John Brown: The f stop of a lens, AKA aperture ratio, is the focal length divided by the clear diameter of the front element of the lens. When you change the f stop, the movable leaves inside the lens,AKA the diaphram, change the central opening and thus reduces the light hitting the sensor. At normal settings, the shape of the aperture has no noticible effect on the image formed.
Gordon, Good comment. I should have mentioned if a technical photo book is not close at hand, go to Google and type in: Circle of confgusion. They have a very readable discussion of it and how it is used.
Your tolerance of low resolution in parts of your final print determines the Hyperfocal Distance that should be selected. Thus, any table has to be based on what the table-maker thought would satisfy most users. In any serious book on photo technolgy, look up Hyperfocal Distance in the index. You will learn more about the allowed "Circle of confusion" and its part in making the tables we all use.
Remember that perspective is determined by, and only by, the position of the camera, not by focal length. Experiment: keep camera in one spot and check images at widely different fl's. Image with long fl will be smaller but relative size of objects and angles between them are unchanged.
Hey David, A quick addition to your Archimedes explanation: The object in question had to be weighed in air before the weighing in water. He then could figure the density of the object, knowing it's volume and the difference in the weighings! Cheers
Hey David, A quick addition to your Archimedes explanation: The object in question had to be weighed in air before the weighing in water. He then could figure the density of the object, knowing it's volume and the difference in the weighings! Cheers
If you don't mind a little math: Take half the horizontal withth of the sensor and divide by the focal length. The answer is the arctangent of half the angle of view. So multiply by 2, and you have the horizontal angle of view.
In summary of the above statements: A lens of a certain f.l. produces an image of your subject with a predetermined size; the angle of view is determined by and only by the size of your sensor
From Port Orchard, contact Seattle Community College, at Broadway and Pine They have a two-year Photography course that is much cheaper than Brooks. Check it out and let us know what you think.
(I'm in Port Ludlow)
I shoot frien's weddings with the 70-200 so I can get or try to get an informal portrait of veryone present. Shoot the musicians if there are any, and any chilfren present. Always shoot the "get-a-way" car with the Just Married paint job.
Remember, the relative size of objects, what we call perspective, is determined by the position of the camera lens,and not by the lens. The lens for a portrait should have a focal length long enough so that the camera can be far enough away from the subject so that facial features look normal. Experiment, with any lens, get up close as possible, shoot, then move away, say, 5 or more times as far from subject. Compare the size of the nose to size of the ear in the two shots. Up close will appear to distort nose size. So a proper portrait lens is any lens with a focal length long enough to allow getting good facial perspective while providing an adequate image size of the subject's head.
Good comments on lenses. And Silver's flowers are super. From an old lens designer.