geniousc wrote:
I\'m not sure if that\'s correct. The diaphram opening size which is a simple ratio between focal length and opening controls the light hitting the film or sensor. Lenses with equal openings (F stop) should let in the same amount of light if calibrated properly. In other words F8 on one lens should be the same as F8 on another lens. This is the founding principle of external light meters, they would never work if it wasn\'t this way. When film was used before digital, the roll would always come with an exposure guide. If lenses let in different amounts of light when set a specific F stop, the whole system would have been useless. So, I say the lenses that over/under expose have improperly calibrated diaphrams. Larger diameter glass in a lens will get you less vignetting though. In a link above from cameraquest, the owner mentions that if you bought a Voightlander from him that doesn\'t expose properly, send it in for adjustment. They are adjusting the chip or diaphram.
I to am not sure it\'s correct, but nothing you wrote truly contradicts it either. The light entering the lens contracts and then expends again in an hourglass shape. A wider front element probably expends both ends of the hourglass. The added light will fall outside of the frame into the light-absorbing coating inside the lens and body, but it\'s still more light and might have some effect.
After the fact, the only repair possible (other than black paint) is to contract the aperture a corresponding amount to the excess light. A cheat of sorts. But you have to believe that the ratio was right on the dot from day one. It\'s too simple and too basic for anyone to miscalculate. Btw, the chip doesn\'t control the aperture opening, the body linkage does that. So if they are adjusting the chip, they\'re not even changing the aperture, only the setting reported to the body. That\'s a quick and dirty fix. It also raises the possibility that the chip is somehow inconsistent in the way it reports the aperture opening to the body and thereby causing these exposure errors. So there are other possibilities and I\'m open to those.
geniousc wrote:
I\'m not sure if that\'s correct. The diaphram opening size which is a simple ratio between focal length and opening controls the light hitting the film or sensor. Lenses with equal openings (F stop) should let in the same amount of light if calibrated properly. In other words F8 on one lens should be the same as F8 on another lens. This is the founding principle of external light meters, they would never work if it wasn\'t this way. When film was used before digital, the roll would always come with an exposure guide. If lenses let in different amounts of light when set a specific F stop, the whole system would have been useless. So, I say the lenses that over/under expose have improperly calibrated diaphrams. Larger diameter glass in a lens will get you less vignetting though. In a link above from cameraquest, the owner mentions that if you bought a Voightlander from him that doesn\'t expose properly, send it in for adjustment. They are adjusting the chip or diaphram.
I to am not sure it\'s correct, but nothing you wrote truly contradicts it either. The light entering the lens contracts and then expends again in an hourglass shape. A wider front element probably expends both ends of the hourglass. The added light will fall outside of the frame into the light-absorbing coating inside the lens and body, but it\'s still more light and might have some effect.
After the fact, the only repair possible (other than black paint) is to contract the aperture a corresponding amount to the excess light. A cheat of sorts. But you have to believe that the ratio was right on the dot from day one. It\'s too simple and too basic for anyone to miscalculate. Btw, the chip doesn\'t control the aperture opening, the body linkage does that. So if they are adjusting the chip, they\'re not even changing the aperture, only the setting reported to the body. That\'s a quick and dirty fix. It also raises the possibility that the chip is somehow inconsistent in the way it reports the aperture opening to the body and therefore causing these exposure errors. So there are other possibilities and I\'m open to those.
Sep 21, 2008 at 06:03 PM
Previous versions of Elan II's message #6193338 « Voigtlander Nokton 58mm f/1.4 II Review »
The diaphram opening size which is a simple ratio between focal length and opening controls the light hitting the film or sensor. Lenses with equal openings (F stop) should let in the same amount of light if calibrated properly. In other words F8 on one lens should be the same as F8 on another lens. This is the founding principle of external light meters, they would never work if it wasn\'t this way. When film was used before digital, the roll would always come with an exposure guide. If lenses let in different amounts of light when set a specific F stop, the whole system would have been useless. So, I say the lenses that over/under expose have improperly calibrated diaphrams. Larger diameter glass in a lens will get you less vignetting though. In a link above from cameraquest, the owner mentions that if you bought a Voightlander from him that doesn\'t expose properly, send it in for adjustment. They are adjusting the chip or diaphram.