|Click here for full size. Nikon D7100, 28mm f/2 AI Nikkor; 1/125 sec @ f/4. 4.655x3.500 px.|
If you want to quickly assess if your lenses are focusing properly, my friend Carsten recommends the “Newspaper Test”.
This works very well, he says, because we are so used to letters that we can judge “readability” much better than a certain degree of blur.
It is also the method of choice to test longer lenses at different distances, because for that both Nikon's “Ruler Test” and my “Domino Test” are a bit tricky; it may be quite difficult to judge the results at a focusing distance of – say – ten meters.
Also, the field curvature of certain lenses may throw you off on the domino test, because of the width of the subject. With this test, this is not a consideration.
This is how it works
Shorter lenses can be shot hand-held, but for the most reliable results you’d want to mount the camera on a tripod.
I found that for the easiest interpretation, a camera-subject angle of about 30-40 degrees is ideal, but if you are farther away from the subject a different angle may be appropriate, especially with long lenses.
You can mount the newspaper on the floor – making sure it is flat, at least around your focus point. Use some tape to keep it in place in case you are doing your testing outside, which is likely if you’re testing a tele-lens.
Using the center focus point and AF-S, focus somewhere halfway in, ideally on a picture with a caption (red bracket in the sample picture), because focusing in the center of a solid block of text may cause hunting on certain lenses.
If the lens is focusing properly, the text is sharpest within the bracket – as is the case here – but you will be able to quickly determine front focus if the text is sharpest closer to the camera or back focus if it is sharper beyond the focusing point.
If that is the case, you can dial in some positive or negative AFFT on the fly and repeat the test.
Obviously, you can also quickly test at different apertures – up to two stops down is recommended – at different focal lengths and camera-subject distances.
While the Domino Test is likely more precise for “normal” lenses (if set up properly), the Newspaper Test is less demanding to set up, particularly useful for long lenses and also for testing focusing distances of 5 meters and more.
You might also want to read:
Back Focus, Front Focus or Spot-on? Do the Domino Test
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