An In-depth Discussion of M + Auto-ISO (Very Long!)

Started Oct 5, 2011 | Discussions
ultimitsu
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An In-depth Discussion of M + Auto-ISO (Very Long!)
Oct 5, 2011

Preamble

The reason I am writing this piece is not to convince everyone that they should convert to an auto-ISO user, but simply to explain why auto-ISO is a very good feature. Seeing that many people tend to dismiss this feature without really understand how to use it, and discourages others at the same time, I feel it calls for a proper discussion.

Introducing Auto-ISO

Auto-ISO is a feature that lets the camera change ISO automatically. The first canon SLR to have real auto-ISO is 7D. Canons before 7d had a non-working auto-ISO that always stuck on ISO 400. Since 7d, auto-ISO would select the ISO that would give you correctly exposed final image based on the calculations of the camera's metering system, in combination with chosen shutter speed and aperture.

Personally I think auto-ISO is the most useful in M mode, I'll explain why and then explain it's application in Av mode. But before we do we will first discussion some surrounding issues.

The Nature of ISO

In digital photography, increasing ISO is increasing the level of amplification to the signal that sensor has received, and base ISO is simply leaving that signal free of any additional amplification. Amplification is either done by hardware (or sometimes called analog) or by software. Canon APS-C SLRs are only capable of hardware amplification at full stops, e.g. ISO 200/400/800 etc. 1/3 and 1/2 stop increments are done by in camera software and you can achieve the same effect in post processing.

Software amplification is manipulation to the image file after hardware amplification is finished, and it does not achieve the same image quality as hardware amplification. the reduced quality is easily demonstrated by comparing two images taken with the same shutter speed and aperture under the same lighting, one shot at ISO 100 and underexposed by 3 stops, then increase exposure by 3 stop in raw processing software, the other correctly exposed at ISO 800, it would be immediately apparent to the viewer that the ISO 800 image have much less noise as well as better contrast and colour accuracy.

This is a very important point to remember, because it means by manually setting ISO, what you are dictating is the amount of amplification the camera will apply to the image after it is captured. Whereas controlling aperture and shutter speed is controlling how that image is to be captured.

Earlier I have said that these in-camera 1/3 stop ISO increments are done by software and that software is not ideal. While this is true in reality 1/3 stop push or pull makes hardly any real impact to image quality, so for all intended purposes it should be overlooked.

On a side note, in the current line up of canon APS-C cameras the upper limit is ISO 6400. ISO 12800 is selectable but is software pushed from ISO 6400 and is not available in Auto-ISO (because you can just push your ISO 6400 is post processing). I do not know if the reason for this is whether it is limited by hardware amplification technology or that at this level, image quality is already destroyed so badly, hardware amplification would produce no better result than software.

Camera Metering

Regardless what some people would like to claim, the human eye and brain adapts to different lighting conditions way too well so that we are unable to correctly judge the actually amount of light surrounds us. Camera engineers recognised this long ago and invented electronic metering system (which they put in cameras). the metering system judges the scene for us and calculates the required shutter speed and/or aperture and/or ISO. If we use these calculated values to shoot the picture we will get a balanced looking image, we call it "correctly exposed image". (for the sake of simplicity we will skip the variation caused by different metering mode, it is also not material to this discussion)

Over the years the metering system improved gradually. As of 2011, the metering system from the world's largest and best camera manufacture is very advanced and very accurate. Majority of camera users - those who use Av, Tv, P, or greenbox mode, are quite happily relying on the metering system. The only people that don’t use it are those who use M mode in its classic fashion (i.e. manual ISO). They rely on their "brain and experience" when it comes to metering. As far as I can see, they are not producing "more correctly exposed" images, and if I was forced to make a guess, I would say they produces a lot more unusable images than the rest of us when they try to find out the correct settings in a given scene.

Now, if by using Av mode, where the user dictates aperture and ISO value, we trust the metering system to determine the correct shutter speed that would deliver a correctly exposed image, then there really is no reason as to where the user is to dictate aperture and shutter speed, why we would not trust the same metering system, using the same calculation formula, to determine the correct ISO that would deliver a correctly exposed image. Such mode is M + auto-ISO.

ultimitsu
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continued
In reply to ultimitsu, Oct 5, 2011

The Ideal Image

The goals of a photographer in making an ideal image are usually to : A, create the image as he saw in his head; and B, have the sharpest image; and C, have the best image quality.

To achieve A we need to control aperture, as it controls the DOF which directly affects the look of the final image.

To achieve B and C, it is a mixture of both aperture control and shutter speed control. Aperture because certain aperture gives the lens its optimal performance in sharpness, contrast and CA/flare resistance. Shutter speed because the slower the shutter speed, the more light hits the sensor and the less amplification required to bring the image to "correct exposure", therefore the better looking the final image; but at the same time it increases the risk of motion blur caused by photographer's own shake or movement of the subject.

There is always a particular shutter speed that is just enough to avoid any motion blur, and that is what we call "minimum safe shutter". since it would give the sensor more light than any other usable shutter speed, it is our goal to use minimum shutter speed in every shot.

Life was never meant to be easy. Depending on the focal length of the lens, movement of the subject, and surrounding support to the photographer, minimum shutter speed changes in every different situation. Because of the complexity involved, it is a call only the photographer can make correctly. The camera cannot, regardless how advanced it is.

Along Comes M + Auto-ISO

Let’s recap what we know so far:

  • To achieve optimal image quality, the photographer must have control over both aperture and shutter speed.

  • Because human eyes are not designed to meter light, camera metering are much better at this job.

  • It is the combination of shutter speed, aperture and ISO that produce a correctly exposed image.

  • Correct hardware amplification produces the best image.

taking all four points into consideration, it should not be difficult work out that the practice that would ensure best image quality consistently is for the user to choose ideal aperture and the minimum safe shutter, and let the camera's metering system decide on what is the best ISO (hardware amplification) for this given shutter speed and aperture combination under the given lighting condition - which is in essence, M mode and auto-ISO.

Comparison to Classic Av Mode Usage

Av mode is where the user sets aperture and ISO, and let the camera select shutter speed. There are several disadvantages when compared to M + auto-ISO:

1, Because user has no control over shutter speed, you could end up with either shutter speed that is too slow or faster than necessary, that If too slow, you end up with motion blur. If faster than necessary, you end up with an image that received less than maximum amount of light, and therefore had to receive more amplification than necessary to bring it back to correct exposure. Neither scenario is ideal.

2, In event of user finding the shutter speed is too fast or too slow and wants to correct it, the user has to go into ISO menu to change ISO in order to maintain aperture and still get shutter speed to change, this is slower than similar the operation in M + auto-ISO mode, in the latter mode, one just have to turn the shutter speed wheel. consider a situation were you are shooting a moving subject, you do not know what is the exact minimum safe shutter, you have to shoot a few images with different shutter speed before you find it. Using M + auto-ISO you can shoot, turn wheel by 1 click, shoot again, turn wheel 1 click again, etc, easily test 10 different shutter speed inside 10 seconds. Now think how long it would take you to do the same using Av mode and having to change ISO.

3, This is perhaps the most significant disadvantage. With the exception of using flash as primary light source, in all other situations, lighting is different between every shot. Consider the situation where you shoot pictures of people in a indoor party using 17-55. The slowest you can hold steadily is 1/20s at 55mm and when you shoot people always pose for you so subject is static. when you shoot people that are close to windows or lights, they would have more light on their face, and the shots would require less amplification (lower ISO), and conversely shots of these who are not close to windows or lights would require more amplification (higher ISO) to get the correctly exposed image. Using Av mode means you would:

  • leave ISO low and end up with motion blurred images half the time, or

  • leave ISO high and end up with half images that could have been much cleaner, or

  • constantly go into ISO menu and make changes.

In contrast with M + Auto-ISO, you just leave the camera on 1/20s and ideal aperture, and shoot away.

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ultimitsu
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continued x2
In reply to ultimitsu, Oct 5, 2011

Other Considerations

Some people mention the lack of exposure compensation in M + auto-ISO, it did bother me initially, but soon I realised it wasn't really a problem. I can only think of 3 situations EC is used, first is where camera's metering system is plain defective and need EC to correct it. It is not the case with 60D. Second is where the photographer prefers to have all images either underexposed or overexposed, I personally do not want them and can see no rationale behind such desire (there is an potential argument for ETTR , for another day). Third is when you want a particular shot to be under- or overexposed. You can still easily do this in M mode by switch ISO to a particular value that gives you the desired exposure, and then switch back afterwards. Note that AE lock does not work on 60D when using M + auto-ISO (for no good reason that I can think of), but works on Av + Auto-ISO.

Av + auto-ISO is a completely different animal. How it works is that the camera will first change shutter speed based on changing lighting condition, but as soon as shutter speed would have to drop below 1/(2xFL) (for example slower than 1/100s for 50mm), it would bump up ISO, in other words it tries to maintain the old rule of thumb (1/FL) err on the side of a bit more shutter speed. It does not take IS into consideration (for no good reason that I can think of).

Personally I do not use it because my minimum safe shutter is much slower than 1/(2xFL), especially with IS. However I think for a novice who is still learning how to hold the camera steady, and on his way to find his minimum safe shutter, or someone who is of age and has trouble hold the camera steady, Av + auto-ISO actually makes a lot of sense. you can be sure that your images will be shake free and IQ will be quite consistent.

Hopefully by now, the rationale and advantages of M + Auto-ISO have been explained adequately. It is the mode I shoot pretty much all the time except when flash is used. I have been very happy with the results. Here are some example images shot with M + Auto-ISO.

Interior of a friend's car, used for advertising. I set SS to 1/5s as that is the slowest that I was sure about in getting keepers, f2.8 was the lens wide open and provided just enough DOF for our purpose. Auto-iso set iso at 1600, which resulted in a correctly exposed image.

1/800s to freeze motion, F5 for DOF, auto-iso set ISO at 320, as accurate as it can be.

1/1000s for motion freeze, F7.1 for DOF, camera metering system picked iso 2500, spot on.

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andersf
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to ultimitsu, Oct 5, 2011

Nicely explained. I agree that M+AutoIso is useful, but I find the lack of exposure compensation to be quite limiting. I (very) often shoot within + - 1 stop and find that I have to use M+AutoIso, see what the iso gets and then change from auto iso to the selected iso, and then change aperture/shutter to give the desired exposure comp.

I'd really like to have a way of locking the auto iso in M mode without having to change the iso value (like exposure lock). That would mean you could use the M controls to get the desired exp.comp. that the AutoIso otherwise has denied.

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aVolanche
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to andersf, Oct 5, 2011

andersf wrote:

Nicely explained. I agree that M+AutoIso is useful, but I find the lack of exposure compensation to be quite limiting. I (very) often shoot within + - 1 stop and find that I have to use M+AutoIso, see what the iso gets and then change from auto iso to the selected iso, and then change aperture/shutter to give the desired exposure comp.

Exactly. And this is where the argument for this auto iso + Manual Mode method falls apart. To "compensate the exposure" as ultimitsu describes, puts one back into full manual control....no automation at all. I, as do many other photographers, routinely use exposure compensation along with an automated mode (Av, Tv). Full manual mode is not easy. More importantly, I believe that most photographers prefer Av or Tv where there is automation, particularly when shooting quickly.

I am adept at using full manual mode because I learned photography before there was automation! I suspect more recently trained photographers find it to be a very foreign and difficult method.

I'd really like to have a way of locking the auto iso in M mode without having to change the iso value (like exposure lock). That would mean you could use the M controls to get the desired exp.comp. that the AutoIso otherwise has denied.

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schmegg
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to aVolanche, Oct 5, 2011

aVolanche wrote:

Exactly. And this is where the argument for this auto iso + Manual Mode method falls apart. To "compensate the exposure" as ultimitsu describes, puts one back into full manual control....no automation at all. I, as do many other photographers, routinely use exposure compensation along with an automated mode (Av, Tv). Full manual mode is not easy. More importantly, I believe that most photographers prefer Av or Tv where there is automation, particularly when shooting quickly.

+1.

Some people don't realise/understand this because they don't shoot in situations that need it - but the lack of EC in M with Auto-ISO is a definite handicap!

Come on Canon - are you reading this? Do you care?

The problem as I see it is a simple issue of ergonomics.

On the 7D you could press and hold the M.Fn button and turn the rear wheel to set EC in M with Auto-ISO. Not sure how you'd do it on bodies that don't have the M.Fn button though. But I'm sure, if they tried, they could come up with something!

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ESfishdoc
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to schmegg, Oct 5, 2011

That all seems reasonable if that is the way you prefer to shoot.

I shoot in manual mode about 90% and Av 10% and I can tell from the light within a couple stops what I'm going to need. I want full control over iso always... so for me..I just don't see 1. a need for it 2. an advantage.

I'm trying to think of any professionals who use auto iso or have even suggested a time when it might be used... I come up with zero.
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Olga Johnson
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to ESfishdoc, Oct 5, 2011

ESfishdoc wrote:

I'm trying to think of any professionals who use auto iso or have even suggested a time when it might be used... I come up with zero.

But not everyone is a professional who knows exactly what to use. When I go to the rodeo I am usually with the 70-200L f/4 and use ISO3200, 1/640, f/4 with it. It works every time.

I wanted to try the 55-250 kit lens on the camera at the rodeo but without the 70-200's constant f/4, I decided to use Auto ISO. This way I didn't have to watch the aperture (which I wanted at maximum) and have to change ISO all the time depending on focal length when the aperture would change. Didn't turn out too badly.

http://yiayia.zenfolio.com/p1070346190

OTOH I didn't like what Auto ISO was doing with the 70-200L, when I tried it. Saw too many too bright or too dark images using Auto ISO with that lens. I haven't tried it since.

I've also found it convenient when shooting birds off a tripod in partly cloudy weather. Lighting kept changing all the time. I set a maximum ISO (with T2i) and used Auto ISO in M mode.

As a rule, I set my own ISO. But I have found Auto ISO convenient quite a bit especially when I went through a very shaky hands period and had to set a higher shutter than someone else would have needed.

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24Peter
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to Olga Johnson, Oct 5, 2011

I have been a long-time fan of Auto ISO on the newer Canon DSLR's (such as my 60D) and would also welcome exposure comp in M mode with auto ISO. (I have also never understood the objection some people to using auto ISO in M mode but whatever.)

I have to say, the lack of true auto ISO functionality in M mode on my 5DII in stills mode is a significant limitation of that camera and I can't get why Canon never updated the firmware to allow for this, esp. since they did update the firmware to allow auto ISO to work properly in M mode while shooting video on the same camera. Weird.
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akin_t
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Eh ... Manual isn't manual if you're using Auto ISO.
In reply to ultimitsu, Oct 5, 2011

Honestly, Canon should just make a new mode called A&Tv, where you pick your Aperture and Shutter values and let the camera pick ISO based on your metering choice.

Manual isn't manual the minute your camera is picking your exposure for you.

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akin_t
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Wtf? Lol comprehension fail ftl
In reply to andersf, Oct 5, 2011

andersf wrote:

Nicely explained. I agree that M+AutoIso is useful, but I find the lack of exposure compensation to be quite limiting. I (very) often shoot within + - 1 stop and find that I have to use M+AutoIso, see what the iso gets and then change from auto iso to the selected iso, and then change aperture/shutter to give the desired exposure comp.

Exposure compensation in Av simply adjusts your shutter value
Exposure compensation in Tv simply adjusts your aperture value

What the phuck do you expect the camera to adjust if you're in manual mode?

I hope you can now see the problem with crying that there's no exposure compensation in M

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Keith Z Leonard
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to ESfishdoc, Oct 5, 2011

I use manual a lot, mainly due to 7d's noise issues when underexposed, I would like compensation in auto-iso though. I do personally use auto-iso in some shooting situations.

Your argument about the "pros" is somewhat lacking. For one thing your implication is that you have polled all of the "pros" out there, or that you personally know all of the "pro" photographers. Being pro merely means being paid, I have been paid for photography work on occasion, therefore I am "pro" or "semi-pro" and I don't know you.

Furthermore I know some people being paid for their photography who use film only, by your argument formation it would be valid to use film only due to this fact. (if at least 1 pro exists using auto iso, then auto iso is validated). There are also many pros who say film is dead, how would you resolve this? And yes I know I am nit-picking formal logic stuctures here, but my point remains. It does not matter what the "pros" you know and have queried do.

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Keith Z Leonard
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Re: Wtf? Lol comprehension fail ftl
In reply to akin_t, Oct 5, 2011

The idea would be to adjust ISO + - when auto ISO is enabled.

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Jerry-astro
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Here's why...
In reply to akin_t, Oct 5, 2011

akin_t wrote:

andersf wrote:

Nicely explained. I agree that M+AutoIso is useful, but I find the lack of exposure compensation to be quite limiting. I (very) often shoot within + - 1 stop and find that I have to use M+AutoIso, see what the iso gets and then change from auto iso to the selected iso, and then change aperture/shutter to give the desired exposure comp.

Exposure compensation in Av simply adjusts your shutter value
Exposure compensation in Tv simply adjusts your aperture value

What the phuck do you expect the camera to adjust if you're in manual mode?

I hope you can now see the problem with crying that there's no exposure compensation in M

Before jumping in, you might want to simply give it a try and see how it operates. You'll likely stumble on the issue pretty quickly, as I did. In M mode, Auto-ISO simply adjusts ISO to properly meter the shot, allowing the photographer to completely control aperture and shutter speed. I can see where the idea might have some merits if you're not terribly sensitive to ISO/noise. However, the big (and I mean BIG) flaw on the 7D is the lack of EC in that mode. If the metering system delivers a shot that is underexposed (not that unusual under some lighting conditions or with some subjects), then there is no way to ask the camera to quickly compensate up or down n stops to correct the exposure (as you can in Av or Tv mode with fixed ISO). You would have to revert out of Auto-ISO mode and temporarily fix your ISO to the correct value to do that compensation. Very time consuming and awkward.

Interesting notion and an awful lot of verbiage spent by the OP trying to justify its use. However, lacking some easy way to do EC, it's a complete "fail" as you put it IMHO.

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AlterHase
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to ultimitsu, Oct 5, 2011

Thanks for the discussion. I generally agree with your points and it created a nice foundation to dive into more details.

I mainly disagree with one point you made early on:

The first canon SLR to have real auto-ISO is 7D.

The auto-ISO implementation in the 7D (while being the most sophisticated today) still lacks in 4 points for me:

1. Av/Tv allow exposure compensation that a user can dial in to override the camera automation. The same concept is needed when using M mode and auto-iso.

2. Depending on your creative choices and your personal threshold for graininess it should be possible to configure a range (for all practical purposes only an upper bound) of ISO values that the auto-iso function is allowed to select. In some situations iso3200 is too high for my taste.

3. When adding flash (e.g. fill flash), the camera sets the iso automatically to iso 400 (when in auto-iso mode). In Av/Tv mode it would be beneficial to use auto-iso, but with a different (configurable) range than used without flash.

4. Lastly, and this is pretty technical, I think advanced users need a way to tweak the camera automation to a larger degree. The camera metering measures the available light level (in broadly simplified terms), and uses a table in Av/Tv mode to adjust the two open variables (shutter speed/aperture and iso value, in P mode it selects from the 3 open variables). This table is often not optimal depending on my hand holding ability (I need a minimum shutter speed > 1/focal length) and needs adjusting as soon as the lens has IS. I'd love to have the ability to tweak the camera behavior to control these values for Av/Tv/P mode and lens specific. If I could I would be more than happy to use these modes more often. The fact that the choices made by my camera are suboptimal (for me) is what makes me use M mode most of the time.

Again, thanks for the nice discussion of the topic of auto-iso.

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ESfishdoc
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Re: An In-depth Discussion of M + Auto-ISO (Very Long!)
In reply to Olga Johnson, Oct 5, 2011

Olga Johnson wrote:

ESfishdoc wrote:

I'm trying to think of any professionals who use auto iso or have even suggested a time when it might be used... I come up with zero.

But not everyone is a professional who knows exactly what to use. When I go to the rodeo I am usually with the 70-200L f/4 and use ISO3200, 1/640, f/4 with it. It works every time.

Olga...

Agreed... not everyone knows exactly what to use... but they can learn. When I see an image I want to make I know what iso I want and what is acceptable for the result I want. When I didn't know that I was chasing my tail trying to make something happen in post processing that I could have done in camera.... shoot it right the first time and everything else is easy (easier).

I am one of those old school people who learned to shoot with either Panatomik X or Tri X and nothing auto and my mother taught me how to use a slide rule before we ever had calculators.... but.. oh how I do love Photoshop... I was looking at the back deck I built 10 years ago and my brain told me I needed to use the healing brush....

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24Peter
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Re: Wtf? Lol comprehension fail ftl
In reply to akin_t, Oct 5, 2011

akin_t wrote:

What the phuck do you expect the camera to adjust if you're in manual mode?

I hope you can now see the problem with crying that there's no exposure compensation in M

The beauty of Auto ISO in M mode (which would be enhanced with an exposure comp setting) is, for the first time in history you can select your aperture and shutter speed based on considerations other than primarily exposure (for instance, DOF on the aperture side and freezing action on the SS side) and still get a proper exposure for your image. Isn't that nifty? Why cry over such innovation? We're no longer stuck in the old paradigm dictated by film cameras! R U afraid of change?
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Olga Johnson
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I would word it differently
In reply to Jerry-astro, Oct 5, 2011

Jerry-astro wrote:

In M mode, Auto-ISO simply adjusts ISO to properly meter the shot, allowing the photographer to completely control aperture and shutter speed.

In M mode, Auto-ISO adjusts ISO to meter in the middle (zero compensation). That may not be the proper exposure for the image you are trying to take. If you try to change aperture and/or shutter, Auto-ISO continually adjusts to meter in the middle. There is no exposure compensation.

I can see where the idea might have some merits if you're not terribly sensitive to ISO/noise. However, the big (and I mean BIG) flaw on the 7D is the lack of EC in that mode. If the metering system delivers a shot that is underexposed (not that unusual under some lighting conditions or with some subjects), then there is no way to ask the camera to quickly compensate up or down n stops to correct the exposure (as you can in Av or Tv mode with fixed ISO). You would have to revert out of Auto-ISO mode and temporarily fix your ISO to the correct value to do that compensation. Very time consuming and awkward.

Interesting notion and an awful lot of verbiage spent by the OP trying to justify its use. However, lacking some easy way to do EC, it's a complete "fail" as you put it IMHO.

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Jeff Peterman
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Re: Continuation of other thread.
In reply to ultimitsu, Oct 5, 2011

Still not convinced, and still don't want to lose control of my ISO setting. And as others have said, the big problem is that in this combination you're forced to accept the metered exposure. A good 40% of the time (or more), I'll use EC in Av mode, with fixed ISO, to get the correct exposure for the subject/scene.

And by the way, when the ISO is modified by the electronics, this is not called "analog." The sensor circuit almost certainly puts out a digital signal, and that digital signal is amplified by adjusting the gain of the circuit, which is also digital. What you want to separate is the amplifaction done by the electronic hardware and that done by firmware once the signal has left the amplification circuit.
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Jeff Peterman
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Re: When I would use auto-ISO
In reply to ultimitsu, Oct 5, 2011

For auto ISO to be useful to me, it would have to have two missing features:

1. Set range limits. E.g., I might set it to 100-400 for normal shooting, or 800-1600 when shooting in low light.

2. It must allow exposure compensation for times when the metered exposure isn't correct for what I want.

If it had those two features, I'd invest the time to get comfortable with using it. Until then, for me, it is just one more feature I don't need. Note that I do use it on my P&S cameras occasionally, but I have different expectations with those.
--
Jeff Peterman

Any insults, implied anger, bad grammar and bad spelling, are entirely unintentionalal. Sorry.
http://www.pbase.com/jeffp25
http://www.jeffp25.smugmug.com

 Jeff Peterman's gear list:Jeff Peterman's gear list
Panasonic Lumix DMC-FZ40 Canon PowerShot S110 Canon EOS 7D Canon EF-S 10-22mm f/3.5-4.5 USM Canon EF-S 17-55mm f/2.8 IS USM +16 more
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