TriX Loc: Raleigh, NC

If your camera performs well with higher ISOs, then manual shutter and aperture with auto ISO is a very valuable tool. You have this device that can always react faster than you can to changing light situations - why not use that capability? Modern cameras have very little noise up to ISO 6400 for crop bodies and 12,800 for FF and beyond, so pick a shutter speed to freeze the action (a blurry image is useless), an aperture for the DOF you need (an out of focus image is also useless), and let the camera pick the ISO (a noisy image is both useful and can be enhanced in post). If your camera supports auto ISO plus EC, you can then chimp and make adjustments to the exposure as needed with EC. Except for flash, where auto ISO plus ETTlL is unpredictable, manual plus auto ISO is my go to mode.

rehess Loc: South Bend, Indiana, USA

My Pentax KP gives fine pictures with virtually no digital noise at ISO levels I would have considered to be absurdly high a decade ago.

https://www.uglyhedgehog.com/t-631428-1.html

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

You might want to look in your user manual under Auto-ISO.

cameranut Loc: North Carolina

Auto iso can/will give you options that don't happen when you set it yourself. For instance, instead of going from 200 to 400, auto iso might give you a 300 or there about. I find it useful when the light is constantly changing, such as a partly sunny day with clouds shading the sun as fast as a blinking neon light. You don't want to be fiddling with the iso setting when you're shooting fast birds, etc.

augieg27 Loc: Central California

Thank you all for your input and clarifications.
I do appreciate it.
Augie

rgrenaderphoto Loc: Hollywood, CA

Become familiar with Basic Daylight Exposure and the relationship between all 3 parts of the triangle. When I started out venturing beyond "P" mode, I carried a printed out copy of this chart in my camera case.

Note, there are no hard and fast rules, but once you become familiar with the basics, then you can expand your talents.

(Download)

CHG_CANON Loc: the Windy City

As suggested, check your manual, not just for AUTO-ISO, but also the behavior of your camera in Manual mode. If your camera in AUTO-ISO will only adjust to maintain the exposure at the 0-mark in the meter, this isn't particularly helpful. Newer cameras will allow for 'exposure compensation' in AUTO-ISO and Manual; your camera manual will explain if this feature exists in your model. Otherwise, use a fixed ISO and manage your three exposure parameters to fix the exposure to a position right, left, or at the 0-mark in the meter in the view finder.

augieg27 Loc: Central California

Thank you again for your response and suggestions.
Perhaps my initial question wasn't clear as to what I needed to know. Actually I have been practicing for about 3 years now and am familiar with the basics, and I use either aperture priority or shutter speed modes with EC as necessary, but had questions about using manual mode properly. I do have a Nikon D5500 and a D90 in addition to several lenses.
Augie

rook2c4 Loc: Philadelphia, PA USA

True. But with a fixed ISO, there are no surprises. I know exactly where it's going to be, and I can fully concentrate on the other exposure-related settings.

Grahame Loc: Fiji

If you know what you are doing with 'Auto ISO' there are no surprises. Allowing the ISO to float is no different to allowing either speed or aperture to float, each could give you results you do not want if you are not aware of what each is/will be doing.

I'm not trying to 'sell' auto ISO but I do wonder why so many times people make reference to it giving "surprises" and "high values".

LWW Loc: Banana Republic of America

Question: who is missing shots fumbling to change ISO when situations change drastically and rapidly?

Answer: you

selmslie Loc: Fernandina Beach, FL, USA

Whenever you allow one or more of the elements of the Exposure Triangle (aperture, shutter speed or ISO) to be determined by the camera you are using auto exposure.

There are lots of situations such as daytime landscapes where this can work or at least come close enough that you can adjust the brightness with some post processing.

But you need to be aware of situations where the camera is likely to do something you don't want:

1. Subjects that you want to look bright overall such as snow or beach scenes, light colored animals in bright surroundings.
2. Subjects that you want to look dark overall like forest scenes, dark colored animals in dark surroundings.
3. Light subjects on a dark background like sunlit flowers against dark foliage.
4. Dark subjects on a light background like back-lit portraits.
5. Mixed lighting where some of the scene is in daylight and some is in shade.
6. People with light or dark skin in light or dark clothing or worse yet, several of these at the same time.
7. Night street scenes, fireworks, nighttime sports, fires, Christmas lighting, floodlit buildings, stars or moon photography, floodlit scenes.
8. Scenes with dramatic lighting or lots of deep shadows.

In each of these cases auto exposure will try to average much of the scene out so that it approaches middle gray. Your remedies can be to bracket, use exposure compensation and take a second or third shot or do a lot of post processing. Or you can just avoid these situations altogether.

The only permanent solution to all of these is something that many photographers try to avoid at all costs - learning how to use full manual - no auto anything.

TerryVS

The ISO floats. Most cameras you can set the range it's allowed to float. Steve Perry is a great resource by the way. The plus is you get to set the aperture (depth of field control) and shutter speed (stop or not stop action). Most of my photography is overnight and spot news such as fires, wrecks, murders etc. I love auto ISO! For me getting the shot regardless of the noise is what matters. If you have a stationary object then set up the tripod use lower ISO and get better quality.

Resqu2 Loc: SW Va

My Canon R has the FV mode where you set Shutter and Aperture and I let the iso float but I set an upper acceptable limit. Mirrorless has shown me a lot as you can see the changes on the screen as you move each setting.

LWW Loc: Banana Republic of America

Amen.

Given the choice of evils:

1-Having blurred action.
2-Having the wrong DOF.
3-Having a bit of noise.

I will take a bit of noise everytime.

A modern DSLR can produce relatively low noise at 3200 and higher.