Wednesday, January 23, 2008

Nikon D80 Use of ISO Auto in Manual Mode

I bought my D80 nearly two years ago and to my surprise I am still finding new things about it.

Now to me Manual means that I set the Aperture and shutter speed and look at the exposure indication in the viewfinder to judge whether it is correct or not. If not then I can either adjust one or both of these or change the ISO setting.

I realised early that this was not necessary the case when using the flash. If the flash is set to its normal default TTL settings then the D80 will adjust the duration of the flash so that the chosen aperture and speed settings give the correct exposure. Of course with the pop-up flash you cannot go beyond 1/200 of sec although the SB600 flash will allow higher shutter speeds.

For none flash photography I often choose to leave the camera in Program P mode and with ISO Auto set (option 7 in the Custom Settings Menu) and depending on lens I usually have ISO Auto set for maximum of 400 (800 in very poor lighting) and shutter set to 1/60 or greater if using longer focal length.

Following some home investigation into sharpness of image for various f settings for a collection of lenses I proved to myself what is well known by almost every photographer that lenses perform much better when stopped down by two or three stops from their maximum. For example 50 mm f 1.8 works much better at f5.6 then f1.8, the 18-70 Nikkor performs much better at f8 then f4.5 etc.

What I wanted was the capability to set the aperture and shutter and let the ISO vary, within limits, to make the correct exposure, and this is basically exactly what ISO Auto achieves when the camera is set to manual. For some reason I had assumed that ISO Auto would have no effect when in manual.

So now I often use this approach. I have also set the "function" button (option 14 in the Custom Settings Menu) to show ISO value in viewfinder. Now on a clear day with say my 50mm f1.8 lens I will set ISO to 100, camera to Manual, Shutter to 1/125 and aperture to f8 (f5.6 if dull).

When taking photo I check in viewfinder and

  1. If meter is in centre then I know exposure is correct.
  2. If ISO Auto is flashing I can press the function button to see what it is and decide to accept or make change to shutter and/or aperture.
  3. If meter shows under exposure then I know that current max value in "ISO auto" is not enough to give correct exposure, so I can adjust aperture and/or shutter until meter is in centre again.
  4. If meter is showing over exposure then I must increase shutter speed and/or higher f-number.

Remember my main emphasis is to achieve a certain shutter/aperture combination. If only one of these is important to a specific shot then choose Shutter or Aperture mode, if neither is important then choose Program mode.

(NOTE: Photos of D80, menus and viewfinder information all taken with Canon Powershot A710 IS. Just think back to pre-digital days and how difficult, if not impossible, for an amateur photographer to take a photo of a small strip of information at the bottom of a viewfinder!)