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Auto ISO to obtain correct exposure?


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On my Fuji X cameras I was able to set manual mode and then choose both a shutter speed and an aperture setting. The correct exposure would be made by adjusting the ISO. That doesn't happen with the M240 - or have I missed something?

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On my Fuji X cameras I was able to set manual mode and then choose both a shutter speed and an aperture setting. The correct exposure would be made by adjusting the ISO. That doesn't happen with the M240 - or have I missed something?

While many people seem to be lusting after this feature I still think it is ultimately misguided. But as nobody cares what I think you may still get your way.

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While many people seem to be lusting after this feature I still think it is ultimately misguided. But as nobody cares what I think you may still get your way.

 

 

I think you're entirely right.

 

I've never used this feature on any of my M's.

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Auto ISO is simply a way of achieving correct exposure when you need the shutter speed and aperture to remain constant, such as to stop movement and give enough DOF etc. What can be wrong with that?

 

Steve

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While many people seem to be lusting after this feature I still think it is ultimately misguided. But as nobody cares what I think you may still get your way.

 

Michael, first let me say that I particularly value your opinion and knowledge, but I am unsure why you consider this "misguided."

 

I saw no real use for it until recently, when I started using the camera (I hate the word "shooting") in dark and downright cavernous industrial environments, and moments later out in bright sunshine, while looking at something hanging on a crane hook.

 

The choices I wanted to make were aperture, usual f 1.4 in consideration of the lack of light, or f 16 because there was too much, and as high a shutter speed as I could, in consideration of camera shake and subject movement.

 

It was at the point that I found myself winding the ISO up and down, that I realized what everybody else was talking about. :p

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Michael, first let me say that I particularly value your opinion and knowledge, but I am unsure why you consider this "misguided."

You might say I’m nitpicking (I hear that all the time so it’s probably true) but ISO isn’t an exposure parameter on a par with f-stop and shutter speed. ISO informs the camera how much light it needs to gather for an optimum exposure, but it doesn’t determine exposure as f-stop and shutter speed do.

 

But the real reason I think the wish for Auto ISO in manual mode is misguided is that you needlessly throw away dynamic range that way. I often use manual mode for saving highlights by deliberately underexposing. Auto ISO would render this void: when the camera cranks up the amplification of the sensor signals the highlights yield voltages overloading the ADC. While I manage to prevent clipping in the sensor by underexposing, Auto ISO ensures the highlights are clipped anyway – by the ADC rather than the sensor, but the result is the same. The only way to effectively prevent clipping is to fix ISO at a low to medium level and to adjust the gamma curve in the raw converter for brightening the image without throwing out the highlights again.

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I often use manual mode for saving highlights by deliberately underexposing. Auto ISO would render this void: when the camera cranks up the amplification of the sensor signals the highlights yield voltages overloading the ADC. While I manage to prevent clipping in the sensor by underexposing, Auto ISO ensures the highlights are clipped anyway – by the ADC rather than the sensor, but the result is the same.

 

If I understood the point of it, you tend to keep the ISO at the lowest level, and than play with the shutter speed, and aperture to preserve the highest possible dynamic range, and even underexpose to save the highlights. This idea is valid, and after some practice I believe it became your second nature.

However, if the light changes very fast, and you need that shot, auto ISO is the best option.

If you are worried about keeping the highlights, EV can be adjusted.

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I could see your point if there was no manual ISO and I think that after the auto-ISO fiasco (I am a staunch defender of auto-ISO), the one and only thing that could get me to upgrade my M 240 to the next model would be to add an ISO dial to the top of the camera. Setting ISO takes way too long!

 

But what's the rationale for the current system? If I am shooting at f 16 and pick a shutter speed of 1/60, the ISO becomes some random ISO that I have I have not set and that remains a mystery to me?

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If that is the only criticism of Auto ISO it is clear we've not quite to the point in photography where the camera and the technical process is more important than the resulting image, but it is close if such ideas spread.

 

It is often said that film has more dynamic range than digital, yet there are countless times in the history of photography where the dynamic range of film has failed, but still given us wonderful photographs. I fail to see why the same cannot be true of digital, and if you lose a stop of DR but gain a great picture hands up who would give up the great picture? Yes, I didn't think anybody would put their hand up.

 

Besides which the premise is flawed anyway as in manual exposure mode Exposure Compensation should be also possible alongside Auto ISO. It is with the M9/MM, so unless Leica screw up the firmware update the camera can still be forced to underexpose via the ISO and hence retain highlights/rescue shadows.

 

Steve

Edited by 250swb
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