Higher and Lower Sensitivity

During a recent visit to the safari park I found myself in a situation where the ISO setting of my camera was to play a big role in how the shoot turned out. Although I have prior experience with adjusting ISO settings, I hadn't previously done so with as wide a range of settings; at this shoot this was from ISO400 to ISO6400.

On arriving at the park, I knew I wanted to make the animals the main subject in the majority of cases, so would need to throw the background out of focus. I also wanted the subjects to fill the frame, so was armed with my Sigma 70-300mm telephoto lens, mostly shooting at the 300mm focal length. I started out using aperture priority at f5.6, and the default setting of ISO100. I realised on the mostly overcast day that I was getting a very slow shutter speed reading, so increased to ISO400. I was perhaps being overly cautious with the ISO setting, considering the capabilities of modern cameras of dealing with noise at higher ISOs. I was now getting a reading of around 1/200s which was still too low for hand-holding at 300mm without vibration reduction, but at least I was able to use my elbow and the frame of the car window as a makeshift tripod (most of these images were taken from the driving seat).

300mm, f/5.6, 1/200, ISO 400

 

300mm, f/5.6, 1/200, ISO 400

A little further on, my shutter speed started suffering again, so I bumped the ISO one more notch to ISO500.

300mm, f/5.6, 1/320, ISO 500

As I ventured further into the park, the light levels falling on my subjects varied considerably, mostly due to shade from foliage or shelters. It was at this point that I realised I would be changing my ISO a lot to preserve a sensible shutter speed, I then remembered my new camera has an auto-ISO setting. I switched to shutter priority, choosing a speed of 1/500s (occasionally switching to 1/640) which I hoped would get sharp images and turned auto-ISO on. This meant the camera would now preserve the shutter speed of 1/500s but automatically adjust the aperture and ISO settings to produce a correct exposure. This meant I could concentrate on the composition and subject of my images and let the camera do the technical spade-work. I've chosen a selection of images from the day that feature a range of different ISOs selected by the camera.

195mm, f/4.8, 1/500, ISO 2500

170mm, f/4.5, 1/500, ISO 3200

300mm, f/5.6, 1/640, ISO 1800

300mm, f/11, 1/640, ISO 800

220mm, f/8, 1/640, ISO 800

170mm, f/4.5, 1/500, ISO 1400

300mm, f/5.6, 1/640, ISO 6400

300mm, f/5.6, 1/640, ISO 5600

100mm, f/4, 1/500, ISO 2200

The above images are all shown after post-production in Adobe Lightroom, and at much smaller than original size. To accurately compare noise, I selected the two extremes of the ISO spectrum used, removed all post-processing from the images, and enlarged them to 100% in Lightroom, before selecting and cropping out a small area of dark and light in the image to compare noise:

ISO6400:

There is definite 'speckling' in both the light and dark areas of this extremely high-ISO image, although to be honest I expected a lot more.

ISO400:

  

It's clear to see the noise is much less evident in these two enlargemements, even though the darker image isn't as dark as the one used for ISO6400.

Conclusion

Higher ISO's clearly introduce noise to an image, however my modern camera (Nikon D610) seems to be excellent at handling even extremely high ISO's. Coupling this with the fact that software like Lightroom and Photoshop have noise reduction filters built into the software, means that noise can be dealt with in post-production, so there's no good reason not to crank up the ISO to get the shots that wouldn't otherwise be possible.