Pentax-DA 50mm F1.8
Vignetting
In simple terms, vignetting is the darkening of the corners of an image that occurs at wider apertures. Every lens, wide open, will exhibit some. Luckily, it need not be a problem for modern photographers. Firstly, it is always possible to shoot at smaller apertures, mitigating the effect. Additionally, cameras released in the last few years often have built-in tools to remove vignetting in a way that's invisible to the user. Lastly, it is always possible to purchase higher-quality lenses that will show milder vignetting.
This section presents how the DA 50mm performs in regards to vignetting.
Vignetting Test
The test was performed by pointing the lens at a blank wall. In order to avoid the bias of the in-camera corrections, we shot each image both in JPEG and in DNG RAW, then used Adobe Lightroom to develop the RAW files (using default settings to develop the files). JPEGs and RAWs were scaled down, converted to grayscale for improved visibility, then exported. The following settings were used:
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|
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F1.8 JPEG |
F1.8 RAW |
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F2 JPEG |
F2 RAW |
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F2.8 JPEG |
F2.8 RAW |
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F4 JPEG |
F4 RAW |
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F5.6 JPEG |
F5.6 RAW |
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F8 JPEG |
F8 RAW |
The following chart illustrates the darkening in the corners in terms of the exposure difference relative to the center.
Verdict
As can be expected, JPEG files with in-camera correction show no visible vignetting, which is more a testament to the quality of the JPEG engine than to the lens. RAW files show surprisingly strong vignetting at F1.8 and F2. At smaller apertures, starting at F2, vignetting becomes essentially invisible. A good but not stellar performance that could perhaps be attributed to a slightly smaller image circle compared to Pentax's other 50mm lenses.
