How to use MINIMUM ISO?

[FMB]

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Today I’ve the purpose of think with this open letter about Auto ISO (Mini and Max) in order to clarify my mind and expose my deliberations. If some of you would be so kind to do a positive critic I’ll be happy.

1. The ISO value is the third component besides aperture and speed used to achieve the correct exposure of a photo.
2. AUTO ISO is a procedure to vary the ISO values according the fluctuations of the intensity of the light to maintain the correct exposure without any alteration in the aperture nor the speed.
3. Maximum ISO is the highest value of ISO we are ready to permit to balance this amount with the expected increment of noise it will produce in order to not decrease the quality of the photo.
4. And Minimum ISO is other type of tool, to limit the range of activity of the values AUTO ISO depending of the Mode used by the photographer:

-If we are in Mode A increasing the Mini ISO we keep without alteration the fixed aperture (DoF) but we introduce a restriction in the capability of reaction to the drop of light for winning a higher levels of variable speeds (better resolution).

-If we are using T Mode increasing the Mini ISO we keep without alteration the fixed speed (resolution) but we introduce in the capability of reaction to the drop of light for winning (or preserving) the initial DoF without need of open the variable apertures.

-If in M Mode, there is useless to put Mini ISO because we want to maintain the values of speed and aperture deliberately chosen for our personal purposes and then select the higher value of AUTO ISO capable of preserve a good exposure with a level of noise aceptable.

 

                I understand all said is may be a ridiculouse exposition of basical knowen concepts. As I’ve told many of us did not manage them so easily.

 

Francisco.

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[IkarusJohn]

That's an accurate summary, Francisco. I'm not sure that having a minimum ISO is any more useless than having a maximum ISO in M mode. There are ISO settings people won't want to use, though I agree they are more likely at the higher ISOs than at the bottom. 

 

You could add that when using AutoISO, even im M mode, EC becomes and important part of the equation. The SL usefully displays the extent of over or under exposure, which is beneficial if you fix the ISO and remain in M mode. 

 

The bug, as I understand it, is if you are in AutoISO, and you move the minimum ISO from 50, then the images become variably exposed. Til that issue has been resolved, the easy fix seems to be to leave the min ISO at 50 ...

[ramarren]

 

Today I’ve the purpose of think with this open letter about Auto ISO (Mini and Max) in order to clarify my mind and expose my deliberations. If some of you would be so kind to do a positive critic I’ll be happy.

1. The ISO value is the third component besides aperture and speed used to achieve the correct exposure of a photo.
2. AUTO ISO is a procedure to vary the ISO values according the fluctuations of the intensity of the light to maintain the correct exposure without any alteration in the aperture nor the speed.
3. Maximum ISO is the highest value of ISO we are ready to permit to balance this amount with the expected increment of noise it will produce in order to not decrease the quality of the photo.
4. And Minimum ISO is other type of tool, to limit the range of activity of the values AUTO ISO depending of the Mode used by the photographer:

-If we are in Mode A increasing the Mini ISO we keep without alteration the fixed aperture (DoF) but we introduce a restriction in the capability of reaction to the drop of light for winning a higher levels of variable speeds (better resolution).

-If we are using T Mode increasing the Mini ISO we keep without alteration the fixed speed (resolution) but we introduce in the capability of reaction to the drop of light for winning (or preserving) the initial DoF without need of open the variable apertures.

-If in M Mode, there is useless to put Mini ISO because we want to maintain the values of speed and aperture deliberately chosen for our personal purposes and then select the higher value of AUTO ISO capable of preserve a good exposure with a level of noise aceptable.

 

                I understand all said is may be a ridiculouse exposition of basical knowen concepts. As I’ve told many of us did not manage them so easily.

 

Francisco.

 

 

This is overall a fairly good statement of the overall interactions of exposure automation. I would separate and rewrite the bolded part this way:

---

Aperture setting, Shutter setting, and Auto ISO use in the different exposure modes.

 

Aperture priority - The aperture is fixed by the user to manage a specific focus zone. The camera is free to pick a matching exposure time based on the meter reading. With Auto ISO enabled, when the meter reading is such that there's too little light for the minimum ISO and the maximum exposure time to achieve correct exposure, the ISO setting is raised until the high limit is reached. 

 

Shutter priority - The exposure time is fixed by the user to manage a consistent amount of motion blur in the image. The camera is free to pick a matching lens aperture from maximum to minimum aperture. With Auto ISO enabled, when the meter reading is such that there's too little light for the minimum ISO setting and the largest available (maximum) aperture to achieve correct exposure, the ISO setting is raised until the high limit is reached. 

 

Manual exposure - Both exposure time and aperture setting are fixed by the user to establish a consistent focus zone and amount of motion blur appropriate to the subject. Auto ISO allows the camera to vary the ISO setting between minimum ISO and maximum ISO to achieve the correct exposure. The minimum to maximum ISO setting range establishes the dynamic range and noise qualities preferred by the user. 

---

 

I noticed that you didn't treat Program exposure mode at all. 

 

That's an accurate summary, Francisco. I'm not sure that having a minimum ISO is any more useless than having a maximum ISO in M mode. There are ISO settings people won't want to use, though I agree they are more likely at the higher ISOs than at the bottom. 

 

You could add that when using AutoISO, even im M mode, EC becomes and important part of the equation. The SL usefully displays the extent of over or under exposure, which is beneficial if you fix the ISO and remain in M mode. 

 

The bug, as I understand it, is if you are in AutoISO, and you move the minimum ISO from 50, then the images become variably exposed. Til that issue has been resolved, the easy fix seems to be to leave the min ISO at 50 ...

 

 

(bolded) In the overall description, it should be noted that, "...in any auto exposure mode (P, A, S or M-Auto ISO), Exposure Compensation should be provided in order to allow the user to override the camera's programmed exposure calibration line because metering alone cannot always distinguish adequately when local high or low values need to be accommodated by adjusting the overall exposure beyond the programmed calibration line. 

 

(red) The bugs are that when the Minimum ISO setting is moved from the minimum value of 50, when using P or A exposure modes with Matrix or Center Weighted metering pattern, two things become apparent: 

 

• The full range of Auto ISO settings are never reached by the camera. (The higher values of ISO are never set regardless of meter reading and lighting situation.)
• The exposure achieved by the camera becomes inconsistent whenever the ISO setting should be moved by Auto ISO higher than the minimum ISO setting. 

One simple workaround is to not alter the Minimum ISO setting limit—leave the camera set to the default minimum ISO 50 setting. 

Another simple workaround is to switch to Spot metering pattern. 

A third simple workaround is to switch to T or M metering modes. (T mode is only available with SL or T dedicated lenses.)

[FMB]

John and Ramarren,

 

I couldn't agree more with both of you. I think you have clarify a lot of concepts and aspects I've forgotten going deeper than me in the Auto ISO behavior, possibilities and advantages. I don’t have anything more to say then I close my participation in this post very happy because I believe many “aficionados”could take photographic profit of all said.

Thank you and bye.

Francisco

[johnbuckley]

Ramarren - could you hurry up, please, and get to that alternative SL manual? Nice clear writing.  Our friends in Wetzlar should reach out to you, oh, about the same time they put a beta version of a new camera in Jono's hands, and ask you to write the manual. JB

[wlaidlaw]

I agree it is an irritating bug. With the M240 and its base ISO of 200 (other than Pull), it is not so important as with the SL and base ISO of 50 but I have found that I am getting overly low shutter speeds quite a lot of the time and getting motion blur (not camera shake, which the OIS sorts out). My work around is to set the minimum shutter speed for a step up of the ISO to 1/2x focal length. 

 

Wilson

[edwardkaraa]

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My approach has been to keep the minimum ISO at 50 and manually selecting the minimum shutter speed depending on the subject matter. So obviously I didn't encounter this bug. I did the same with the M9 and M240.

[wlaidlaw]

What you need to do is to re-don your Kodachrome 64 mental hat and keep an eye on what EV your image is, so what shutter speed you would expect, compared with what is showing up on the VF. The controls of the SL are so flexible, at a quick push on the back rotor, you can go to shutter priority or manual, then reset your shutter speed plus aperture and auto ISO will ramp up to match. It requires a little bit of finger gymnastics but it's all good for my arthritis.

 

Wilson

[ramarren]

Mostly R lenses here so no T or P mode available.

 

My standard arrangement until they sort out this issue is to set Auto ISO range at 50-10000, bottom limit 1/f for longer lenses and 1/2f for wides/ultrawides. I switch to M mode when light levels drop and set my minimum comfortable exposure time for the lens and scene.