Hasselblad X2D 100C sensor sensitivity

[JimKasson]

The Fuji GFX 100 and GFX 100S have a base ISO of 100. The Hasselblad X2D, which seems to have the same sensor, has a base ISO of 64. How can that be?

I can think of two possibilities, which are not mutually exclusive.

• Hasselblad allows a greater deviation from linear sensor response than Fuji.
• The Hasselblad color filter array (CFA) blocks more light than the Fuji CFA.

I set up a test:

• Camera on Foba stand -- GFX 100 and X2D
• Electronic shutter for both cameras
• Aputure LED set to 5500 K with diffuser
• Leica 90mm f/2 Apo-Summicron M ASPH lens
• f/2
• ISO 100 for GFX
• ISO 64 and 100 for X2D
• Measured brightest patch in Sekonic/XRite step wedge using RawDigger

The results:

Saturation is strong at 1/25 for the X2D at ISO 100, mild at 1/25 for the GFX at ISO 100, and at mild at 1/20 for the X2D at ISO 64.

Looking at the relative sensitivities in stops for the three shortest exposures:

• When both cameras are set to ISO 100 (the leftmost set of bars), The GFX 100 is about a third of a stop less sensitive than the X2D.
• The X2D at ISO 64 is about 0.57 stops less sensitive than the same camera is at ISO 100. So the relative ISO calibration of those two stops is off by about a tenth of a stop. You wouldn't see the effects of that in real world photography.
• When the X2D is set to ISO 64 and the GFX is set to ISO 100, the GFX 100 is about 0.2 stops more sensitive than the X2D.

So the reduced base ISO is achieved through a combination of things. There's a real loss of sensitivity of 0.2 stops from the GFX 100, which is a lot less than the 0.67 stops you'd expect from the ratio of the two ISOs. A tenth of a stop of that difference comes from the relative calibration of ISO 64 and ISO 100 in the 'blad. The rest might come from the CFA, it might come from taking small liberties with linearity, or it might come from both.

There seems to be less here than meets the eye.

I will be happy to answer questions.

--
https://blog.kasson.com

 

[JimKasson]

Note that this accuracy of this test depends on the timing of the electronic shutter speeds on the two cameras being identical. In the past, I have found those shutter timings to be very accurate.

 

[Erik Kaffehr]

Thanks for doing that study.

Would it be meaningful to compare SNR ratios after the same exposure?

Best regards

Erik

 

[JimKasson]

Thanks for doing that study.

Would it be meaningful to compare SNR ratios after the same exposure?

Best regards

Erik

I’ll be doing photon transfer curves later.

 

[bobby350z]

So bottom line any advantage of that ISO64? Why you think they did it?

 

[JimKasson]

So bottom line any advantage of that ISO64?

I will let you know after I have done the photon transfer curves.

Why you think they did it?

I need more information before I can answer that question.

 

[Erik Kaffehr]

Thanks for doing that study.

Would it be meaningful to compare SNR ratios after the same exposure?

Best regards

Erik

I’ll be doing photon transfer curves later.

Thanks

Erik

 

[SrMi]

I briefly checked the metering of a homogeneous surface. GFX100S at ISO 100 and X2D at ISO 64 measure similar exposures (shutter speed and aperture), but I need to do proper testing to confirm that.

I do not know if either camera has biased metering to protect the highlights or reduce the noise in the shadows.

As with all cameras that offer ISO 64 (Nikons, Leica), I would not expect higher DR at ISO 64 than other cameras have at ISO 100.

 

[bobby350z]

So bottom line any advantage of that ISO64?

I will let you know after I have done the photon transfer curves.

Why you think they did it?

I need more information before I can answer that question.

Thanks.

BTW - Are you getting that GF 20-35mm too?

 

[JimKasson]

So bottom line any advantage of that ISO64?

I will let you know after I have done the photon transfer curves.

Why you think they did it?

I need more information before I can answer that question.

Thanks.

BTW - Are you getting that GF 20-35mm too?

Yes. Looking forward to receiving it, but I'm busy right now with the X2D, so maybe it's just as well I don't have it.

 

[TechTalk2]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

 

[JimKasson]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

It really doesn't make much difference in the exposure required to achieve sensor saturation. A couple of tenths of a stop is all.

 

[TechTalk2]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

It really doesn't make much difference in the exposure required to achieve sensor saturation. A couple of tenths of a stop is all.

The camera makes the ISO setting available to the user nonetheless. How it's used, whether it's used, and how it affects the image are all additional considerations which would be null were that ISO setting not available to use for whatever reason the end user sees fit.

 

[JimKasson]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

It really doesn't make much difference in the exposure required to achieve sensor saturation. A couple of tenths of a stop is all.

The camera makes the ISO setting available to the user nonetheless. How it's used, whether it's used, and how it affects the image are all additional considerations which would be null were that ISO setting not available to use for whatever reason the end user sees fit.

It’s kind of like the knob on the amp in Spinal Tap. Or maybe it’s the GFX that goes to eleven.

--
https://blog.kasson.com

 

[TechTalk2]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

It really doesn't make much difference in the exposure required to achieve sensor saturation. A couple of tenths of a stop is all.

The camera makes the ISO setting available to the user nonetheless. How it's used, whether it's used, and how it affects the image are all additional considerations which would be null were that ISO setting not available to use for whatever reason the end user sees fit.

It’s kind of like the knob on the amp in Spinal Tap. Or maybe it’s the GFX that goes to eleven.

The utility, or the lack thereof, of having an ISO 64 will possibly be one of debate in forums while perhaps generating less passionate attention to the fractions of a stop in gain or difference for many users. Just a hunch.

 

[Doppler9000]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

It really doesn't make much difference in the exposure required to achieve sensor saturation. A couple of tenths of a stop is all.

The camera makes the ISO setting available to the user nonetheless. How it's used, whether it's used, and how it affects the image are all additional considerations which would be null were that ISO setting not available to use for whatever reason the end user sees fit.

It’s kind of like the knob on the amp in Spinal Tap. Or maybe it’s the GFX that goes to eleven.

The utility, or the lack thereof, of having an ISO 64 will possibly be one of debate in forums while perhaps generating less passionate attention to the fractions of a stop in gain or difference for many users. Just a hunch.

Maybe. On the other hand, perhaps “It goes to 64!” will become a Hasselblad catchphrase.

 

[spilla]

So bottom line any advantage of that ISO64? Why you think they did it?

I would assume to expand the range of exposure combinations available to the user, but there may have been other considerations as well.

It really doesn't make much difference in the exposure required to achieve sensor saturation. A couple of tenths of a stop is all.

The camera makes the ISO setting available to the user nonetheless. How it's used, whether it's used, and how it affects the image are all additional considerations which would be null were that ISO setting not available to use for whatever reason the end user sees fit.

It’s kind of like the knob on the amp in Spinal Tap. Or maybe it’s the GFX that goes to eleven.