回到最初的感動：連續三個晴夜的高橋 FC-76 小折射鏡觀星 Stargazing with Takahashi FC-76 refractor on three consecutive starry nights

07/21~07/24

這三個晴朗的晚上利用上半夜沒有月亮干擾的好天氣看星星，以3"螢石鏡搭配好目鏡在鞍部觀看一些大又明亮的深空天體，ㄧ邊享受山上的涼爽，在酷熱的夏夜也是種享受呢。

前陣子我從日雅拍買了支二手高橋FC 76。一來是想重溫、僅記當初以自己負擔不起的小望遠看到在宇宙深處的星雲的感動（詳述在後），再則因為過去幾年在鞍部完成的282個深空天體眼視素描使用的多是4‘’折射，6‘’牛頓，8‘’DK反射以及小雙筒，用Pentax 75來眼視非常少，所以我便想在鞍部使用FC-76 來針對較亮的深空天體來眼視觀賞，看看3"折射於此處適合觀賞些什麼，也可加入紀錄資料庫中提供有興趣的星友参考。

Weeks ago I bought a used Takahashi FC -76 (early version) from yahoo auction Japan. mainly because I want to relive the wonderful feeling of watching the nebula under the  night sky with a small (but nice) telescope, the Takahashi FC-76,  that I could not afford before, and also because the  282 DSO's sketches which I’ve finished here were mostly made by 4'' refractor, 6'' Newtonian and 8'' DK reflector.  so I want to take a look at the deep sky via FC-76 to see what objects are suitable for 3” here(Anbu, bortle 5 sky), and I will add the observations to the database to provide references for interested friends.

7/21

今晚先看了一下 C/2017 K2 彗星，正走在蛇夫座，很暗，在+9.6等的SAO 141339附近，雖比其暗，不過彗星彗髮受透明度與光害的影響很大，在六十倍下除假核與其周圍，未能見到的範圍更大，因此估計彗星在+9~10等間。

M57環狀星雲（Ring）是我從前開始觀賞深空天體的第一個深空天體（除M42, M31, M45這幾個特別明亮的芭樂目標以外），所以特別有感覺，無需濾鏡使用FC-76即相當明顯，雖然M57已經算是比較大的行星狀星雲了但也不過約4x4'大小，必須拉高倍率來看，以120x 觀賞仍是相當袖珍，但因夠亮所以出瞳徑雖僅剩0.6mm左右仍很明顯。

在往M27啞鈴星雲移動的路徑上剛好M71星團在附近，雖然不難看見，當你想要拉大倍率仔細觀看小星團時，個人覺得口徑至少10公分以上會較為輕鬆，因為口徑限制了適合的放大的倍率，簡言之FC-76 適合大且明亮的目標。也觀賞了另一個星團Harvard 20，這是一個疏散星團，是不在預定的333觀測清單中、以前沒觀看過的，這次因為經過，時間很悠閒，便停了下來觀賞（其中有顆黃超巨星）—— 這也是自己 hopping 找星才會有的樂趣，如路過看到不錯風景或小店便臨時興起駐足參觀。

啞鈴星雲雖不用濾鏡但加上濾鏡後輪廓會變得較清晰，尤其西側的起伏。

最後來看一下南方的螺旋星雲，現在已升到仰角40度左右快接近中天，是不錯的觀測時機，如預期的在使用20x 加上LP2濾鏡後浮現，毫無懸念，這個星雲對於LP2的反應相當好，無使用濾鏡時在鞍部要辨識出有其困難但一旦加上濾鏡便彷彿從魔術師的高帽中騰空變出一樣，相當神奇。

對了，今晚來停車場觀星的都是P家ASTROTRACER 的朋友，也很神奇。

First, I took a look at Comet C/2017 K2. It was near a magnitude +9.6 star,  SAO-141339 , in the constellation Ophiuchus. The K2 was very dim, fainter than the +9.6 star, but because the visibility of the comet's coma is usually greatly affected by transparency and light pollution, so I estimated the  magnitude of comet was between +9 and 10.

There are several bright nebulae that can be easily seen here without filter even with 3" small telescope, such as M57 Ring, M27 Dumbbell, M8 Lagoon, etc. However, the contrast is greatly increased after using the LP2 filter, and for the nebula in the south sky, the effect of the filter is particularly remarkable, reducing the sky background to extremely dark (but little impact to emission nebula), which brings a very wonderful visual feast.

Then I turned the telescope to M57, the Ring Nebula (Ring) , was the first deep sky object that I've seen when i started to be interesting in stargazing long time ago (except for M42, M31, and M45 ,naked eyes targets), so I has a special feeling about it. M57 was quite obvious in the view of eyepiece ,but it is only about 4x4' in size,  must be viewed at a higher magnification. it is still bright enough even the exit pupil diameter is only About 0.6mm left .

On the path to the M27 Dumbbell Nebula, I also watched the M71 star cluster which happens to be nearby. Although it is not difficult to see,  I  think it will be easier to watch the star clusters by using at least 10 cm or bigger lens, because the aperture limits the suitable magnification. I also watched Harvard 20, an open star cluster. This is also the fun that you can only have when you are hopping for objects by yourself .

Although the Dumbbell nebula does not need a filter, the outline became clearer after adding the LP2 filter, especially the undulations on its west side.

At last, I watched the Helix nebula in the south sky. it has risen to an elevation angle of about 40 degrees and was approaching the meridian, It was a good window to observe. As expected, it appeared  via 20x and LP2 filter.  The Helix is difficult to identify without the filter under the bortle 5 sky, but once the filter is added, it seems to be conjured out of a magician's top hat, which is quite magical.

LP2

說到LP2濾鏡，使用OAKS-LP2 (OIII+Hb)濾鏡時降低的天空表面亮度約為 1.5mpsas，對於bortle5的郊山來說，加上濾鏡觀看時的天空亮度南至北約降為 20.5至 21.5間。若再考慮倍率的效果，譬如當使用 FC-76(FL=600mm) 搭配XW20目鏡時得30倍出曈徑為2.5mm，則天空與有面積天體表面亮度會同時下降約3 mpsas左右，則加上LP2濾鏡觀賞時背景亮度約為23.5~24.5 mpsas ，是接近於無光的深邃，因此郊山使用LP2濾鏡對於受其影響小的發射星雲的效果相當驚人，如果暫時忘卻自己周圍的環境只專注於目鏡裡的視野，幾近高山觀星的感受。

個人經驗出曈徑1mm以上比較適合使用LP2，若出曈徑小於1mm時再加上LP2，那麼進入眼睛的光將會變得太少而開始看見雜訊，當使用FC-76，搭配XW20時（30倍，出曈徑2.5）使用LP2還相當舒服，使用XW10(60倍，出曈徑約1.2mm) 也Ok，但搭配XW5(120倍，出曈徑為0.73mm) 再加上LP2個人覺得已太暗，除非如行星狀星雲這類相當明亮的天體即使達到0.5mm也仍很明顯，像M20這類黯淡的發射星雲個人便覺得很吃力。

Pentax K3II , Samyang 16/F2 , Kenko Red enhancer filter, ISO3200, 固定攝影 30秒

SiriL 背景校正

Harvard 20

7/22

有好幾個明亮的星雲在鞍部即使只使用3"鏡 FC-76 仍無需濾鏡可以輕易看到，譬如M57 Ring, M27 啞鈴, M8 礁湖等，但使用濾鏡後很大地增加了對比，輪廓變得較明顯，而針對南方的星雲（除M20之外）而言，濾鏡的效果特別顯著，尤其在降低天空背景至極黑暗帶來非常美妙的視覺饗宴。

今晚到停車場時王哥跟難得從基隆來的志安已在上面。感謝傑洛米的狗骨頭雞蛋糕。

昨晚空氣相當乾燥，今晚則濕度很高，尚未到午夜便需要開啟加熱，但仍不影響觀測，以FC-76 觀賞南方銀河中的M8, M17 相當明亮突出，順帶一說我覺得M17 Omega 星雲應該可以當成眼視與攝影差異的對照的經典範本，因為以業餘小望遠鏡眼睛看見的僅是星雲中央OIII波長最強的範圍的“ㄟ”形（私以為像雞翅），而若以相機曝光尤其改過機的話則會曝到包覆其在內的大上許多的Ha紅光的範圍，完全像兩個不同天體。

觀賞礁湖星雲時它正過中天附近且透明度尚不錯的時刻，看起來bling bling的非常漂亮，畫著畫著吹拂過身上的涼風都帶著熱帶島嶼的風情。

題外話，如果你使用很好的望遠鏡一定要搭配好目鏡才能發揮它的性能，志安今晚使用我的Pentax 目鏡在他的FL102螢石鏡上，發現他的平價Vixen SLV目鏡的星像差了許多，XW目鏡解放了FL102，觀看土星很清晰。

午夜後開始有雲不斷飄來，月亮也差不多要升起了。

The M8 and M17 in the Milky Way were very bright, they popped up in the view of  eyepiece. By the way, I think M17 Omega is a very classic example of showing the difference between visual observation and photography, because the only part you can see with an amateur small telescope is the " L " shape in the central of the nebula, the area of most OIII emissions. 

When viewing the lagoon nebula, it was passing near the middle of the sky and the transparency was quite good. It looked very beautiful , and the cool wind , with the style of a tropical island, made me feel comfortable.

7/23

這三晚的寧視度都相當不錯，目鏡中的星點很細且穩定。

今晚試著以FC-76 觀賞面紗星雲，在bortle 5的鞍部看面紗星雲 以3" 鏡有可能是最低極限了，西面紗需要用Averted vision (側視、眼睛餘光) 才能看見，一來因為易見的部分很細，又因為其上的Cyg 52星實在很亮，不過我認為透明度更好的情況應能更清楚。

M31星系雖很容易看見，但低倍並不會看得更清楚，因為背景天光較亮，以較大口徑使用高倍雖然無法容下整個星系，但可以嘗試觀看細節的部分，話說回來，雖然今晚使用FC-76我特別僅用20倍讓目鏡視野大小能容納下整個星系，其實看到星系的部分僅約三分之一的部分（與攝影的影像大小相較）。

小啞鈴M76 在LP2濾鏡下現蹤，觀察時間拉長，隨著仰角漸高逐漸明顯。

PAC Mac 吃豆人也是需要藉助於Averted vision，其[OIII]波長的光並不強，且集中在其嘴角小範圍。
這些秋天的深空天體仰角猶低，過些日子等它們再升高一點受到大氣消光影響會較小而更適合觀測。

午夜時天空暗度達到了SQ20，當達到20 mpsas可以很明顯的察覺整個鞍部似被黑布蓋住的變化，頭頂的天空相當深邃，銀河突出許多，於是我便開啟ASTROTRACER來做追蹤曝光 50秒的銀河，相當明顯。

The seeing was quite good, and the stars looked like pin points in the view of eyepiece.

I tried to watch the Veil Nebula with FC-76 tonight,  seeing the Veil Nebula with a 3" telescope is maybe the minimum requirement under the bortle 5 sky i think(bigger is better). The West Veil needs to be seen with Averted vision, but I think it will be clearer with better transparency.

Although the M31 galaxy is easy to see, it will not be seen more clearly at low magnification , because the background sky will be bright.  since I used the FC-76 tonight, I tried to used only 20x to make the field of view fit the entire galaxy, but I actually saw only about one-third of the galaxy.

The small dumbbell M76 was traced under the LP2 filter, while the observation time is prolonged, it became more obvious as the elevation angle increases.

These autumn deep sky objects are still low in elevation, and when they rise a little higher in a few days , they will be less affected by atmospheric extinction and more suitable for observation .

At midnight, the reading of sky darkness reaches 20 mpsas. you could clearly notice the change of entire Anbu, it seemed to be covered by black cloth. The sky in the 

zenith was quite dark, and the Milky Way was much more prominent, so I turned on ASTROTRACER to do tracking exposure for 50 seconds. the Milky Way was quite obvious on the image .

Pentax K3II , Samyang 16/F2 , Kenko Red enhancer filter, ISO3200, Pentax ASTROTRACER 50sec

SiriL- background extraction , Deconvolution

reduced stars

NGC6910

回到原始的感動

N年前第一次看除了M42獵戶座星雲,M45七姐妹星團,M31仙女座星系以外的第一個深空天體是指環星雲（M57 Ring，甜甜圈)，記得那時候是在阿里山的祝山停機坪借看某位星友的高橋螢石小折射鏡FC-76（有點不太確定，因我眼視過即使是60mm口徑在鞍部也看得到M57，所以高山肯定沒問題那麼也許是FC65 或60也說不定），對於目鏡視野裡從深邃黑暗蹦出來的立體的環狀星雲印象相當深刻，那份悸動銘刻在心。

那時高橋的望遠鏡設備對於我們一般平民來說應該算是夢幻奢侈品吧，要存薪水好幾個月不吃不喝才有辦法買一套。

現在終於有能力以相當低廉的價格從日本雅拍收“二手”的高橋老設備了，一來是現代人多習慣使用能自動找星的goto赤道儀了，所以中古老赤道儀便被更新設備的使用者以打對折以上甚至是原價的三分之一左右的價格釋出（Vixen的中古品價格更經常低到誇張，有時瀏覽網頁看著價格心裡不免會想：您這是秤重在賣吧。星友不妨多逛逛二手市場。），但赤道儀這種單純的機械結構尤其是早期日製品其實是很耐用的，轉速低，運轉頻率相對一般機械設備來說又相當低，只要不要去摔到使用個幾十年都沒問題，所以如果能自己找天體能不依賴電子自動尋星那麽接收一台功能正常的老赤道儀實在相當划算。另一方面，也因為數位攝影的畫素不斷增加感光能力不斷增強，同時顯示器的解析能力亦不斷提升，因此對影像的品質的要求也比以往更高，現代的攝影專用的APO複消色差望遠鏡的色像差修正要求隨之增強（尤其是紅光的部分），因此早期的望遠鏡同樣的也正被以低廉的二手價格在中古市場販售，對於主要以眼視為興趣的星友相當受益（日幣目前也相當吸引人）。

back to the first touch

Many years ago, my first deep sky object observation other than M42 Orion Nebula, M45 Seven Sisters Cluster, M31 Andromeda Galaxy was the Ring Nebula (M57 Ring, donut), I remember it was in Alishan (Taiwan) at that time on the Zhushan tarmac, I saw the ring nebula through my friend's Takahashi FC-76 fluorite refractor , I was quite impressed by the three-dimensional ring that popped out of the deep darkness in the view of eyepiece, and the throbbing was etched in my heart.

At that time, Takahashi's telescope equipment should be considered a dream luxury for us ordinary people. It is necessary to save a salary for several months without eating or drinking to buy a set.

Now I finally have the ability to collect the "second-hand" old Takahashi equipments from Japan at a relatively low price. Modern people are more accustomed to using goto equatorial mounts that can automatically find objects, so the ancient(old) equatorial mounts have been released at a discount of more than half or even about a third of the original price. but because the simple mechanical structure of the equatorial mount, especially the early Japanese products, is actually very durable, with low rotational speed and relatively low operating frequency compared to general mechanical equipment. it can be used for decades if you don’t drop it to the ground , so if you can find celestial bodies by yourself without relying on goto, then it is quite cost-effective to get a functioning old equatorial mount. 

On the other hand, because of the continuous increase in the number of pixels in digital photography and the photosensitive ability of cmos is continuously enhanced, also the resolution capability of the display is continuously improved, so the the requirements  of 

CA correction of modern telescope have been strengthened (especially the red light), so the early telescopes are also being sold in the auction market at low second-hand prices, which is quite beneficial to friends who are mainly interested in visual observation (less bother with red light) .

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