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keepcoding

Sigma 56mm F1.4 decentered

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Hi

I've had 2 copies of the Sigma 56mm F1.4 and both showed a rather severe decentering issue. The left side of the frame is quite blurry compared to the right side, especially between F1.4 and F2.8. Here is an example at F2.8, focused at infinity:

sigma_56mm_decentered.jpg

 

Note that it is not just the edge that is unsharp, it is approx. 50% of the left side of the frame.

I wonder if this is an issue with all lenses or just a faulty batch. Is there anyone with a good copy?

 

If you don't know how to test your lens, here is a simple recipe:

  • choose a scene that fills the entire frame with distant objects (should be several hundred meters away)
  • set the focus manually in the middle of the frame (should be around infinity)
  • set the aperture to e.g. F2.8 and take a photo
  • now rotate the camera 180° and take the same photo again (upside down) without changing the focus
  • compare the two shots
Edited by keepcoding

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Since editing my post is no longer possible, here some corrections:

  • the photo above was taken at F1.4, NOT F2.8
  • for the mentioned test procedure, it is better to use the max. available aperture of the lens

The decentering is also visible at F2.8, but is less severe.

Edited by keepcoding

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Interesting, seems like pretty bad decentering indeed... I've not yet seen any reports about this lens being prone to decentering, but then two lemons in a row sounds like really really bad luck... The second shot seems pretty darn sharp for corners at f/1.4 though, quite in line with the analysis in my other topic about the comparison to the Sony Zeiss 55mm.

Let us know if you get lucky on the 3rd one! I'm just about to order one myself.

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