New Lens Calibration; Not Good News!

Bicycle & Flowers, Nantucket Island, MA

www.dennismook.com

As part of my process to "check out" a new lens I have acquired, and after I have conducted some preliminary examinations of the lens, as mentioned on July 11, 2013 in the post, "New Lens, First Order of Business," I run the lens through the FoCal software (by Reikan) to calibrate my particular copy of the lens to my camera bodies.  Additionally, the software tests the lens' ability to focus consistently and will determine the best aperture.  It may do some other things, but these are the three tests that are important to me.

So, how did my lens do?  Long story short--I'm sending it back.  Why?  Here is why.

The focus consistency is all over the place.  The software program I use will tell me how consistent a lens focuses after it is focused, defocused, refocused, defocused, refocused, etc.  When looking at 10 repetitions, the consistency was just not there.  Those red diamonds should be pretty close to being straight across the chart.  They are in my Nikon lenses.  In this case the only patter I see is back focus, front focus, back focus, front focus, etc.  I can't keep a lens which cannot consistently focus accurately.

Without consistent and accurate focus, one can never be guaranteed of getting optimum results.  For example, you take a picture.  You look at the image and it looks great-nice and sharp.  You take another one.  This one is not quite as sharp.  Is it the lens/camera combination or is it your technique.  No way to tell unless you have tested all the parameters.

In the other tests, I ran the calibration (setting micro-focus on the camera body to get optimum focus for the camera/lens combination) test 4 times and got 4 different micro-focusing adjustment results.  They were -2, +1, +2, +7, +8.  That shouldn't happen.  In my Nikon lenses, repeated tests were very, very close if not exact.  I can understand + or -1 point variation, but not more than that.  Additionally, two additional tests I ran would not complete as the software said it couldn't determine the micro-focus adjustment at all!  Not good.

In the aperture sharpness test, I don't know what to think.  I ran the test twice and got two different results.  That may be from not nailing the focus.  Both were close, but not the same.   The first was F/3.5 and the second F/4.  But the computer should come up with the same number.  It shouldn't vary.  The other aperture values were also slightly different.  My confidence level in this lens is very low at this point.

I did find it interesting that an F/2.8 macro lens' best aperture would be less than or equal to 1 stop down rather than the traditional 2 stops down from wide open as always has been widely assumed.  This is the second lens where I found that.  On my Nikon 70-200 F/2.8 VRII, the best aperture, according to the software, is F/3.2.  That was interesting.  My other lenses are closer to middle apertures.

So, after preliminarily testing the lens I was excited as everything looked good, but then my balloon was deflated after running it through the software tests.  Oh well.  That is why I do it.

I have a friend who bought the same lens from a different source last week.  He will be bringing it over and we will calibrate it to his D800E.  If the results are more consistent, I may buy another one.  If not, I'll look for a different macro lens to accomplish my slide copying project.

Thanks for looking.

Enjoy!
Dennis Mook