Micro-adjusting your focus
For the past little while, I’ve been dissatisfied with the sharpness of some of my images, especially with the wonderful, professional, Nikkor AF-S VR 70-200mm f/2.8 lens. You would think that with this almost-$2000 lens, this would be the last issue you would expect. I’ve had the uneasy feeling that something is wrong.
I experimented. The autofocus, or even manual focusing was off. The image would look sharp through the viewfinder, but not on the finished image. Somehow, the big Nikon zoom and my D-300 were not getting along. My guess is that normal wear and tear changes the alignment of the lens in the mount. I never dropped or banged the lens or camera, so there was no abuse. I figured it was inevitable that I'd have to send my equipment in to Nikon for adjustment. Not under warranty, either — I bought the lens from B&H in New York.
My first clue of a solution was when I read a review of a piece of software called “LensAlign Pro” in the latest issue of Photoshop User magazine.
This is a software package that comes with some focusing targets and a ruler. In the article, and on their website, http://www.lensalign.com/, they mentioned that some of the current higher end DSLR’s have a menu-driven micro adjust of AF-tuning built in. Sure enough, the D300 has it. So do a lot of other DSLR’s — here’s a list that I found through that site:
If your camera does not have this feature, it may have to go back to the manufacturer for adjustment, which I know is time consuming and expensive. You would have to ship the body and any lenses that need alignment to them.
Now with all due respect to the makers of this “LensAlign” product, I’m not sure why you actually need it. Here’s what I did without spending dime one.
I took a tape measure and tied it to the tripod then let it run outward along the ground, straight away from the camera at about a 30° down angle. I focused on the red 7’ mark, took a shot and here’s what I got (click the image to blow it up):
Now I went into the menu and after about 10 trial-and-error adjustments (I ended up at +7 on a scale of -20 to +20, here’s the same shot. Enough said?
And it obviously worked: check this out!
In the D300 (I don’t know about other cameras), the AF-tuning is specific to the lens. Change lenses, and set an adjustment for that lens. It knows which lens you have mounted and will microadjust automatically for that lens. Also the camera will save up to 99 different adjustments for each lens – so I’m guessing it might be different at minimum focus distance (like I used) or at other distances, so you might need more than one setting. I’ll experiment when I have time – but the most critical adjustment is when you’re focusing close and wide open. In this case, 7’ and f/2.8. But I get that when you shoot portraits, for instance, the near eye has to be tack sharp. The next lens I'm going to do is the 50mm f/1.8.
This is cropped out of an image captured from about 8' to 10' away, at
200mm, f/2.8. If I hadn't cropped it, you would be able to see focus fall-off at
the edges of the leaf because it wasn't exactly at right angles to the focal
plane. In other words, the top of the leaf was further away, so it was out of
focus. Oh by the way: September 13. Fall is imminent in Northern Ontario.
Dual Monitor Bridge Trick
Another trick I picked up in the same magazine is for Bridge users who have dual monitors. I clicked on Window --> New Synchronized Window, then dragged the new window to the big monitor. By dragging the boundaries of the file list, the thumbnails and the metadata, you’re left with one huge preview window. Now if you click on an image on the other monitor, it comes up full size on the big one. Even better (this wasn’t in the article): click on the big image then hit the spacebar. That puts a full-screen image on the big monitor and the scroll wheel on your mouse will let you zoom in up to 800%. Scroll through your images with the arrow keys. That’s how I selected the sharp leaf image.
Just before I go away, here are a couple of images I took from my dock a couple of evenings ago. This blue heron was fun to watch. Have you ever watched a cat hunting? Same thing: the bird spots a fish and moves into position in ultra slow motion and then strikes. I got him just as he caught a little minnow. Later I tossed a pebble to make him fly off so I could get a photo in flight.