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

Started Apr 6, 2013 | Discussions thread
teddoman Senior Member • Posts: 2,469
Re: LX7 - does its IQ compete with e.g. Sony RX100?

ultimitsu wrote:

Sean Nelson wrote:

ultimitsu wrote:

"Faster" refers to the ability to use faster shutter speed while maintaining the same IQ.

I know what you mean by "faster shutter speed to maintain the same IQ", but I doubt many other people think that way.

They should, because that is what it ultimately comes down to.

For example, does "same IQ" mean a shutter speed fast enough to eliminate motion blur?   No, that's not what you mean.   You mean a shutter speed that lets enough light hit the sensor to end up with the same amount of noise.   That's really not the way most people think about shutter speed.

Then they are mistaken, wouldn't you say?

For the record, a lens of f/2.8 aperture and the same field of view shooting the same scene at the same ISO setting can be used with the same shutter speed on cameras with varying sized sensors.  That's because lenses set to the same f/ratio illuminate the sensor with the same brightness per unit of area (number of photons per square millimeter, for example).

We are agreement.

By "total amount of light" he doesn't mean the brightness of the image (that's solely governed by f/stop), he means the brightness times the sensor area.   A larger sensor requires more total light to illuminate because there's more area to cover - just like a 60" TV requires more total light to illuminate than a 30" TV, even if the brightness per square inch is the same.   You need more bulbs back there to illuminate the extra area of the larger picture.

Actually I think you have misunderstood me. I do mean the the image.

What determines the quality of the image is the amount of light received by the whole sensor (which turns into the whole image).

For example assume we have a small and large sensor getting the same FOV. If we have the same sized aperture (same sized hole), the F-number will be different, and for the large sensor, light is spread across a larger area, for the smaller sensor light is more concentrated. but the two images should be the same IQ.

But if we have two different sized holes which result in the same F-number, then the larger hole passes more light and the larger sensor collects more light. its IQ must be better than the small sensor getting less light from the smaller hole.

My impression from your last few posts is that you are essentially making a full frame equivalency argument (or 1" equivalency argument in the case of the RX100), though you are only now finally getting around to the whole argument so it was kind of confusing for me at least. I had to reread some Falk Lumo to make sure that's what you were doing, but it appears so.

Yes, assuming sensors of different sizes but of the same generation and technology, and if you are trying to produce absolutely equivalent images (FOV, image noise, etc) then the f stop must scale with the crop factor, mainly because of the effect that the additional light and sensor size have on noise I think. More light across a larger sensor increases the signal to noise ratio on the image, which explains the general superiority of larger sensors of the same generation of technology.

But once most people choose a camera, they stop worrying about comparisons with other cameras.   They decide how much noise they're willing to live with, choose a maximum ISO accordingly, and from that point on they only worry about f/ratio and shutter speed.

That is what people normally do. In this thread however the comparison is between LX7 and RX100. RX100 has a much larger sensor with a larger-but-not-proportionally-larger aperture hole. Net result is at the same FOV RX100 will get more light and it would result in higher IQ, or it can afford faster shutter speed and get the same IQ as LX7. Thus it is false to claim LX7 has a faster lens.

LX7 does have a brighter lens if we are only concerned with per area brightness. If we are concerned with per image brightness, LX7's lens is not brighter.

I do see what ultimitsu is saying here. He's basically using full frame equivalency type arguments to say that to capture the same exact image with the same amount of image noise, a large sensor camera can use smaller f stop, higher ISO and/or faster shutter speed to capture what a small sensor camera has to do at a wider f stop, lower ISO and/or slower shutter speed.

In terms of equivalent apertures, the RX100 full frame equivalent aperture range is f/4.9-f/13.4 while the LX7 full frame equivalent aperture range is f/7.1-f/11.7 according to dpr. RX100 is "faster" in an equivalency sense at the wide end but even using ultimitsu's equivalency point of view, LX7 is "faster" at the tele end. But of course let's not forget the RX100's wide end is 28 mm, which is in the "easy" range of lens focal lengths. Only the LX7 even attempts the more expensive and difficult lens focal length of 24 mm equiv. So LX7's f/7.1 equivalent aperture is a lot faster than the RX100 at its non-existent 24-28 mm focal lengths.

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