我在CanyonCreek帖子的一個跟貼拋磚說“風光攝影為主的,該買D800,喜歡天文攝影的,該買馬克水。”引來老U的寶玉。老U的理論讓我覺得自己的說法的確過於簡單。不過曆來在DSLR天文攝影中,Canon比Nikon受歡迎的確是事實,而無敵兔是公認的最好的天攝DSLR(極少人會用比無敵兔這個檔次更高的DSLR來做天文攝影的,因為更高一檔的Pro DSLR(如Canon的1Ds)的價錢,完全可以買性能更好的冷凍CCD天文攝影專用相機如SBIG的STL-11000M)。我在前麵提到的跟貼裏講了兩點:Canon的“better noise control”和“真正的raw”。它們是Canon讓天文愛好者更傾心的原因。我隻重點談談關於第二點(Raw的純潔性)的資料:
資料出處:文1:http://www.astrosurf.com/buil/d70v10d/eval
文2:http://www.astropix.com/HTML/I_ASTROP/NIK_CAN.HTM
(對不起,在杭州呆久了)
我的理解和說明(如發現我的理解有誤或我有故意斷章取義之嫌望不吝磚頭):所引的文1是比較舊的,比較的是Canon 10D vs Nikon D70. 所以就具體機子而言,其結論自然不能不加論證/實驗地用到無敵水 vs D800。但該文的確用事實說明了“Canon的Raw更raw”。說白了(老鄉懂的)就是:Canon的raw原汁原味,Nikon的raw在寫到CF卡上前已經摻了水(有興趣可細讀引文1 for details,就不贅述了)。而且據Jerry Lodriguss(文2),D70是唯一Nikon機裏還可以得到原汁原味raw image的機型(此乃pre-D800說法,D800是否改變,我還沒看到有關資料),但要做到這一點也得通過一個unofficiall的操作(竟然是要shutdown DSLR for a fraction of second?!)。
Well,Raw Purity, Big deal. So what?
的確對天文深空攝影,這是一個big deal。請看並對比下麵的圖例(取自文1):
D70非raw Raw (怎麽這麽拗口?)
D70 raw Raw (obtained thru an ”illegal" operation, see details in the source above)
比較這兩幅圖,我們可以看到Nikon的“摻水”Raw會把星星當噪點洗掉 (至少D800的前輩們如此)。
下麵是同一星域Canon 10D所攝:
這篇文章接下去還有更多的關於noise control的比較,我就不再多言,大家有空去看看。
但最後,還是如Jerry Lodriguss所說:
I recommend Canon EOS DSLR cameras for long-exposure astrophotography because of their proven performance, low noise and ease of use in working with true raw files.
However, it is possible to take excellent astrophotos with Nikon equipment as well as the Canons. The final result will come down more to the technique and expertise of the photographer, and how much work he is willing to do, than to the particular camera model he uses, provided he uses a camera with low-noise characteristics.
If you are interested in red emission nebulae, both the Nikons and Canons can have their long-pass filters removed or replaced to make them good for astrophotography of hydrogen-alpha nebulosity.