Photo at top: Holland sun Stock Dove (Holenduif) size 33cm distance 40m sun. Z50 Nikkor 500mm f/5.6E PF VR equivalent 1500mm standard camouflage ISO 560 f/11 -1.0EV.

More about ISO sensitivity (“ISO”)

“ISO” (short for ISO sensitivity) (lichtgevoeligheid image sensor) is the value in stops (stops) of the sensitivity of the camera’s image sensor. This sensor will produce electric signals corresponding to the light intensity “seen” by the individual pixels (beeldpunten) each of them corresponding to the pixels of the picture produced. The camera will store this information at high speed in its data buffer in a file – RAW or JPG format – and at the same time start writing this file onto the memory card of the camera, at lower speed.

Sensitivity curve of image sensor

Every type of image sensor has its own sensitivity curve reflecting the relationship between the amount of light a pixel (beeldpunt) af the image sensor is receiving during EXPOSURE TIME and the electric voltage of the electronic signal it will produce.. This analogue number will be digitalised and stored in a special format in the JPG or RAW image file together with extra information (EXIF data) like date/time, copyright, location, equipment used, etcetera. A rough sketch of the sensitivity curve of a full frame D800 Nikon DSLR is shown below. (We ever measured the sensitivity curve of our D800.)

blacks shadows whites highlights

The overal contrast range (contrastbereik) covered by the image sensor of D800 is about 10 stops. More recent D500 or Z50 image sensors offer almost 15 stops light contrast.

Thes diagram showed here is representative for the shape of the sensitivity curve of almost any digital camera. Try to memorise the general shape of this curve and the effect of various intensities of incoming light the image sensor receives described below.

• The middle part of the sensitivity curve contains a continuous straight line upwards however this line gets progressively curved in areas Whites and Shadows

• At lower input light levels the sensor produces a non-proportional lower output signal and as side effect noise (ruis), particularly in the Shadows and Blacks area’s of the picture.

• Higher input light levels produce output signals reaching a sudden maximum potentially causing “clipping” (lack of detail in the Highlights of the picture). This can be prevented by underexposing the picture for example about 0.5 – 2.0 EV (stops).

• Average light levels (the relatively “straight” line in the curve) produce output signal values which are more or less linearly proportional to the amount of light received by the sensor pixels. This results in clear and natural light in the Whites and Shadows and somewhat less proportionally in the Highlights and Blacks.
• —————————————————————————- side effects: ——————————————————————————–
• Low ISO values will mostly give you clean, clear, colourful and almost noisefree pictures with fine detail and good light contrast and colour contrast.

• Using High ISO values will progressively cause more noise (ruis) in the Black areas of the picture. This is obviously visible however often less apparent in very busy background areas of the image.

Generally however, when you are using DSLR‘s or MLC‘s with today’s sensor technology, you should not worry too much about noise (ruis). Look for example at the photograph below of a Great Spotted Woodpecker (Grote Bonte Specht) using D500 at ISO 12.800 in dark cloudy autumn wheather in Holland. Our personal expericience, as already mentioned before, is, that up to ISO 6.400 overall image quality remains rather acceptable using for D500, Z50, Z50, Z7 or Z7 II or equivalent camera’s.

Thereafter things get progressively worse: we feel we are getting BORDERLINE CASES from ISO 6.400 and upe. This may differ at older or newer type camera’s. At D500 and Z50 though this ISO 6.400 sensitivity is our personal upper limit. And if we got sufficient available light we try remaining under 2.200 ISO, even in action photography if short EXPOSURE TIMES are required.

Trying to get correctly focussed pictures in darker winterdays in Holland can be difficult or even frustrating if one is anticipating fast action and needs short EXPOSURE TIME’s! Look at the next picture: ISO 2.200 1/750 second was the best trade off we could squeeze out of this situation considering the very dark wheather and marginally acceptable amount of noise (ruis) using a supertele 500mm f/5.6 and at the same time being prepared for some fast action like the Kingfisher (IJsvogel) forcefully shaking or killing its prey somehow as it usually does.

The next picture of the Sparrowhawk is another example of rather High ISO value with acceptable result.