ISO FOR A SCENE...IS IT THE SAME FOR ALL CANON CAMERAS?

[Drpaulhett]

that is to say:  ALL THINGS BEING EQUAL (shutter speed, aperture, lens, subject, lighting) will a $5000 DSLR body yield a lower ISO than a $500 DSLR body?

[johnrmoyer]

Maybe a more expensive sensor will have less random photon noise at the same ISO than a less expensive sensor with all else equal. I do not know whether this answers the question.

For the same chip technology, larger photosites (lower resolution or larger sensor chip) will collect more photos per photosite and each will have a better signal to noise ratio. This will permit using a higher ISO at the same signal to noise level. There is an explanation at https://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

and at https://www.cambridgeincolour.com/tutorials/image-noise.htm

Others use a different definition of noise.

I hope this helps.

[Drpaulhett]

Thanks for the links.  Quite "illuminating".