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Mark_Levesque
02-19-2008, 05:51 PM
Ch 5 Exposure

Q1) An incident exposure reading for a fair skinned subject indicates f8, 1/125 at ISO 100. The next client is very dark skinned. The proper exposure for this client at the same subject position is thus:


A) f5.6, 1/125, ISO 100
B) f11, 1/125, ISO 100
C) f8, 1/60, ISO 100
D) f8, 1/125, ISO 100

Q2) An in-camera reflected meter reading of a very light toned scene indicates an exposure of 1/250 at f8 is called for (automatic exposure mode). For a correct exposure the photographer should:

A) press the button; the camera has done the work
B) employ positive exposure compensation
C) employ negative exposure compensation
D) use a custom white balance

Q3) which of the following exposures is not equivalent to 1/60, f5.6, ISO 100

A) 1/30, f5.6, ISO 50
B) 1/250, f4, ISO 200
C) 1/500, f2, ISO 200
D) 1/15, f22, ISO 400

KirkDarling
02-19-2008, 07:20 PM
Q1. I note that we're taking an incident reading, but the term "subject failure" (a misnomer, but that's the "common" term) comes to mind. This one will call for discussion.

Cassandra_Sullivan
02-19-2008, 07:23 PM
Q1: D
Q2: B
Q3: This one makes me feel stupid. I can't wrap my brain around the 3 different variables, without one constant. I can do it with 2 variables, but I can't with 3. I even made charts and none of them matched up. Whyyyyy??? Am I trying too hard?? :confused:

Cassandra_Sullivan
02-19-2008, 07:26 PM
Q1. I note that we're taking an incident reading, but the term "subject failure" (a misnomer, but that's the "common" term) comes to mind. This one will call for discussion.

Kirk, can you define "Subject failure"? I've never heard of it - I googled and came up with nothing.

KirkDarling
02-19-2008, 07:30 PM
can do it with 2 variables, but I can't with 3. I even made charts and none of them matched up. Whyyyyy??? Am I trying too hard??

Fortunately, the same terms are used between the stem of the question and the responses.

Just jot a note for each response in terms of how many stops each factor is changing like this (examples!):

a. -1 +1 0 (in effect, no change)
b. +1 -2 +3 (an increase of two stops)
c. -3 +2 -2 (a decrease of three stops)

Mark_Levesque
02-19-2008, 07:47 PM
Q1. I note that we're taking an incident reading, but the term "subject failure" (a misnomer, but that's the "common" term) comes to mind. This one will call for discussion.
I am torn between having that discussion here or elsewhere. If we have it here, it's relevant, but will it detract from those studying and practicing? This is one of the questions I believe I answered incorrectly on my actual exam.

KirkDarling
02-19-2008, 07:52 PM
Kirk, can you define "Subject failure"? I've never heard of it - I googled and came up with nothing.


Well, an incident meter tells you how to properly expose a gray card. That works for any subject that is within a stop or two of middle gray for all the subject tones you want to capture detail in.

But what if the subject is wholly within the upper end of the range, such as white lace on white satin--and you want to retain the fabric texture even in the highlights? Or what if you're shooting a black Labrador and you want to maintain some detail of the dog's coat even in the shadows?

In that case, the middle-range incident measurement may fail to give you what you want (it's actually "measurement failure," but people have called it "subject failure"). In those cases, you may have to change some factor to get the range you want.

It might be exposure--you may have to decrease the incident setting to keep all of a totally high-end scene within the range of your materials, or you may have to increase exposure to keep all of a totally low-end scene within range. Or you may be able to change the subject lighting--specifically lower the contrast in some way.

If there was some need to keep the background identical between clients (such as with school photography), then you'd change the lighting, not the exposure.

The concept of this question is that because the reflectance of the subject doesn't change the incident reading, the exposure wouldn't change. But in the real world where some subjects are far from middle gray...it might.

Cassandra_Sullivan
02-19-2008, 08:16 PM
Fortunately, the same terms are used between the stem of the question and the responses.

Just jot a note for each response in terms of how many stops each factor is changing like this (examples!):

a. -1 +1 0 (in effect, no change)
b. +1 -2 +3 (an increase of two stops)
c. -3 +2 -2 (a decrease of three stops)

Thank You! I knew there was a way...I kind of had that in my head, but didn't know how to translate it...if that makes sense!

Q3: A (right? :o )

Kim_Critchfield
02-19-2008, 10:33 PM
D
B
C

Q3 gave me a headache.

TerryMiller
02-20-2008, 01:06 PM
1 D

2 B

3 A This question should not be answer in the morning:eek: now I'm going to be thinking about this problem all day!!

Heather_L._Smith
02-22-2008, 03:51 PM
I'll sneak my answers in before Mark lists the real answers :)

A) f5.6, 1/125, ISO 100
B) employ positive exposure compensation
C) 1/500, f2, ISO 200

Mark_Levesque
02-22-2008, 03:59 PM
Q1) An incident exposure reading for a fair skinned subject indicates f8, 1/125 at ISO 100. The next client is very dark skinned. The proper exposure for this client at the same subject position is thus:


D) f8, 1/125, ISO 100

Q2) An in-camera reflected meter reading of a very light toned scene indicates an exposure of 1/250 at f8 is called for (automatic exposure mode). For a correct exposure the photographer should:

B) employ positive exposure compensation

Q3) which of the following exposures is not equivalent to 1/60, f5.6, ISO 100

A) 1/30, f5.6, ISO 50 +1,0,-1 = 0
B) 1/250, f4, ISO 200 -2,+1,+1 = 0
C) 1/500, f2, ISO 200 -3,+3,+1 = +1
D) 1/15, f22, ISO 400 +2,-4,+2 = 0

Cassandra_Sullivan
02-22-2008, 04:20 PM
Re: Q3 - Okay so I can't do math.
I checked the 'worksheet' I used to figure the question and see my mistakes - frankly I'm not sure how I arrived at those in the first place. I must have been distracted or something...yeah, that's it. :o

Mark_Levesque
02-22-2008, 05:44 PM
It's REALLY important that you be able to do this. You have to know how many stops and in which direction a change of shutter speed, aperture, or ISO is. That's why I suggest memorizing the standard f stops, and writing them down. It's then very easy to determine the change in exposure represented by a change in aperture. You can do the same thing with standard shutter speeds if you need to, but it's pretty much just multiplying by two to move between shutter speeds.

Heather_L._Smith
02-22-2008, 06:05 PM
You know, this was an interesting question - the suggestion that Kirk had was very, very helpful to figure out the change when there were three factors involved.

The one thing I did wrong the first time I looked at the question was to write the film speeds the wrong direction. For example, I always write my apertures down first (don't know why!), starting with 1.0 and going down to smaller apertures (I now think of it as starting with a situation that gives me very little light, then moving across the scale to a situation that gives me more light), then I write my shutter speeds, starting with 1/2 or thereabouts and moving on to faster shutter speeds (again, situation that gives me very little light to situation that gives me a lot of light).

When I first wrote down the ISO speeds for this question, I went the wrong way, so my answer made no sense. When I realized that I needed to flip my ISO chart (starting with less light situation - 400 - and moving to more light situation - 50), the math worked perfectly. That probably makes no sense to anyone else!

So, I started with this:
1/2 - 1/4 - 1/8 - 1/15 - 1/30 - 1/60 - 1/125 - 1/250 - 1/500 - 1/1000

and this
1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 64

and this (wrong!)
50 - 100 - 200 - 400 - 800

when I flip-flopped my ISO chart, it worked perfectly:
800 - 400 - 200 - 100 - 50


I don't know about anyone else, but when I read the questions, I like to read the question first and try to come up with my own answer BEFORE I look at the multiple choice options.

Anyone have any other suggestions for helpful studying practices?

Mark_Levesque
02-22-2008, 06:28 PM
Not to nitpick, Heather, but between f32 and f64 is f45. :o

Heather_L._Smith
02-22-2008, 06:42 PM
Oops. Good catch! Typing too fast! Thanks, Mark!!

Cassandra_Sullivan
02-22-2008, 07:06 PM
You know, this was an interesting question - the suggestion that Kirk had was very, very helpful to figure out the change when there were three factors involved.

YES! I totally agree, even tho I screwed it up. :p


The one thing I did wrong the first time I looked at the question was to write the film speeds the wrong direction.

That's sort of what I did too the first time and that's why I screwed up - counted some + as -'s.


(I now think of it as starting with a situation that gives me very little light, then moving across the scale to a situation that gives me more light), then I write my shutter speeds, starting with 1/2 or thereabouts and moving on to faster shutter speeds (again, situation that gives me very little light to situation that gives me a lot of light).

This is such an EXCELLENT tip! Thank you!!

KirkDarling
02-22-2008, 08:25 PM
As Mark has mentioned here and in the past, be sure you have the color wheel and the aperture scale nailed down and be prepared to write them down on your scrap paper during the test. Multiple questions will depend on these. Notice that the aperture numbers double every other number, by the way.

Also make sure you understand filter factors and light ratios.

Cassandra_Sullivan
02-22-2008, 08:56 PM
I was doing the online tests and came across this:



5.Doubling the film speed will have the effect of:

Your Answer:
increasing the exposure by one stop

Correct Answer:
decreasing the exposure by one stop


Doubling the film speed decreases the exposure.

Is that right? I thought doubling the ISO means letting in more light which means increasing exposure.

KirkDarling
02-22-2008, 10:26 PM
Doubling the film speed decreases the exposure.

Is that right? I thought doubling the ISO means letting in more light which means increasing exposure.

No, when you change the ISO from, say, 100 to 200, you've got to cut the exposure in half with the aperture or the shutter to maintain the same image density.

Doubling the ISO tells the exposure meter that the sensor is twice as sensitive, so the exposure meter will want to set a smaller aperture or a faster shutter speed to compensate.

Actually, you've told the camera to double the signal amplification as though the light was half as bright. It's less confusing with film--using a film that's twice as light-sensitive obviously would require less exposure. It may help to remember that the camera exposure meter doesn't really know anything directly about the sensor--it only knows what you tell it through the ISO setting.

Eric_Merrill
02-22-2008, 11:03 PM
I'm pretty sure 3 is C.

It's not A. +1, 0, -1...balances out

C is -3, +3, +1, which doesn't balance


Eric

Erin_L._Clark
12-18-2008, 11:05 PM
Does anyone have tricks for this dyslexic to remember how to do the math for this?

Stephanie_Millner
12-19-2008, 06:08 AM
It looks more complicated than it is. Just think of it this way... More Light is PLUS, Less Light is MINUS.

Going from 1/60 to 1/125 is -1 (less one stop of light).
Going from f11 to f8 is +1 (one more stop of light)

So go column by column in each of the 3 sets of #'s (shutter speed, aperture, ISO) and mark em straight down. First go through all the shutter speeds, then f stops etc. Then just total those numbers straight through and which ever one totals out to ZERO is your correct answer... provided of course that the question asks for an exact reciprocal exposure!
___
I wrote a whole big example here that I just realized was off. I'll fix it tomorrow.