Digital Photoguide

Lens Quality

The quality of the final Image depends critically on the quality of the lens used to create the image. When you choose a lens you base the decision on many different factors but generally assume that the quality of your lens will be comparable to that of your friend’s or the one tested by a magazine. Generally this is true, but not always. Individual lens quality can vary and you might end up with a “lemon”. An RI reader experienced just this. The sharpness of the images from his camera with Nikon 80-400 zoom lens was disappointing, even when shooting in Raw format. By trying a completely different lens we established that the camera was capable of producing sharp images so there was no problem with the camera. He was able to borrow another lens of the same 80-400 zoom type and shoot some comparison pictures. The results are quite interesting.

Below are shown sections from two images, one using the “old” lens and the other the “borrowed”. Move your mouse over the image to display the other image. The lens was a Nikon 80-400 f4-5.6 set at 400mm using an exposure of 1/500 sec @f5.6 and a sturdy tripod was used. This is quite a severe test because the lens was set at full aperture. A lens is always sharper when stopped down 1 or 2 stops from maximum, so f11 should give best sharpness for this lens when set at 400mm. Both images were shot in Raw format and converted using the Adobe converter with “as shot” default settings and no additional sharpening applied.

(Place your mouse over the image and watch it change)

Can you see a difference between sharpness of the two images?

Pay particular attention to the clarity of the tiny bolts brackets on the grey poles. Remember that these are two different examples of the same lens, using the same photographic technique to take each image.

This is quite a large enlargement. The full size image is shown on the right with the area in the test section ringed in red. The rather unusual subject is the roof of an aquarium in Hull. Although not a railway-related there are plenty of edges which are a good indication of sharpness, as well as some fine detail in the brackets.

The author’s opinion is that the second lens is sharper although the difference is harder to see on an image prepared for web viewing than when viewing an enlarged image on the computer at home.

The first lens would appear to be faulty. Of course the final test is shooting a train not a roof !