Nikon D300 ISO question

[duraace]

The D300 has a nominal ISO range of 200 to 3200, with additional 1 EV high (6400 ISO) and low (100 ISO) settings that can be reached in 1/3 EV increments. The additional low ISO settings are marked L 0.3, L 0.7, L 1.0.  I took a shot at L 0.3 and the metadata displayed in software displayed ISO 160.   My question is, if it's ISO 160, why not call it that instead of L 0.3, unless below 200 is not a true ISO setting.  What's the difference? Also, what are you compromising by using lower than 200?

[Colorado David]

All digital sensors are opimized for a single ISO setting.  In the case of the D300, it is 200.  Everything above ISO 200 is a function of gain or amplification.  Every setting below ISO 200 is a downward attenuation.

[duraace]

All digital sensors are opimized for a single ISO setting.  In the case of the D300, it is 200.  Everything above ISO 200 is a function of gain or amplification.  Every setting below ISO 200 is a downward attenuation.
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Thanks. With high ISO you get noise. What do you get with levels below the minimum?

[bernie west]

All digital sensors are opimized for a single ISO setting.  In the case of the D300, it is 200.  Everything above ISO 200 is a function of gain or amplification.  Every setting below ISO 200 is a downward attenuation.
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I'm not sure about the Nikon case, but as a general rule I don't think this is exactly true.  The H and L iso setting in canons is a post-processing fudge; basically a 1 stop digital push and pull on the discrete digital data.  The amplification performed from base iso to get to higher isos is performed on the continuous analogue data straight off the sensor.  Amplification of a continuous signal results in a better result than doing the same to a discrete (ie. digital) signal.

In the case of the canon's L setting, you should get a better signal to noise ratio, but at the expense of dynamic range (ie. it will be lower).

[Panopeeper]

if it's ISO 160, why not call it that instead of L 0.3, unless below 200 is not a true ISO setting.  What's the difference? Also, what are you compromising by using lower than 200?

The issue was originally (with film) "sensitivity". The sensor does not have different sensitivities, but the gained charge can be interpreted with different "gradation" - these are the normal sensor sensitivity settings.

3200 with the Canon 40D and 3200 and above with the Nikon D300 are not "gradations" in this sense, they are simple numeric derivatives of 1600. (The highest true "sensitivity" of the D3 is 6400.) The 1/3 and 2/3 stop "sensitivities" of the Canon 40D are fakes as well, derived from the next lower respectively higher setting.

These settings are useful for JPEG. They are not only useless with raw, but even counterproductive, because they don't contribute any information, but reduce the dynamic range.

ISO 100 with the D300 is probably blocked, because it loses details at the dark end (I guess ISO 200 is the native setting with the D300). In this case its usefulnes is limited to cases, when the exposure needs to be increased - like when shooting waterfalls in strong light.

[JeffKohn]

From a practical standpoint, I can tell you that in my experience going below ISO-200 on the D300 will improve shadow noise at the expense of highlight dynamic range. There seems to about about 1/3 to 1/2 stop loss of highlihght range at LO-1. I've found LO-.3 (ISO160) to be the sweet spot, as there's no discernable effect to the highlights but a slight improvement in the shadows.

[Moynihan]

All digital sensors are opimized for a single ISO setting.

Would anyone know the "optimum" iso setting for the D200?

[BJL]

The only "natural" ISO speed of a sensor is the minimum value (maximum amount of exposure) that gives acceptable highlight headroom, which with the D300 seems to be about ISO 200. Special lower settings are akin to "overexposure and pull processing" with film, and sacrifice some dynamic range through greater risk of blown highlights. The ISO standard for base ISO speed of a sensor is akin to the lowest exposure index to which a film can be safely pulled, and has no direct relation to the ISO speed of a film, which is instead based on adequate shadow handling, rough to four stops below mid-tones.

DSLR sensors typically give four or more stops below mid-tones to ISO speeds well above their base ISO speed, with output shadow handling at low ISO speeds typically limited by standard JPEG conversion rather than noise in the raw output. So a DSLR sensor's "film-like" ISO speed limit is typically well above its base ISO speed.

As far as I know, it is not true that any one ISO speed setting involves "no amplification" or "unit amplification" with all higher settings involving "amplification" and all lower settings involving "attenuation". Instead there is a conversion from charge (in electrons) to the voltage that goes into the A/D convertor, with each different ISO setting having a different conversion factor in mV/e-.  (I understand that the CMOS sensors in DLSRs do this charge-to-voltage conversion at each photosite; with CCD's it is done off the sensor itself.)

Since this conversion factor has physical units, there is no meaning to a value of "one" for a particular ISO speed. Instead, there is just a range of options in shadow noise levels and highlight headroom.

[John Sheehy]

The D300 has a nominal ISO range of 200 to 3200, with additional 1 EV high (6400 ISO) and low (100 ISO) settings that can be reached in 1/3 EV increments. The additional low ISO settings are marked L 0.3, L 0.7, L 1.0.  I took a shot at L 0.3 and the metadata displayed in software displayed ISO 160.   My question is, if it's ISO 160, why not call it that instead of L 0.3, unless below 200 is not a true ISO setting.  What's the difference? Also, what are you compromising by using lower than 200?
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When lower ISOs get special treatment, it usually means that they don't have the same highlight headroom as the other ISOs, because the sensor itself doesn't have enough headroom for them.  For DSLRs, the headroom in the RAW data is usually about 3.5 stops above metered "middle gray" in the green channel, which is usually the most sensitive color channel.

In some cases, there is more headroom in the sensor than what the lowest full-headroom ISO has, but not enough for a full stop lower.  The Canon 5D is like this; it has compromised headroom for its "Low" (ISO 50), but it has enough headroom for a full ISO 80.

[smthopr]

When lower ISOs get special treatment, it usually means that they don't have the same highlight headroom as the other ISOs, because the sensor itself doesn't have enough headroom for them.  For DSLRs, the headroom in the RAW data is usually about 3.5 stops above metered "middle gray" in the green channel, which is usually the most sensitive color channel.

In some cases, there is more headroom in the sensor than what the lowest full-headroom ISO has, but not enough for a full stop lower.  The Canon 5D is like this; it has compromised headroom for its "Low" (ISO 50), but it has enough headroom for a full ISO 80.
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When one lowers the ISO below the recommended range, one loses dynamic range as has been mentioned already. This is because one is over exposing the chip beyond it's ability to record detail and hence it clips the highlights.

That said, one might find that one can "get away" with some lowering of the ISO, but the success of this will depend upon the color balance of the lighting.  If the scene's color balance is close to the native color balance of the chip, then Red, Green, and Blue will clip at about the same point.  If color correction is required, then one color may clip before the others causing a color shift at the clip point. IOW, when you loose highlight detail, it may shift color - either too blue or too orange typically.

I think there is little to be gained by lowering the ISO beyond being able to use a slower shutter speed. A ND filter would be a much better solution. If one is just concerned about the shadow noise, one can always over expose at the recommended ISO and come to the same result I would think.