 BetterPhoto Member |
Film vs. digital camer angles Will someone please sgare how a Nikon D70 19MM lens is equal to a 35MM camera 28MM lens (angle view)?
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Ibarionex R. Perello |
The sensor on a digital camera is smaller than the area of your a 35mm film frame. As as a result, the smaller sensor will only render an image from a smaller percentage of the image circle projected by the lens. On the Nikon this translates into a 1.5 conversion factor, thus a 19mm performs like a 28mm on a Nikon D70. It's a slight disadvantage with if you have ultra wide angle lenses as they are not as wide on your digital camera, but it's a boon if you enjoy shooting with telephoto lenses, because then a 200mmm lens performs like a 300 with no loss in aperture.
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Alan N. Marcus |
Hi Barbara & Tom, As you know a camera lens projects an image of the outside world onto the surface of the film or digital chip. The focal length of the lens determines image magnification. We say magnification even if the image produced is a reduction. Now let’s shoot using a 35mm film camera, a portrait with a subject distance of 10 feet. You shoot, and examine the resulting negative and measure the head size. You find chin to forehead distance on the negative measures 4mm. Now you mount this lens on a typical digital and re-shoot from the same 10 foot mark. If you could examine the image produced by the lens on the surface of the chip, you would find the same head size and thus the same magnification. Therefore you might conclude that the lens performance is the same even though the media used is different as to size. You would be right as to magnification but wrong as to angle of view. You see, most digital cameras are made with a chip that is about 66% of the size of a 35mm film format which is 24mm x 36mm. Now all lenses project a large circular image. Sorry to report that only the central portion is usable. The outer edges are weak as to brightness and jam-packed with errors and distortions. All cameras discard all but the central part using baffles and mask. A lens made for a 35mm film camera is so designed that the 24mm x 36mm film area just fits inside the useable center. Now this lens will have a definite angle of view. Mount this same lens smaller format camera and the angle of view decreases because more of the central good image is cropped away by baffle and mask. To calculate how big the typical non-full size digital format is, we reduce the 35mm format by 66%. We do this by multiplying each side (height and width by 0.66. Thus 24 x .66 =15.84 and 36 x .66 = 23.7. The result is a chip that is about 15.84mm x 23.7mm. Now if we work this problem backwards we must divide by .66. Many find division thorny, so we have another method; we can multiply by the reciprocal which is 1.5. Thus 15.84 x 1.5 = about 24 and 23.7 x 1.5 = about 36mm. That’s where the 1.5 factor comes in. Using math, we know, as to angle of view, of a 19mm mounted on a non full size digital performs like a 28.5mm when mounted on a 35mm. How do we know? We solve like this 19 x 1.5 = 28.5. We used the 1.5 conversion factor. Sorry, working with lenses required math. No math for you? Then you must just believe. Luck to you, Alan Marcus
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Alan N. Marcus |
Hi again, After I wrote the above long-winded, math intensive and insensitive explanation, I suffered from self criticism. I woke up thinking, how can I explain in an easy-to-understand way? Then a light turned on in my head! You are at the super bowl, way up in the nose bleed section. Your 35mm film camera is mounted with a 28mm wide angle. You shoot a wonderful picture covering the field from goal post to goal post. What an angle of view! You love it so you have a big print made, 40 x 60 to mount over your mantelpiece. Home you go from the lab with your framed and mounted masterpiece, lighter by $350. To your chagrin, when you get home, it won’t fit, too big. Measuring you find that space will only support a 26 x 40 framed print. You take the print to a frame shop and they dismount and cut the print down and re-frame. The cut down print is 66% of the original but it fits. Sorry to report the cut-down print no longer shows goal post to goal post. The new framing omits the goal posts as its view is only from 20 yard line to 20 yard line. Could it be that the smaller format has reduced the angle of view? Consider that the same thing will happen when you remount your 28mm on your non-full frame digital. Have a nice day! Alan Marcus
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Andy |
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Alan N. Marcus |
A tip of the hat to Andy. You are right on! We must mount the lens closer to get a wider angle of view. How do we do that? Well the lens to image plane distance must be shorter so we must use a shorter focal length lens. Andy your diagrams are right on target. Alan Marcus
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