A PRACTICAL EXAMPLE OF DEPTH OF FIELD AND FOCAL LENGTH.
Following my search for spectacular Barcelona photos taken with tele lenses I remembered one image standing out. There was a picture shot by Antonio Espejo using a colossal tele.
The tele lens used was of 1.200 mm. The so called “normal lenses” (similar to the human view) are the 50 mm, so in this case Espejo took the photo with a lens with a focal length that is twenty four times the 50 mm !I decided to take the same photograph using different lenses. I live very close to Plaza España so I took my tripod, my D80 Nikon and a bag full of lenses and climbed the steps that go from Plaza España to the MNAC. You have an exceptional Barcelona view from there that I have used in many occasions. And those are the results. I used three Nikon lenses: a 18-70 zoom, a 180 f:2,8 and a 300 f:4. In the captions I multiply the focal lengths by the 1,5 digital conversion factor to compare them with Antonio Espejo’s 1.200 mm lens.
NIKKOR 105 mm
NIKKOR 270 mm
TECHNICAL CONSIDERATIONS
Antonio Espejo needed to solve several technical problems to get his photo. A tele lens of such a long focal length needed to be shot using a high shutter speed or fixed to an extremely sturdy tripod. Espejo told me that he got a 15 kilos tripod from the Canon Professional Service. The second challenge was to get all the planes sharp, a greath DEPTH OF FIELD known as the distance between the farthest and closest sharp elements in the picture in relationship with the point we focus. Depth of field depends of three factors that can be controlled by a photographer who works in manual mode:
1) F-number. The smallest the f-number (less light entering through the lens) the longer will be the depth of field.
2) Lenses focal length. The longest the focal length the shorter will be the depth of field and vice-versa.
3) The distance. The distance between the camera and what we want to photograph. The longest the distance the longer will be the depth of field and vice-versa.
To get all the planes sharp in the image Espejo had two fixed variables, one positive and one negative. The positive one was that the distance of the subjects in the photo was very big. The first elements appearing, the Venetian Towers, were about 700 meters from the point the camera was, as I calculated on a Barcelona map. The negative and fixed variable was that the 1.200 mm focal length was very big.
Antonio could only play with the third variable left: the number f. Usually he should had used the smallest f-number and the correlative slow shutter speed allowing the right amount of light needed to get the right exposure. But there was a problem as Antonio told me:” I couldn’t use a slow shutter speed because, in spite of having the camera on the tripod, the focal length was so huge that the photo would be blurred, so I have to use a middle f-number and a pretty high shutter speed with Velvia 50 ASA slide film".
The photo was taken on a sunny day (a must to get this result) at 14h 8 minutes (Guess how I know that?).
The final result was fantastic. Chapeau Antonio!
NIKKOR 270 mm
TECHNICAL CONSIDERATIONS
Antonio Espejo needed to solve several technical problems to get his photo. A tele lens of such a long focal length needed to be shot using a high shutter speed or fixed to an extremely sturdy tripod. Espejo told me that he got a 15 kilos tripod from the Canon Professional Service. The second challenge was to get all the planes sharp, a greath DEPTH OF FIELD known as the distance between the farthest and closest sharp elements in the picture in relationship with the point we focus. Depth of field depends of three factors that can be controlled by a photographer who works in manual mode:
1) F-number. The smallest the f-number (less light entering through the lens) the longer will be the depth of field.
2) Lenses focal length. The longest the focal length the shorter will be the depth of field and vice-versa.
3) The distance. The distance between the camera and what we want to photograph. The longest the distance the longer will be the depth of field and vice-versa.
To get all the planes sharp in the image Espejo had two fixed variables, one positive and one negative. The positive one was that the distance of the subjects in the photo was very big. The first elements appearing, the Venetian Towers, were about 700 meters from the point the camera was, as I calculated on a Barcelona map. The negative and fixed variable was that the 1.200 mm focal length was very big.
Antonio could only play with the third variable left: the number f. Usually he should had used the smallest f-number and the correlative slow shutter speed allowing the right amount of light needed to get the right exposure. But there was a problem as Antonio told me:” I couldn’t use a slow shutter speed because, in spite of having the camera on the tripod, the focal length was so huge that the photo would be blurred, so I have to use a middle f-number and a pretty high shutter speed with Velvia 50 ASA slide film".
The photo was taken on a sunny day (a must to get this result) at 14h 8 minutes (Guess how I know that?).
The final result was fantastic. Chapeau Antonio!
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