Workshop 4 - Lens Testing

There were no real surprises with this lens test. Having last year learned about the various forms of distortion, chromatic abberations and correction methods when printing images for assignments that used this lens the problems were evident and corrected post production. It was stated in one of our early classes that there is no such thing as a perfect lens due to the properties of the glass and the refaction of light of varying wave lengths.

Lens testing by placing five targets - 4 corners and centre - on wall, see below. Two tungsten lights set up at 45 degree angle one on each side of target. Camera mounted on tripod, leveled and all planes level. Images taken at a set focal distance at various apertures.  Use light meter to determine correct exposure.

Lens tested was the Canon 70-200mm, f 2.8 at 70mm and 90mm focal length.

This first set of photos are the results using the 70mm focal length test chart to show lens quality at various aperture settings to determine the sweet spot. Examples shown are but a few of the overall test results. Below are screen shots of blown up sections of target groupings.

Centre target group f/2.8 - shot specifications on screen capture. Relatively good image with some detail softness observed in all images, spherical aberration. When viewed 2:1 chromatic aberration visible with red fringing around edges. Noticed slight pincushion distortion. The LR3 lens profile enabled corrects the pincushion distrotion and the chromatic aberration.

Bottom Left target group f/2.8. Similar quality and spherical abberation as identified on above centre target shot but the chromatic abberation is more pronounced.

Centre Target @ f/11. This was the sharpest of all the images. Chromatic abberation as above still present as was the pincusion distortion. Both of these again corrected by LR3 profile enabiling.

Bottom Left @ f/11. Very similar to the centre image above. I couldn't detect any difference between the centre target and the external targets. "The Sweet Spot" for this lens is about  f/11.

Centre target at f/22. Relatively good image with some detail softness observed in all images. When viewed 2:1 chromatic aberration visible with red fringing around edges. Noticed slight pincushion distortion. The LR3 lens profile enabled corrects the pincushion distrotion and the chromatic aberration."

Bottom Left @ f/22. Chromatic abberation on this shot more pronounced than in the centre shot.

The results of the 90mm lens testing are almost the same as with the 70mm above with f/11 being the sweet spot at that focal length. As the owner of the L Series 70-200mm f/2.8 I'm quite happy with the test results and the abberation and distortion noticed being correctible either manually or using the LR3 Profile Corrections makes it a good lens to have in my kit.