The lux at the sensor is the same for a given aperture, BUT if you're tryng to mentally compare low light performance between sensor sizes it helps to think of equivalent aperture.
The APS sensor is gathering as much light with the f2.8 lens as a FF with an f4.2. The MFT sensor is gathering the equivalent of an f5.6 lens even if it has an f2.8 lens.
Tony Northrup's point is that when, for example, Panasonic touts their LX-7 as having an f1.7 lens and therefore good in low light, they're misleading you, because the camera only has a 1/1.7" sensor
Also, like I said lux at the sensor is the same BUT that's irrelevant. We aren't exposing film so that value has no meaning to us.
This is completely wrong, or at best, misleading.
Consider a hypothetical camera company that makes cameras with the same physical piece of silicon for a sensor, with one model at 24x36mm (i.e. FF) and one at m4/3 dimensions (i.e. ~1/4 the area, or a 'crop' factor of ~2x).
You stick a 50mm f/1.4 lens on both cameras and go outside on a sunny day. You meter your scene. Both cameras tell you the exposure is f/16, 1/125 at ISO 100. You take the shot with both cameras. Now, how do the shots compare:
1. The m4/3 camera produces an image with 1/2 the horizontal angle of view of the FF camera. Indeed, it's the same angle of view as a 100mm lens would have on the FF camera (NOTE: aspect ratios are different, meaning it's not *precisely* 1/2 the AoV, but it's close enough for our purposes here).
2. The exposures are identical, for those elements that are in both images.
3. The depth of field on the FF shot is 1/2 that of the m4/3 camera. Or, put another way, you'd have to open the lens up to f/8 on the m4/3 camera to get the same DoF as the FF camera gets at f/16. But, of course, this also would increase your exposure by 2 stops, so you'd need to shoot at 1/500 to compensate.
4. When enlarged to the same print or JPEG size, the FF image is cleaner.
It's this last point that (generally) confuses people. The reason that larger sensors (all other things being equal) are cleaner is that
*they require less enlargement for a given output size*.
This is why people choose MF or LF film over 35mm film when very large enlargements are required; the film grain is the same size on all formats (the film is the same, after all), but the elements of the photograph don't need as much enlargement from a LF negative than from a 35mm negative. In fact, if you're making an 8x10 print from an 8x10 negative, you don't need to enlarge at all, and grain is virtually invisible, even with very high speed films.
That's it. That's all there is to it.
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even in the digital age, there's nothing like a good old fashioned field camera to understand photography.
yes!!!!!!!!
