As I try to read some reviews, there is always an in depth comparison of ISO. ... Is this a major component in comparing cameras?
It's important if you take pictures in low light (which you stated in your other thread that you do).
The LX7 seems to have a faster lens so does it mean that it’s better in low light and could be better than the RX100?
No, because, as noted in the previous thread, the sensor in the RX100 is much bigger than the sensor in the LX7. (There are other reasons, too -- different sensor tech and processing engines (Sony vs Panasonic) -- but the large sensor size difference in this case has the most impact.)
(Also note Gordon's High ISO comparison between the RX100 and LX7
in which he says, "Compared with the Panasonic Lumix LX7 there isn't much in it at the lower sensitivites up to around 400 ISO, but the smaller sensor in the LX7 can't match the RX100 and starts to fall behind from there on. At 3200 ISO I'd put the LX7 about a stop behind the RX100."
When is this high ISO used?
In low light, there are three things you can do to compensate:
- use a slower shutter speed. The problem with this is that people have a hard time staying perfectly still, even when they're posing. (Also, it can be difficult for the photographer to hold the camera perfectly still.) So for handheld (i.e. not on a tripod) candid photos, it's generally recommended that the shutter speed stay above 1/60.
- use a larger aperture. The main issue here is that, at some point, you will hit the largest possible aperture that the lens is capable of.
So when you are already at the slowest possible shutter speed and the largest possible aperture, your only other option is:
- increase ISO. The main problem here is that the higher the ISO, the more "noise" there is.
If it were not for the zoom, I probably would take out Nikon P7700 on the list.
Quick note: the 20MP of the RX100 allows you to crop the picture and simulate an additional (digital) "zoom". i.e. if you crop out the middle 10MP to make an image equivalent to the LX7's resolution, it would be similar to the RX100 at 140mm (Full Frame equiv.). Similarly, if you crop out the middle 12MP to match the P7700's resolution, it would be like the RX100 at 130mm (Full Frame equiv.). Still much shorter than the P7700's 200mm, but somewhat less so.
Is the aperture of f2.0 a big difference from the f1.4 of LX7 or f1.8 of RX100?
Full f-stops are: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, etc. (every other one doubles: 1, 2, 4, etc. and 1.4, 2.8, 5.6, etc.)
So there is one full stop difference between f1.4 and f2.0 and note that each full stop doubles (or halves, if you want to look at it the other way) the amount of light.
In other words, each full f-stop slower (from, say, f2.0 to f2.8) is the same as either doubling the ISO (from, say, 400 to 800) or the shutter speed (from, say, 1/100 to 1/50).
In short (I know, too late), I think your decision parses out as follows:
Do you need more zoom than 130mm? If so, then your only option is the P7700.
If not, then is the better image quality of the RX100 worth the higher price?