When to change the ISO


The exposure is the combination of Aperture and Shutter speed at a given ISO. Now, what should be the given ISO? Lower is better as increasing the ISO leads to more noise in the photograph. At aperture priority, as you shoot keep an eye on the shutter speed so that it does not drop down lower than 1/60th of a second, the minimum shutter speed at which ideally you should be shooting handheld. In case the shutter speed drops lower, just open up the aperture and this will correspondingly let the photograph be shot at a higher shutter speed. If the subject is not moving, any shutter speed above 1/60th of a second does not influence the motion blur in the photograph as there is no motion in the subject. At slower shutter speeds it is the camera shake that gets registered on the sensor. On can certainly use a tripod for such situations but do keep in mind that the tripod does not take care of the subject movement but only the camera shake.

This is where ISO comes into play when you cannot use a tripod because you dont have one or need more flexibility while shooting or you cannot add a flash because you are not carrying one or you wish to be discreet while shooting.

With drastic improvements in technology, the image quality at higher ISO settings is also relatively very good compared to how it was in the early 2000s as the digital cameras were introduced. More professional cameras like the Canon Eos 5D Mark III is known for its image quality at higher ISO. This does not mean that one would use a higher ISO when not required. First exhaust the other options like opening up the aperture, using a tripod or flash (flash can always be used as a fill, bounced or off camera so that the images do not look flat). Even with a good camera, we do not really compare the same shot taken with two different ISO settings so it does not matter if the quality to lower as there is nothing else to compare with. In terms of comparison, the one with a lower ISO would definitely be better, something again you may not be able to notice on the small screen of your camera.

Good quality at higher ISO is a great boon for street photography and has opened up more shooting possibility over an extended period of time, one gets as the sky turns dark. Especially for us who have seen the Film era as well when it was not really possible to shoot handheld, in low light, increasing the ISO and shooting is a great change. A Canon camera is expected which can shoot in absolute dark (as of mid-2015) 

At times you may also shoot a bit under exposed and bring it up later on through the RAW converter in the computer.

In good light actually, it is a good idea to shoot at the lowest available ISO. Through the custom settings in many cameras, you can set the lowest ISO to 50 instead of 100.

Getting the shot at the right moment is more important than the noise at the higher ISO when shooting in uncontrolled situations.

  Not the last lightNot the last light

NIKON D200 18 mm 27 mm f/3.5
1/800 at f/8 Not fired -2/3 EV Aperture priority ISO 100 Center-weighted average

Canon EOS 5D 84 mm 1/100 at f/4 Not fired, compulsory mode 0 EV ISO 800

Canon EOS 5D
105 mm
1/160 at f/4
Not fired, compulsory mode
0 EV
Auto
ISO 800

Canon EOS 5D Mark II
200 mm
1/60 at f/4
Not fired, compulsory mode
-1/3 EV
Auto
Aperture priority
ISO 800
Partial

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Canon EOS 5D Mark II 81 mm 1/40 at f/4 Not fired, compulsory mode -1 EV ISO 5000

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NIKON D200
18 mm
27 mm
f/3.5
1/45 at f/8
Not fired
0 EV
Auto
Aperture priority
ISO 400
Center-weighted average

Canon EOS 5D Mark II
50 mm
1/40 at f/1.8
Not fired, compulsory mode
ISO 1600

Canon
Canon EOS 5D
35 mm
1/60 at f/5 -2 EV ISO 200

Canon EOS 5D
105 mm
1/800 at f/6.3
-2 EV
ISO 200

You will notice that I have been shooting with much higher ISOs with canon 5 D mark III compared to the original 5D or mark II.

Canon EOS 5D Mark III
40 mm
1/50 at f/3.2
Not fired, compulsory mode
0 EV
Auto
Aperture priority
ISO 1600
Pattern

Canon EOS 5D Mark II
70 mm
1/80 at f/4
Not fired, compulsory mode
-1/3 EV
Auto
Aperture priority
ISO 800
Partial

Canon EOS 5D Mark II
160 mm
1/125 at f/4
Not fired, compulsory mode
-1/3 EV
Auto
Aperture priority
ISO 800
Partial

Canon EOS 5D Mark III
40 mm
1/60 at f/2.8
Fired, compulsory mode
0 EV
Auto
ISO 200

Canon EOS 5D Mark III
40 mm
1/60 at f/2.8
Fired, compulsory mode
0 EV
Auto
ISO 200

Canon EOS 5D Mark III
50 mm
1/160 at f/1.4
Not fired, compulsory mode
0 EV
Auto
ISO 2000

Canon EOS 5D Mark III
50 mm
1/80 at f/1.4
Not fired, compulsory mode
0 EV
Auto
ISO 500

Q My images are dark, will increasing ISO help ?

Ans - If you are shooting at Aperture priority mode, increasing the ISO will only let you get a higher shutter speed at the set aperture. Higher ISO does not let in more light to enter but allows you to shoot a scene in lesser light. Increasing the ISO lets you manage to get the same exposure with less light but at the cost of NOISE. Check if there is any other reason of under exposure, maybe the exposure compensation dial is rotated towards under exposure ( towards minus ) In general, at aperture priority the exposure, if not absolutely correct is closer to the desired exposure.  

This may vary based on the metering mode set on the camera. In other words, one may say that increasing the ISO lets you have the same shutter speed at a given aperture as one would have got if the light was more. In bright daylight, lets say, if you get a shutter speed of 1/8000th of a second at f2.8, the shutter speed starts dropping towards 1/60th sec or even lower as it starts getting darker. with shutter speed dropping bellow 1/60th sec it gets difficult / impossible to shoot hand held with a camera shake recorded. To counter this, by increasing the ISO one can achieve a higher shutter speed. You are making the sensor behave differently. It amplifies the signals and achieves the same exposure as it would have achieved with higher light.

 

You may also check

http://www.completephotographer.com/single-post/2017/01/01/My-images-are-dark-will-increasing-ISO-help-