X2D True Expose option

[ALAIN]

Hello,

I'm very satisfy with the X2D/XCD38, after severals days of test
Like with X1D, Iso auto is not possible in Manual mode (I like that with the M11).

I saw the option "True Exposure" in the page "Exposure".
I don't understood what is it : what change and in witch mode ?
Thank you per advance

I tested also the X2D with Profoto A1/nikon version in TTL : perfect !

Best Regards,

Alain (from France)

[asfeir]

With central shutters, when the lens is stopped down say at f8, as the shutter opens, it opens progressively (i.e. with less light than f8) but after few milliseconds it reaches the f8 opening and spends some time behind the closed diaphragm, the light passing is f8 as long as the shutter blades are behind the diaphragm, then progressively closes and the light passing will decrease from f8 until the shutter closes completely.
Without True Exposure, the timing T of the shutter is measured from the time the shutter blades are half hidden by diaphragm blades while it is opening and while it is closing, with True Exposure, the timing T is measured from the time the lens is fully open at f8, ie. the shutter blades are fully behind the diaphragm blades.
T without TE is larger than T with TE.
The difference between the two are more important as the setting of the shutter speeds gets shorter than 1/500 of a second.

[ALAIN]

Ok, thank you for that
If I understand correctly, this option only has advantages?
What would be the reason not to use it all the time?

[JCM-Photos]

true exposure is an electronic exposure time correction as in all leaf shutters exposure increases when aperture is closed.
true exposure makes no sense with very long exposures because the leaf shutter exposure drift becomes negligible compared to the long exposure.

With XCD lenses true exposure is automatically disabled for the range 1/1000s and shorter because exposure starts delayed with ES after full shutter opening

[asfeir]

The subject if covered with great details on this page from the Hasselblad website:
https://cdn.hasselblad.com/f/77891/x/5e4fbb1583/shutterathighspeed.pdf

To my understanding, and as far as the end user is concerned, it makes no difference whether TE is on or off. I have tested this some time ago, and this was the case. I did not test smaller opening beyond f16 and faster shutter speeds than 1/1000, nor with flash.

To address the different exposures depending on whether TE is on or off, the system compensates by adjusting automatically the timing to get the same exposure, but according to Hassy documents this adjustment is quasi impossible to do when the shutter speed is too short. In this case, the adjustment is done by correcting the aperture. The documentation specifies clearly that setting TE on, will not make any compensation using shutter speeds. That's why TE must off when using flash.

To my understanding, and as far as the end user is concerned, it makes no difference whether TE is on or off in moat cases. I have tested this some time ago, and this was the case. I did not test smaller opening beyond f16 and faster shutter speeds than 1/1000, nor with flash.

Note that True Exposure adjustments ON or OFF are only possible with Hassy HCD and XCD lenses.

[ALAIN]

Ok, but actually, with an X2D/XCD38 set, is the option really useful without flash? And should it be avoided with flash?
(I tested it with an A1 in TTL without any effect: everything happens as if it were off)

[asfeir]

I think that it is not advisable to use TE with flash as this might affect the shutter speed and hence synchronization. All in all, I have not yet found a case with the TE on or off has effectively produced an observable effect on the picture. But there may be cases with very high speeds and lens stopped down a lot, that effects can be noted.