Hi Simon,
Av Setting (or Aperture variable) will allow you to specify the aperture on the lens whilst the camera selects the shutter speed.
Assuming you are shooting a row of bottles lined up on a table at 4 meters away, the depth of field (DOF) resulting from the smaller aperature will yield a picture with more bottles being clear while the larger aperture will only show a bottle being clear, assuming all other settings being constant.
So....
1. Depth of field is more apparent on longer lense. Wide angle setting/lens normally has more depth of field. So if you were shotting on the wide end of the lens, it will not be apparent as compared to shooting with a 100mm lens.
2. Distance from the subject will also affect depth of field. The further away, the more apparent it will be. If you are shooting from 10 meters away, it's possible to isolate a subject and blur the background totally using the depth of field to your advantage. Similarly, close up subject suffer from a shallower depth of field. Even at F22, sometimes it's just not possible to get the subject totally sharp.
Therefore, to experience the difference in Depth of Field, try shooting non aquatic subjects such as a row of bottles on a table from 3 to 5 meters away. Use a tripod to enhance sharpness.
Cheers,
I have dwarf cichlids in my tanks! Do you?
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