Olympus Camera ISO

[Youngjun]

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DxOMark Derived Measured ISO

I currently own two camera bodies: Olympus PEN E-PM2 and Panasonic DMC-G5.
Last night I noticed my Panasonic body is more sensitive to light than the Olympus body.
I was taking star trails, @ISO200 on Olympus, @ISO160 on Panasonic on two different nights.
The same lens was used at the same aperture, and I expected the images from the Panasonic to include less number of stars; however it was the opposite.

E-PM2 at ISO200:

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DMC-G5 ISO160:

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It could've been the transparency issue, but I did a quick google search and found the link above.

According to DxO, Olympus body's ISO setting is displayed as twice as it actually is (I may have worded it wrong, for the lack of knowledge). I assumed the ISO value to be an international convention; meaning ISO400 is the light sensitivity of the sensor that is going to be the same for all the sensors.

Looking at the graph, Panasonic was actually taking photos at ISO160, while Olympus was taking photos at ISO100 (although the settings were showing ISO 200).

Can anyone explain what is actually going on? To my understanding so far, Olympus messed up the ISO settings on their system.

This may have been discussed somewhere else, but I can't find the thread, so I am starting this one.

 

[Growltiger]

Looks like you had two very different exposure times.
(I don't understand DxO's approach. Most cameras seem to be faulty according to their measurements.)

 

[Janez]

Sensitivity of the sensor and ISO number are actually two different things. When you change the ISO you don not really change the sensitivity, sensitivity of the sensor is fixed and manufacturers strive to make it as high as possible. When you take a photo at 100 ISO or at 1600 ISO the sensitivity of the sensor does not change. What changes is the amplification of the analog amplifier which amplifiers the signal from the pixel. Then comes the analog to digital conversion and the signal data from each pixel is stored into RAW file.

I am not sure why Olympus chose to use different ISO designation than the others.

The experimental data will always differ slightly from the theoretical data, no matter how advanced the science behind the measurements of the hardware is.

Also one important thing to know. Usually the analog amplification goes just to 1600 ISO, everything above that is software amplification of the digital values. So practically it would make sense that the highest ISO you would use is 1600 and that you bring the exposure yourself in post processing. Since you have complete control you can do it more intelligently than the camera does it since it is also doing it in post processing.

 

[MichaelSewell]

I can confirm the E-M1 ISO rating aligns with the Nikon D4
However, there is a difference between the D4 and the Nikon D810 that is seen again between the E-M1 and the D810

ISO values in the digital arena are simply to give us something to gauge where we are on the sensitivity scale, and is an approximation to the original ISO grades of film (originally ASA).
To be honest, there used to be a fair amount of latitude in ISO values amongst manufacturers of film.

 

[Youngjun]

Looks like you had two very different exposure times.
(I don't understand DxO's approach. Most cameras seem to be faulty according to their measurements.)

Yes I did have two different exposure times, Panasonic one is longer, but that is not a factor there I think. Longer exposure = longer trails.
In fact both were taken at 30 s intervals. Just different number of shots combined.

I am not sure why Olympus chose to use different ISO designation than the others.

Yes, that is what I meant! Thank you for clarifying. So Olympus is using a different scale on the "ISO"?

 

[Youngjun]

I can confirm the E-M1 ISO rating aligns with the Nikon D4
However, there is a difference between the D4 and the Nikon D810 that is seen again between the E-M1 and the D810

ISO values in the digital arena are simply to give us something to gauge where we are on the sensitivity scale, and is an approximation to the original ISO grades of film (originally ASA).
To be honest, there used to be a fair amount of latitude in ISO values amongst manufacturers of film.

Oh so it is not the manufacturer dependent. The same manufacturer may choose different scale/range for the ISO. Thank you for the additional info!

 

[Youngjun]

So there is no set convention for ISO vs physical light amount(photons hitting the sensor surface)?
In other words, ISO 200 alone does not mean the same on one system from another, but ISO200-400-1600 is meaningful within the same system.

 

[MichaelSewell]

Oh so it is not the manufacturer dependent. The same manufacturer may choose different scale/range for the ISO. Thank you for the additional info!

LOL
I wouldn't say they choose to have a different scale of sensitivity.
The difference within a manufacturer's range of camera bodies can be linked to the different sensors.
The D810 is a completely different sensor to the D4

I suppose it would be nice if there were a defined sensitivity scale that was measurable, and therefore enforceable, in the same manner that we have shutter speeds and apertures. And yet, shutter speeds used to be subject to variation between bodies, even within the same model at one time, when they were mechanically timed, rather than electronic. Apertures weren't necessarily as accurate as they are now either.

 

[MichaelSewell]

So there is no set convention for ISO vs physical light amount(photons hitting the sensor surface)?
In other words, ISO 200 alone does not mean the same on one system from another, but ISO200-400-1600 is meaningful within the same system.

Usually they are close enough across systems to be within the ballpark.
I have noticed some quite large differences whilst teaching/mentoring lighting courses.

I found there to be consistent differences between Nikon and Canon, and anything up to a full stop (1EV) difference.
The main thing is that the difference along the ISO scale is accurate. 100ISO is a full stop difference to 200ISO etc

 

[MichaelSewell]

Incidentally, talking of Nikon and Canon, I found the greater differences were in the entry level models, whereas the High end bodies were much, much closer.

 

[Youngjun]

I found there to be consistent differences between Nikon and Canon, and anything up to a full stop (1EV) difference.
The main thing is that the difference along the ISO scale is accurate. 100ISO is a full stop difference to 200ISO etc

This was where I failed to describe in words, thank you!

So say ISO100 to ISO200 is the same difference in EV for any systems,
but ISO100 in system A does not have to be the same brightness as ISO100 in system B.

 

[maritan]

1. You mentioned two different nights. What were the moon phases on each of those nights?
2. Were at the same location on both nights?

 

[David A]

Looking at your graph, the measured ISO for the Panasonic is higher than the measured ISO for the Olympus when both are set to the same ISO. A higher measured ISO means that the camera will give less exposure, a lower measured ISO means it will give more exposure. If you give more exposure then in a scene like your star scene, you will see more stars. The graph predicts the result you're getting, you're just interpreting it the wrong way around.

There is a standard for light meters and you probably won't see much variance in a test like the DxO test if you compare hand held meters since they are calibrated based on a standardised target. The problem for camera manufacturers is that people aren't photographing the standard test targets used to calibrate meters, they're photographing real life scenes in which different parts of the scene have different levels of brightness. If they set the meter so that it suggests more exposure, people will clip the highlights a lot more than if they set the meter to suggest less exposure. Camera manufacturers make a decision about how people are going to use their cameras and what kinds of scenes people are going to be shooting. They don't want users who simply put the camera on Auto and shoot to clip highlights and end up getting ugly photos too often, and they make an assumption about how much brighter than a standard test target the brightest highlights that people are going to want to keep detail in will be. Panasonic are setting their meter so that the sensor will preserve highlight detail but you will get slightly less shadow detail in scenes which contain bright highlights and areas of shadow. Olympus are setting theirs to preserve more shadow detail but that means that you will lose a bit more highlight detail if you shoot the same scene. It's just that the camera manufacturer has to make a decision about what's going to be more important to the user, highlight detail or shadow detail, when you shoot a real life scene with a range of different brightnesses in the frame and Panasonic and Olympus have made different decisions on what is going to be more important to the user.

 

[MichaelSewell]

This was where I failed to describe in words, thank you!

So say ISO100 to ISO200 is the same difference in EV for any systems,
but ISO100 in system A does not have to be the same brightness as ISO100 in system B.

Pretty much, although they should be fairly close.
An easy test is to shoot a scene correctly exposed. (first image)
Drop the ISO by a full stop and take a second shot, therefore underexposing by a full stop.
Now drop the ISO by another full stop and take a third shot.
Reduce the shutter speed by a full stop, and take a fourth image.
Reduce the shutter speed another full stop and take a fifth image.

The first and fifth images should be identical
The second and fourth images should be identical
The third should be underexposed

In your post processing software, you should see the difference illustrated in the histograms. Some software shows vertical lines in the histogram, indicating Stop values (or Exposure Values if you are younger than I!!)

 

[Youngjun]

1. You mentioned two different nights. What were the moon phases on each of those nights?
2. Were at the same location on both nights?

There were four days apart, and were at the same location.
I think the moon phase won't be an issue for the star counts. If the moon was brighter, the background would be brighter, and the number of stars "detected" on the sensors won't change, unless the background gets too bright, even brighter than the faint stars.

Looking at your graph, the measured ISO for the Panasonic is higher than the measured ISO for the Olympus when both are set to the same ISO. A higher measured ISO means that the camera will give less exposure, a lower measured ISO means it will give more exposure. If you give more exposure then in a scene like your star scene, you will see more stars. The graph predicts the result you're getting, you're just interpreting it the wrong way around.

I do agree with the graph. Where I was confused was that G5-ISO160 was more sensitive than PM2-ISO200.
Now I understand that G5-ISO and PM2-ISO are not the same. When both are converted to DxO-ISO, PM-ISO is twice as G5-ISO.

There is a standard for light meters...

Light metering is irrelevant when shooting Manual mode I thought.

 

[Youngjun]

Pretty much, although they should be fairly close.
An easy test is to shoot a scene correctly exposed. (first image)
Drop the ISO by a full stop and take a second shot, therefore underexposing by a full stop.
Now drop the ISO by another full stop and take a third shot.
Reduce the shutter speed by a full stop, and take a fourth image.
Reduce the shutter speed another full stop and take a fifth image.

The first and fifth images should be identical
The second and fourth images should be identical
The third should be underexposed

In your post processing software, you should see the difference illustrated in the histograms. Some software shows vertical lines in the histogram, indicating Stop values (or Exposure Values if you are younger than I!!)

These are very informative to me. I am still in the beginning of camera-photography learning stage, and so many terms I see are very ambiguous/confusing.

 

[MichaelSewell]

These are very informative to me. I am still in the beginning of camera-photography learning stage, and so many terms I see are very ambiguous/confusing.

Unfortunately, there are many terms that are from the film era of photography, and I apologise for using them. A stop used to refer to the difference in exposure between 1/125th sec and 1/250th sec, or between f5.6 and f8, or between ISO200 and ISO400.
The correct term utilised today is the Exposure Value, or EV, and all the above mentioned differences of one stop are equal to a difference of one EV

Most photographers tend to set their cameras for adjustments of 1/3rd EV
So you would see f5.6, f6.3,f7.2,f8 where the two figures between f5.6 and f8 are 1/3rd values
ISO200, 250, 320, 400
1/125th sec, 160, 200, 250

 

[Amin]

View attachment 106654
DxOMark Derived Measured ISO

According to DxO, Olympus body's ISO setting is displayed as twice as it actually is (I may have worded it wrong, for the lack of knowledge). I assumed the ISO value to be an international convention...

Can anyone explain what is actually going on? To my understanding so far, Olympus messed up the ISO settings on their system.

This may have been discussed somewhere else, but I can't find the thread, so I am starting this one.

Here is an old post where I addressed this issue: DxOmark Finally Tests the Olympus OM-D E-M5

 

[David A]

I do agree with the graph. Where I was confused was that G5-ISO160 was more sensitive than PM2-ISO200.
Now I understand that G5-ISO and PM2-ISO are not the same. When both are converted to DxO-ISO, PM-ISO is twice as G5-ISO.


Light metering is irrelevant when shooting Manual mode I thought.

There is a standard for light meters, and it defines the exposure the meter suggests when it is used to measure a standard target of uniform reflectance under standard conditions. People do not usually photograph standard targets of uniform reflectance under standard conditions. They photograph real life scenes under varying conditions and parts of those scenes are going to be brighter than a standard target, other parts of the scene are going to be darker. The proportion of brighter and darker parts of the scene vary from one scene to another, and the average brightness level of the scene can be brighter or darker than the brightness of the standard target. In addition you don't always want to achieve the same result. You can photograph a person against a bright background. If you want them to appear in silhouette you need to give a very different exposure than if you want to show detail in their features, yet the person and surroundings are the same and the meter is going to give you exactly the same reading regardless of how you want the resulting photo to look because the light that's falling on the meter is the same regardless of how you want the image to eventually look.

Manufacturers make decisions about what is the best way to ensure you get a good result with a range of different subjects under a range of different conditions, and also about whether or not it the user is going to want to preserve detail in highlight areas or in shadow areas. Your DxO graph shows that Olympus and Panasonic made different decisions about those things. Neither one will be right all the time. One will be better in some situations, the other in different situations. There's no way to program the camera so that it will always give you the result you want. You need to learn how your meter works, in what kinds of situation it gives a recommendation that delivers the kind of result you want and in what kinds of situation it doesn't, and how to adjust the meter's recommendation to get the result you want when you know it isn't going to be reliable.

The light meter gives you information and information is always relevant. Sometimes the light meter is all the information you need to consider, sometimes it's only one of a number of pieces of information you need to consider. It's up to you to know when it's all you need and when you need to consider something else. Your camera/meter doesn't know what you're pointing it at or how you want the eventual photo to look. You're the only person to know those things and it's up to you to take what you know into account. In fact only you can take those things into account.

 

[CWRailman]

According to DxO, Olympus body's ISO setting is displayed as twice as it actually is (I may have worded it wrong, for the lack of knowledge). I assumed the ISO value to be an international convention; meaning ISO400 is the light sensitivity of the sensor that is going to be the same for all the sensors.

You might find this blog of interest. The Online Photographer: Why ISO Isn't ISO