Canon 1N RS light loss

Hi to every one:

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I am new to Canon EOS and I have a question about the 1n-RS. I will like to know which is the effect of the fixed mirror on the lens F stop. If, for example, I use the 85 F/1.2, which will be the resulting F stop due to the light loss ? (because of the fixed mirror).

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Any Comments ?

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Thanks in advance,

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Jorge Saravia

The RS (and RT) has a 2/3 stop penalty. It's the same as putting a

2/3 stop filter on any lens on any other EOS body. You get the same

DOF, but less light at any given f-stop

An interesting piece of trivia, often overlooked concerning the 1NRS:

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Only 65% of the light passes through the mirror, resulting in about

2/3 stop light loss (compared to the mirror flipped up as with the

1N). But since the EOS 1N mirror passes only 37% of the light, about

twice as much light is available for the AF and spot meter sensors

behind the INRS mirror. Therefore the INRS specs call for 1 stop

"better" sensitivity (AF and spot meter) than the 1N.

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-Dave