cgarcia wrote:
I don\'t see how an f/4 lens on FF is \"equivalent in effective light gathering\" to an f/2.8 lens on 1.6x crop? Light is light, no?
I said that because a FF sensor has 2.6 times the area of a canon 1.6 crop. Since 2^1.38 = 2.6, that means that a FF sensor made with the very same technology should gather 1.38 f-stops more of light. In fact, one can crank up the ISO by 1.38 f-stops, getting the same noise at the image level (full picture) and turning the F4 lens \"as bright\" as a F2.5 lens is in a crop sensor, with the same noise. At the same time, that F4 lens is equivalent to 4/1.6 = F2.5 crop lens in terms of depth of field. The same reasoning may be applied to diffraction for a given resolution, concluding that both systems (Xmm F4 in FF compared to 1.6*Xmm F2.5 in crop) are totally equivalent.
Well, no. Depth of field, yes, exposure, no. The FF sensor doesn\'t gather \"1.38 f-stops\" more light, it gathers more light in total, but spreads it over a larger area, and in the end is no further ahead. If a shot is properly exposed at f/4 on crop, then it is properly exposed at f/4 on full-frame, with the same shutter speed and (real) ISO setting. There is no \"equivalence\" measure here.
This is one of the advantages of the smaller formats. Smaller lenses, same light gathering ability, for the correct exposure. For example, the Olympus 150/2.0 is really one stop faster (i.e. light gathering) than the \"equivalent\" (angle of view) 300/2.8 full-frame lens, even though the smaller lens will have more depth of field.
cgarcia wrote:
I don\'t see how an f/4 lens on FF is \"equivalent in effective light gathering\" to an f/2.8 lens on 1.6x crop? Light is light, no?
I said that because a FF sensor has 2.6 times the area of a canon 1.6 crop. Since 2^1.38 = 2.6, that means that a FF sensor made with the very same technology should gather 1.38 f-stops more of light. In fact, one can crank up the ISO by 1.38 f-stops, getting the same noise at the image level (full picture) and turning the F4 lens \"as bright\" as a F2.5 lens is in a crop sensor, with the same noise. At the same time, that F4 lens is equivalent to 4/1.6 = F2.5 crop lens in terms of depth of field. The same reasoning may be applied to diffraction for a given resolution, concluding that both systems (Xmm F4 in FF compared to 1.6*Xmm F2.5 in crop) are totally equivalent.
Well, no. Depth of field, yes, exposure, no. The FF sensor doesn\'t gather \"1.38 f-stops\" more light, it gathers more light in total, but spreads it over a larger area, and in the end is no further ahead.
If a shot is properly exposed at f/4 on crop, then it is properly exposed at f/4 on full-frame, with the same shutter speed and (real) ISO setting. There is no \"equivalence\" measure here. This is one of the advantages of the smaller formats. Smaller lenses, same light gathering ability, for the correct exposure. For example, the Olympus 150/2.0 is really one stop faster (i.e. light gathering) than the \"equivalent\" (angle of view) 300/2.8 full-frame lens, even though the smaller lens will have more depth of field.
cgarcia wrote:
I don\'t see how an f/4 lens on FF is \"equivalent in effective light gathering\" to an f/2.8 lens on 1.6x crop? Light is light, no?
I said that because a FF sensor has 2.6 times the area of a canon 1.6 crop. Since 2^1.38 = 2.6, that means that a FF sensor made with the very same technology should gather 1.38 f-stops more of light. In fact, one can crank up the ISO by 1.38 f-stops, getting the same noise at the image level (full picture) and turning the F4 lens \"as bright\" as a F2.5 lens is in a crop sensor, with the same noise. At the same time, that F4 lens is equivalent to 4/1.6 = F2.5 crop lens in terms of depth of field. The same reasoning may be applied to diffraction for a given resolution, concluding that both systems (Xmm F4 in FF compared to 1.6*Xmm F2.5 in crop) are totally equivalent.
Well, no. Depth of field, yes, exposure, no. The FF sensor doesn\'t gather \"1.38 f-stops\" more light, it gathers more light in total, but spreads it over a larger area, and in the end is no further ahead.
If a shot is properly exposed at f/4 on crop, then it is properly exposed at f/4 on full-frame, with the same shutter speed and (real) ISO setting. There is no \"equivalence\" measure here. This is one of the advantages of the smaller formats. Smaller lenses, same light gathering ability, for the correct exposure. For example, the Olympus 150/2.0 is really one stop faster (i.e. light gathering) than the \"equivalent\" (angle of view) 300/2.8 full-frame lens, even though the smaller lens will have more depth of field.
cgarcia wrote:
I don\'t see how an f/4 lens on FF is \"equivalent in effective light gathering\" to an f/2.8 lens on 1.6x crop? Light is light, no?
I said that because a FF sensor has 2.6 times the area of a canon 1.6 crop. Since 2^1.38 = 2.6, that means that a FF sensor made with the very same technology should gather 1.38 f-stops more of light. In fact, one can crank up the ISO by 1.38 f-stops, getting the same noise at the image level (full picture) and turning the F4 lens \"as bright\" as a F2.5 lens is in a crop sensor, with the same noise. At the same time, that F4 lens is equivalent to 4/1.6 = F2.5 crop lens in terms of depth of field. The same reasoning may be applied to diffraction for a given resolution, concluding that both systems (Xmm F4 in FF compared to 1.6*Xmm F2.5 in crop) are totally equivalent.
Well, no. Depth of field, yes, exposure, no. The FF sensor doesn\'t gather \"1.38 f-stops\" more light, it gathers more light in total, but spreads it over a larger area, and in the end is no further ahead.
If a shot is properly exposed at f/4 on crop, then it is properly exposed at f/4 on full-frame, with the same shutter speed and (real) ISO setting. There is no \"equivalence\" measure here. This is one of the advantages of the smaller formats. Smaller lenses, same light gathering ability, for the correct exposure. For example, the Olympus 150/2.0 is really one stop faster (i.e. light gathering) than the \"equivalent\" (angle of view) 300/2.8 full-frame lens, even though the smaller lens will have more depth of field.
Dec 05, 2012 at 07:18 AM
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