> On Jan 26, 2017, at 7:19 AM, Mark Roberts <[email protected]> wrote: > > Eric Weir wrote: > >> There are things that were said, though, that I did not hear. That is, >> didn’t understand. >> And probably am not going to understand when you explain it to me. What’s an >> “ISO invariant” camera? > > In the early days of digital it was standard practice to apply some > amplification to the signal from the sensor prior to analog-to-digital > conversion. This was how one increased the ISO setting. It's still > used in some sensors today but other sensors change ISO setting > strictly through software. These are said to be "ISO Invariant". (Most > Sony sensors are ISO Invariant and all the ones used in recent Pentax > cameras. > > What this means is that if you set the camera to, say, ISO 800 and > have a scene that meters at 1/100 sec. at f/5.6 you can, using manual > exposure, turn the ISO setting down to ISO 100 while keeping the > shutter speed and aperture at 1/100 f/5.6 even though the meter will > tell you you're 3 stops underexposed. If you just compensate later in > Lightroom or Photoshop the results will be the same as you'd have if > you'd shot at ISO 800 in camera. (This assumes one is shooting raw > format, of course.)
Some modern sensors have a multi-modal sensitivity curve at the low end of the range: their performance from base to some point (usually two-three EV along) rises and falls, then a second curve takes over. I've even seen one or two with a third such rise and fall. These sensors can be "ISO Invariant" in certain ranges of the curve, as long as you are not crossing the sensitivity curve at the wrong points. My Sony A7, when tested, did not show full "ISO Invariance", where my Leica M9 did. I haven't bothered to test my SL or M-D ... because in most cases the use of extreme underexposure and pulling up the data in software means you have no ability to check focus or other capture specifics on the camera in the field. >> If I’m to ETTR just enough to avoid clipping highlights, how much is >> too much? I shoot RAW. Should I ignore the histogram? > > Don't ignore the histogram! *Any* clipping represents image data > that's gone forever. That's probably too severe a recommendation. In contrasty circumstances, you are bound to be out of the dynamic range of the sensor from time to time. You have only two choices: add light to the dark areas so that you're in range or allow unimportant parts of the scene to clip. The goal is to get a good representation of the scene, not to make a perfect histogram. :-) G -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
