Sometime in the next few hours, my 5D should arrive! Excited? Yep!
Sometime during last night a though occurred that connected three things:
1. Michael's passing comment about apparent increased sensor dust on the 5D during his recent trip.
2. A comment from the Canon 5D whitepaper about the new anti-aliasing filter.
3. A discussion I had with someone once about the construction of glass-sandwich, laser-etched reticles for rifle scopes.
On point 3 first: when scope manufacturers construct a reticle that is laser-etched onto a piece of glass, they then bond a second glass plate over the top of it. This is not done simply to protect the etching (not really required inside a sealed, nitrogen-filled, scope), but is done so that any dust that might settle on the reticle will not be on the focal plane of the reticle and, therefore, will be thrown out of focus and be less intrusive to the operator.
On point 2: The Canon 5D whitepaper makes the following comment about the new anti-aliasing filter:
"The anti-aliasing filter, which also functions as the
CMOS sensor package’s cover glass, consists of an
infrared-blocking filter, a primary low-pass filter, a
phase plate and a secondary low-pass filter. While
other cameras, such as the EOS 20D camera, have
three crystal plates, the EOS 5D model’s filter has one
independent crystal plate doing double duty as the
cover glass. This reduces cost without affecting the
filter’s performance." (Page 7)
And now on point 1: with the single crystal plate over the sensor instead of three used in other cameras, any dust settling on the cover plate will be closer to the surface of the actual sensor and, therefore, closer to the focal plane, bring the dust into sharper focus.
Michael, could it be that the apparently "dustier" 5D is actually more a function of this? There is no actual increase in the amount of dust, but that dust is just more visible?
Andrew
