but certainly able to reach so many of the beautiful targets.... A good APO has collector value, resale value, less maintenance, do not need to be recoated, and also provide great utility both visually and now with CCD imaging. They provide the cleanest, most pleasurable viewing experiences, and certainly generate the most excitement with the young and old. I think that says a lot... Of course, both would be even better, but I feel like the big APO is the rarer, more memorable experience... with the advantages I have described... Now if we are talking really large mirrored scopes, they take on their own aura also.... for me, though, it is the refractor that I would choose first...

You also ask about air spaced vs oil spaced, which is better for a changing temperature environment.... I cannot comment on the extreme environments you are dealing with. No one is making new 8" oil-spaced refractors right now. And everything above 8" has been air spaced.... For me, seeing has been the major consideration affecting my APO observing. When the seeing is good, all my APO's have performed well over the changing night temperature, including the 10" TMB. Perhaps, though, I might have better opinions if I were at a darker sight, with better seeing, and bigger temperature changes.... I guess I'm not set up to make such opinions. I can say that the 10" TMB seems to handle temperature changes very well in times of good seeing... I've never noticed the change of temperature to be a limiting factor.... only seeing and transparency.... But I do not experience the extreme cold here. I also do not know what effect the extreme cold would have on the oil in oil spaced scopes..... Those are questions for an expert....

我的問題二：Markus Ludes說他從自己的304 f12 APO折射鏡中看到最難忘一幕是火星山呈立體感的奧林匹斯山，你的經驗如何?

他的回應：It is hard to single out one experience. I love viewing the planets. I love seeing the colors of the stars in globular clusters against pitch black background. The level of detail on the moon is astounding. I like viewing Jupiter and the movement of the moons around the edge and in front of the planet. I really enjoy the 3D effect of bino-viewing, and the level of detail and image scale on the planets. Mars at opposition was amazing, but had I been at a darker site, I would probably have even more to say.... My scopes have not been tested to their potential.... not even close. Clearly, the 10" has outperformed my AP 206 EDF and my TEC 200 FL.... but it is a big scope to handle. Your 8" TMB F/7 is the "fastest" 8" inch refractor in the world. I don't know of another manufacturer of an 8" F/7 scope. It must be a pleasure having such a compact, fast and well performing 8" APO, especially with the retractable dew shield making it so portable. And what imaging potential also! That kind of scope simply hasn't existed in the past.... and will continue to be a very rare scope. I believe we are witnessing a small open window in which such incredible APO's are being made, especially the larger ones. I think these are special times....

[Nebulas]

很多关于-fra- vs -fle-，看俩高端玩家也不是直接针对性回答。