Sigma 60mm long portrait lens

Both lenses used here are designed for a larger sensor than in the cameras pictured:

The Sigma 60mm f/2.8 DN used on the Olympus E-M5 II (left) is designed for mirrorless cameras with an APS-C sized sensor, e.g., Sony E, where it becomes equivalent to 90mm, a classic portrait lens. However, it also comes with a Micro Four Thirds mount, where it becomes a 120mm equivalent lens, i.e., a long portrait lens.



On the right, there is the Nikon 85mm f/1.8G. It is designed for use on fullframe cameras, where it is a, you guessed it, 85mm equivalent lens. However, I have mounted it to a Nikon D3300. As it has an APS-C sized sensor, the lens becomes equivalent to 128mm, also a long portrait lens.

To understand why 85mm is commonly referred to as the portrait lens focal length, please read this article.

Lens	Sigma 60mm f/2.8 DN	Nikon 85mm f/1.8G
Lens elements/groups	8/6	9/9
Minimum focus	0.50m	0.80m
Diameter	61mm	80mm
Length	56mm	73mm
Filter thread	46mm	67mm
Weight	190g	350g

How do they compare in terms of image quality? To find out, I took some example images at different apertures find out. These were taken at a focus distance of about 15m, at ISO 200.

I used a tripod, of course, and I used live view for the most precise autofocus. That avoids the potential problems of frontfocusing (FF) and backfocusing, a major concern for some DSLR users. Click for larger images:

Sigma 60mm f/2.8 DN @ f/2.8	Nikon 85mm f/1.8G @ f/1.8

To make the images easier to compare, here are 100% crops from the centre of the pictures:

And from the lower left corner:

And here is a series taken from a bigger distance:

Sigma 60mm f/2.8 DN @ f/2.8	Nikon 85mm f/1.8G @ f/1.8

Again, here are 100% crops from the centre of the image, click for a larger view:

And from the lower right hand side:

Conclusion

The Nikon 85mm f/1.8G is the fastest of the two, in terms of aperture, of course. But the test here shows that the Sigma 60mm f/2.8 DN is still sharper at f/2.8. The Nikon lens needs to be stopped down to near f/4 to obtain the same sharpness.

On the other hand, there are times when you'd want to trade a faster aperture for less sharpness, and if so, you may still want the larger aperture of the Nikon lens. But if you value compactness and are prepared to use a high ISO, the Sigma lens is the way to go.