bleirer

That can be fraught with danger, because ISO, even invariant, is not technically part of exposure. Exposure is only how many photons hit the sensor, controlled by time and size of the opening. So one should still try for as many photons as possible.

A high ISO can lead to underexposure and noise and loss of shadow detail in terms of too few photons striking the sensor. That said, modern 14 bit sensors have a lot of latitude to handle underexposure, so you can get away with a lot of underexposure if you have no other choice.

dave.m

I find this whole debate interesting in that is a mix of 'in the day' and 'now'.

In the days of film the film speed A.S.A was the essential 1st choice - unless you had loads of cash once the film was in that was the A.S.A you had. The choice was very important slow film gives very sharp results but often led to long exposures or made carrying a flash almost essential. I remember vividly trying to shoot a landscape when I had A.S.A 800 in the camera and not being able to get depth of field.

The choice of film speed not only affected the operational shutter speed and aperture choices, it also had a great impact on sharpness. To get faster film speed the grains of silver were exponentially larger to catch more light and sharpness dropped off exponentially as well.

What you got was what you loaded before you went out. Get it wrong and either change films of live with it.

With digital cameras the position is completely reversed - ISO choice is a function of what shutter speed and aperture we want at the time. So now at last we can decide on what aperture we want for depth of field we want, what shutter speed we want for sharpness / blur effects we want. And most times in reasonable light, let the camera take care of ISO as it has very little effect on the outcome of the image.

This is simply because ISO setting just affects the sensitivity of the sensor - a 20Mpx sensor has the pixels at a set distance. Changing the sensitivity doesn't change the spacing so it is still a 20Mpx sensor with the same sharpness. Withing very wide limits compared with film, ISO has no great bearing on the final output. Yes of course if you push to the very limits then you will get noise but rest assured you can push ISO many many stops further than film A.S.A and still get a result.

So I for one of many am happy to let the camera set ISO. I often use Aperture priority to ensure I get the DoF I want, and the camera then sets shutter speed according to what lens I have fitted (seems to take inverse of focal length + 1) and then sets ISO accordingly. Occasionally I set full manual particularly with night shots when I want to force a particular aperture shutter speed. So need to set ISO to prevent it going into the noise zone.

selmslie Loc: Fernandina Beach, FL, USA

So if the camera's meter suggests the wrong exposure it's the photographer's fault? I'm certainly not buying that!

I don't "measure" light with my eyes. But I can tell if the sun is shining and there are no clouds between it and the subject.

I can also recognize several stages of cloudy from hazy sunlight (soft shadows) through heavy overcast (no shadows)". Any darker than heavy overcast and I resort to an incident meter.

Although the sensor's DR might be challenged in broad daylight, the scene's DR gets a lot narrower when the clouds roll in and the light is no longer directional.

photoman43

I shoot with Nikon Dslrs so this answer might apply only to them. I set Aperture priority and Auto Iso. In auto iso I set me minimum desired shutter speed and my max allowed iso. I manually select the aperture I want. So I end up almost being in manual mode. As light changes my camera changes the iso automatically so I do not have to do that. This gives me enough control without setting manual shutter speed.

The key is to find something that works for you and your camera.

selmslie Loc: Fernandina Beach, FL, USA

You can't use a single order for all cases.

For low noise, low ISO is more important. It forces you to get enough exposure.

For stopping movement of the subject or camera, high shutter speed is more important. When DOF is a consideration, aperture is more important.

TriX Loc: Raleigh, NC

It’s the photographer’s fault if he chooses the wrong metering pattern, meters the wrong thing in a scene or interprets the (accurate) reading incorrectly. The meter, like any instrument, is measuring what YOU tell it to measure, and how you use that data is up to YOU. It’s just a tool, and like any tool, you can use it correctly or incorrectly.

SonyA580 Loc: FL in the winter & MN in the summer

Some cameras allow you to set the "Auto ISO" to a range, i.e., 100-400, or 400-1000. I use the 100-400 quite regularly when shooting everything else "Manual" because I know the results will be OK at any point within that range.

Leinik Loc: Rochester NY

Hi Augie,
typically ISO is the first setting I set when working in manual mode (most of the time) in the same way I used to do that when choosing a roll of film before going out. Depending on the light, whether you are working indoors or outdoors for instance you may choose 200 or 1600 ISO respectively. Today is overcast (and snowing in fact) I would choose 200 ISO for a start (instead of 100 which I would use on a sunny day, so that I would gain 1 f-stop/ shooting at f 5.6 instead of f 4 or 1/60th s instead of 1/30th s), if at f 5.6 or 8 depending on my purpose (depth of field) my shutter speed is too low than I would go up one step to 400 ISO and work like this for the rest of the time. Always try the lowest ISO possible for the available light to make sure you get the best results. Increasing ISO in fact just boosts the information gathered by the sensor and with it also boosts the defects and creates noise. The highest the ISO the more noise. Every sensor has a nominal sensitivity (most of the time 100 or 200 ISO) anything above is "amplified" by the processor of the camera.
Now I'd like to comment on one thing: the USE OF WHITE BALANCE. In my opinion and practice Automatic White Balance is only useful when one is in an environment with multiple light sources of different colour temperatures (natural light and artificial, tungsten (regular bulb) and neon, etc. ...), or when someone works indoors with artificial light. AWB will "fix" that faster than you would in an image-processing software... if you want the white surfaces to look white that is... which in such cases they do not. Remember we see the world because it reflects light. A surface that looks white just reflects white light (and we assume it is "white", if the light source is yellow (bulb) then that surface will reflect yellow light and look yellow. Where does this idea of "white" come from? From the world seen and remembered by our brains under sunlight (away from sunrise and sunset though). Under sunlight (our idea of "white" in the middle of the day) a surface that reflects the whole spectrum of the sun looks white; if it only reflects the yellow of the spectrum (and absorbs the rest) it looks yellow to us. Obviously during a pink or orange sunset, a surface we see "white" in midday sunlight will then only reflect the pink or orange light coming from the sun and should look pink or orange in your photographs (unless you want it to be artificially white because that is what it looks like at midday and that is what AWB does). That is when AWB is confusing because it will correct your sunset light to make it more neutral, less pink or less orange, bending it more towards neutral white. Thence my advice toward the white balance setting is to always leave it on "Daylight" (usually the radiating sun icon) when you are outside during the day so that your jpg will render the actual light not an artificially corrected light. As for the setting beyond AWB and "Daylight" they are totally arbitrary and useless most of the time (all the time for me as I strictly never use them).

rvenn

Doesn't the camera select the lowest ISO in "auto" ISO mode? So if you need the manually selected shutter speed, you need the manually selected F/stop, and if you were to set the ISO you would select the lowest ISO setting; wouldn't you? It just takes time to determine the appropriate ISO setting as a cloud passes or a subject moves into the shade or sun. The bottom line is that if you did have time to determine the appropriate ISO setting, it would be the same as the ISO setting selected "automatically" by your camera, dictated by the manually selected shutter speed and F/stop. Yes or no?

selmslie Loc: Fernandina Beach, FL, USA

I agree completely. I keep my cameras set to Daylight all of the time, even outside at night.

Since I only look at the JPEG result on the camera's LCD, it gives me a way to see the color of the ambient light. I can always override it during raw processing but I almost never do unless the light source is tungsten or fluorescent.

Leinik Loc: Rochester NY

Strictly speaking a good exposure is the right amount of light hitting the film or sensor at a chosen sensitivity (ISO) to produce an image we can read. So obviously the 3 factors are inter-dependent; it all depends of the well-known triangle ISO / SHUTTER SPEED / APERTURE if you change any of these THREE setting you will modify the result. What you are talking about here is the AMOUNT OF LIGHT REACHING THE SENSOR. I think we know the same things but your use of "exposure" (namely the quantity of light reaching the sensor) is different from the one most of us use (and teach by the way) = exposure is the right set of choice (ISO, shutter speed, aperture) for a given situation if you have reach a "good" exposure, modify any one of the three settings (without modifying the others thence proving that EACH one plays a role including the ISO setting)and you will get a "bad" exposure, it is that simple.

tomad Loc: North Carolina

It depends on your subject. I use manual mode all the time with auto ISO for wildlife moving from light to shadow or flying birds going between backgrounds of bright sky and dark trees. If I was shooting a landscape where the light was constant I would probably set the ISO manually. Also, when using auto ISO I limit the upper ISO the camera can choose to 800 to avoid noise.

Leinik Loc: Rochester NY

Yes Slemslie, good point: we do not always remember the quality (color temperature) of the light we worked with, photographing in Daylight mode (white balance) does that for us.

TucsonDave Loc: Tucson, Arizona

You have received a ton of good advice from the Hogs. Clearly there are many ways to take good photographs whether or not you use Auto ISO, full manual, or otherwise. As others have mentioned, Steve Perry has several terrific e books on metering and exposure, plus his site, Backcountry Video has many relevant videos. He is easy to read and easy to follow along on his videos. Bryan Peterson's fourth edition of "Understanding Exposure" is also good reading.

There is nothing particularly magic about shooting on full manual. You have more control to get the shot you want. Also, more ways to miss photo opportunities. Just continue to take a lot of photos and read good references.

Have fun!!

R.G. Loc: Scotland

What I was saying was that I agreed with his order of significance. The reason I agree is because it conforms with what I've experienced. A secondary reason is that it conforms with what I would expect the majority* of people are going to experience.

*Note I said the majority, not everybody.