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11/29/2005 12:51:06 PM · #1 |
| when a lense for example the 18-55 mm says 3.5/5.6 does that mean it can do 3.5 on both 18 and 55 mm ? |
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11/29/2005 12:52:57 PM · #2 |
| usually at 18mm it does 3.5 and anything above that is 5.6 when set to widest aperature. |
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11/29/2005 12:53:48 PM · #3 |
No. The physical size of the aperture remains constant in the zoom, so the effective size gets smaller. It's a 5.6 at tele, a 3.5 at wide. In between on zoom, the f/stop is somewhere in between.
F/stop is defined as focal length divided by diameter of aperture. 25mm aperture on 50mm lens is f/2.0. 25mm aperture on 100mm lens is f/4.0.
R.
Message edited by author 2005-11-29 12:55:35. |
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11/29/2005 12:55:12 PM · #4 |
No. It will be f3.5 at 18mm and f5.6 at 55mm and somewhere in between when in between.
I don't know the change points (you can set the camera to AV mode, zwizle to the lowest f-stop and zoom to see where or they are - no doubt they are published somewhere) but they likely fairly quickly move towards f5.6 not too far towards 55mm. |
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11/29/2005 01:02:20 PM · #5 |
As posted, the wider aperture is available at the widest zoom setting, and the smaller aperture (larger number) is at the longest zoom setting.
Between the "ends" of the zoom range, the effective aperture changes continuously. What shows up in the viewfinder is the closest setting the camera can display.
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11/29/2005 01:10:49 PM · #6 |
| alright.. that explains it.. thanx |
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