Thom posts his views on the Nikon AFS and Sigma HSM 50mm

Started Apr 27, 2009 | Discussions thread
Thom Hogan
Thom Hogan Forum Pro • Posts: 13,661
Re: Well..why do you use such a lens?

rockjano wrote:

That is the main question I think.

Let's assume that your contention is correct ; ):

1. for short DOF and than the question is BOKEH not corner
performance (that out of focus anyway)

Then the Sigma wins by a very slight margin. Both lenses have nice rounded highlights, but both tend to have "edging" on the highlights due partly to the longitudinal aberrations. The Sigma loses its very visible edge by f/2, the Nikkor keeps it further into the apertures (maybe f/4 before it's equal in my mind).

2 low light photography (similar story)

I'm not sure I'd agree that you don't need corner sharpness for this, but here the story reverses: the Nikkor performs a bit better (except for light falloff) than the Sigma when used wide open. The Sigma just has lower contrast wide open and very bad corners on FX (less so on DX, but still visibly worse than the Nikkor).

I think these lenses are kind of special ones. I dont want to use
them at f 5.6,

If I didn't get it across, there's another aspect here. The Sigma is worse than the Nikkor at f/1.4. If you're buying the lens solely for maximum aperture, I'd get the Nikkor. But the Sigma improves considerably at f/2, the Nikkor less so. So in the f/2 to f/4 range the Sigma may be the better choice (true on DX, less so on FX due to corners). From f/5.6 onward, the difference is really only that the Sigma's corners are a bit weaker than the Nikkor's.

And that is where I think the Sigma is clearly better or at least I
like more the very smooth out of focus rendition. The Bokeh of the
two lens are very different and I don't see that in this review.

Still working on getting a repeatable bokeh test in place. Right now, you'll have to trust my prose observations. The Sigma has a clear ring at f/1.4, the Nikkor has a clear color fringe at f/1.4. The Sigma settles down fast, the Nikkor is still showing a busy fringe on highlights at f/4, though much muted.

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Thom Hogan
author, Complete Guides to Nikon bodies (19 and counting)
http://www.bythom.com

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