Does the camera ISO change exposure?

[PakkyT]

Are you saying that increasing ISO has no effect on the brightness of a RAW file ?

I am guessing he misspoke and meant to say that ISO setting does not effect the light hitting the sensor, rather than the raw file.

 

[Deleted member 29285]

I am guessing he misspoke and meant to say that ISO setting does not effect the light hitting the sensor, rather than the raw file.

I just did a series of test exposures, and found that increasing ISO above base level (200 ISO) increased the RAW file brightness, ie the histogram moved to the right.

 

[Hendrik]

I just did a series of test exposures, and found that increasing ISO above base level (200 ISO) increased the RAW file brightness, ie the histogram moved to the right.

Absolutely as expected, but if you only increased ISO rather than exposure time or aperture, you only changed the value of the ISO tag and the accompanying interpretation of the file, but, other than that, it's a mathematical illusion and the result is something you could have done in your photo editor without too much trouble. The articles referenced earlier in the thread by @Mack should help spread light on the question.

 

[Stanga]

Absolutely as expected, but if you only increased ISO rather than exposure time or aperture, you only changed the value of the ISO tag and the accompanying interpretation of the file, but, other than that, it's a mathematical illusion and the result is something you could have done in your photo editor without too much trouble. The articles referenced earlier in the thread by @Mack should help spread light on the question.

This is not strictly correct. The increase in ISO introduces random colour artefacts into the image digital data. That's one reason why photo stacking is used, namely to subtract those random artefacts. This is especially critical in Astro photography, where random artefacts are sharing the same location as genuine low light level information. Taking an astro picture at a low ISO and then bumping it up in post to amplify the colours and detail captured of a dark space object doesn't work in practice. Each sensor pixel has to have captured enough detail of the light falling on it for it to be above the artefacts noise level, and given a valid digital value. At too low an ISO, the genuine info can get lost amongst the amplification error.

 

[Machi]

Absolutely as expected, but if you only increased ISO rather than exposure time or aperture, you only changed the value of the ISO tag and the accompanying interpretation of the file, but, other than that, it's a mathematical illusion and the result is something you could have done in your photo editor without too much trouble. The articles referenced earlier in the thread by @Mack should help spread light on the question.

Changing ISO changes read noise of camera for non isoless cameras (ISO variable cameras).
That's why there is a visible difference in the darkest part of image.
This comparison shows that effect for the 16 Mpix Olympus with Sony sensor
(aperture and exposure time was the same for every image).

Subscribe to see EXIF info for this image (if available)

 

[BushmanOrig]

I just did a series of test exposures, and found that increasing ISO above base level (200 ISO) increased the RAW file brightness, ie the histogram moved to the right.

The histogram

One of the problems with the histogram is the following. When the ISO is set to AUTO the histogram has very little value as an exposure tool, because it's not clear if the histogram displays brightness or exposure.

A simple method to correct that is to set a fixed ISO value. The moment you fix the ISO to for example ISO200 the histogram becomes an exposure tool. The reason is the only variables that now change the histogram are shutter speed and aperture.

Amplification (brightness or ISO)

Another interesting topic some posters touched is what amplification takes place when. There are three interesting elements:-

- the inherent sensor gain (set at the factory & linked to sensor technology)
- the analog gain amplifier
- the digital gain amplifier

Looking at only the two gain amplifiers.

• The noise coming from these two amplifiers are different. The analog amplifier has its own SNR plus a variable noise component linked to what amplification is selected at any time.
• The noise coming from the digital amplifier is different because this amplifier is in the digital path and linked to reference tables.

It might be worth isolating these two amplifiers to see which you prefer for example astrophotography. This is a way you could test the results:-

• I read in one of the posts the EM5 II analog gain amplifier operates from ISO200 to ISO3200. I think 3dpan mentioned he tested this amplifier with different settings.
• How to test the digital gain amplifer? It's simple, just do your tests from ISO3201 upwards. Above ISO3200 we know the analog gain amplifier is fixed at its max (its a constant) and its only the digital working.
• This is only an idea - I haven't tried this at all...

It would be interesting to see the differences.

It will be really great if Olympus gives us a little more control...

 

[RS86]

The histogram

One of the problems with the histogram is the following. When the ISO is set to AUTO the histogram has very little value as an exposure tool, because it's not clear if the histogram displays brightness or exposure.

A simple method to correct that is to set a fixed ISO value. The moment you fix the ISO to for example ISO200 the histogram becomes an exposure tool. The reason is the only variables that now change the histogram are shutter speed and aperture.

I asked this earlier in the thread, but this again contradicts how I have understood certain things.

I use Auto-ISO in Manual Mode and adjust it with Exposure Compensation so I don't burn highlights. I thought "ETTR" works in this case on top of it, but it doesn't.

Anyway, this is a feature people wanted to cameras and both PEN-F and GX9 of my cameras can do it. So why did people want it if Exposure Compensation in this case doesn't work as exposure tool? It makes no sense.

This type of shooting is very good in low-light. I can put certain shutter speed (something like 1/100 and fully open aperture of course with our sensors) to freeze movement. Now the Auto-ISO here makes shooting very fast in changing light situations. This gives me maximum quality in low-light (because I would otherwise have to up the fixed ISO just in case), it freezes the movement I want and also gives me fast way to not burn highlights. Without Auto-ISO I will miss shots as adjusting it is not so fast.

Why doesn't the histogram work as exposure tool in this case? How should I know how to expose then?

 

[PakkyT]

I use Auto-ISO in Manual Mode and adjust it with Exposure Compensation so I don't burn highlights. I thought "ETTR" works in this case on top of it, but it doesn't.

If you are in full manual mode and thus are setting both the shutter and aperture yourself, then Exp Comp (which is only available if you are using Auto-ISO?) is just changing the ISO. So you are just changing the analog gain, I believe, on the data before it is digitized into the RAW data. So the histogram is showing you the over all brightness of the scene as it predicts it will be when the shot is taken and that brightness is made up of the actual light hitting the sensor (shutter and aperture) and the ISO setting amplifying the analog data.

Since you have already locked down your shutter and aperture then when you use Exp Comp the changes you are seeing in the histogram represent the amplification effects only since there is no change to the light hitting the sensor. Part of the confusion is the terminology being used in this thread. Typically "exposure" is shutter, aperture, and ISO settings, but in this discussion some are breaking this out into "Exposure"=S+A and brightness = exposure+ISO amplification.

Anyway, this is a feature people wanted to cameras and both PEN-F and GX9 of my cameras can do it. So why did people want it if Exposure Compensation in this case doesn't work as exposure tool? It makes no sense.

It would seem to me (unless others have other uses I didn't think of) using Manual + Auto ISO is for when you must control both shutter and aperture at the same time and then to get the final brightness of the image to look "proper" you would then need to adjust the ISO. Since S+A are the two settings that you actually care about and will be adjusting the ISO to whatever it needs to be, why not ask the camera to do that for you then. That is why I think people wanted it; let the camera take care of the third setting for which they don't have a strong need to control.

This type of shooting is very good in low-light. I can put certain shutter speed (something like 1/100 and fully open aperture of course with our sensors) to freeze movement. Now the Auto-ISO here makes shooting very fast in changing light situations.

Right but if the only thing you are concerned about it shutter speed to freeze movement then really you are talking about Shutter Priority mode. You are manually setting the aperture fully open to capture as much light as you can, but in any situation where your ISO is going to auto increase anyway, you could just use shutter priority which will automatically open the aperture fully anyway. The advantage of Shutter Priority over Manual+Auto ISO is if somehow the scene got a lot brighter, with your method, once the ISO got back to 200 is can not go lower and you risk overexposing. If you used S mode instead, then after the ISO got to 200 it could then also start closing down the aperture as well to maintain proper exposure.

 

[RS86]

If you are in full manual mode and thus are setting both the shutter and aperture yourself, then Exp Comp (which is only available if you are using Auto-ISO?) is just changing the ISO. So you are just changing the analog gain, I believe, on the data before it is digitized into the RAW data. So the histogram is showing you the over all brightness of the scene as it predicts it will be when the shot is taken and that brightness is made up of the actual light hitting the sensor (shutter and aperture) and the ISO setting amplifying the analog data.

Since you have already locked down your shutter and aperture then when you use Exp Comp the changes you are seeing in the histogram represent the amplification effects only since there is no change to the light hitting the sensor. Part of the confusion is the terminology being used in this thread. Typically "exposure" is shutter, aperture, and ISO settings, but in this discussion some are breaking this out into "Exposure"=S+A and brightness = exposure+ISO amplification.



It would seem to me (unless others have other uses I didn't think of) using Manual + Auto ISO is for when you must control both shutter and aperture at the same time and then to get the final brightness of the image to look "proper" you would then need to adjust the ISO. Since S+A are the two settings that you actually care about and will be adjusting the ISO to whatever it needs to be, why not ask the camera to do that for you then. That is why I think people wanted it; let the camera take care of the third setting for which they don't have a strong need to control.



Right but if the only thing you are concerned about it shutter speed to freeze movement then really you are talking about Shutter Priority mode. You are manually setting the aperture fully open to capture as much light as you can, but in any situation where your ISO is going to auto increase anyway, you could just use shutter priority which will automatically open the aperture fully anyway. The advantage of Shutter Priority over Manual+Auto ISO is if somehow the scene got a lot brighter, with your method, once the ISO got back to 200 is can not go lower and you risk overexposing. If you used S mode instead, then after the ISO got to 200 it could then also start closing down the aperture as well to maintain proper exposure.

Yeah. Well I use that method in low-light such as indoors or when it is dark outside, when I'm photographing people etc. I'm not sure if there are situations when ISO will get to 200 in low-light, any examples?

Also I find it better to have it fully open or some other aperture than it bouncing unpredictably to some totally different look. With the exposure compensation dial it is pretty fast to tune it.

 

[PakkyT]

Yeah. Well I use that method in low-light such as indoors or when it is dark outside, when I'm photographing people etc. I'm not sure if there are situations when ISO will get to 200 in low-light, any examples?

Ya I think most of the time the dark situations we are in for this type of shooting it is not likely to suddenly get brighter than it is (dinner party, basketball game, etc.). But it could happen on rare occasions, say shooting a play and in one scene suddenly it gets MUCH brighter on the stage (I don't know, a scene where God is now talking to the actor and God is represented by a super bright spot light on the actor). Or you are out shooting sport on a dark rainy day but momentarily the sun breaks through the clouds and everything is significantly brighter at a key moment you are shooting some action. But ya, exceptions rather than the rule.

Also I find it better to have it fully open or some other aperture than it bouncing unpredictably to some totally different look. With the exposure compensation dial it is pretty fast to tune it.

Right, that is when you sometimes need to control both and have to let ISO go where it may.

I thought of another reason why people might have wanted Auto-ISO. Zoom lenses without a fixed aperture. As you said, you might want to set your lens wide open so you are not changing the look to much. But variable aperture lenses will still close down as you zoom to longer focal length. So Auto-ISO in manual helps keep your brighten levels the same as you zoom in or out when using a fixed S+A.

 

[BushmanOrig]

I asked this earlier in the thread, but this again contradicts how I have understood certain things.

I use Auto-ISO in Manual Mode and adjust it with Exposure Compensation so I don't burn highlights. I thought "ETTR" works in this case on top of it, but it doesn't.

Anyway, this is a feature people wanted to cameras and both PEN-F and GX9 of my cameras can do it. So why did people want it if Exposure Compensation in this case doesn't work as exposure tool? It makes no sense.

This type of shooting is very good in low-light. I can put certain shutter speed (something like 1/100 and fully open aperture of course with our sensors) to freeze movement. Now the Auto-ISO here makes shooting very fast in changing light situations. This gives me maximum quality in low-light (because I would otherwise have to up the fixed ISO just in case), it freezes the movement I want and also gives me fast way to not burn highlights. Without Auto-ISO I will miss shots as adjusting it is not so fast.

Why doesn't the histogram work as exposure tool in this case? How should I know how to expose then?

Hi, I see PakkyT already gave you an answer, I had a quick look and I think we on the same page. Here a few more thoughts...

When you read my posts you will see I like to isolate things. This is why I focus only on those technical aspects that give us understanding and which we can control. This is why it is so critical to know shutter speed and aperture is exposure and ISO is image brightness or the total camera system gain. From my above answer, you saw I isolated analog gain from digital gain. I could only do that because I made sure I know how it works. The image below explain this well...

Subscribe to see EXIF info for this image (if available)

We also know it is key to expose the sensor well. The sensor performs at its best just before clipping. For many, this is a big change because we like to expose the scene in the camera and in the process we could underexpose and have more noise and less tonal or image data. (See further down - another level)

One can go to the extreme and expose for each individual image and in some critical cases, I do that. On the other hand, when you photograph a concert and focus on the stage only, you can set up the exposure once, and from there on, use one configuration with small exp comp corrections.

For example:

- Set the ISO to the best value for the stage and what you want (freeze or a little blur)
- Use Shutter mode (Auto) and set the shutter speed (freeze or blur)
- The shutter & ISO are now isolated (fixed) - Now exp comp will vary the aperture
- Exposure comp will now set the final exp - use the histogram when fine-tuning exp

You could also decide to select aperture mode (A-mode) - this basically fix or isolate aperture & ISO. The exp comp will now vary the shutter speed (exposure) and the histogram...

With a little practice, this all becomes second nature. A process of isolating variables and the histogram readout and your control over exposure and image brightness become very accurate...

Few comments:-

1. I originally started talking about ETTR. As the discussion developed I realized ETTR is confusing to many. I like to re-name ETTR as a simple technique to optimize the exposure. The are many techniques to optimize exposure - ETTR is one of them.
2. For every ISO there is an optimum exposure. We know Olympus cameras tend to expose conservatively and we need to help the camera to exposure optimally by shifting the histogram to the right

You can add another level:-

1. If you selected your ISO and you have set the exposure then we know for a specific ISO the sensor is optimally exposed...
2. You can now adjust the image brightness with the curves function. This helps those who like to have a ready jpeg. (Adjust the mid-tones, center point on the curves function)
3. The only difference is for each curves adjustment the histogram will change. If you were setting up a concert average keep the "new curves" histogram position in mind so that you do not overexpose when applying exp comp...

I hope this wordy explanation is helpful. I think you can see the concept of isolation or step by step makes the histogram a very powerful tool plus the Olympus unique flexibility...

Siegfried

 

[BushmanOrig]

More on the concept of isolation:-

See my post above where I explain how we can isolate variables like shutter speed or ISO to only see the changes in the aperture on the histogram. Why is this important? Because we want to know if we adjust exposure (optimize the sensor) or if we adjust image brightness.

You can add another layer to the concept of isolation:-

Some posters already mentioned it but I did not see it discussed much. If we go back to the concert example above, let's assume we selected the following settings:-

- The camera is in S-Mode (Shutter speed mode)
- ISO - 1000
- Shutter Speed - 1/100
- We checked the "stage" exposure and set an exp comp of +2/3EV to move the histogram as far right as possible
- The camera is now set - all we will do from here onward is small exp comp adjustments if needed.

What is the next layer?

- We went from a place where the histogram represents ISO, aperture, and shutter speed all at the same time. Using the technique of isolation we changed the histogram to only display changes in the aperture. (It's possible to only display ISO changes if that is what you want)
- The next layer is following a similar process of isolation to how the camera read exposure. Think of ESP as (ISO, shutter & aperture displayed on the histogram). If you switch to center-weighted you isolate parts of the metering and you focus on the center of the image. If you select spot metering you isolate one more step...

Going back to the evening out at a concert. By following a simple process of isolation you can set up your camera to become extremely specific and accurate. Why is this process new to many? I think it because we used to program buttons. Assigning a function to a button is completely normal to us. If you think about it, the process of isolation re-program (like a button) the histogram. The histogram is a powerful key tool helping us expose the sensor to its best possible performance...

Best

 

[RS86]

When the ISO is set to AUTO the histogram has very little value as an exposure tool, because it's not clear if the histogram displays brightness or exposure.

Hmmh. I tried to understand why you said histogram has little value as an exposure tool with Auto-ISO. I don't know if you answered that?

What are you suggesting we use as an exposure tool if not the histogram with Auto-ISO? Just shoot blind and hope for the best? Or is there a misunderstanding what we mean by "exposure tool" or something?

As I have understood it with help of PakkyT, when I have Auto-ISO and adjust with exposure compensation, I will change the ISO manually basically even if it is automatic otherwise. And I would have thought the histogram will reflect the situation that is going on in jpeg's as always.

 

[BushmanOrig]

Hmmh. I tried to understand why you said histogram has little value as an exposure tool with Auto-ISO. I don't know if you answered that?

What are you suggesting we use as an exposure tool if not the histogram with Auto-ISO? Just shoot blind and hope for the best? Or is there a misunderstanding what we mean by "exposure tool" or something?

As I have understood it with help of PakkyT, when I have Auto-ISO and adjust with exposure compensation, I will change the ISO manually basically even if it is automatic otherwise. And I would have thought the histogram will reflect the situation that is going on in jpeg's as always.

xxxx

When the ISO is on auto it could happen that when you apply exp comp that instead of the "aperture or shutter speed" (exposure) changing the ISO change. When the ISO changes the histogram is an image brightness tool and not an exposure tool. You need to decide do you want to change exposure or image brightness. If you want to exposure optimally then its exposure you like to adjust.

To understand exposure (aperture & shutter speed) and then ISO (gain/brightness) see this great video...

If you saw the video you seen the mathematical link between ISO and exposure. Many here refer to this link. What the presenter did not talk about is sensor performance. Its when you study the sensor that you see aperture and shutter speed is key to get the sensor to perform at its best.

I hope this clears your questions...


I just want to add:- we a little deep into this subject. On your day to day photography you probably never change exp comp. That's OK. Its only in unique situations that one really go through the details. Its also then that you need a practiced skill.

 

[Robstar1963]

I found this thread quite interesting for the first two pages or so
By page 4 it got to be hard work and I was no longer gaining anything by reading it !
I think it has reinforced some things I already knew but to summarise my understanding:-
It is best to get your exposure correct or even better to sometimes optimise it by using ETTR which by all accounts just requires slightly overexposing you’re shots by 1/3 - 1/2 stop ?
It is best to keep your ISO setting as low as possible but only to the point where you hit your camera’s optimal ISO setting ie ISO 200 for most M43 cameras
Increasing ISO will increase noise in your images because the function of the ISO setting is to amplify the signal you start off with but this is necessary when you are faced with perhaps low light and resulting slow/ unsuitable shutter speeds and aperture values for example
Larger sensors will produce less noise because they generally collect more light (assuming sensors compared are of a similar generation and of similar technology)
Smaller sensors can perform as well as larger sensors of an older generation because of technological advances
Sony’s A7 111 performs better than the A7 11 because the technology has moved on and is of a completely different generation

Now could anyone advise as to anything I have got wrong and if not this would seem to be a summary I can use
Assuming I have got this about right - anyone joining late could easily use this summary to save themselves reading through the thread ?
Please note I did not get as far as page 5 so if I’ve missed anything then please forgive my error ???

 

[RS86]

xxxx

When the ISO is on auto it could happen that when you apply exp comp that instead of the "aperture or shutter speed" (exposure) changing the ISO change. When the ISO changes the histogram is an image brightness tool and not an exposure tool. You need to decide do you want to change exposure or image brightness. If you want to exposure optimally then its exposure you like to adjust.

To understand exposure (aperture & shutter speed) and then ISO (gain/brightness) see this great video...

If you saw the video you seen the mathematical link between ISO and exposure. Many here refer to this link. What the presenter did not talk about is sensor performance. Its when you study the sensor that you see aperture and shutter speed is key to get the sensor to perform at its best.

I hope this clears your questions...

I just want to add:- we a little deep into this subject. On your day to day photography you probably never change exp comp. That's OK. Its only in unique situations that one really go through the details. Its also then that you need a practiced skill.

Well I just use the Auto-ISO in low-light to get best results fast. If I had to change ISO manually to get maximum image quality, it would slow down my shooting considerably and give blurry results more easily.

In this case I want to have aperture fully open all the time with our sensors. Also I want to get maximum quality, so I want to have the slowest possible shutter speed to freeze movement. So usually the settings will be something like f/1.8 & 1/100.

So I think the confusion here lies in the word "exposure". Exposure compensation in this case gives me very handy and fast "tool" to get the results I want in different cases, eventhough the ISO is automated, which is also very handy. When I'm shooting people I don't care much if the ISO goes up and I can put maximum ISO limit to something like 10000 or 12800 with PEN-F. The moments are more important than some noise and you can always make it B&W.

For me it doesn't matter in this case if the histogram or exposure compensation is "brightness tool" or "exposure tool". It is a great "tool" nonetheless in my opinion. I can just roll the dial to see changes in histogram (it still works, no?) and if highlights are clipped or not and if I want it or not.

 

[BushmanOrig]

Well I just use the Auto-ISO in low-light to get best results fast. If I had to change ISO manually to get maximum image quality, it would slow down my shooting considerably and give blurry results more easily.

In this case I want to have aperture fully open all the time with our sensors. Also I want to get maximum quality, so I want to have the slowest possible shutter speed to freeze movement. So usually the settings will be something like f/1.8 & 1/100.

So I think the confusion here lies in the word "exposure". Exposure compensation in this case gives me very handy and fast "tool" to get the results I want in different cases, eventhough the ISO is automated, which is also very handy. When I'm shooting people I don't care much if the ISO goes up and I can put maximum ISO limit to something like 10000 or 12800 with PEN-F. The moments are more important than some noise and you can always make it B&W.

For me it doesn't matter in this case if the histogram or exposure compensation is "brightness tool" or "exposure tool". It is a great "tool" nonetheless in my opinion. I can just roll the dial to see changes in histogram (it still works, no?) and if highlights are clipped or not and if I want it or not.

You and RS86 summed it up perfectly. Probably the most important statement in the complete discussion is:-

The moments are more important than some noise and you can always make it B&W.

I also think you understood the concept of "brightness" versus "exposure" tool. For that day you really want to push out every little detail & low noise from the sensor you will also know what to do...

This morning I was walking in our local forest with an old Panasonic LC1and the dynamic range was so wide that no matter how I moved the histogram, no joy. I ended up taking bracketed exposures to create HDR shots in PS.

Best - love to see some of your images...

 

[Erich_H]

What! My eyes are tearing up again, and my will to live has definitely decreased. I should've known better!

I think I'll just go out and take some pictures, with ISO set to Auto, to resuscitate my mental health... ?

Note: No insults implied or intentionally intended!

 

[BushmanOrig]

What! My eyes are tearing up again, and my will to live has definitely decreased. I should've known better!

I think I'll just go out and take some pictures, with ISO set to Auto, to resuscitate my mental health... ?

Note: No insults implied or intentionally intended!

Interesting Erich, you had the courage to post emojis all over the place, make weird statements throughout but not the self-confidence to debate? That's OK ? would probably not have been really interesting. Don't forget to take a lens with you...?

 

[Brownie]

Interesting Erich, you had the courage to post emojis all over the place, make weird statements throughout but not the self-confidence to debate? That's OK ? would probably not have been really interesting. Don't forget to take a lens with you...?

Only one of the reasons people tend to dislike you.