Hi Steve

The white cone is used for incident measurements. That means that you are measuring the amount of light falling on the subject. This is done by standing at the subject and pointing the white cone at the camera.

When you can't stand at the subject - for example, when shooting a distant landscape - you can measure the light reflected from the subject that arrives at the camera. To do this, you don't use the white cone - typically, you can either slide it away or physically remove it from the sensor. Then stand where the camera is and point the sensor towards the subject. It is usually a good idea to point it down a bit so you don't get too much light from the sky affecting the reading (unless of course the sky is the principal subject). Sky is typically brighter than the landscape, so measuring the sky brightness will result in under-exposure of the landscape, which is difficult to recover. Conversely, exposing for the landscape will result in over-exposure of the sky but this can often be recovered by burning-in the sky when printing (or by using a graduated ND filter when taking the photo).

Alternatively, if you are confident that the light falling on a distant landscape is the same as the light falling where you are then you can measure incident light at your location (using the white cone, standing away from any obstructions and pointing the meter in the same direction it would be pointed if you were standing at the subject and pointing it back towards the camera) and then use this reading.

Andrew