Review of Sigma 50mm 1.4 Lens ( for Canon )

There are hundreds of reviews for this lens on the internet. Some are good but still lack one aspect, that although acknowledged by all reviewers – is still not explained to its entirety. I have tried to accomplish this in the below review. I have kept it bare minimum from technical verbiage & focused more on deficiency experienced by a general user & how to address those in real time.

If you know about this lens, you probably are aware of the characteristic I am insinuating here. To start – this is an amazing piece of engineering & fun to use.  I have more positives than negatives to say about this lens. So, if you are planning to purchase this go for it… It will please you more as compared to small disappointments.  I will review the reason for disappointment & its solution below.

Primary reason for anyone in in the market to buy this lens is because of its fast aperture 1.4. Other characteristics of this lens like its amazing build quality, huge glass inside, excellent BOKEH, tack sharp lens ( on aperture 2.0 + )  are just icing on the cake. It can vary based on different samples but fair to say – this lens’ sweet spot is 2.0.

Now coming to lens negatives. Generally, you would consider this characteristics of any lens like unsharp-ness,  chromatic aberration, vignetting, spherical aberration, distortion  as flaws of a lens. Fortunately this lens passes quite well in these basic tests. ( A grade ). This lens has a other peculiar issues  ( two – both  are related to focus. I know issue with focus sounds iffy – as focus should be the bread & butter for any lens’ life. But its not that scary if you learn the reason for focus issue with this lens ( which is technical & optically correct). The whole discussion of this engineering requires another blog so instead of taking you in another tangent of engineering for this reasoning, I will keep it brief to explain both of these issues with this lens.

The two focus characteristics:

  1. Front focus / Back Focus
  2. Focus shift

Front focus / Back focus ( FF /BF ) –   This is characteristic of the lens results the focus either just in front of your subject (FF) or focus a little back of your subject (BF). Technical Reason for this:Optically, when you use a viewfinder in your camera to capture snaps, you are using the phase detection technology because that’s what an optical viewfinder uses ( at least the better ones)  Reason for engineers to use phase detection approach is because it uses the largest aperture of the lens to focus. For instance, if you take a snap at f3.2 & your lens max aperture is f1.4, optical viewfinder will use f1.4 so that it can focus faster. Optically when you are doing so, ( although you are unaware of this & its all happening in the camera) camera rays focus on the subject using f1.4 & when you actually take the snap which is taken at f3.2 some rays diffraction occurs, – so focus is moved front or back by that tad. Whether it focuses in front or at the back will vary form lens samples across.

Solution – There are few ways to correct this, I have seen myself using the fusion of these two  a) If your camera supports do the lens calibration. How to do that is another topic of discussion but it works & if you have any questions, please feel free to write to me & I can reply you. b) Shoot at an aperture f1.8+. I agree its not why you bought this lens, & you probably want that creamy BOKEH at f1.4, but you will be surprised what this lens can provide at f1.8. Excellent BOKEH – which won’t be a deal breaker and not quite disarray from f1.4.

Note: There is one technique to totally avoid this FF/BF situation at f1.4 – which is if you use Live-View Mode to focus instead of optical viewfinder. Not the most fastest & practical solution but always handy to keep in mind-purse.

Focus Shift is another characteristic of the fast lenses, those with apertures f1.4 or less. This behavior is capricious in nature. In this lens will focus little on right side of the subject. Again this is more prevalent on large apertures. Way to work this around this either use small apertures OR – the one that I use 90% of the times when I am using this lens. Focus on a bit left of the subject – but it lets you use your aperture f1.4. How much to focus on left of the subject may vary from sample to sample but its fair to say keep left of the subject as much is the length of a pen-cap.

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