[hokahon]

鏡頭上面寫住f4-f5.6 係代咩意思?

咁點解又可以係部機到set 到 f22都可以映到?

f2.8個d 係恆等光圈, 但點解有時用program 去映
去有時自己會自動去左f3.5映?

[jacprodv]

Ex:24-120mm F3.5-4.5 mean when the lens set 24mm the large aperture is F3.5 max./set the lens at 120mm the large aperture is F4.5 max. So you can set any aperture in manual mode.
Ex:In 24mm can set start from F3.5 / in 120mm can set start from F4.5
If the lens is fix F2.8 but you use program mode
the camera will auto select the aperture.

[mcca]

1. it means the maximal aperture ranges from f4 to f5.6; this only happens in a zoom lens, like 70-300mm/f4-5.6, i.e. maximal aperture could achieve f4 while at 70mm end, f5.6 while at 300mm end

2. ? f4 is the maximun, of coz you can lower it down to f8, f11, f16, f22

3. becoz you're using "programmed" setting. the CPU will adjust the aperture according to the shutter speed. we know that the image quality of all lens improve while stopping down the aperture by 2-3 f-stops. so the camera maker programmed the CPU to stop down the aperture whenever possible, provided that the shutter speed value is larger than the focal length of the lens. if you want to keep the aperture always wide open, then you should switch to aperture-priority mode.
say for example, you are using a prime 105mm/f2.8, in bright sunlight, in program mode, the aperture/shutter readings will be something like 1/125th + f5.6, but not 1/500 + f2.8.

hope this help

[肥笨]

EX>>>>>>>>EF24-85mm F3.5-4.5
1.用EF24影 F3.5 用85影 4.5
2.Set AV f22未可以映到
3.f2.8個d 係恆等光圈 EX>>>>>>>>>>EF70-200mm F2.8用70-200都可以用2.8光圈影