*image ganked from Wiki.
A friend (Ryan Harvey) just got an old Canon EOS-1N RS, and after letting me play with it and hearing the speed and quietness of the shutter, I became instantly fascinated with the Pellicle mirror concept and wondering why it's no longer used.
• Viewfinder never goes dark
• No mirror shake
• Pictures can be taken a faster rate (10 frames/second)
• Very quiet shooting
• Light loss to film (2/3 stops)
• The mirror needs to be kept perfectly clean
• Pellicle mirrors are thin and especially fragile
• So, cleaning a Pellicle mirror is difficult
• Image degradation due to linear astigmatism from the thickness, refractive index (higher than air), and distinct angle of the mirror
• Possible image fogging due to light from viewfinder and non sealed-off focusing screen
While, as the technology exists now, its cons tend to outway its pros (light loss probably being its biggest drawback); its ease of speed (9 fps SLR in 1972!), quietness, and constant viewfinder image make it a very enticing concept, especially to outdoors, sports, and photojourn shooters.
So, why no Pellicle mirror dSLRs?
I would think that certain "recent" digital advances could lessen its other flaws. For instance, internal sensor cleaning techniques could be adapted to solve the mirror dust/cleaning problem. The fragile nature of digital sensors makes the Pellicle mirror's safety somewhat of a non-issue, because dSLR shooters already have to pay extra care when changing lenses, handling camera bodies, etc. Image fogging from the viewfinder could simply be solved by an included eyepeice cup, and cover or hatch (such what's already on high-end Nikon SLRs). And even the light loss problem is lessened with the advances in low-grain high-ISO speeds.
So, again I ask, why no Pellicle mirror dSLRs?
Hopefully, it won't go the way of other lost photo-technologies, like the Foveon chip, and be grabbed-up by Sigma and slapped on some less-than-worthy, low performance, prosumer body...
Cameras with Pellicle Mirrors:
• Canon Pellix QL (1968)
• Canon F-1 High Speed (1972)
• Nikon F High Speed Type 2 (1976)
• Nikon F2H (1978)
• Nikon F2H-MD (1984)
• Canon EOS RT (1989)
• Canon EOS 1N RS (1994)
• Nikon F3H (1998)
Comments, opinions, and questions welcomed.