Tom_W wrote: Jman13 wrote:
The f-value itself doesn’t change at all. It’s still a 45mm f/1.2 lens. It will have the field of view and depth of field a 72mm f/1.9 lens on full frame but the aperture doesn’t actually change.
Exactly. In terms of light gathering, it's an f/1.2. The math to calculate the f/stop does not change.
But the depth of field and field of view are as you stated.
Depends on what you mean by "light gathering". For the same scene and shutter speed, f/1.2 on FF will put 2.5x more light on the sensor than it will on crop whereas at f/1.9 on FF the same amount of light would be projected on the sensor as f/1.2 on crop. However, as the FF sensor has 2.5x the area, the amount of light per area (exposure) will be less at f/1.9 than f/1.2. With regards to the ISO setting, then, it's the amount of light per area that matters, not the total amount of light on the sensor. But with regards to noise, what matters is the total amount of light on the sensor, not the amount of light per area (regardless of the ISO setting). Thus, for a given scene and shutter speed, we'd use a different ISO setting at f/1.9 on FF than we would at f/1.2 on crop (since the light per area on the sensor would be different), but the noise would be the same (because the total amount of light on the sensor would be the same).
Tom_W wrote: Jman13 wrote:
The f-value itself doesn’t change at all. It’s still a 45mm f/1.2 lens. It will have the field of view and depth of field a 72mm f/1.9 lens on full frame but the aperture doesn’t actually change.
Exactly. In terms of light gathering, it's an f/1.2. The math to calculate the f/stop does not change.
But the depth of field and field of view are as you stated.
Depends on what you mean by "light gathering". For the same scene and shutter speed, f/1.2 on FF will put 2.5x more light on the sensor than it will on crop. However, the FF sensor has 2.5x the area, so the amount of light per area (exposure) will be less. With regards to the ISO setting, then, it's the amount of light per area that matters, not the total amount of light on the sensor. But with regards to noise, what matters is the total amount of light on the sensor, not the amount of light per area (regardless of the ISO setting). Thus, for a given scene and shutter speed, we'd use a different ISO setting at f/1.9 on FF than we would at f/1.2 on crop (since the light per area on the sensor would be different), but the noise would be the same (because the total amount of light on the sensor would be the same).
Tom_W wrote: Jman13 wrote:
The f-value itself doesn’t change at all. It’s still a 45mm f/1.2 lens. It will have the field of view and depth of field a 72mm f/1.9 lens on full frame but the aperture doesn’t actually change.
Exactly. In terms of light gathering, it's an f/1.2. The math to calculate the f/stop does not change.
But the depth of field and field of view are as you stated.
Depends on what you mean by "light gathering". For the same scene and shutter speed, f/1.2 on FF will put 2.5x more light on the sensor than it will on crop. However, the FF sensor has 2.5x the area, so the amount of light per area will be the same. With regards to the ISO setting, then, it's the amount of light per area that matters, not the total amount of light on the sensor. But with regards to noise, what matters is the total amount of light on the sensor, not the amount of light per area (regardless of the ISO setting). Thus, for a given scene and shutter speed, we'd use a different ISO setting at f/1.9 on FF than we would at f/1.2 on crop (since the light per area on the sensor would be different), but the noise would be the same (because the total amount of light on the sensor would be the same).
