I think you have hit the nail on the head there Tonka - and I wish I had thought that one out. I too found it isn't so much of a problem at longer ranges. I've made some plastic friction fit "aperture caps" to experiment with different hole sizes and will make them available when I find the ideal compromise between focus field improvement and low light losses. Meanwhile a diy guy could make something out of a flip up lens cover.
At the beginning of this video I could not get the photon to remain in even reasonable focus with any movement of the focus wheel. With the reduced aperture I was able to move the coaster knob on the focus wheel nearly half an inch and remain 'almost focused'
http://www.youtube.com/watch?v=4F-BxiP63MQ