new 50 mm lens not sharp at 1.8

Hi all, I just got a new Canon EF 50 mm f 1.8 STM lens. I did a lengthy tripod test on it, keeping the ISO at 200 for every shot, using a 2 second shutter delay so my hands were not on the camera when the lens was open, and took the same shot every time. I also used 2 different cameras, my newish Canon 77D and an older Canon Rebel SL 1, both compact sensor. Both gave me the same results using this lens. At 1.8, the lens was NOT sharp at the focus point. At 2.8, it was quite sharp. At 5.6, 8.0, and even up through 16.0, it was still quite sharp. At 22.0 it degraded again and was not sharp.

I don't really care that it is not sharp at f22. I bought this to use in low light and for general portraits (hoping for some nice bokeh), so I am very concerned that it is not sharp at f 1.8.

My question is, is this normal for this or a similar lens, or is this particular lens defective? If I need to send it back and exchange for another one, I will do that. Thank you in advance for any thoughts on this issue.

Most lenses are not optimally sharp wide open, excepting the most expensive ones which are often optimized for maximum sharpness at full aperture. As you discovered, most consumer grade lenses sharpen up when closed down 1-2 stops. Having said that, some camera bodies provide for adjusting the point of focus, usually in 1mm increments, to ensure maximum sharpness. Testing is often done by owners using a scale like this one: http://www.kscameraclub.org/docs/pdfs/focus_test_chart_edited.pdf

Thank you for this reply. Interestingly I also just found a detailed review of the lens online, and they said their tested lens was not sharp at f 1.8. In the review they said it got sharper at 2.8, and much sharper at 4.0. So I see now more about how this works. I am thinking I can use 4.0 for portraits with some nice bokeh but will test it out on that shortly.

My question is, is this normal for this or a similar lens,

Yep, pretty common. Lenses vary, there may be some more expensive lenses that perform a little better wide open. The lens is not defective, it's just the physics of the lens.

Yes, as you now realize, the results you achieved are typical.

But the bigger question is: "How much does that matter in real world photography?" - I address that question, basically and generally in two fundamental ways:

1. Typically I use my Fast Primes (including my L Series) stopped down a little bit, and that is because they are all a tad sharper when stopped down a bit - BUT if I am in a shooting situation where I choose not to further compromise ISO because of Noise or Dynamic Range and I also choose not to furher compromise Shutter Speed because of Subject Motion Blur, then I will choose to use F/1.8 (or whatever 'wide open' means). That's one main reason for having a fast lens, to use it when you need it.

2. Post Production Sharpening is necessary for all digital mages if you want the 'best' outcome (apropos 'sharpness')

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I have seen sharp Portraiture made with all the Canon EF series 50/1.8 lenses - I suspect your Lens will be no different.

I don't think you need to use F/4, because I think that F/2.8 should suffice - try F/2 - and I suggest you learn good post production technique.

Whilst Lab test have their place and will quantify "lens sharpness" - Photography is a mix of the technical and the arts and, moreover, the lens is only one factor (albeit an important factor) in the chain of events in the making of a photograph - my advice is not to get too hung up on Lab Tests.

WW

see Optical Limits (formerly Photozone.de) review at Canon EF 50mm f/1.8 STM - Review / Test Report

the summary (in part)

The Canon EF 50mm f/1.8 STM is a slight improvement over the old EF 50mm f/1.8 II - more so mechanically rather than optically. Now the old EF 50mm f/1.8 II was already a good lens actually especially when stopped down. The EF 50mm f/1.8 STM has a much higher center sharpness at fully open aperture though. The low contrast in the image borders/corners remains an issue but the resolution is quite decent here. Stopping down to f/2.8 helps to lift the overall quality but the lens really shines between f/4 and f/8 where it doesn't really get any better than that actually. The low CAs also contribute to the high sharpness perception at medium aperture settings. Just like its predecessor, it produces a hefty amount of vignetting at fully open aperture. Some photographers are actually after such an effect e.g. for portraits. However, otherwise you probably prefer to stop down a bit or correct the issue during post-processing. Image distortions aren't completely negligible but still very low. An unfortunate weakness of the lens remains the bokeh. There's also some bokeh fringing at large apertures but this is nothing out of the ordinary actually.

Yes, as you now realize, the results you achieved are typical.

 

But the bigger question is: "How much does that matter in real world photography?" - I address that question, basically and generally in two fundamental ways:

 

1. Typically I use my Fast Primes (including my L Series) stopped down a little bit, and that is because they are all a tad sharper when stopped down a bit - BUT if I am in a shooting situation where I choose not to further compromise ISO because of Noise or Dynamic Range and I also choose not to furher compromise Shutter Speed because of Subject Motion Blur, then I will choose to use F/1.8 (or whatever 'wide open' means). That's one main reason for having a fast lens, to use it when you need it.

 

2. Post Production Sharpening is necessary for all digital mages if you want the 'best' outcome (apropos 'sharpness')

 

*

 

I have seen sharp Portraiture made with all the Canon EF series 50/1.8 lenses - I suspect your Lens will be no different.

 

I don't think you need to use F/4, because I think that F/2.8 should suffice - try F/2 - and I suggest you learn good post production technique.

 

Whilst Lab test have their place and will quantify "lens sharpness" - Photography is a mix of the technical and the arts and, moreover, the lens is only one factor (albeit an important factor) in the chain of events in the making of a photograph - my advice is not to get too hung up on Lab Tests.

 

WW

I did an outdoor portrait shoot yesterday and had really nice results with this lens at f3.5. Thank you for all the great ideas.