Canon EF 40mm STM 2.8 not a replacement for a Nifty Fifty

Started Jul 25, 2012 | Discussions thread
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Timbukto
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Canon EF 40mm STM 2.8 not a replacement for a Nifty Fifty
Jul 25, 2012

and vice versa.

I have finally found a really good copy of the Nifty Fifty and it took many tries but the AF on it is both fast, confident, and accurate. The Nifty Fifty can only have excellent AF if its wide-open performance is also pretty good. I picked up a 40mm STM anyways because I had a coupon deal, etc...like getting two primes in one for less than the cost of a 50 1.4 anyways.

With that said I just got the 40mm STM 2.8 and thought at first that the AF was alright especially on the 5DMKII, but in real use it is without a doubt noticeably slower. In fact it is slow enough that I would rate its AF speed as not much better than kit lens like the 55-250 or 18-55. Not sure if there is an actual speed difference or difference in subject distance testing, but on APS-C Rebel you definitely feel AF slowness. If you are coming from 18-55 or 55-250 consumer grade lens however it will be on par and nothing to notice. If you are an AF speed lover like me and enjoy lens like the 85mm 1.8, or 17-55 2.8 for focusing speed, you'll feel the slowness. So in short, 40mm STM focus speed is closer to your kit lens, and a good copy of the 50mm 1.8 focus speed is closer to the fastest AF performers out there (i.e. 85mm 1.8, 17-55 2.8, and 70-200's). But again I stress I have no doubt some people have slower or crappier AF focusing nifty fifties out there...I had them too.

That said the IQ and edge to edge sharpness is outstanding...probably better than my nifty fifty stopped at f2.8, but at this point they are both good enough. At f2.8 obviously nifty fifty bokeh highlights are polygonal compared to 40mm STM which maintains round highlights throughout the usable aperture range where you'd get visible bokeh highlights anyways. However I'm not really a bokeh nazi anymore however and don't shoot portraits of people standing in front of pine trees or barb wire as a determination of bokeh quality or wax poetic about french cheese...I think they both work here. However the closer MFD completely equalizes both lenses ability to shoot equivalently shallow DOF but with both more pop and perspective distortion due to f2.8 sharpness and shorter MFD vs f1.8 nifty fifty with longer MFD. The MFD difference is rather significant as is the focal length and perspective differences.

The vignetting on the 40mm f2.8 at f2.8 is exactly inbetween the nifty fifty at f1.8 and f2.8. Did a really poor informal test where after viewing histograms in LR4, it was the 40mm STM 2.8 that was more contrasty at f2.8. An application of +10 contrast in LR4 easily equalizes them however. In addition perhaps not a fair test since on my informal test I was handholding, but the much closer MFD of the 40mm STM allowed me to brace the camera, and the 50mm 1.8 was shot completely unbraced, so higher contrast could easily come in from camera shake reduction (i.e. so in real world usage you may find yourself more able to elbow tripod your camera on the dinner table for a food shot compared to the 50mm 1.8 which requires you to stand back). I would actually ignore my sharpness findings unless you really do a tripod test, but for me quick tests showed me that both lens are more than sharp enough, probably the 40mm STM would slightly win in consistency with a brick wall or infinity focused shots but also have more vignetting.

A good copy of the nifty fifty at f1.8 will perform better at low-light AF obviously with its greater speed...but that is only if your copy of the nifty fifty is good otherwise its roulette focusing. 40mm f2.8 AF is supremely confident, but takes its time in comparison.

Nothing I say here is really news to anyone whose done research already, but from my personal findings I think now that the 40mm STM can not easily replace the nifty fifty because they do have significant differences. I also want to stress that any judgement on Canon's hybrid-pdaf sensor AF speed absolutely should not use the 40mm STM which again is closer to consumer kit lens speed. It might be possible that due to size constraints the EOS-M's 22mm f2 also suffers from slower AF as well (as does the Panasonic 20 1.7).

So the bad news is they have different enough qualities that you might buy both anyways, and the good news is they have different enough qualities that you might buy both anyways.

If I just had to keep one I'd probably pick my good copy of the Nifty Fifty because believe it or not, the AF is just always spot on and fast. But the focal range and MFD difference as well as overall bang for the buck of the 40mm STM still makes it also a keeper even though they appear pretty close on paper. It might be the difference of giving you just enough framing to get a better cramped indoors shot on an APS-C for example or the better food shot due to MFD. Again they look close on paper but there are definitely a lot of differences in perspective and framing and advantages/disadvantages of either. Also although a great value at $200, absolutely do not ignore the 85mm 1.8 with a street value close to $300 either!

To be able to have a good copy of the 50mm 1.8, 40mm 2.8, and 85mm 1.8 for $570 street price is amazing however. In MFT or Nikon land, it'll just buy you 2 out of 3 primes...or maybe just one 85mm 1.8 G or one PanaL 25mm 1.4, etc.

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