Regardless of the focal length of lens used (with some very minor exceptions), if you keep the image size the same on the film, that is, if you are shooting a ruler, and 1" appears as exactly 1/2" on the film (any size film or digital sensor), the DOF is the same for all lenses.
Horizontally, on 35mm film, you will see approximately two inches of the ruler. On 4x5 film, you will see ten inches of the ruler (one inch on the ruler is 1/2" on the film), and on 8x10 film, you will see twenty inches of the ruler.
The image size in all cases is the same. The film size has nothing to do with DOF. Three cameras, a 35mm, 6x6, and 4x5, all sitting at the same palace, photographing the same scene, all with 150mm lenses, will all exhibit the exact same DOF at the same f/stop. Move the cameras so that the exact same scene fills the neg on each film size, the the DOF will be different. The 35mm will exhibit the most DOF (it moved the farthest away from the scene) and the 4x5 will exhibit the least DOF at that f/stop (it moved the closest to the scene).
This is why LF camera lenses have f/stops going to f/64 and sometimes f/128 in order to obtain the needed DOF. This is also why digital cameras with small (tiny) sensors (P&S digitals in particular) have a huge DOF at wide f/stops (f/2.8, f/4, etc.).
Jim On Dec 4, 2007, at 8:44 AM, Justin F. Knotzke wrote:
On 04/12/2007, Jim Brick <jim@xxxxxxxxx> wrote: There is no free lunch! You've never worked in consulting then. ;-) Ok.. this needs more explaining then.Take my Nikon F5. I own two lenses for it. A 50mm and a 17-35 zoom (great lens BTW). The 50mm starts to resolve images at I believe just under a meter. The 17-35 starts at .28m.The 50mm goes into infinity focus just after 3-4 meters. The 17-35 does so after 1 meter.Take my pond scene. Place the camera at equivalent distance for each of the lenses so that the image size is the same for both.My 50mm is going to have DOF issues from 1 meter to 4 meters. My 17-35 is going to have DOF issues from .28mm to 1 meter. Clearly my 17-35 is going to give me less DOF grief then the 50mm. With the 17-35, I only have to worry about getting everything in focus from . 28m to 1 meter of the total subject whereas the 50mm requires that I worry about everything from 1 meter to 5 meters.Does that make sense ? J -- Justin F. Knotzke jknotzke@xxxxxxxxxx http://www.shampoo.ca
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