Upload & Sell: Off
Okay guys and girls, I couldn't wait! I setup an impromptu test of my Sigma USB dock and 35mm f/1.4 with the gear I had on hand, and I thought I'd share some of my results. In fact, lets put those first:
My findings support the notion that the Canon body MFA and Sigma lens MFA increments are linked in a 1:1 ratio. I ran several tests at 3 different focus distances, including inputting and changing USB dock lens settings 5 times. All Focal recommendations were eventually input directly as-reported into the Sigma lens, with the result being a new Focal retest with an offset recommendation of zero each time. Impressive!
Here's my methods: I used 2xAB400s for lighting, simply putting the modeling lights at full blast. They were close enough to the Focal target to put me at a 9.2EV. I used my 5D Mark III on a sturdy Manfrotto tripod with a geared head. All test shots were taken at ISO 100, using mirror lockup, most-stringent test settings and target optimization (more on that later.) I chose to bundle the ~MFD and ~.4 meter distances, as they were simply too close for me to justify two sets of tests. Maybe when I've got more time. I ran initial Focal tests at distances of .4m, .85m and 5.4m.
Initial recommendations were: +17 at .4m, +16 at .85m and +2 at 5.4m (approaching infinity.) The +2 recommendation at 5-plus meters fit well with my shooting around the house, as I'd decided off the cuff that +3 worked best for those distances.
I did all the focal recs first, finishing at the 5.4 meter distance. From there, I plugged the lens into the USB dock and put the setting at the recommended +2. Having read the earlier post about the possible correlation between body and lens MFA, I didn't really know what to expect. It came back with a best value of (0). Sweet!
From there, I moved into the .85m distance. The focal recommendation was for +16, but just to test the system I put +11 into the USB dock. After running Focal, it recommended that I put the MFA at +5. Well, 11+5=16, so that's pretty good. Put it at the correct +16 and ran it again, and got a best value of (0). Double Sweet!
Then, I put the camera back to the original .4m distance, plugged in +16 again, even though Focal called for +17. Again, it called my bluff and recommended a +1 MFA. I'm really impressed with the consistency of the Focal system here.
All in all, I couldn't be more enthusiastic about the possibilities of this little setup. As mentioned earlier, many lenses have a large swing of MFA numbers between MFD and infinity, and this tool helps account for that. Here's what I didn't like:
-I only tested one body, lens, and dock. And, only in one type of lighting.
-I've not had time to extensively shoot with the lens after calibration
-Outliers had to be manually rejected, as Focal gave some obviously wrong scores. Even using optimization, which accounts for any shift, some obviously misfocused shots were scored very high. It's easy to just right-click them during analysis, but it is annoying.
I'm sure there are plenty of other issues with my data, and just like the other report, mine is simply one more data point. It proves nothing, but it does support the theory that Sigma hooked us up with a 1:1 ratio.
I'll get some pics up at some point. Thanks for playing!