Originally posted by LV Dan Could the exposure problems on older manual lenses be related to "F" stops verses "T" stops?
For those that don't know, F-stops are calibrated based on the physical opening of the apeture and doesn't compensate for light losses. An F-stop difference is exactly half the area, but not necessarily half the light.
T-stops are calibrated so that the next stop is exactly half the light and the physical opening is adjusted to make sure it is exactly half the light.
Still photography mainly uses F-stops and not T-stops. Todays lenses are designed and fabricated much better, making T-stops and F-stops almost equivalent. However, older lenses suffer from differences, especially as one stops down to a smaller apeture. And some lenses will not lose as much light as others as it is stopped down because of differences in design and materials.
If the new cameras meter based on the light levels while the lens is wide open, their could be a difference from the actual amount of light that the program assumes will get through the smaller apeture.
Perhaps this isn't the case at all.. it is just a thought.
Unfortunately no. You can get the errors w/ "modern" f stop lenses. ie "a" lenses off a ect....These same lenses performed well on d series and k100 as far as I know. It is just some oddity of the new "bright" screen/ meter interaction at reduced light levels. The physics/engineering/logic behind this is somewhat baffelling.
And the lenses are used in "stop down" mode so even t vs f would be a moot issue.
An off the top of my head guess is that the dimmer light/smaller aperature is no longer being spread out over the lightmeter (as they would in a more matt/diffuse screen) and therefore the edges of the meter (even center weighted) are darkened in proportion to the amount of the tighter the beam is caused by the aperature blade opening. Thus the "average" is reduced and exposure time is increased.
Of course the problem w/ this theory (besides my lack of basic knowledge
) is that it should behave better in "spot meter" mode. Not sure this is the case.
Anyways, just rambling...