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Base or Pull

steppenw0lf

By steppenw0lf,
in Leica SL System

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mjh
mjh

The sensor’s native sensitivity is ISO 100. ISO 50 is a pull setting which, however, can be used without sacrificing a significant amount of dynamic range.

Jared
Jared

Base ISO is theoretically determined by the combination of quantum efficiency, pixel size, read noise characteristics, and full well capacity. Basically, it's the amount of gain at which you get the best dynamic range. It's generally inherent in the sensor, but your implementation can make a small impact as well.   With a "pull" ISO you are allowing the pixels to saturate (hit the anti-blooming gate cutoff) by allowing in "too much" light for a correct exposure then pulling the exposure back

digitalfx
digitalfx

I understand that the base ISO is 100, but that at ISO 50 there is little to no loss of dynamic range.   I use ISO 50 when shooting wide open on Summilux and Noctilux and have not noticed any issues.

steppenw0lf

steppenw0lf

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Posted (edited)

And if ISO 50 is only a pull, why does the "automatic" in the SL have a tendency towards ISO 50 ?   (referring to the autoISO setting).

 

The SL produces many more photos with ISO 50 than I would ever have thought possible. 

And I find it not "nice". How about others ?  

I would prefer a tendency towards ISO 100. (As long as I cannot gain anything with ISO 50).

Edited by steppenw0lf
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dgktkr

dgktkr

Posted
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    The sensor’s native sensitivity is ISO 100. ISO 50 is a pull setting which, however, can be used without sacrificing a significant amount of dynamic range.

     

     

    What, exactly, does it mean that the sensor's native sensitivity is ISO 100? What measurements would one make to establish that?

     

    Don't DxO measurements show best S/N and best dynamic range at ISO 50 in the SL? http://www.dxomark.com/Cameras/Leica/SL-Typ-601---Measurements

     

    dgktkr

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    ramarren

    ramarren

    Posted
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      I've done detailed comparisons of photos made in all kinds of lighting, etc, at ISO 50, 100, 200, and 400. There is so little difference to dynamic range and noise at any of these ISO settings that it simply cannot affect my photographs. What I'd like to do for most of my shooting is leave my camera set to Auto ISO, top ISO limit at ISO 800, and the exposure time cutoff at 1/f. That would suit most of my lenses from 15mm up to 90mm pretty nicely in average lighting situations...

       

      Now if only I could tell the SL to override the cutoff when all other options bang into the limits so I don't lose a shot simply because it might be 1/30 second instead of 1/50 with a 50mm lens. 

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      Jared

      Jared

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        I'm not certain why everyone says base ISO is 100.  Is it just because that's the base on the 'Q', and the SL is stated to have a very similar sensor?  

         

        Based on my checking dynamic range, and DXO's measurements of dynamic range, I'd have to say that 50 is NOT a pull ISO.  Base is 50, not 100.  That would also explain why Leica allows the auto ISO function to choose 50 whenever possible.  The camera's best performance (and therefore it's base ISO) is at 50.

         

        - Jared

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        ramarren

        ramarren

        Posted
          Posted (edited)

          here (exactly at 8 min)

          http://www.l-camera-...-stefan-daniel/

          Stefan Daniel says, base ISO is 100 (and ISO 50 pull)

           

           

          OK, it seems there are different statements. Last days I ask exactly the ISO base question to technical Leica people

           

           

          If you can't tell the difference between them, what does it matter what is base or pull? 

          My standard ISO setting is 400. I can hardly tell the difference between that and ISO 50 or 100 ...

          Edited by ramarren
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          Steve Spencer

          Steve Spencer

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            If you can't tell the difference between them, what does it matter what is base or pull? 

            My standard ISO setting is 400. I can hardly tell the difference between that and ISO 50 or 100 ...

             

            ISO 400 still is very good on the SL, but signal to noise ratio, dynamic range, and colour sensitivity are all better at ISO 50. You might not notice the difference until you post process, but you should be able to brighten the shadow about a stop more (before they get noisy) if you shoot at ISO 50 instead of ISO 400. That might not matter for a lot of shots, but for some landscape shots I take it would matter at least a little.

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            ramarren

            ramarren

            Posted
              Posted

              ISO 400 still is very good on the SL, but signal to noise ratio, dynamic range, and colour sensitivity are all better at ISO 50. You might not notice the difference until you post process, but you should be able to brighten the shadow about a stop more (before they get noisy) if you shoot at ISO 50 instead of ISO 400. That might not matter for a lot of shots, but for some landscape shots I take it would matter at least a little.

               

               

              Certainly  ... for situations where I need the full extent of the sensor's capabilities, I set the lowest ISO I can get away with and enjoy the widest DR and lowest noise.

              But those situations are a minuscule percentage of my shooting, that's all. 

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              ramarren

              ramarren

              Posted
                Posted

                So, for the technically knowledgeable, what does "pull" mean? I believe that higher ISOs above base employ some sort of signal amplification in-camera (on-sensor?), but what's happening with pull ISOs?

                 

                 

                Not being a hardware engineer, I doubt I can explain in precise technical terms. But lets say that you have a sensor designed to operate at a specific input voltage level. At that voltage level, you measure its ability to respond to a reference amount of light energy falling on it in unit time and make some constraints (like specifying a maximum noise level and a minimum dynamic range). That becomes the sensor's base sensitivity (aka ISO). 

                 

                Then you reduce the input voltage by some amount and measure the sensor's response curve again, and you find that it is half as sensitive to light. Presuming that it will achieve the same maximum noise level, you make allowance for an acceptable amount of dynamic range reduction. Now you have a "one-stop pull" sensitivity, and if the maximum noise is good, and the DR is acceptable, you know you can put a switch on the camera that sets the sensor to operate at this voltage level. 

                 

                Then you increase the input voltage from the specified normal and measure the sensor's response curve again ... and you find that it is twice as sensitive, maximum noise has grown a little, and dynamic range has shrunk a little. All within acceptable limits, voila!, you have another switch that allows the chip to operate at a one-stop push sensitivity. And so forth. 

                 

                That's the concept, to first order approximation. I'm sure a more hardware savvy individual will shoot it full of holes and explain the realities more clearly. 

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                Jared

                Jared

                Posted
                  Posted

                  OK, acknowledging the statement by the Leicoa product manager, Stefan Daniel, how can one have a pull ISO with better dynamic range and lower noise than base? Because every test I have seen including those I have run myself show that the maximum dynamic range is at ISO 50.

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                  • 2 weeks later...
                  steppenw0lf

                  steppenw0lf

                  Posted
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                  Posted (edited)

                  OK, it seems there are different statements. Last days I ask exactly the ISO base question to technical Leica people

                   

                   

                  Ferdinand,

                  did you ask the question ? And did anybody from Leica give a clear answer ? This is still open.

                  My life does not depend upon it, but why is it it so difficult to get a clear answer for such a simple question ?

                  Stephan

                   

                  (You probably meant in the next days ...)

                  Edited by steppenw0lf
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                  jonoslack

                  jonoslack

                  Posted
                    Posted

                    I hope someone with a "direct wire" can tell us, if ISO 50 is the base setting of the sensor.

                    Or is ISO 100 the base, and ISO 50 only a pull ? 

                    This will make this thread a short one.

                     

                    A direct wire is an interesting concept . . . and several direct wires might give different answers!

                     

                    We had quite a lot of discussion about this, and what I understand is that 'base' ISO is theoretically 100 . . . but that nobody could see any disadvantages of 50 ISO, so it wasn't classified as 'Pull' 

                    Certainly, I happily shoot at 50 ISO, so I think the whole thing is rather academic . . 

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                    dgktkr

                    dgktkr

                    Posted
                      Posted

                      A direct wire is an interesting concept . . . and several direct wires might give different answers!

                       

                      We had quite a lot of discussion about this, and what I understand is that 'base' ISO is theoretically 100 . . . but that nobody could see any disadvantages of 50 ISO, so it wasn't classified as 'Pull' 

                      Certainly, I happily shoot at 50 ISO, so I think the whole thing is rather academic . . 

                       

                       

                      Hi Jono,

                       

                      Yes, the issue is rather academic.

                       

                      Nevertheless, the base ISO is theoretically 100 because of what considerations?

                       

                      dgktkr

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