Olympus OMD EM1 Gordon Laing, January 2014

Olympus OMD EM1 diffraction compensation

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The Olympus OMD EM1 becomes the first Olympus camera to offer compensation for the effect of optical diffraction, where choosing small apertures can result in the overall image becoming soft and losing detail. According to Olympus, the EM1 now applies additional sharpening to images with small aperture to reduce the effect.

I was particularly interested by the diffraction compensation as you don't need to close the aperture too much on the Micro Four Thirds system for it to become an issue. To put it to the test I took a series of photos with the EM1 fitted with the Olympus 75mm f1.8, which is an extremely sharp lens. I took the same composition in RAW+JPEG at every aperture and processed the RAW files using Adobe Camera RAW with the sharpening set to 50 / 0.5 / 36 / 10, which delivers very crisp results.

  Olympus OMD EM1 results
1 Olympus OMD EM1 Quality JPEG
2 Olympus OMD EM1 Quality RAW
3 Olympus OMD EM1 Noise JPEG
4 Olympus OMD EM1 Noise RAW
5 Olympus OMD EM1 diffraction compensation
6 Olympus OMD EM1 Lumix 7-14mm flare
7 Olympus OMD EM1 long exposure noise
8 Olympus OMD EM1 Sample images

Below you can see 100% crops from the in-camera JPEG and Adobe-processed RAW file with the lens set to f2.8 where it's arguably performing at its best. As you can see there's loads of fine and crisp details and little to choose between them on detail and sharpness. The big question then is what happens as you close the aperture and keep the processing setting the same.

Olympus OMD EM1 with 75mm f1.8 at f2.8
100% crop from in-camera JPEG
Olympus OMD EM1 with 75mm f1.8 at f2.8
100% crop from RAW processed with ACR
75mm f1.8 at f2.8   75mm f1.8 at f2.8

Below is the same shot taken at f22, the minimum aperture for the 75mm lens and one that's well within the murky depths of diffraction. As you can clearly see from the JPEG crop, it's considerably softer than the one at f2.8, with many fine details wiped-out by diffraction. This isn't surprising, but what's interesting is to compare the JPEG against the RAW file, the latter processed using exactly the same sharpening settings as the f2.8 sample above. It's clear to see the in-camera JPEG is delivering a much better result than the processed RAW file, and no amount of extra sharpening to the RAW file in Adobe Camera RAW could bring it to the same level.

Olympus OMD EM1 with 75mm f1.8 at f22
100% crop from in-camera JPEG
Olympus OMD EM1 with 75mm f1.8 at f22
100% crop from RAW processed with ACR
75mm f1.8 at f22   75mm f1.8 at f22

While there's no documentation on how the diffraction correction is implemented, I'd say it's definitely being applied to the in-camera JPEG and not to the RAW file. And while the JPEG at f22 still looks soft compared to the one at f2.8, it looks a lot better than the processed RAW file could. Maybe there's better results with different RAW converters, but based on my own workflow with ACR I'd say I'd prefer the in-camera JPEG for overall detail when shooting at very small apertures.

Hungry for more tests? How about my EM1 long exposure noise or EM1 with Lumix 7-14mm flare?! Or if you've seen enough, check out my EM1 sample images or skip straight to my verdict!

Olympus OMD EM1 results : Quality / RAW quality / Noise / RAW Noise / 7-14mm flare / diffraction / long exposure

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