Foto at top: typical example of deliberate small depth of field using a telelens with average APERTURE value: Red Kite (Rode Wouw) is sharp and getting full attention of the eye, the people in the background are unsharp but nevertheless present in this picture. Holland, a Red Kite juvenile, after being cured from unknown feather disease in dutch portection centre, is released into freedom, cloudy autumn 2020. Tripod D500 Nikkor 500mm f/5.6E PF VR equivalent 750mm f/ 5.6. This picture is a good example of using bokeh (unsharp background not distracting attention from subject in foreground).
APERTURE values
A large APERTURE value will result in faster, more accurate autofocus and fine bokeh (geleidelijk verlopende onscherpte voorgrond en achtergrond).
A large APERTURE (lensopening) will result in maximal bokeh (onscherpte van achtergrond en voorgrond) and faster and more accurate autofocus. However in bird photography the APERTURE value will usually be more or less fixed because you need all the light you can get. Lightweight telelenses usually have APERTURES equal to f/4.0 or f/5.6 or f/6.3. You will most likely work with maximum value unless you wish to gain extra detail by stopping down lensor even be forced ro values f/8 or f/9 when you use converters. So anyway you will most of the time be working with more or less fixed values of APERTURE.
A small lens APERTURE yields somewhat higher image quality and somewhat more detailed images. It may even help to stop the lens a bit down. This “stopping down“-effect varies largely with the type of lens used:
- Nikkor 300mm f/4E PF VR: 1 stop down yields clearly visible effect.
- Nikkor 500mm f/5.6E PF VR: Nikon rightfully claims no loss of detail using TC-14E III (lens goes to f/8). If in addition you stop down: you will loose Nikon AF f/8 support and advanded Af functions 3D and auto.
- Nikkor 200mm-500mm f/5.6E: 1.0 stop: some effect but again: “autofocus may be more important.
- Sigma 150-600mm f/5.0-6.3 1.0 stop: (lens goes to f/9) clearly visible effect (even with 1.4 converter!)
- Tamron 150-600mm f/5.0-6.3 1.0 stop: (lens goes to f/9) clearly visible effect (even with 1.4 converter!)
Stopping down (afstoppen) a lens too far may cause diffraction (diffractie), an optical physical phenomenon that will seriously deteriorate the image. This will typically start at unusual small aperture values like f/16, f/22, etcetera.
