15th November 2004, 04:43 PM
who taught you that, ought to be shot. apparent focal length has nothing to do with the aperture, it's the sensor crop factor that's important by itself.
Originally Posted by kegler
the apparent angle of view would be pretty similar, but the DOF is affected by the obviously smaller aperture on the 828. you have mixed and compared oranges and pineapples this time.
Originally Posted by kegler
the 828 has the focal length at the widest end, at 7.1mm. the EF-S 18-55 has the shortest focal length at 18mm.
the EF-S 18-55 has (at wider end) an aperture of 18/3.5 = 5.14mm diameter wide.
the 828 has (at wider end) an aperture of 7.1/2.0 = 3.55mm diameter wide.
the angle of view at both cannot be compared directly, because the EF-S lens has a reduced imaging circle size, that gives the apparent 1.6x sensor crop factor, hence the apparent 28.8mm FOV which gives 74.27 degrees of view, while the 828 at widest gives 75.02 degrees of view. but IF the EF-S was a full image circle lens, it would have been giving 100.11 degrees FOV.
at ANY given aperture, ANY lenses compared will have the same amount of light going though. the only difference would be the DOF affected by the actual absolute size of the aperture diaphragm.
15th November 2004, 04:55 PM
somehow its abit too much for me to absorb....but i got a rough idea of wats going on liao....the first paragraph...i wanna compare 2 lens at the same distance n same F no..... wonder if the difference would be great or not
Originally Posted by sehsuan
but from wat u mention.... i think its hard to compare this way...heehee....
15th November 2004, 05:42 PM
16th November 2004, 11:22 AM
16th November 2004, 02:15 PM
I have a simple mind.
Frankly I do not care whether one uses a digital camera, a film camera, a medium format camera, a larger format camera.
When a lens says that its maximun aperture is f2.8, it means just that. Barring production quality control, all lenses with f2.8 should let in the same amount of light provided the shutter speed is the same. This is the principle of the light meter. If the meter have to take into account whether the camera is a digital one or otherwise, it will be a nightmare! I am not sure if there is such a thing as a light meter made for digital camera.
However the quality of the light that falls on the sensor, whether it be digital or film, can be different because of things like the number of lens elements that can degrade image, and coatings which can reduce flare.
Another thing. Looking through the lens, a f4.5 with a shorter focal length can actually look darker than a f8 in one with a longer lens. This is due to the fact that in a longer focal lens, the light is concentrated whereas in a wide angle lens, the light spreads out.
So when I meter a scene, and it says F2.8 at 1/125, I can use any lens on any camera, and get a correct EXPOSURE. The quality of the image is another thing!