f/stop shift?

[tategoi]

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I am not sure if thats the right term to use. Basically what I did was set my 35 'cron to f/5.6 on the lens, but when I imported the image to LR, it shows f/5.7. What gives?

[twittle]

Because the lenses are completely manual the camera doesn't actually know your f-stop, so all Lightroom can do is estimate it.

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[adan]

The reported f/stops in the M9 EXIF are a guesstimate based on comparing the scene illumination as read by the little blue dot above the Leica logo with the ttl illumination as read by the internal meter.

 

The guessimates are just that - I just looked at a series shot at f/2 with a 75 'cron, and the camera guessed anywhere from f/2.0 to f/2.4 to f/2.8. (and one could ask - why f/2.4, instead of f/2.5?)

 

As to why 5.7 instead of 5.6 - the camera decided your shot was just a tad too dark to have been at f/5.6 (in its ineffable wisdom, as compared to the scene brightness), so it guessed a notch darker on a fairly fine scale. A little darker yet and it would have guessed f/5.8, no doubt.

 

My M9 regularly reports that my 35 Summilux was set to f/1.2 or f/1.5 in the EXIF data. Despite the fact that Leica hasn't actually made an f/1.5 lens since the early 60's, and the Summilux can't be set to f/1.2.

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I can see where tategoi is coming from - if the meter guessed within a 10th of a stop of f/5.6, why not just report "f/5.6" - It might be a fun winter project to figure out all the possible fractional f/stops the M9 will report in EXIF, by everyone looking for oddball numbers in their EXIF and adding them to a list.

 

My own guesstimate is that the M9 reports its guesses in decimal f/stops (which are not the same thing as 10ths of a stop - e.g. there are only four decimals between f/1 and f/1.4, and they are logarithmic anyway) up to f/8 or so, and then integer stops. So one might see f/1.1, f/1.2, f/1.3, f/1.4..............f/2.3, f/2.4, f/2.5, f/2.6, f/2.7.........f/5.6, f/5.7, f/5.8, f/5.9, f/6............f/10, f/11, f/12.

Edited January 9, 2010 by adan

[scott kirkpatrick]

Andy, when things are working right, the guesstimated f-stop never is less than the maximum aperture or more then the minimum for that lens ("max", "min" are confusing, aren't they, but you know what I mean...). But Leica and Jenoptik don't always complete all the tables when they ship new firmware, so there have been cases of lenses that show a maximum guesstimated aperture of 1.0 even though the lens can't do that. 1.0 was the default for the 21 and 24 Summicrons in the last M8 software release. It may still be, but I haven't checked. The way to check for this little peculiarity is to take a picture with your finger covering the blue dot, causing the external light level to be less than the internal level. That will produce an aperture guesstimate pinned at the maximum aperture.

 

I have CV and ZM lenses that offer f/22, but only show f/16 as the minimum aperture in the EXIF because the Leica lenses that they impersonate only go to f/16.

 

scott

[Samir Jahjah]

Andy, when things are working right, the guesstimated f-stop never is less than the maximum aperture or more then the minimum for that lens ("max", "min" are confusing, aren't they, but you know what I mean...). But Leica and Jenoptik don't always complete all the tables when they ship new firmware, so there have been cases of lenses that show a maximum guesstimated aperture of 1.0 even though the lens can't do that. 1.0 was the default for the 21 and 24 Summicrons in the last M8 software release. It may still be, but I haven't checked. The way to check for this little peculiarity is to take a picture with your finger covering the blue dot, causing the external light level to be less than the internal level. That will produce an aperture guesstimate pinned at the maximum aperture.

 

I have CV and ZM lenses that offer f/22, but only show f/16 as the minimum aperture in the EXIF because the Leica lenses that they impersonate only go to f/16.

 

scott

 

My 24mm lux often resulted in a reported aperture of f 1...like in this picture :