CHAPTER 8 COMPONENTS OF THE MINI-PAM
Fig. 5
Two spacer rings may be used to define fixed distances. The
fiberoptics exit plane is positioned at a 60° angle relative to the
sample plane. In this way shading of the sample is minimized, if the
fiberoptics are pointing towards the sample from the side opposite to
incident light. The sample may be placed either below the hole or,
preferentially with normal leaves, above the hole. In the latter case,
the leaf can be held between the folded part of the clip. The former
possibility applies e.g. to thick leaves, lichens and mosses. The
distance between fiberoptics exit plane and sample has considerable
influence on signal amplitude and effective light intensities.
Unavoidably, with a 60° angle between sample plane and fiberoptics
there is a range of distances between fiberoptics and leaf which will
result in a light intensity gradient. The relative magnitude of this
gradient is reduced with increasing fiber distance. However, this
point should not be of too much concern, as there is anyway a larger
vertical light gradient within the leaf due to chloroplast shading by
the top chloroplast layer. Also, the measured signal will be
dominated by that part or the leaf which receives maximal intensity,
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