ISO: To Push or Not To Push?

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Low-light situations always require you to consider what to choose for compensation of insufficient lighting – either longer shutter speed, open aperture, ISO increase or flash usage. Let’s presume that technical aspects are clear – shutter speed is responsible for motion freezing-blurring, aperture affects depth of field, ISO increase brings up noise, and flash alters the lighting in general.

The choice is of course different for every situation. But what I have noticed – the most painful for me is the decision of ISO increase. No one wants extra noise, so this option is usually the least wanted.

Girl DSLR

There are situations when off-hand flashless shot is out of question due to light being really poor. But there are also times when everything is “on the edge”, and you have to decide for longer shutter speed or higher ISO, presuming we are not using any photo lighting equipment, and have an aperture which we do not want, or can not alter – say, the most open aperture we have on the lens with acceptable sharpness throughout the frame and appropriate depth of field.

What we have left is shutter speed. If the conditions make it impossible to make it even longer, we take “extreme measures” – push the ISO. There are certain “common situations” for which corresponding ISO values are recommended, such as ISO 100 for bright sunshine, 200 for mild shade, 400 for deeper shade, 800 for twilight and so on. But this does not always work, because these notions are just too vast.

So here come some questions, by answering which we can decide whether we really have to increase the ISO value.

1. Is your lens a long one?

Long Lens

image by Ian Muttoo

There is a rule stating that shutter speed must be “1/x” sec for a focal length of “x” mm. For example, for a 50mm lens, the longest acceptable shutter speed is about 1/50sec. Don’t take it for a strict rule, sometimes you still need even shorter shutter speeds. Even your current physical state matters, for if you are nervous or too tired, your hands might be shaking more than usual. So if you are using something like 200mm, you will most likely need a speed of 1/250 or faster. If you just can’t have it with current ISO, well, you do not have much of a choice – push your ISO. By the way, using optical stabilization can let you use considerably longer shutter speeds, if you have it in your camera/lens. So, if your shots start getting blurry because of handshake at 1/50, turning on Image Stabilization might make them sharp even at 1/25 or longer.

2. Is your subject moving?
Portrait Hand Blur

It is not only about walking, running and jumping. It is also about talking, laughing, eating etc. Even if a model is sitting in one place, her head, lips or hands can make rather fast movements which will cause blurring. Image stabilization or shorter focal length does not help here. Raise your ISO.

3. Is the scene unpredictable and rapidly changing?
Bike Blur

If you never know how a subject will behave, can not predict the changing of lighting conditions, and you must quickly react to the rapidly changing circumstances, I go for ISO increase for having short shutter speeds of at least 1/250 (once again, not a rule), because if you get a unique shot with noise, this is still a manageable thing. But if you get a series of shots and half of them are blurry… I bet the most interesting and lively shot will also be the most blurry. Call it another Murphy’s law.

4. Is your exposure correct?

Histogram No Correction

1/200sec f/5.0 @90mm ISO 200

Histogram Exp Correction

1/200sec f/5.0 @90mm ISO 200 [exposure +1.0 in Adobe CameraRAW]

I sometimes tend to fool myself by underexposing the photos. The images on the camera’s LCD seem just fine, the histogram looks okay, but when post-processing, you realize that you just had to make it one stop brighter. This saved me an extra ISO stop, but in the end I got even more noise pushing brightness in RAW converter. So, expose correctly and raise ISO rather than adjust exposure during post-processing.

5. Maybe change location?

Portrait Ice Cream

1/80sec f/4.0 iso 800 @85mm

Portrait Shade

1/125sec f/4.5 iso 200 @105mm

This goes beyond technical reasoning, but still – think of moving somewhere, where the light is better. When shooting outdoors, your eyes might not always notice the difference in intensity of lighting. Mild looking shade might force you to shoot at ISO 400, while walking 50 meters away may let you decrease it back to 200 or even 100. Try to watch how the light is distributed, bright surfaces on the ground or walls will give you more reflected light. But that is another long story of taking advantage of “natural reflectors”. (The above given examples were shot at the same time of day, both in mild-to-moderate shade, but as you can see from the camera settings, the light intensity appeared to be quite different.)

One more thing you can do to make a sharp photo with lower ISO is shooting several frames in a row. Make yourself as stable as possible, hold your breath and pull the trigger. I do this when I have no tripod and want to try having a less noisy image. I won’t recommend it for some serious shooting though, because it’s still a gamble.
Three Shots Night Scene

P.S. Do not forget to check your images’ sharpness at 100% magnification, because fit-to-screen images always look deceitfully fine. Special thanks to the gorgeous models – Julie and Maria!

About the Author
George Bailey is an enthusiast photographer and editor of Photodoto.com, who focuses on both studio and outdoor photography, always seeking interesting and creative shooting and retouching techniques.

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  1. Will

    Nice thoughts on ISO usage.

    However, you mention that “No one wants extra noise, so this option is usually the least wanted.” I do a lot of gig photography and actually find the best option is to lock down the shutter and aperture and let the camera push the ISO for the correct exposure. I think noise in certain situations like gig work is actually acceptable and in some cases even add character to the grungy scene of a metal gig.

    That being said I totally agree for it with my other photography work, the lower the ISO the better.

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