Chapter 4 CPP Study Questions

[Mark_Levesque]

Ch 4 Light and Film

Q1) A filter with a filter factor of 8 requires an increase in exposure of

A) 8 stops
B) 1 2/3 stops
C) 3 stops
D) 4 stops

Q2) You would use a circular polarizer over a regular polarizer because

A) you have an autofocus camera
B) a digital sensor won't work with a regular polarizer
C) it polarizes more effectively
D) it requires less exposure compensation

Q3) The most commonly used type of black and white film is

A) Orthochromatic
B) Infrared
C) Blue-sensitive
D) Panchromatic

[TerryMiller]

1 B

2 A

D D


...and remember folks I'm tring to do this without a book

[Cassandra_Sullivan]

Q1) C

Q2) A

Q3) D

[Heather_L._Smith]

Ugh...

D) 4 stops
D) it requires less exposure compensation
D) Panchromatic

[Andrea_Chapelo]

1)c
2)a
3)d

[Ellen_Duperret]

1. C
2. C
3. D

Can you post the answers tomorrow morning before I go to take the test? I'm curious about #2. Thanks Mark!

[KirkDarling]

Ellen,

The reflex mirror in an autofocus camera is semi-silvered to split the light--about 60 percent reflects upward to the pentaprism and about 40 percent reflects downward to the autofocus system. That semi-silvered mirror also acts as a polarizer--it polarizes the light that's being reflected in each direction.

If you put a linear (regular) polarizer in front of the lens on an autofocus camera, you then get a double polarizing effect--which is heavy neutral density. You begin to cut off all light at certain angles.

A circular polarizer polarizes the light (filters out all light waves that are vibrating out of sync with its set direction) and then gives that polarized light a "twist" so that it's effectively not behaving as though it's polarized. So you don't get neutral density when it strikes the mirror and gets polarized again.

Notice this all has to do with the semi-silvered mirror, not the digital sensor. Cameras that don't use a semi-silvered mirror (most P&S digital cameras) can use regular (linear) polarizers just fine.

[Ellen_Duperret]

Thanks Kirk. That's all new to me. So what you're saying is that point and shoot cameras can use linear polarizers, and other autofocus cameras need circular polarizers?

[KirkDarling]

So what you're saying is that point and shoot cameras can use linear polarizers, and other autofocus cameras need circular polarizers?

I can't speak for all P&S cameras, but the ones I'm familiar with don't have semi-silvered mirrors, so they can use linear polarizers.

[Michael_Gan]

Hint for a couple of you in question #1 (in a form of a question): Is a filter factor of 8, eight times more density, or....?

hint, hint: a filter factor of 2 is 1 stop.

hint, hint, hint: Think logrithmically like you would for f stops.