09-02-2010, 01:47 PM
(This post was last modified: 09-02-2010, 02:10 PM by Brightcolours.)
[quote name='Klaus' timestamp='1283433007' post='2420']
Light reflected from the sensor will ultimately hit the "mirror" again. The mirror has an angle of 45 degrees or whatever. So what happens ?
[/quote]
We are not talking about light reflected from the sensor, here, though.
We are talking about light entering the mirror glass at surface one. It travels through the glass, towards surface two, where most will exit it again. Part of the light, however, will reflect off surface two, upwards at 90 degrees (think of your prism experiments in science class in high school).
That light will travel through the glass till it will meet surface one again, at a 45 degree angle. There, part of the light will reflect back at an angle of 90 degrees, towards surface 2 again. And most will proceed there towards the sensor to be registered.
Since the mirror is reflecting up, the ghost image will appear down the "real" image on the photo (images get projected mirrored through the optical axis in cameras).
The reason you never noticed this with for instance an EOS RT probably has to do with the thickness of the pellicle. The RT (and 1N RS) used a very thin membrane that was actually quite delicate (and often would break just from cleaning).
It appears Sony used a much thicker mirror.
What happens with light that gets reflected back from the sensor, I do not know. I guess one thing we can be sure about is that ghost lights caused by UV "protective filters" in night photography will be less intense than on other cameras, because the light will lose 1 whole f-stop by passing through the mirror twice more, again.
Light reflected from the sensor will ultimately hit the "mirror" again. The mirror has an angle of 45 degrees or whatever. So what happens ?
[/quote]
We are not talking about light reflected from the sensor, here, though.
We are talking about light entering the mirror glass at surface one. It travels through the glass, towards surface two, where most will exit it again. Part of the light, however, will reflect off surface two, upwards at 90 degrees (think of your prism experiments in science class in high school).
That light will travel through the glass till it will meet surface one again, at a 45 degree angle. There, part of the light will reflect back at an angle of 90 degrees, towards surface 2 again. And most will proceed there towards the sensor to be registered.
Since the mirror is reflecting up, the ghost image will appear down the "real" image on the photo (images get projected mirrored through the optical axis in cameras).
The reason you never noticed this with for instance an EOS RT probably has to do with the thickness of the pellicle. The RT (and 1N RS) used a very thin membrane that was actually quite delicate (and often would break just from cleaning).
It appears Sony used a much thicker mirror.
What happens with light that gets reflected back from the sensor, I do not know. I guess one thing we can be sure about is that ghost lights caused by UV "protective filters" in night photography will be less intense than on other cameras, because the light will lose 1 whole f-stop by passing through the mirror twice more, again.