Minolta 135mm f/2 MD
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Light Falloff (Vignetting) and Chromatic Aberration

For a lens designed to be used at wide open or near wide open apertures, light falloff, or 'vignetting' is also a critical factor. The term vignetting is commonly used to refer to when the corners of an image are obscured by something in front of the lens (eg. a filter or hood), but its correct use is to describe the gradual darkening of the corners of an image which often occurs at wider apertures.

Chromatic aberration is the colour fringing that can be seen on areas of very high contrast in images. This is commonly seen as a slight green and red fringe on a high contrast edge, and is caused by the nature of light. Light comprises different colours, each of different wavelengths. The focus point of these wavelengths varies very slightly, (eg. blue light is refracted more by a lens than red light) leading to the fringing. Modern professional lenses often use special types of glass such as fluorite elements or apochromatic ('APO') glass, which can reduce this. The 135mm f/2 uses achromatic lens design using glass with different refractive characteristics to address the issue.

The performance of the 135mm f/2 with respect to light falloff and chromatic aberration is shown below. The left crop is from the middle of the frame, with the crop on the right from the extreme upper left corner of the image.

Performance at f/2
Performance at f/2.8

As was identified in the previous crops, at f/2 the 135mm records some vignetting at the extremities of the image, albeit this is not severe, and really would only be noticed with slide film. With negative film the prints would simply be printed at a marginal overexposure, and the resultant vignetting would be all but unnoticeable. Close inspection of the corner crops reveals a minor amount of chromatic aberration, albeit not a significant amount, and certainly not something that would be apparent on a print except at extreme enlargement.

Improtantly, the evaluation of vignetting shows that it is completely eliminated by f/2.8, an outstanding result. It is noted that the lines in the corner crop are hand drawn, not printed, and accordingly are not as defined or as wide as the lines on the centre crop.

Performance at f/4
Performance at f/5.6
At f/4 and f/5.6 the chromatic aberration is still evident, but equally as minor as shown in the previous crops. Minolta have obviously made a significant effort to eliminate this issue and achieve the best possible performance achieveable with this lens.

Distortion refers to the tendency of a lens to distort a straight line that appears at the edge of an image. This normally is evident as barrel distortion (lines bowing out in the middle), or pincushion distortion (with lines bowing in). I had planned to include an image of the performance of the 135mm f/2 in this respect, but I was amazed to find that the lens records no measurable distortion whatsoever! This finding impressed me once again with the quality of this lens.

This image was shot at f/2, and demonstrates the outstanding bokeh that the lens can deliver. Note that even at f/2, in real use the contrast is exceptional..

The 135mm f/2 MD is a very fast, high performing telephoto lens designed for use at wide apertures. It features high resolution, excellent corner to corner performance, and outstanding contrast. These factors together with the complete elimination of vignetting by f/2.8, the minimal chromatic aberration and the total absence of any measureable distortion whatsoever have made me reach the opinion that this lens is one of the greatest achievements of the Minolta lens design team during the manual focus era.

As mentioned earlier, the 135mm f/2 MD is one of the rarest lenses in the Minolta manual focus system, and as a result of this it normally demands a price in excess of US$350 on ebay, or $500+ at a dealer. Despite this, I believe it is worth every cent. It is truly a lens that the Minolta enthusiast should aim to acquire and use, because the results will amaze you, and help you achieve photographs that you and your subjects will treasure.

The Minolta 135mm f/2 - A truly outstanding optical performer
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