ISO, & the use thereof

says here directly

ISO sets the shutter speed indirectly as was shown in the example because the shutter speed is set according to ISO and will vary as ISO varies.

I think it would that on most cameras but the example I posted only the image lightness remained the same while the exposure in Setting B was halved.

Why would I need auto ISO when I already know the settings and conditions I shoot in. Yes RAW only. Lens wide open, ISO locked and the shutter speed is the only variable needed.

No-one is saying you need auto iso. I am saying that after setting the exposure for my needs and to maximise the quality of the raw data in terms of minimising noise, it doesn't matter to me what iso the camera sets as long as important highlights are not clipped.

That is why I always set aperture and shutter speed first and then let the camera set iso. Image lightness is set in post.

If at base iso there is still too much light hitting the sensor I normally set a faster shutter speed.

Aperture priority with a minimum ss and auto iso work best for me when pointing and shooting. I also sometimes use Manual + Auto iso.

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no comment

Do you use the in-camera meter as a reference? I shoot full manual and will often make adjustments based on the meter's response to changing light conditions. The meter is a handy reference confirming that my adjustments are maintaining a desired image lightness.

Why would base ISO only be usable when on a tripod with no movement in the scene? ISO selection is more driven by how much of the available light is getting to the sensor, in my experience. In midday light, f/2.8 is compatible with a shutter speed of 1/2000 and an ISO of 100. That's base ISO for a lot of cameras and the shutter speed makes freezing movement in the frame rather trivial.

I'm in Arizona and am arguably on the downslope of life's hill. This morning before work, I went out for a sunrise wildlife shoot. I started at f/5.6, 1/30, ISO 6400 and ended the morning at f/5.6, 1/1000, ISO 400. There was a 20 minute window while Sol was clearing the eastern horizon during which I was making adjustments every minute or two to ISO or shutter speed (along with white balance) going from 1/30, ISO 6400 to 1/100, ISO 400.

I didn't get any good photos - the animals embargoed my location - but I enjoyed a fine monsoon sunrise in Arizona 😀

You cannot personally change the sun, but the change happens over time of day, day of year and location. And yes, you take these changes into account, even if implicitly
So "ISO"is at best a [distant] fourth variable.

My primary wildlife and bird camera is built around a dual-gain sensor. The system is invariant from ISO 400 on up. The lens I use for this photography has a maximum aperture of f/5.6. At that f-stop, a shutter speed of 1/2000 not only guarantees most of the birds I photograph will be sharp about the head and body, but also makes the exposure my camera is working with compatible with an ISO of 400.

That puts me in the invariant range for the camera. If I'm photographing kestrels or peregrines (earth tones and whites abound) and a turkey vulture makes a nice, close pass, I'll usually slow the shutter speed to 1/1600 to gain 1/3-stop of light. But I'll leave ISO at 400 with confidence that any lightening I do in post won't result in an image any noisier than if I'd used ISO 640 or 800.

So, yeah, ISO is something photographers who shoot raw sometimes pay close attention to. Just this morning, I was adjusting ISO in 1/3-stop increments going from ISO 6400 to 400 over the course of about 20 minutes while the Sun was rising. Those adjustments combined with the adjustments I was making to shutter speed took advantage of the gradually increasing ambient light level and maintained the image lightness I wanted to have should some critter wander into my field of view. Of course, that last part didn't happen 😆

Nowhere at all have I ever said base ISO is usable only when I am using a tripod so I don't see the point of your question.

I said I set aperture and shutter speed first and then let the camera set ISO because it makes no difference to me what ISO the camera sets as long as important highlights are not clipped.

Using your example settings in midday light, if I first set f/2.8 for my DOF need and then 1/2000s for my blur need then the Auto ISO would probably set base ISO and that is fine 🙂

My 90D works like this with aperture priority, minimum shutter speed and Auto ISO - it first sets base ISO. To zero the meter, if the shutter speed it then wants to set is slower than the min. set then the ss is set to the min. and ISO is raised to zero the meter. If the shutter speed it wants to set is faster than the min. then base ISO is retained and the faster shutter speed is set to zero the meter.

As I mentioned earlier, sometimes I use manual plus auto iso.

The bottom line for me for every shot is that I try to get as much light onto the sensor as possible within my DOF and blur needs without clipping important highlights.

Then I would have a faulty camera because my 90D has never done that........so far 😁

My 90D works like this with aperture priority, minimum shutter speed and Auto ISO - it first sets base ISO. To zero the meter, if the shutter speed it then wants to set is slower than the min. set then the ss is set to the min. and ISO is raised to zero the meter. If the shutter speed it wants to set is faster than the min. then base ISO is retained and the faster shutter speed is set to zero the meter.

As I mentioned earlier, sometimes I use manual plus auto iso.

The bottom line for me for every shot is that I try to get as much light onto the sensor as possible within my DOF and blur needs without clipping important highlights.

There are a lot of opinions about how to consider ISO, but IMHO it's just another camera control we can choose to adjust or choose to let the camera adjust for us. We need to understand what it really does and doesn't do (no, it doesn't add light). But mostly we need to understand what changing the ISO setting causes to happen for our particular equipment and in what situations. Nowadays you also need to know what your noise reduction program (I am thankful for them!) is capable of handling. Assuming that there is a universal approach that is always right is too risky for me, but that is at least partly because of my choice of gear.

I probably make different choices with my m43 camera than some of you do with full frame cameras. There are times when I use auto ISO (indoor birthday party with wild running kiddos) and times I use base ISO (yesterday's sunrise). There are times when I set the parameters of the auto ISO differently. My most common presets are saved into slots on the dial so I can access them quickly without fiddling.

When I'm teaching someone to use their new, fully capable camera, I have them start in Manual mode with auto ISO, then learn ISO control, then proceed to the Aperture and Shutter Priority modes. I've tried other sequences but this one seems to work best for most learners who are motivated to master their equipment.

The camera will use base ISO whenever possible if you use Auto-ISO in Aperture Priority mode and set the minimum shutter speed according to your constraints.

IMO ISO doesn't deserve all that attention, mastering focusing and exposure settings is much more important.

I think I've got that under control mostly, even manual focusing, so I think I might be allowed to play around with ISO & give that a bit of attention.