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Lenscracker
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« on: July 16, 2011, 05:23:51 PM »

This a comment for this page on the website
     Received the replacement Sigma 150mm EX DG OS HSM APO last week.  This lens seems to be very sharp at f2.8.  I have my own routine for testing new lenses and this one passed easily.  The lens is a fine replacement for Sigma's original 150mm f2.8. 
     With my 5D2 I can hand hold the lens to 1/25th second in flourescent lighting that requires F2.8 at ISO 3200 with -1 stop exposure adjustment. I do not know the lux value of that setting. I think that is EV -1.  I do not think the OS is really good for 4 stops as advertised,  but it is good for 2 stops for sure under these lighting conditions.  That puts it on par with my Canon 300mm f4 L IS lens.  I have no scientific evidence,  but that's what it seems like to me.
    The auto focus with my 5D2 is a little quirky under the very dim conditions described above. By that I mean that it I can not always use the center af point alone. I have not tried this same test with my 7D, which has a better autofocus system than the 5D2. 
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dosdan
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« Reply #1 on: August 04, 2011, 08:56:21 PM »

<div id="linkdxomark">
     With my 5D2 I can hand hold the lens to 1/25th second in flourescent lighting that requires F2.8 at ISO 3200 with -1 stop exposure adjustment.

1/25s, f/2.8, ISO3200 = 2.6 LV

If you have to use -1 EVcomp in camera to get the exposure you want, that means that you are getting the camera to expose shorter (considering just the variation of shutter speed) than its metering wants too, and that otherwise the camera would treat it as a 1.6 LV exposure.

If instead you apply -1 EV in post processing in your raw processor and no EVcomp in camera, that means that you think that the 2.6 LV exposure that the camera chose is too long and, in your opinion, the metering should have treated the scene as a 3.6 LV exposure.


A Light Value calculator can be found here:

http://www.pentaxforums.com/forums/photography-articles/88197-excel-2003-lv-light-value-calculator.html

Dan.
« Last Edit: August 04, 2011, 09:25:39 PM by dosdan » Logged
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