LX7 - does its IQ compete with e.g. Sony RX100?

Started Apr 6, 2013 | Discussions thread
Sean Nelson
Sean Nelson Forum Pro • Posts: 12,863
"Envelope" is a more useful concept than "equivalence" IMHO

tedandtricia wrote:

If the image is 100% equivalent, it must include exposure, no? I'm not really personally confident how the exposure triangle and equivalency interact, given this apparent contradiction with Falk Lumo.

I assume this is coming from the idea that "equivalent" includes noise, and in order to get the same noise on a smaller sensor you need a lower ISO and therefore a longer / brighter exposure.

IMHO this argument breaks down because under good conditions (plenty of light, dynamic range that isn't excessive, final viewed image size that's not overly large, etc.) the difference in the amount of noise from a small vs. a large sensor is indistinguishable.   In that case, the idea that a longer/brighter exposure is required on a smaller sensor to produce an equivalent image to that of a larger sensor is no longer valid.

So it seems to me that thinking about things this way is inconsistent and can be confusing because sometimes it's true and sometimes it isn't.  Rather than thinking of "equivalencies" between smaller and larger sensors/lenses, I prefer to think in terms of the "envelope" of shooting conditions and end results under which you can get acceptable pictures.

"Acceptable pictures" means properly exposed, noise-free images with the desired amount of motion blur (usually none) and depth of field.

"Envelope" includes factors such as the amount of light available when shooting, the limits of DOF control, the planned reproduction size (noise is less of an issue for small images than large), etc.

Seen this way, small and large sensors and their associated lenses are "equivalent" as long as you're shooting within the envelope of conditions that provide acceptable results with the smaller sensor.   The extra margin beyond the edge of the small-sensor envelope (shallower DOF, dimmer light, etc.) is irrelevant if what you shoot doesn't require it.

I think the idea of a "shooting envelope" is easier to understand and makes a lot more sense when comparing cameras and lenses.

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