For this exercise I’ve used my Nikon D200 with the Sigma 150 mm macro lens. The D300s with its larger sensor was giving acceptable results throughout the range, so opting for the older model was a logical answer. The macro lens was chosen because of its wide aperture (f/2.8) which gave better control over the minimum shutter speed. I chose this African leather mask which is mounted on the wall of my study. The light was natural daylight on a hazy day, shining into through the study window. I disabled the long exposure and high ISO noise reduction on the camera. The camera was tripod mounted. I used aperture priority at f/5.6, which facilitated a starting shutter speed of 0.5 sec at ISO 100. The ISO was increased one step for each exposure. The images were converted with the standard RAW settings only.
As the images look quite acceptable when viewed at a relatively small size, the ISO 100 and ISO 3200 are shown for a general overview with small sections selected for each step to show the noise more accurately.
African Mask ISO 100, 0.5 sec at f/5.6
African Mask ISO 3200, 1/50 sec at f/5.6
Although there is some noise in this image, compared to the previous one, it cannot be appreciated at this size.
There now follow 16 images of detail taken from the above pictures with ISO ranging from 100 to 3200. The black areas in the eye and the shadows on the wall show the noise to best effect, so this is the area chosen for the detail.
No adverse noise to be seen.
ISO 125, 0.4 sec 
No adverse noise or loss of detail.
No adverse noise or loss of detail.
ISO 200, 0.2 sec 
No adverse noise or loss of detail.
No adverse noise or loss of detail.
ISO 320, 1/8 sec
There’s a small amount of noise in the eye and the shadows, but it’s still a perfectly acceptable image.
The noise has increased slightly, particularly in the eye. The edge of the mask is losing its relative sharpness.
ISO 500, 1/13 sec 
Noise is now becoming more apparent in the darker folds of the mask. Detail in the leather is starting to become confused with the noise, so the detail must be suffering.
Noise has increased with the blacks now becoming lighter. Shadows to the bottom right are beginning to merge with the lighter wall.
ISO 800, 1/20 sec
Noise is now apparent across the image, extending now into the lighter areas. The darker areas are becoming lighter while the lighter areas are becoming darker. The detail is diminishing more markedly and the image is losing its contrast.
Exposure was exactly the same as for ISO 800. No great difference is seen between the two images.
ISO 1250, 1/30 sec 
A further increase in noise can be seen with an associated loss of detail and contrast.
It should be said that viewed at full size in high resolution jpeg, the image would still be acceptable – maybe not as a print, but for display on a monitor it would look OK.
As the exposure was exactly the same as for the ISO 1250 image, no great difference can be seen between the two.
ISO 2000, 1/40 sec
The noise is so great here that sharp detail has been lost. Look at the edges of the eye compared to earlier exposures.
I think this would now be unusable as a quality print.
With greater noise and more loss of detail, the outer fold of leather is now losing its crease and the shadows on the wall are less distinct. The image is becoming much flatter
ISO 3200, 1/50 sec
If this image had been taken to show the detail in the mask it would have been useless. It could still be used at a smaller size, but I feel that the noise here is too great for most purposes.
The exercise has demonstrated the relationship between ISO setting and noise. It’s also worth noting that the noise reduction in camera had been turned off. Certainly with the D300s it was difficult to show anywhere near the amount of noise exhibited in the exercise. With its noise reduction working I’m sure the images, even up to ISO 6400 would have been easily acceptable. Noise reduction software – e.g. Topaz Labs DeNoise - would also help improve the image.
High ISO settings can be very useful when fast shutter speeds are required – sport action or freezing animal action etc. – or for shooting in low light conditions, so provided the implications of noise are appreciated they can be used effectively.
No comments:
Post a Comment