長時間曝光技巧及心得(Long exposure technique and how-to)

 

春夏交接之際在台灣東北角的海邊岩石上都佈滿厚厚的青苔,尤其是在淡水老梅地方的槽狀岩石海岸更甚,當漲退潮時槽內因海浪拍打岩石形成乳白的海水與岩石上翠綠的青苔間形生強烈視覺對比,前去拍攝時應先上網了解潮汐的時間,在漲退潮的1個小時內拍攝最佳。

In between the seasons of Spring and Summer, there is a landscape of the moss growing in the NE Taiwan coast, especially in a grooved rocks shore called “Lau Mei”, in between groove the milky water formed by the waves  turn out to be a strong contrast with the moss on the rocks during the Low/ high tides, it needs to know the timing of the tides every day before the tour to get a good shoot.

                                            

拍攝時應使用三腳架以長時間曝光來表現海浪的流動,光圈須縮小至少f/16以上以獲得較大的景深(也就是影像從鏡頭前到無限遠都清楚),個人喜歡使用f/18,不致因光圈太小(如f/22以上)而產生鏡頭的暗角及色差。

You need to use tripod for a slow shutter speed to get the long exposure effects, such as the flowing of the waves, for getting a deep depth of field (DoF), you should set a f/stop of 16 or higher, so the image will be sharp from in front of the lens to the infinity, I would like to set f/18, the reason is too small exposure like f/22 or smaller might cause vignettes and chromatic aberrations depends on the lens.

                                                               

長時間曝光的重點在快門速度,借重腳架可儘量延長其速度,一般至少要在1秒以上,時間越長影像越能產生柔和的風景表現,如雲彩的移動、海浪的拍打等的動態視覺,個人喜歡使用4秒以上,因此在強烈光線下須使用減光鏡來減光以達到長時間曝光的效果。

The key point of the long exposure technique is the shutter speed, with tripod we can set as long as we want the shutter speed, normally it should be more than a second as the starting point to get the effect, the longer the shutter speed the result of the image can be more soft and calm, such as the motion of the cloud moving、sea wave slapping etc.. I set normally 4 seconds or more, under the bright ambient I should use the neutral density filter normally over 5 stops to reduce the light.

                                           

ISO值一般應設在相機的最小值如Canon 相機的ISO100,以獲得銳利的影像。

As to the ISO setting, normally should be the lowest of the camera ISO value for a clean image , it might be different from camera to camera, for example ISO100 is for Canon.

                                                                       

至於要獲得大景深及銳利的效果,拍攝時須關閉相機自動對焦(AF)功能,做法為先以自動對焦在鏡頭前找一對焦點,至於要在多遠處須依不同相機的CoC(Circles of confusion)值、鏡頭焦段及光圈大小等3個數據來計算,網路上有一手機App “DOF Master”可使用,用時輸入相機種類、鏡頭焦距和光圈值即可獲得對焦點的距離。

For deeper DoF and sharper image, first step you should close the auto focusing function of the camera and use manual, the way to do is to find a focus distance first by AF (auto focusing) of the camera, regarding to how far this focus distance should be depending on camera format (CoC,Circles of confusion)、lens focal length and f/stops, there is an app on the web called “DOF Master” can be used to quickly calculate the focusing distance after importing the camera format、lens focal length and f/stop.


拍攝時以自動對焦(AF)依上述方法找一對焦點,對焦後關閉自動對焦使焦距固定(MF),防止後續動作如重新構圖等時產生改變而造成失焦。
Once you find the focus distance by AF (camera auto focusing), then switch”AF” to “MF” (manual focusing) to avoid the further focusing movement of the lens when recomposing and get a blur image.

更有效的作法為使用測光表,依不同相機的感光能力設定正確的曝光數據,而不須以試拍來找正確的曝光值以提高效率,個人使用的是Seknoic的L-758DR測光表。

I like to use the light meter (Seknoic L-758DR) for a better operation, the softer-ware of the meter can find the middle point of your individual camera’s exposure, in practical you don’t need to do many test shots to get the appropriate one.