Methods and systems for variable wavelet correction are described. The porous pad comprises a porous material formed by spraying a chemical substance that cures to form the porous material which has a body and an outer surface. Assuming that a time width where illuminance is at a level enough for displaying an image of the sample is TF, a time width where illuminance is lower than the level enough for displaying an image of the sample is TN, and a value is as follows:TFthe value is changed according to a velocity of a stage or the like. The output network can therefore be designed low priced and accurately. Additionally, while the first handle arm typically comprises a first bowed portion that opens in a first direction and a second bowed portion that opens in a second direction, the second handle arm comprises a third bowed portion that opens in the first direction.