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depth of field with different lenses
On Wed, 9 Mar 2011 12:13:09 -0800, Savageduck
wrote: On 2011-03-09 10:39:15 -0800, Eric Stevens said: On Tue, 15 Dec 2009 20:25:18 -0600, Allen wrote: Troy Piggins wrote: * Wally wrote : On Wed, 16 Dec 2009 08:30:30 +1000, Troy Piggins wrote: [---=| Quote block shrinked by t-prot: 14 lines snipped |=---] of view as the 150mm lens shot: http://piggo.com/~troy/images/usenet...-f2_8-crop.jpg With the wider focal length lens, same aperture, same camera, same focus distance, there is more stuff acceptably in focus. First of all, good for you for doing tests. You will learn real things. Experiments beat theory. Secondly, you are right, shooting with a wide angle lens and then cropping to the same image size will give you much better DOF. But thirdly, if you move in with the wide angle to get the same image size, then the DOF will be the same. Except that it might not be -- I suspect the latter case will show the long lens to give better DOF. That's because the exit pupil is usually smaller than expected for tele lenses. Look at the front of the lens, then at the back. Do the apertures look the same size? It will probably look smaller from the back, and that should give better DOF. The perspective is different too. That's not what I was trying to test. As to whether the DoF will be the same, don't know and don't care at the moment. I was trying to illustrate a point raised in another thread. I know if you move closer, ie reduce focus distance, the DoF narrows as well. So it makes sense that at some point if you take a shot with a longer lens, and another shot closer to the subject with the same aperture, you could end up with similar/same DoF. But the perspectives will be different, and the field of view may or may not be the same. In 1941, when I was 12 years old, I bought a book titled "How to Make Good Pictures" from Kodak for something like 50 cents. (I believe this edition was from 1939 or 1940.) It was a wonderful introduction to photography. Many of the questions I see here (basic lighting, posing, composition, optics, depth of field, shutter speeds, filters and such--and an intro to darkroom work, useless now) are answered in that 70 year old, approximately 150 page book. Looking in bookstores, I don't see anything like that book. What I see now weigh as much as a 4x5 Graflex (a conparison from the time when that book was published) and difficult to find answers to your questions. I practically wore the ink off the pages in a year. We need a digital-age equivalent. Allen I agree. My introduction was via the 'Ilford Encyclopaedia of Photography'. I don't know what happened to my copy but I've been fruitlessly hunting for an eqivalent for the last several years. Regards, Eric Stevens A little searching shows that the 'Ilford Encyclopaedia of Photography' first published in 1890 by Britannica Works Co. became the "Ilford Manual of photography". A check with Amazon shows it somewhat available; http://www.amazon.com/Ilford-Manual-...9700789&sr=1-1 or http://thurly.net/111a They show other used editions dating from 1897; http://www.amazon.com/s/ref=nb_sb_ss...of+photography or http://thurly.net/1119 That looks like the one. Regards, Eric Stevens |
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