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I’m sure this is probably a novice question, but I’m asking anyway. 

So when talking about exposure there are multiple factors to take into account—aperture, shutter, ISO, any other accessories you may be using, etc.

I think I have an ok grasp of WHAT stops are. But I’m still a little confused as to how people know how many stops up or down they are shooting at? Like how do they quantify it? 

For example when they say “I brought it down three stops” are they referring to the marks on the aperture ring? Or are they just really good at “feeling” it or what? What if you’re changing the exposure of a shot without messing with the aperture? 

Like using a variable ND filter, for instance. “I under exposed the shot by like 3 1/2 stops using the variable ND”.

 

I hope this question makes sense

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7 hours ago, Max Field said:

This image might help a bit:

ISO-Shutter-Speeds-Fstops-Copyright-2009

 

Actually, it doesn’t. Not completely anyway. 

The halves, whole, and thirds columns represent stops of light? 

So if I’m shooting shutter: 1/30 - Fstop: 16 - ISO: 3200...that image is “properly” exposed? And if one wants to overexposed one stop, they either change shutter to 1/15, fstop to 11, or ISO to 3200? 

 

 

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5 hours ago, Justin Oakley said:

 

Actually, it doesn’t. Not completely anyway. 

The halves, whole, and thirds columns represent stops of light? 

So if I’m shooting shutter: 1/30 - Fstop: 16 - ISO: 3200...that image is “properly” exposed? And if one wants to overexposed one stop, they either change shutter to 1/15, fstop to 11, or ISO to 3200? 

 

 

I think you mean change the ISO to 1600...

But that said, you are correct about the shutter speed and F stop.  And lowering the ISO to 1/2 should add one stop more exposure.  But with some digital cameras this will not always be the case.  For example, shooting stills with my Canon 5d, when I change the ISO setting, the camera also changes the gain of the signal before recording the frame.  So, when I simply lower the ISO by 1/2, such as from 800 to 400, the needed F stop will change from f16 to f11 for example.  Here, changing to f11 will double the amount of light reaching the sensor, but the change from ISO 800 to 400 will darken the image by the same amount, and the result is that the image is not "over exposed" but, seems to be exposed exactly the same.

Other cameras such as the RED cinema cameras don't change the brightness of the recording with a change of ISO.  The recording is the same, only the meta data, or instructions for how to view the image change.  And in this case lowering the ISO actually shows an increase in exposure.  But in the end, it does change the instructions for the RAW conversion, and if you convert at the ISO settings from the camera capture, the exposures will look the same.  But you could, if you chose, change the ISO setting in the RAW conversion software to get a different exposure.  With my Canon camera, the ISO setting is not changeable in the RAW processing and the recording has this change baked in.  One can still change the "exposure" in RAW processing, but any gains or losses of highlight details will have already been lost.

Yup, all this will be too confusing to you, I suspect.  So, let's leave the ISO part out of the equation.  Let's define "over exposure" or "under exposure" as relative to the chosen ISO setting.  And this means to "over expose" by one stop, one would open the iris by one stop from the recommended or metered exposure at a particular ISO.  Or to increase the exposure time by one stop, as from 1/60th sec to 1/30th sec.  And in this way, you will get the desired result.  Under exposure would be just the opposite.

Be warned that a lot of what you read in articles etc. about over and under exposure is kind of BS.  I remember reading in American Cinematographer about a movie many many years ago that "quoted" the DP as saying that he "under exposed" all the night exterior shots by 2 or 3 stops.  But, in reality, he had exposed his film exactly correctly.  Much of the scene was 2 stops under "full" exposure or a little more, but also, in the scenes were highlights that were "fully" exposed or even blown out.  He had exposed correctly for the final image and any poor beginner who read the article would likely be disappointed when viewing their own movie actually under exposed by 3 stops!

I think a good way to get a "feel" of what a "stop" change looks like would be to shoot a test in a still film camera using slide film.  I'm choosing slide film here as the development is standardized, taking away a lot of variables for your test.

I would try placing your camera on a tripod and setting a white towel on the wall.  Light the towel as evenly as you can with the light coming slightly from the side to show the texture of the towel.  Set your light meter to the recommended ISO on the film box.  Put your camera in manual mode and measure the exposure using a reflective meter (not incident).  This exposure will be your "middle gray".  Then increase the exposure by 1/2 stop increments until you've exposed 5 stops over and decrease your exposures until you've exposed 5 stops under. (it is best to slate each exposure to avoid any confusion).  Then get the film developed and view all the slides on a light table arranged from darkest to lightest.  Examine each slide through a loupe to see where you begin to loose details in the towel.

This test will show you how much difference in "look" each stop of change results in and you should begin to get a "feel" for how much is "one stop" 🙂

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Posted (edited)
7 hours ago, Bruce Greene said:

I think you mean change the ISO to 1600...

But that said, you are correct about the shutter speed and F stop.  And lowering the ISO to 1/2 should add one stop more exposure.  But with some digital cameras this will not always be the case.  For example, shooting stills with my Canon 5d, when I change the ISO setting, the camera also changes the gain of the signal before recording the frame.  So, when I simply lower the ISO by 1/2, such as from 800 to 400, the needed F stop will change from f16 to f11 for example.  Here, changing to f11 will double the amount of light reaching the sensor, but the change from ISO 800 to 400 will darken the image by the same amount, and the result is that the image is not "over exposed" but, seems to be exposed exactly the same.

Other cameras such as the RED cinema cameras don't change the brightness of the recording with a change of ISO.  The recording is the same, only the meta data, or instructions for how to view the image change.  And in this case lowering the ISO actually shows an increase in exposure.  But in the end, it does change the instructions for the RAW conversion, and if you convert at the ISO settings from the camera capture, the exposures will look the same.  But you could, if you chose, change the ISO setting in the RAW conversion software to get a different exposure.  With my Canon camera, the ISO setting is not changeable in the RAW processing and the recording has this change baked in.  One can still change the "exposure" in RAW processing, but any gains or losses of highlight details will have already been lost.

Yup, all this will be too confusing to you, I suspect.  So, let's leave the ISO part out of the equation.  Let's define "over exposure" or "under exposure" as relative to the chosen ISO setting.  And this means to "over expose" by one stop, one would open the iris by one stop from the recommended or metered exposure at a particular ISO.  Or to increase the exposure time by one stop, as from 1/60th sec to 1/30th sec.  And in this way, you will get the desired result.  Under exposure would be just the opposite.

Be warned that a lot of what you read in articles etc. about over and under exposure is kind of BS.  I remember reading in American Cinematographer about a movie many many years ago that "quoted" the DP as saying that he "under exposed" all the night exterior shots by 2 or 3 stops.  But, in reality, he had exposed his film exactly correctly.  Much of the scene was 2 stops under "full" exposure or a little more, but also, in the scenes were highlights that were "fully" exposed or even blown out.  He had exposed correctly for the final image and any poor beginner who read the article would likely be disappointed when viewing their own movie actually under exposed by 3 stops!

I think a good way to get a "feel" of what a "stop" change looks like would be to shoot a test in a still film camera using slide film.  I'm choosing slide film here as the development is standardized, taking away a lot of variables for your test.

I would try placing your camera on a tripod and setting a white towel on the wall.  Light the towel as evenly as you can with the light coming slightly from the side to show the texture of the towel.  Set your light meter to the recommended ISO on the film box.  Put your camera in manual mode and measure the exposure using a reflective meter (not incident).  This exposure will be your "middle gray".  Then increase the exposure by 1/2 stop increments until you've exposed 5 stops over and decrease your exposures until you've exposed 5 stops under. (it is best to slate each exposure to avoid any confusion).  Then get the film developed and view all the slides on a light table arranged from darkest to lightest.  Examine each slide through a loupe to see where you begin to loose details in the towel.

This test will show you how much difference in "look" each stop of change results in and you should begin to get a "feel" for how much is "one stop" 🙂

Wow, thanks for this! It’s cool that you took the time to respond with such a thorough explanation. Yes, ISO 1600...that’s what I meant. 

I think I understand most of what you wrote. That chart almost made sense but I got a little confused as to what information it was trying to convey. 

I shoot with the new pocket 4K from Blackmagic and recently started cranking away at a short I wrote. I filmed in Blackmagic RAW and I’m familiar with being able to change the iso and all that. This is my first time working with any flavor of RAW (I guess “technically” it’s not true RAW, but whatever. Another conversation that is out of my scope). 

I don’t have a light meter so I can’t really do what you had suggested...but I do get the gist. 

Again, I thought I kind of knew how stops worked. But I would see a camera test, or a test of the highlight recovery feature in Resolve for example, and there would be some remark like “I over exposed by 2 stops”...and I just kind of wondered how did he know exactly how many stops? Aside from the aperture ring on the lens I don’t really know how somebody would determine this. 

And of course, adding something like a variable ND filter like I use, I have NO idea how many stops up or down I am shooting at...as there are no markings or anything. 

Again, thanks for schooling me here. I’ve been trying to figure out how to form this question and you’ve helped me out a bit. 

Edited by Justin Oakley

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Posted (edited)

I think you're going to have to acquire a meter if you want to have a fuller understanding. You can even get a phone app to start with.

Many DPs prefer to over-expose negative film somewhat- just set a lower ISO setting on the meter. You can't- or shouldn't- shoot film without one.

Edited by Mark Dunn

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Posted (edited)
13 hours ago, Justin Oakley said:

Wow, thanks for this! It’s cool that you took the time to respond with such a thorough explanation. Yes, ISO 1600...that’s what I meant. 

I think I understand most of what you wrote. That chart almost made sense but I got a little confused as to what information it was trying to convey. 

I shoot with the new pocket 4K from Blackmagic and recently started cranking away at a short I wrote. I filmed in Blackmagic RAW and I’m familiar with being able to change the iso and all that. This is my first time working with any flavor of RAW (I guess “technically” it’s not true RAW, but whatever. Another conversation that is out of my scope). 

I don’t have a light meter so I can’t really do what you had suggested...but I do get the gist. 

Again, I thought I kind of knew how stops worked. But I would see a camera test, or a test of the highlight recovery feature in Resolve for example, and there would be some remark like “I over exposed by 2 stops”...and I just kind of wondered how did he know exactly how many stops? Aside from the aperture ring on the lens I don’t really know how somebody would determine this. 

And of course, adding something like a variable ND filter like I use, I have NO idea how many stops up or down I am shooting at...as there are no markings or anything. 

Again, thanks for schooling me here. I’ve been trying to figure out how to form this question and you’ve helped me out a bit. 

Hopefully you can send in some finished work with the pocket 4K. I'd like to buy one too. 

I don't use / have a light meter. Just do test shots with digital and go with that. But it if for doc work, on the fly. In film era, I used a light meter.

Edited by Daniel D. Teoli Jr.

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I still use a light meter even when shooting with an Arri Alexa.  It's much faster than running to a video village (if you have one!) and I will always know my exposures are near correct.

I sometimes also use a light meter app on my phone when shooting still photos on film as well, and the app works quite well! 

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