With the anticipation of receiving my new 70-200 f/4 VRIII, I decided to do some shooting with one of the very first lens I ever purchased. When I started shooting a few years back, I probably read somewhere that you should go shooting first with a smaller prime like a 50 or 35 mm. Not me, I wanted to charge into it and decided to get the big gun, the most versatile lens that Nikon made. That was and still is the 70-200 VR2. I shot the heck out of the lens, and always kept it clean, warm and safe. It has special rubber lens coat on it to protect it from the elements of rain, snow and sweat and always travels with me. All my trips, bar none, it has racked up a few miles.
So when I was shooting in Hull, Mass in November, the shot focus was looking ugly in my preview screens. I went to work and tried different focal lengths and apertures, thinking that was the issue. But it was not…In due time I started to come around to the fact that my longtime friend had pulled a hammy and was out. I was getting good acceptable center focus, but the buque and focus was not there on the edges.
So eventually back home, I began THE TEST. I thought I’d share how to set this up and go thru this just in case you need to either tweak you lens front/back focus or check to see if your gear needs to head for repair.
Here are a few easy steps.
- Download the focus test target chart and print on normal 8 1/2 X 11 white office paper.
- You need to tape the chart to any flat wall about 4-5′ off the floor. (use level)
- Set your DLSR on a tripod, put your 2 axis bubble level in the hot shoe and level camera
- You need to have camera perpendicular and square to the wall
- Looking thru the view finder, set center focus point at center of test target.
- Frame at least 40% of target in viewfinder frame. (see test image above)
- Make sure you have sufficient light source on target for shutter 1/350, 1/500, 1/750 second range
- Camera Settings, VR off, Aperture mode, lowest focal length, highest aperture f/2.8, f/4, ISO 100,
- use a camera release,mirror lock up can be used also.
- turn off any fine tuning, vinetting, ect
- I think single servo is better than continuous.
- Your goal is a clean, vibration free, single test shot.
- With Camera set to Manual Mode LiveView, depress shutter half way, allow camera to prefocus and fire.
- With Camera set to Normal Manual, depress shutter half way, allow camera to prefocus and fire
That is it. Now analyze the two images. Do not get to excited if the live view image is more accurate because it is focusing in a contrast detect mode, (fancy words for high contrasts, it is more of a mechanical slow process which provides higher precision focus results). You’ll want to resize this image up to 100% in your camera display and then compare it to your 2nd Normal image which was taken with your cameras fancy sensor in phase detection mode. The two are typically very very close with the live view having slightly tighter contrasty edges. What you are looking for as you move you focus cursor is to see if any part of the target image is soft and out of focus. You can shoot this image in raw or Jpeg and of coarse you can upload and compare on your computer.
A good best practice ( is when you buy a new lens to set up the test targets and grab a few images to see how good your selected lens is, and keep the test target for future reference. If your target shows your lens has focus issues, I’d head back to where I purchased it with a printout of the focus chart. (its hard to fake a focus problem if you have documented it.)
One thing to keep in mind, is that you really need to do this with two lens. You need to rule out the camera body. In my case I took another round of images withe the Nikon 70-200 f/4 and wow it blew the socks of my old out of focus friend. So that test rules out the body. If both lens had a wacky left side focus, then I’d be thinking my D4 focus was a problem.
For my image above, I uploaded the image to my digital dark room and looked at the distraught out of focus lines on the left side and will be sending the test targets with my old friend to Nikon for hopefully some repair work that will bring it back to normal.