DamianOz wrote in post #16041913
Received my Dock this morning, so I spent the past 10 hours testing my S35, with TheLensGuy's, findings in mind.
Firstly, the Vignetting is evident and constant, I hadn't laken much notice in the past, in LR, I have lens correction set to apply when I import. No need to do any extra steps in PP.
I do not have the 35L to compare, so any comparisons are with my 24-70ii.
However i did play with the LR's Lens correction profile for the 35L, according to the Adobe profiles, Sigma does have a slightly darker vignetting in the very corners.
However, the difference between the two profiles is very minor, check it for your self. load a even colour image and switch profiles.
IMO, the issue of vignetting is mute, I could see no ill effect from the default correction at any variations in exposure combinations and lighting.
Now on to the interesting tests.
Prior to any Dock adjustments, I wanted to be certain of what values to change.
I used my 6D for this test, then after adjustment, re AFMAed the 5D3 also.
The focal distances tested were as per Sigma's image in the software, 0.3m, 0.4, 0.8, ∞. (figures are rounded estimates, I set the distances as per the image).
Firstly I used FoCal software, then DotTune method. both these methods showed a similar pattern, however the results did not determine the same MA values at each focal distance. Both methods were repeat 2 more times, Focal showed lest variation, but both methods left me a little uncertain, with variations of +2 points at any distance. So I thought I will try another method.
I used a steel rule attached to my test target tripod, tilted to approx. 45˚
In this method, I took photos of the target, viewed on the rear LCD at X10. Then adjusted the AFMA to shift the center of the focus field to the focus point mark.
The results were dissimilar to that of the previous methods. So I moved the target and camera to various location, inside and out, tested the same focal distance with the determined AFMA setting. Every shot was consistent, or with in 0.25mm at worst. As this methods is preformed in the same way the camera would be used in real shooting situations, and proved to be most consistent, I proceeded to adjust the lens using the Dock. The following values. -5, -3, -5, -1 used. (note, the -1 setting for ∞ was determined by the first two testing methods, as I did not have materials to make a larger target at such a long focal distance, however the DOF is much greater allowing a very broad setting range with little to no effect on the image).
After flashing the new settings to the lens, I confirmed again with the 6D's AFMA set to 0.
Although it is now dark, focus around the house proved to be spot on, with the target and other subjects. I tested 34 shots at random distances (using tripod/remote), all were spot on focus.
I then set up the 5D3 and determined an AFMA of +2, I didn't tests as extensively, however 6 random shots proved to be fine.
So why was the Ruler method so much more curate?
Simple, the camera AFMA points are not linear, moving one point often moved the focus in the wrong direction with respect to points either side, when testing with the ruler at 0.3m (12") f/1.4, and the target at 45˚, the DOF is about 5mm, about the size of the focus point square in the view finder. This enables very accurate visual judgment of where the camera/lens focused. The other methods use an averaging method, open to error with non linear AFMA points.
May be some thing to consider if your finding focus drift.
I later tested the 20-70ii at 24mm 35mm and 70mm, unfortunately, this lens does vary slightly with different focal distances, not enough to put the focused point out of the field of focus, and being f/2.8 wide open, the DOF isn't as thin either, so its quite acceptable and less critical.
I didn't test exposure consistency, I was shooting in Manual mode with Auto ISO, so will leave that for another day.
My Sigma lens does not drift focus to any degree near close enough to put the focal point out of the focus field, the few shots that appeared shifted was extremely slight, and could possibly be caused by shutter vibration.
Stock, it was no different to Canons latest L lens with similar FL (although a zoom, sorry I didn't have the 35L to compare). Tuned it is acutely accurate.
TheLensGuy is correct about vignetting, but IMO its not even closely as drastic as made out.
Sharp, you bet, I thought my 24-70ii was very sharp, its not as sharp as the S35.