amfoto1 Loc: San Jose, Calif. USA

Non-interchangeable lens cameras like the RX100 use a wide assortment of different image sensor sizes, so they have quite a lot of variation in "crop factor". As a result, manufacturers have gotten in the habit of stating the "35mm equivalents" of their lenses. They use that as sort of a common denominator, to be able to offer comparisons (and in some cases to be able to make some pretty extreme marketing claims).

The actual focal length range of the RX100 vii's zoom lens is 9mm to 72mm (as imprinted on the front of the lens itself). The sensor the RX100 vii uses is a so-called 1" (one inch), which is approx 9x13mm dimensions.... for an area of 116mm square. This is actually a rather large sensor for a camera of the non-interchangeable lens type. But it's a lot smaller than the 24x36mm (864 sq mm) image sensor used in so-called "full frame/35mm format" cameras.

As a result, the RX100 vii has a 2.7X "lens factor".... as compared to "full frame" cameras. This means that in order to compare their lenses' angle of view, you need to multiply the actual focal length of the RX100's zoom by that factor... 2.7x9=24 and 2.7x13=194. So on the RX100, that 9-72mm zoom will "act like" a 24-194mm lens would on full frame.

Because your a6500 also uses a sensor smaller than "full frame", but different from the RX100's, you also have to apply a lens factor to it's lens focal length range. The APS-C size sensor is approx. 16x24mm (370mm sq.), which results in a "lens factor" of approx. 1.5X when compared to "full frame". 18X1.5= 27 and 135x1.5X=202. So on the a6300 that 18-135mm lens will "act like" a 27-202mm lens would on full frame.

All this is being done in simply to compare how lenses might be expected to work on different formats of digital sensors. This is nothing new and not limited to digital.... we had to do similar calculations back in the days of film due to the wide variety of different formats in it, too.

Why is everything referenced to the 24x36mm image area that's used with 35mm film? Probably just because that's what many people are familiar with... cameras producing images close to those 24x36mm dimensions on 35mm wide rolls of film were the most dominant type of film cameras during the second half of the 20th Century. Of course, now there are many people who have never used film... have only ever shot digital. But the need to compare different formats remains and we're kinda stuck with using that common 35mm film format... now often called "full frame" digital.

More info than you ever wanted to know about digital sensor formats can be found here: https://en.wikipedia.org/wiki/Image_sensor_format

SteveR Loc: Michigan

The term equivalent is a sales gimmick.

bull drink water Loc: pontiac mi.

I shoot sometimes with a sony a-850, mount a 200mm lens and switch between fx and dx and you will see the difference. on that camera however when you go from fx to dx you go from 24mp to 12mp images.

rehess Loc: South Bend, Indiana, USA

No, it has uses. I have cameras of several different sensor sizes, and "35mm equivalent" gives me a quick way to make comparisons.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

"35mm equivalent" is what B&H and Adorama, and many others use as a sales point. And guess what, it works for them and everyone understands it. Otherwise they would use something else.