View Full Version : Equivilant Exposure Help

02-02-2012, 05:55 PM
I really need help with my Equivilent exposures. I need them explained in a you're a dummy mode. I can do them all day long on my camera but on paper, I'm an utter failure at it.

Does anyone have a link to something that explains it in bare basics? I have the London and Upton Book, plus several study guides but for me its like listening to the teacher on Charlie Brown. Wah Wah Wah.

If someone is willing to skype and help this dunce out that works for me too. Help, Please!

02-02-2012, 06:08 PM
Jill, this is definitely one I struggled with on the exam. Honestly, I was annoyed that instead of your ISO, shutter and fstop going up or down equal stops the answers had your ISO going up 4, shutter down 2 and fstop down 1 ( I know my calculations aren't correct here, but you get the idea). I know the purpose of the question being that way, but I was still annoyed ;)

Steff suggested drawing and studying your ISO, shutter and fstop charts and I agree. I didn't do any of those for my test and spent a lot of time analyzing those questions.

I was surprised at the amount of math required on the exam ;)

02-02-2012, 06:10 PM
I have the charts, and I've drawn them on the times I've tested. I just realized I'd been doing my ISO's backwards.

This test has done a good job of making feel like I don't have a freaking clue.....

02-02-2012, 06:28 PM
Jill - hang in there! Sometimes you will discover that things have come naturally to you while you are doing it, but don't seem to make sense when you put them on paper. Just keep plugging away - you can do it!

02-02-2012, 06:37 PM
The fundamental issue you have to understand is that equivalent exposure is about comparing two exposures and accounting for the differences in stops for each factor (shutter speed, aperture, ISO) that contributes to the final exposure.

Here's an example question. Is 1/200, f5.6, ISO 200 equivalent to 1/100, f8, ISO 100?

consider this exposure as your baseline: 1/100, f8, ISO 100

compare each factor individually.
shutter speed at 1/200 = -1 (stops)
aperture at f5.6 = +1
ISO 200 = +1
Add them all together: = +1, so no, it's not an equivalent. If I were showing you on a piece of paper, I'd be putting the +1 or -1 directly over each factor, and adding up to the right. If the sum is zero, then the exposure is equivalent.

Let's do another. What shutter speed makes the equivalent exposure of 1/500, f4, ISO 200 if aperture is f5.6 and ISO is 100?

aperture of f5.6 is -1; ISO of 100 is -1. This makes -2. So our shutter speed needs to be +2, or two stops greater than 1/500. +2 stops of shutter speed = 4X the shutter speed. 4/500 = 1/125, so the answer is 1/125.

So the bottom line is you need to know that halving the shutter speed (e.g. from 1/500 to 1/1000) reduces the exposure by one stop, and doubling the shutter speed (e.g. from 1/500 to 1/250) increases the exposure by one stop. Don't get confused; remember that shutter speed is fractions of a second. The smaller the fraction, the shorter the duration, and the lower the exposure.

Aperture works similarly. Open a stop ADDS one stop to the exposure (e.g. going from f5.6 to f4) whereas closing a stop (e.g. from f5.6 to f8) reduces exposure by one stop.

ISO does the same thing. Increase ISO by a stop (e.g. 200 to 400) increases exposure by a stop, and decreasings ISO by a stop (e.g. 200 to 100) decreases exposure by a stop.

With this knowledge in hand, answer this question:

Which of the following is the equivalent exposure to 1/200, f11, ISO 800?

A) 1/400, f8, ISO 400
B) 1/400, f16, ISO 800
C) 1/200, f8, ISO 1600
D) 1/800, f8, ISO 1600
E) 1/100, f16, ISO 400

02-02-2012, 07:03 PM
I've seen the add and subtract thing before....

You threw the ss200 in there and I don't have that on my handy chart.

I'm going to take a break for a few hours, and come back to this. I've been on this for 2 hours, and my brain hurts.

02-02-2012, 08:21 PM

Thanks for taking the time to type that all out. Hope you don't mind, but I'm going to borrow it to give to several of my candidates that are going to take the test in March. They have a study group starting, and I think this will be something that will make it easier for them to understand (than the book, at least). :)

02-02-2012, 09:45 PM
You threw the ss200 in there and I don't have that on my handy chart.
The reason you probably don't have 1/200 listed on your shutter speed is that it not a standard setting - it's about a third of a stop off of 1/250 which is a standard speed.
Starting from a 1 second exposure - cut it in half repeatedly and you get
1 sec
1/2 sec
1/4 sec
1/8 sec
1/16 sec - usually written as 1/15 - but you may find a few old lensboard mounted lenses with 1/16
1/32 sec - written as 1/30
1/64 sec - written as 1/60
1/128 sec - written as 1/125
1/256 sec - written as 1/250
1/512 sec - written as 1/500
1/1024 sec - written as 1/1000
1/2028 sec - written as 1/2000

02-02-2012, 11:41 PM
Thanks Rick!

02-02-2012, 11:55 PM
This is so much easier for us old dudes who spent so much time looking at the full scales of apertures and shutter speeds on mechanical cameras and lenses.

02-03-2012, 12:44 AM
You're right, Kirk.
After 25-30 years of seeing the aperture scales on the lenses and the shutter sppeds on the knobs, it becomes second nature. The new cameras have digital dials and don't have scales on them anymore...

02-03-2012, 01:00 AM
In my defense...I started learning photography when I was 17....that was 20 years ago.

I'm not a digital debbie/mwac.

02-03-2012, 01:26 AM
Heather smith has a cool way of drawing them........heather?

02-03-2012, 02:26 AM
Thanks, Jeff! This was something I struggled with as well... so I had to make a chart that I could understand and recreate and that made sense to my little brain. I'm only good at math when I use Excel, so I needed something that would help me do the math in a pinch.

Now, bear with me, because I'm going to walk you through each step of this chart, and explain each build. Here we go!

As you look at the chart, on the upper left you see "Less Light" and on the upper right you see "More Light". As we begin to build this chart, keep in mind that the numbers on the left side are what we use when we have less light available to us, while the numbers as we move to the right of the chart are what we use when we have more light available to us.

Let's start with apertures. Like I said earlier, do you know all of your apertures in full stops? Well, never fear... there are really only TWO numbers you need to remember.

1.0 & 1.4


02-03-2012, 02:27 AM
If you can remember 1.0 and 1.4, then the numbers from there simply double.
1.0 becomes 2.0
1.4 becomes 2.8

And then the rest of the numbers continue to double
1.0 > 2.0 > 4.0 > 8.0 > 16 > 32 > 64 and
1.4 > 2.8 > 5.6 > 11 > 22 > 45
Y'all with me so far??

02-03-2012, 02:28 AM
Next up, we're going to add our shutter speeds to the chart.

I like to start with 1/500th (I've left off the fraction portion in this chart, simply for ease of viewing), because it's essentially in the middle. Again, just 1 number to remember.

Once you've got your 500th shutter speed down, then we DOUBLE the numbers to go up, and halve the numbers to go down
(going up) 500 > 1000 > 2000 (see, we're doubling!)
(going down) 125 > 250> 500 (see, we're cutting in half!)
And then the full scale looks like this:

02-03-2012, 02:29 AM
Finally, we add in ISO speeds. Again, I start in the middle with ISO 400. In this case, though, when we get MORE light (going UP the scale) we're going to halve the amount of ISO we need, and when we have LESS light (going DOWN the scale) we're going to DOUBLE the amount of ISO we need.
(going down) 400 > 800 > 1600 (doubling the ISO to compensate for less light)
(going up) 400 > 200 > 100 (halving the ISO to compensate for more light)

02-03-2012, 02:29 AM
Okay, now that you have all three lines together, it can really simplify any math you need to do. Here's how it works…

Which of the following would be the equivalent exposure of f/8.0, 1/500th, ISO 200?
A) f/11, 1/1000, ISO 1600
B) f/4, 1/2000, ISO 200
C) f/2.8, 1/500, ISO 400
D) f/16, 1/1000, ISO 400

Let's look at our chart. We were given the starting point of f/8.0, 1/500, ISO 200

So, with the options they've given us, let's do the math.
Starting with the aperture in option (A), we started at f/8.0, and we're moving UP the chart ONE stop to f/11, so we're going to call that a +1.

Moving on to the shutter speed in option (A), we started at 1/500, and we're moving UP the chart ONE stop to 1/1000, so we're going to call that a +1 as well. So far, that puts us at +2 stops total (+1 for the aperture, +1 for the shutter speed)

Finally we have our ISO. We started at ISO 200, and we're moving DOWN the chart THREE stops to ISO 1600, so we're going to call that a -3. The simple math tells us that our total is -1 (+1 for the aperture, +1 for the shutter speed, -3 for the ISO). So, these are NOT equivalent. Option (A) is 1 stop less than what we were given.,

02-03-2012, 02:30 AM
If we do that same math with the other options, we come to see that Option B is the correct answer.

02-03-2012, 02:31 AM
So, when you walk into that room to sit for your exam, jot this chart down on the back of your paper (yes, you can write on the paper that has the questions on it… just don't write on the bubble sheet!). Then, any questions that come up about equivalents, or full stops, or anything like that… you've got your guide right there! Now, you can't take this into the room already written down… you can't take ANYTHING into the room with you (I take that back... you can take a calculator), so make sure you've got it memorized before you go in.

I really hope this chart is helpful. I warned you that there was some explaining that needed to go with it… but hopefully it make sense! If not, I'm sure you guys will let me know!

02-03-2012, 02:58 AM
Heather, you may well have just become my best friend. ;-) Thank you!

02-03-2012, 03:22 AM
You're so welcome, Robin! If you have any questions as you go through the chart, let me know!

02-03-2012, 03:33 AM
This is so much easier for us old dudes who spent so much time looking at the full scales of apertures and shutter speeds on mechanical cameras and lenses.

I remember those days.

02-03-2012, 04:28 AM
Thank you so much! I'm going to have to digest this in the morning when I'm more alert.

02-06-2012, 09:34 PM
Okay, my stupid question of the day: As long as all factors combined equal zero, it's equivalent, right? So each factor doesn't need to go up or down the same number of stops, as long as the total is the same, right? In other words, if the shutter speed is increased TWO stops, and aperture and ISO both go down ONE, it's equivalent?

02-06-2012, 09:55 PM
Yes. The aggregate change needs to add up to be 0, which can be accomplished in any combination.

02-06-2012, 09:56 PM
Okay, I think I've got it then. Thanks Mark!

02-07-2012, 02:38 PM
Heather, those scales need to be on some kind of old-school slide rule. Actually, I think their used to be--I think it was a circular slide rule in the old Kodak Photoguide, the one with the dark brown cover.

I might still have it buried somewhere.

These look promising:

However, I'd only treat them as learning tools--in the long run, you want to learn to do this semi-automatically. You don't want to have to depend on a slide-rule in the middle of a session.

02-07-2012, 03:47 PM
Jill, the biggest advise I can give you is that the whole certification process is designed to test good practicing methods in the profession.

Because of all this new technology, good, or bad, it has really clouded the way new professionals such as yourself in all the fundamentals of photography.

So, here is a big suggestion that will take a lot of nerve to do. It's sort of like going into film mode: put tape over your display (LOL, not clear tape) and use purely manual mode at all times you're using the camera. You will then force yourself to learn exposure compensation and learn about the behavior of a light meter at the same time. Better still, get a handheld meter and learn the difference between incident light and reflected light. There is a big difference in exposure.

02-07-2012, 05:27 PM

I'm not new, I've been shooting since I was 14, and I've been shooting professionally since I was 26, which was 10 years ago. I am most certainly NOT a Digital Debbie. I can do this all day long on my camera. Its on paper where I get in trouble, which I have stated several times throughout this post. I've been studying for my CPP exam for over a year, and have worked dilligently on furthering my eduation.

I primarily shoot in manual. Please don't make assumptions because I'm having issues on the paper side of this. I'm more than a little offended by your assumptions, especially since you know nothing about me, my skill level, nor the amount of time, effort, and money I've put into learning and furthering my skills in this craft.

02-07-2012, 05:46 PM
Jill... let me just jump in and play peacemaker for a sec (in my best Mom voice). I'm absolutely certain that Michael meant no disrespect by his comments because I know him... (just like you mentioned that he doesn't know you... you don't know him, either, right?). He's been around since the dawn of time, and this is a question that pops up from almost every newbie photographer trying to pass the certification exam. We serve together on Certification Commission, and this is one of the heavier topics that always trips people up. I'm not saying YOU are the newbie... just that this is a question we see all the time from newbies who don't actually know exposure on their cameras OR on paper.

All of that being said, I totally understand where you're coming from - I, too, can do this all day long on my camera, but when I sit down to take an exam, my mind goes blank and I feel like an idiot because I can't add 1 and 1.

Don't sweat it... and don't read too much into comments. Generally speaking, comments here are meant to be helpful, not hurtful :)

02-07-2012, 08:59 PM
Actually, getting an old-fashioned, non-digital exposure meter would be a dandy way to learn this stuff. Seriously, go on eBay and look for meters like an old Sekonic studio delux or any meter with full dials. I'd bet that would do the trick with no more than a couple of hours playing with it.

I see they have an ancestor of the Sekonic Studio Delux (under the "Norwood" name) for sale for only $12.95. I may buy that one right now as a collector's item--the only reason I hesitate is because it's non-functional, and I already have a working 30+ year-old Sekonic.

But take a look at this picture and see how this would help you learn the relationships quickly:


02-07-2012, 09:54 PM
I have it all sorted out now. Persistance paid off. I just had to approach it in a way that my brain could SEE it on paper.

I know it doesn't make sense but when I try to read and assemble it on paper it falls apart for me. I've always had this problem, so I have to find workarounds for the way my brain works. I learn by doing, not by reading or being told.

02-08-2012, 05:06 AM
He's been around since the dawn of time, LOL, this is the second thread today that has made reference to my age;)

Jill, no disrespect intended. Like Heather said. The thing about the exam is that if you have been practicing a while, and you have been practicing good solid techniques, you will probably pass without studying! Just read the questions and figure out how you would do it in your real life practice. Also, don't get too hung up on certain aspects of the exam because the exposure compensation makes up only a few of the questions. You have another 95 or so questions to negotiate.

As Don Cornelius would say (rest his soul train)

"Love, Peace, annnd soul"