Manual with Auto ISO Operation ?

[Marc Hildebrant]

Group,

Came across an interesting feature on my EOS 90D, namely setting exposure and shutter speed with manual settings (as I did with film many years ago), but having the ISO set automatically to try and make the exposure and shutter speed correct for the subject.

With my new camara I am not as concerned about "low ISO" speeds as this subject has been discussed in the forum with regard to picture noise.

Is this a mode of operation used by you?

Marc

 

[Ysarex]

It's a very popular mode of operation especially for those who have stricter shutter speed and f/stop requirements and have to work in action conditions, eg; sports, wildlife.

 

[minuteman1976]

For sports and wildlife, many photographers will shoot in manual mode with Auto ISO dialed in. Trying to adjust your ISO in environments where the lighting is ever changing then trying to adjust your ISO to meet those lighting changes is just not very practical.

If shooting in areas where the lighting is static or your subjects will not be going in and out of various lighting conditions, then setting a static ISO is fine.

 

[Marc Hildebrant]

Coming from years of using a film with a fixed ISO, the concept of a variable ISO to fit the needed exposure and shutter takes a while to "sink in".

It does open up some interesting uses.

Marc

 

[Ysarex]

Coming from years of using a film with a fixed ISO, the concept of a variable ISO to fit the needed exposure and shutter takes a while to "sink in".

It does open up some interesting uses.

Marc

As the camera engineers have continued to reduce read noise to negligible levels the use of ISO in camera for raw-only shooters becomes increasingly meaningless. It doesn't do anything of consequence except to potentially clip critical highlights in the raw file.

With a modern sensor camera I can produce the exact same image from the same exposure shot at ISO 400 and ISO 3200 as long as the ISO 3200 shot's raw file isn't ISO clipped. As such it's safer to not raise the ISO as much if at all. In the field the only advantage from applying ISO is providing a viewable JPEG to chimp.

This fact when coupled with the camera set to full manual and auto-ISO engaged suggests a possible advantage to also setting a negative EC which the camera would then apply to the auto-selected ISO value avoiding any possibility of ISO clipping the raw file.

 

[minuteman1976]

As the camera engineers have continued to reduce read noise to negligible levels the use of ISO in camera for raw-only shooters becomes increasingly meaningless. It doesn't do anything of consequence except to potentially clip critical highlights in the raw file.

With a modern sensor camera I can produce the exact same image from the same exposure shot at ISO 400 and ISO 3200 as long as the ISO 3200 shot's raw file isn't ISO clipped. As such it's safer to not raise the ISO as much if at all. In the field the only advantage from applying ISO is providing a viewable JPEG to chimp.

This fact when coupled with the camera set to full manual and auto-ISO engaged suggests a possible advantage to also setting a negative EC which the camera would then apply to the auto-selected ISO value avoiding any possibility of ISO clipping the raw file.

Yes, dynamic range on many newer sensors are excellent and in many cases, shooting at a static ISO and then adjusting exposure in post could yield satisfactory results.

Unfortunately, for sports and wildlife, setting a static ISO and then trying to edit hundreds or even thousands of photos in post is just not time efficient.

As for clipping highlights, the exposure compensation becomes an essential tool when shooting in manual with auto ISO to help negotiate possible blow out highlights.

But as you have stated, newer camera sensors have come a long way and actually do a great job with managing exposure more accurately and in many cases, get exposure pretty darn close to a proper exposure in semi auto mode such as with auto ISO.

In short, the photographer should use what works best for them. I would suggest to the OP to go out and experiment with different settings and see what they feel most comfortable with.

I'm always looking for different ways to shorten my post editing work and for me , 95% of the time auto ISO nails exposure correctly.

 

[Ysarex]

Yes, dynamic range on many newer sensors are excellent and in many cases, shooting at a static ISO and then adjusting exposure in post could yield satisfactory results.

Exposure isn't adjustable in post. You set a shutter speed and f/stop on the camera and that determines exposure. Once you click the shutter release it's done.

Unfortunately, for sports and wildlife, setting a static ISO and then trying to edit hundreds or even thousands of photos in post is just not time efficient.

As for clipping highlights, the exposure compensation becomes an essential tool when shooting in manual with auto ISO to help negotiate possible blow out highlights.

But as you have stated, newer camera sensors have come a long way and actually do a great job with managing exposure more accurately and in many cases, get exposure pretty darn close to a proper exposure in semi auto mode such as with auto ISO.

If any one of my cameras set in a semi-auto mode generates a good looking JPEG then for me that would represent a poor exposure -- a failure to set the best possible exposure of the sensor which I would have done controlling the camera. My experience is that all of my cameras have their metering and auto-modes adjusted to generate a good looking JPEG. My goal is a best possible sensor exposure and all my cameras do that rather poorly leaving the sensor in many cases as much as 50% underutilized. Here's an example: Last photo taken with my Canon camera. Below is my photo processed from the raw file along with the camera SOOC JPEG. Looking at the camera JPEG you'd think I overexposed when in fact the raw file is 1/3 stop underexposed (my excuse is I was walking in the park with my wife and she was patiently waiting for me to grab a snap). To take the photo I set the EC value to +1.3 and, confident it was safe, clicked the shutter.

If I had set the EC to 0 and took the exposure the camera meter selected I wouldn't have a raw file 1/3 stop underexposed I have a raw file 1 and 2/3 stops underexposed. Yikes! Not doing that.

In short, the photographer should use what works best for them. I would suggest to the OP to go out and experiment with different settings and see what they feel most comfortable with.

I'm always looking for different ways to shorten my post editing work and for me , 95% of the time auto ISO nails exposure correctly.

ISO isn't a causal component of exposure and as such the only thing auto-ISO can "nail" is the lightness of the camera processed JPEG. We use our cameras very differently, and we define "exposure" differently.

You're judging "exposure" by looking at the JPEG output of the camera, and that could well be appropriate for you. I don't judge exposure visually at all and define a best exposure as full utilization of the sensor's recording capacity which when achieved with most of our cameras results in a trashed blown-to-hell JPEG.

Exposure is technically defined as the amount of light per unit area hitting the sensor. It's a function then of the brightness of the scene, the time of exposure (shutter speed) and attenuation of the light through the lens (f/stop). That definition doesn't include ISO.

 

[minuteman1976]

Exposure isn't adjustable in post. You set a shutter speed and f/stop on the camera and that determines exposure. Once you click the shutter release it's done.

If any one of my cameras set in a semi-auto mode generates a good looking JPEG then for me that would represent a poor exposure -- a failure to set the best possible exposure of the sensor which I would have done controlling the camera. My experience is that all of my cameras have their metering and auto-modes adjusted to generate a good looking JPEG. My goal is a best possible sensor exposure and all my cameras do that rather poorly leaving the sensor in many cases as much as 50% underutilized.

ISO isn't a causal component of exposure and as such the only thing auto-ISO can "nail" is the lightness of the camera processed JPEG. We use our cameras very differently, and we define "exposure" differently.

You're judging "exposure" by looking at the JPEG output of the camera, and that could well be appropriate for you. I don't judge exposure visually at all and define a best exposure as full utilization of the sensor's recording capacity which when achieved with most of our cameras results in a trashed blown-to-hell JPEG.

Exposure is technically defined as the amount of light per unit area hitting the sensor. It's a function then of the brightness of the scene, the time of exposure (shutter speed) and attenuation of the light through the lens (f/stop). That definition doesn't include ISO.

sigh.....

 

[greybeard]

Yes, manual with auto ISO is my setting for static subjects. For fast moving subjects like little birds I use Shutter priority with auto iso. Only 2 settings I use.

 

[Marc Hildebrant]

Ysarex,

Your picture of the park is useful for explaining how to fully use the sensor.

I did not totally understand your comment about auto ISO. Was your point that the use of Auto ISO could over-expose or under-expose the shot more often than using a fixed ISO?

Marc

 

[Ysarex]

Ysarex,

Your picture of the park is useful for explaining how to fully use the sensor.

I did not totally understand your comment about auto ISO. Was your point that the use of Auto ISO could over-expose or under-expose the shot more often than using a fixed ISO?

Marc

No. Auto-ISO can ISO-clip the raw file and since we no longer have a read noise suppression benefit from applying ISO then there's no loss in forcing ISO lower as long as the JPEGs from the camera don't matter.

This thread is in the context of using the camera in Manual mode. In M mode exposure is set by the scene brightness, shutter speed and f/stop. So with the exposure set manually auto-ISO can't alter exposure over or under. It can lighten or darken the camera JPEG. Most commonly however ISO achieves that lightening/darkening of the JPEG by permanently altering the values in the raw file and that's where a risk occurs. ISO applied to the sensor signal can clip (ISO clip) the raw file.

ISO correlates with exposure/JPEG lightness but isn't a casual exposure component. I suspect that's what made our newest member sigh. But it's a critical distinction because exposure matters where ISO doesn't. If you define exposure as a function of scene brightness, shutter speed, f/stop, and ISO (Exposure Triangle) then you'll be likely to identify these two choices as the "same exposure,"
a) 1/250 sec., f/8, ISO 200
b) 1/500 sec., f/11, ISO 800
and you'd be wrong. Choice b) has a lower SNR and lower DR than choice a) with two stops less exposure and two stops of ISO lightening applied to the raw file.

Common sloppy usage has photographers referring to exposure as how light/dark the image appears. And familiarity with the Exposure Triangle has them believing ISO is a causal exposure component. It may not be terribly harmful, and it is very common, but I'd rather have a more fundamental understanding of what I'm doing.

 

[Marc Hildebrant]

Ysarex,

Thanks for the clarification.

Marc

 

[Ysarex]

Ysarex,

Thanks for the clarification.

Marc

I had some time this morning so I went ahead and shot this for you. I think seeing an illustration helps.

CAVEAT: The overriding condition requires we must have a specific shutter speed and f/stop, probably because we're shooting action. As such we don't have the option on the table for a full capacity sensor exposure -- we have to give that up but we're still going to take the photo; our cameras are amazing.

What I did then is setup a lighting condition (high contrast with a bright light in one corner) that would likely push the camera metering system to calculate an exposure giving up the very brightest highlights. I set the camera to full Manual mode with auto-ISO and I locked in an exposure (that's shutter speed and f/stop). I set the camera to it's default metering (matrix) and the EC to 0 and I took the photo. The camera calculated and set an ISO value of 1800.

Then I made one change and took the photo again. The change: I set the EC to -1.3. In this case EC doesn't change the exposure since I've locked that in on M. So the camera changed the auto-selected ISO from 1800 to 720. (Exposure comp no longer necessarily means exposure comp).

I loaded both raw files into C1 and started to process them and what I want to show you is screen shots of the two because the screen shots show C1's highlight clipping warning active in one photo and not in the other. I'm adjusting the photos to the same basic lightness and the brightest highlights are clipping in the photo with the ISO at 1800 and not in the photo with the ISO at 720. With software like C1 and/or LR I could pull back the highlights in the ISO 1800 shot to remove the clipping warning but unfortunately what I'll get is a flat white turning to a flat grey -- detail isn't there because the action of applying ISO in the camera clipped that detail in the raw file -- it's gone for good. But in the ISO 720 shot the camera applied less ISO lightening and didn't clip highlights so full detail is retained.

Let's look at the histograms for the two files. You can see in the ISO 1800 shot that the green channel has started to clip. In the ISO 720 shot the same highlights are no where near clipping.

DOWNSIDE: The camera JPEG is too dark at ISO 720 and if you want/need that JPEG immediately you have to lighten it by removing that -1.3 EC I set. As you do that you run the risk that ISO could permanently clip highlights in the raw file as it's doing in the ISO 1800 shot. So a too-dark camera JPEG is the downside.

Any other downside: Not any more. There used to be another downside. When the analog signal is read off the sensor and we've been forced to underutilize the sensor because of our working circumstances, then a raised ISO most commonly amplifies the analog sensor signal before it's passed through the ADC and converted to digital values. You see that in the two histograms below. The one for the ISO 1800 shot is farther to the right. ISO did that. Both shots are the same exposure which means both shots start with the same analog sensor signal. The clipping then that's begun in the ISO 1800 shot is caused post exposure by the application of ISO amplification. We call that ISO clipping. Since the exposure isn't causing any clipping it's a rather stupid thing that we've gone and done it after the fact when we didn't have to.

Back up: Cameras from the past (decade ago or more) benefited from the ISO increase and so there was another downside. ISO amplification suppresses read noise. So raising the ISO made the photo less noisy and it mattered that we follow through and do that. That's history now. Our modern cameras have the read noise almost entirely engineered out at the hardware level. So the noise suppression that we used to get from raising the ISO has been made moot. So ISO lightens the JPEG and that's it's only benefit now. Do you really need that lightened JPEG? If you do so be it, but if you don't you can remove the risk of ISO clipping.

Is the photo processed from the lower ISO 720 shot noisier? No. Shot noise level is determined by exposure. Same exposure for both then same noise for both.

Does the photo processed from the lower ISO 720 shot have less shadow detail? No. Also determined by exposure.

Is there any other UPSIDE: Beyond avoiding the risk of ISO clipping highlights there is one other upside and that's increased DR. ISO clipping takes off two things: 1. brightest highlights and 2. dynamic range. Hope the illustration helps.

 

[Marc Hildebrant]

Ysarex,

Thanks for your example as it helps.

Marc

 

[RacePhoto]

Different people will have a different view of this. Personally I want to control the ISO. I can adjust in other ways for what I want. But true, the newer cameras do much better at higher ISO with less noise. I generally never go over ISO 200. That's me.

I don't know if the data will show or not? Welcome new system. I'm not blocking anything.