Recently Don published a newsletter to our registered members titled "Those Fuzzy Wuzzy Things". It was a great article so I'm re-publishing it here (with Don's permission) so more people can enjoy it. Next time you see Don thank him! And, if you want to be included in the mailing of these newsletters just join our club and register on our web site!
With no further ado, Don's article:
I do a fair amount of closeup – macro shooting. Over the years I've made a number of slightly fuzzy images with the subject just a little less than sharp. I always chalked that result up to my declining vision [right now my nose is 4 inches from the keypad.......so, I've been less than truthful lately?]
My shots most always were pretty sharp a little behind my subject. I had my viewfinder diopter adjusted to approximate what my cameras auto-focus indicated was sharp, but the end result was short on sharpness.
Thanks to trial and error in the digital world I was able to make educated guesses where I'd focus a wee bit in front of my subject and I'd managed to improve the focus performance of my capture attempts. Since I'm a 'make-doer', not uncommon for a wish-washy centrist, I was willing to live with manual focus only for closeups and finding something slightly in front of the subject to focus on in auto focus.
Then came an old thread on a web site I frequent about “back-focus” issues with the D70 and the remedy for my fuzzy malaise. I was directed to: http://FocusTestChart.com for a test procedure and a couple charts that can be printed out to facilitate sharpening my efforts.
Nikon and probably Canon and Sony would rather we not fuss with fine adjustments to our cameras. Likely with good reason. I frequently ignore good reason, and am more than ready plunge into fine adjustments.
It turns out my D90 has two adjustment screws visible to the right of the mirror. Locking the mirror up exposes them. The front screw is to adjust the manual focus mirror and the rear screw the auto focus mirror.
So, the plan is to mount the camera on a tripod with the pan head tilted down at a 45 degree angle. I oriented the target such that the focus line is across the center of the camera view finder.
At the start I centered the page. I used one of my more commonly used lenses. A 28 – 105 mm f3.5 to 4.5 lens. I figured my first effort should be with what I used most and then migrate to a macro lens for finer adjustment.
The best thing to do is tether the camera to a computer. The idea here is to examine the test shots on the computer monitor right away rather than going through the tedium of transferring the test images.
At first glace at the first image it looks like the “Focus Line” is pretty sharp, but the sharpest area of the image is between 2 and 6 mm beyond the Focus line.
Take a look at the following close up:
Maybe I am fussy, but I think the focus could be better. By the way, I am in manual focus for these shots.
After examining the test shot, I locked the mirror in the”up” position as if I were going to clean the camera. I used a hex key to turn the front (manual focus) adjustment cam. It took some trial and error because my first adjustment over shot the focus center. I had to come back a bit, taking test shots every time an adjustment was made.
After a time I got the following result:
It looks like the focus is quite sharp at the focus line and softens reasonably equally in both directions.
I made another adjustment and got the focus a pretty close:
I repeated the process for the auto focus. I did find the auto focus pretty close, but made a slight adjustment anyway to make it better. Generally speaking, I feel pretty good about the effort. Here I am, having the body for 3+ years and not bothered to check this out earlier.
The last image was made with a macro lens. Pretty close, don't you think?
I checked out my other DSLR and found it's manual and auto focus is excellent.
You may want to download the test chart from Tim Jackson's web site. Ignore the fact he is a Nikon shooter. The test chart is what you want. May be worth knowing how sharp your focus!