Getting straight lines straight is extremely important in architecture photography and so lenses used in architectural photography should be thoroughly tested for curvilinear distortions.
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| architecture photography tips practical lens testing. photo by: Jijo John |
As a general rule longer focal length lenses are of better quality than wide angle lenses. Ultra wide focal length lenses (lenses wider than 24mm on a full frame camera) are the ones mostly used for architectural work and it is the barrel distortion of those lenses we are most worried about.
Here is a practical method to critically test lenses for distortions.
Photograph a scene which has perfectly straight lines in it. Use the lens at its widest setting (assuming it is a wide angle zoom lens). Compose your frame in such a way that you have straight lines in the foreground towards the borders of the frame.
Now compare the picture given above with the one given below, the picture given below shows some serious distortions, notice the distortions are more pronounced towards the edges of the frame, left, right, top and bottom.
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| curvilinear distortion of wide angle lens |
Door frames, windows, pillars etc are all suitable subjects for our testing.
Download the picture on to your computer and open it in Photoshop or any similar image editing program. In most cases, any distortion present could be easily noticed by simply looking at the image. To precisely check the amount of distortion or to correct it in editing one easy way is to place guides on to the straight lines in the image and any deviation from a perfect straight line could be easily noticed and corrected.
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| testing camera lens for distortions |
If the lens shows a great amount of barrel distortion it is best to reject the lens in favor of a better one. A similar test can be devised to test for pincushion distortion in tele photo lenses, but it is seldom a severe issue in architecture work and so we need not delve deep into it.