A technical question to do with dynamic range.

http://www.dpreview.com/reviews/canoneos5d/page22.asp

This is an article from dpreview, arguing that native iso on the tested dslrs is 100, and that shooting at 50 iso actually reduces dynamic range as it is actually 'fudged' on board.

Does this apply to mfdbs and in particular Leaf A65? As a photographer who has always tended towards lower iso settings when shooting film, and looking at the extreme drop off in image quality with higher iso images on digital, I had assumed the lower the better - with the usual juggling involved of speed vs dof.

Any pearls of wisdom?

See the analysis by Roger Clark for the EOS 1D MII. It has similar characteristics to the 5D. His conclusions are quoted below:

"The data for the 1D mark II indicate some important aspects for people making images. The lowest ISO, 50, does have higher signal-to-noise ratios than ISO 100, but at the expense of lower dynamic range and danger of saturating highlights. An ISO of about 75 would be a better match to the sensor range and would not sacrifice dynamic range. Unfortunately, ISO 75 is not available."

The native speed of the A65 (and A75) is 50 iso and therefore there is no such "fudging" done to the data when shooting at that speed.

In addition, when pushing the iso to 100,200,400 and even 800, we still manage to retain full 12 stops of DR. Of course with increasing noise level, but with the same wide DR.

I hope this helps, yair

Thanks Yair. That confirms that the way I work is OK. Good to see Leaf watch the other forums.

Had a helpful reply along the same line from Steen at Baltronics - your distributor in Australia.

I look forward to LC11 - hoping it performs as well as my A65!

What Yair says makes sense: without the sensitivity boost of micro-lenses (and with the high electron well fill factors of full frame type CCD's) MF sensors would be expected to have a lower minimum highlight headroom limited ISO speed (base ISO speed) than a Canon CMOS sensor with micro-lenses.

The 5D at ISO 50 is clearly "pushing", but the 2.5 stops are probably fine for many situations where there are not highlights too far above the metered mid-tone level but one is interested in holding shadow detail well below mid-tone level.

The exception that proves the rule is the 32MP Kodak KAF-31600 sensor that does have micro-lenses, and is rated at ISO 100-800, vs ISO 50-400 for Kodak sensors without micro-lenses like the KAF-39000. (These ratings given by Hasselblad-Imacon for the models that use these sensors.)