When you use the Sigma SPORT 60-600 mm ƒ 4.5-6.3 lens, with the Viltrox 0.71 focal reducer on a Olympus OM-1 camera, you get a lens that in effect is a 85 - 850 mm ƒ 3.2 - 4.5 lens !!

Note however that the above photo is NOT representative for the quality of this lens-adapter-camera combo - due to the extreme conditions when you make images of the moon near the horizon - things turn very blurry). There is also a slight focus difference between moon and the Globe arena, and i have to choose one. In the photo above I had to use pretty coarse AI sharpening, in order to get an impression of "sharpness".

For normal photography though, the lens-adapter-camera combo is very sharp !

Intriguing combo

What i find intriguing is the quality out of that combination. Even the widest 60mm [-> 85mm] focal length appears optically better than when i use it natively with the Canon R6. It is almost as if any optical errors are too getting reduced. The Sigma SPORT has a bit of chromatic aberrations / fringing when you use it at 60 mm, especially at wide open aperture.

But with the Viltrox reducer on a Olympus OM-1, which turns the 60 mm into an effective 85mm focal length - the optical quality is superb.

I really like this combination. It is unexpected good. The one stop brighter aperture due to the focal reducer - actually helps at night, to make the live-view a notch brighter - and therefore it is easier to set the sharpness correctly in manual mode.

Indoors i noticed that the AF did actually work well, except at the extreme of 850 mm. Perhaps it has to do with the light levels. It seems to work much better (of course) in good light. But I have to examine that further.

The basis of using a focal length reducer, is that the lens itself is of good optical quality. Which the Sigma SPORT provides, whether you use it natively on a Canon EOS, or with help of a focal length reducer on a Micro Four Thirds camera.