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For a long time, I was making closeup photographs of flat surfaces using my cropped DLSR and Canon EF 50/1.4 lens. The scene was illuminated by an external flash. The focusing distance was the closest as the lens could give (0.45m). The sharpness of the image at the center and the corners was suitable to me.

Recently I have switched to a full frame camera and noticed that all the photographs are very soft at the corners (however sharp at the center). For the first time I understood that this lens (50/1.4) may be not the best lens for the kind of the photos I'm taking. Some people say that macro lens is more suitable for my situation.

Here's the 100% crops from the photo I've made using Canon EF 50/1.4 on a full frame sensor at the closest focusing distance (approx. 0.45m), f/11, ISO 100, manual focusing using liveview, camera standing on a tripod, direct external speedlight type flash to the right of subject:

Center: center part of the image 100% crop. Canon 50/1.4 @ f/11 on full frame sensor, closest focusing distance

Left top: left top part of the image 100% crop. Canon 50/1.4 @ f/11 on full frame sensor, closest focusing distance

Right top: right top part of the image 100% crop. Canon 50/1.4 @ f/11 on full frame sensor, closest focusing distance

Left bottom: left bottom part of the image 100% crop. Canon 50/1.4 @ f/11 on full frame sensor, closest focusing distance

Right bottom: right bottom part of the image 100% crop. Canon 50/1.4 @ f/11 on full frame sensor, closest focusing distance

So, here's the question: what lenses could solve the problem of soft sharpness at the corners in my situation?

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  • \$\begingroup\$ Check out analysis at dXOmark. It includes measurement shots of exactly this feature. \$\endgroup\$
    – JDługosz
    Jan 8, 2015 at 14:34
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    \$\begingroup\$ You can also avoid the edges by shooting a larger field and cropping it. Also, how close are you? Closer focus is also more troublesome. \$\endgroup\$
    – JDługosz
    Jan 8, 2015 at 14:47
  • \$\begingroup\$ I thought about cropping, but in this case we get too small image. My full frame is only 24 Mpx. If we crop the central part of the image, we leave with only about 10 Mpx. I don't know how this is better than a cropped camera then. About the focusing distance, as I wrote in my question, I take photos at the closest (minimal) focusing distance. \$\endgroup\$
    – Sunny Reborn Pony
    Jan 9, 2015 at 8:42
  • \$\begingroup\$ How large is the object you're shooting? I absolutely love the Canon 70-200 f/4 L using a 12mm extension tube for close up work. Not sure it would fit your need though without knowing the size of the object. \$\endgroup\$
    – OnBreak.
    Jan 9, 2018 at 16:23

4 Answers 4

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For the reason TFuto noted, that the in-focus region is actually a sphere "touching" the center point of your plane, it is best to use a lens with a rather large focal distance, and shoot from farther away. This will increase the radius of that sphere, which means the difference between center and corner won't be as big. Of course, it should still be a lens with good corner sharpness characteristics...

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  • \$\begingroup\$ Later posts here discussing good lenses for portraits indicate that this is not true. The shape of the in-focus surface will vary between lenses. \$\endgroup\$
    – JDługosz
    May 12, 2017 at 9:11
  • \$\begingroup\$ The focal surface is not a explicitly a sphere, nor a plane. It is a shape described by a polynomial series ax^2 + bx^4 + cx^6 ... Some solutions to that are planes, others are a parabola, or more complex "W" or "U" shapes for example. \$\endgroup\$
    – Brandon Dube
    Jan 10, 2018 at 1:33
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Your observation is correct. However, all lens shows this effect, but to a different degree.

I suggest checking out e.g. this lens comparison tool. You will see the actual behavior of different lenses.

For better understanding, you should learn to read and use MTF charts. A very good explanation (with examples for the Canon 50 mm f/1.4 !) can be found through this link.

In general, you want the lines for your aperture to be as higher up and as flat as possible.

You can

  • either buy a lens of better characteristics or
  • use your lens and use only a cropped area from the section that is of acceptable quality.
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  • \$\begingroup\$ I have already used DXOmark to compare my lens with popular Canon 100mm Macro, but the sharpness was nearly the same at closed apertures on the charts: dxomark.com/Lenses/Compare/Side-by-side/… \$\endgroup\$
    – Sunny Reborn Pony
    Jan 8, 2015 at 14:47
  • \$\begingroup\$ There are two Canon 100 Macro lenses, the f/2.8L IL USM and the f/2.8L USM. Here is the comparison. Roll over the image to see the second objective performance. The IS USM seems to be much sharper. \$\endgroup\$
    – TFuto
    Jan 8, 2015 at 14:51
  • \$\begingroup\$ Here is the EF 50m f/1.4 and the f/2.8L IS USM macro at f/11 comparison link. The EF 50mm seem so be softer in the middle and mid frame, and show about the same sharpness at the corners, but shows more vignetting than the macro lens. \$\endgroup\$
    – TFuto
    Jan 8, 2015 at 14:55
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    \$\begingroup\$ You can use e.g. this DOF calculator. Typing in EOS-1D, 50mm, f/11, 45cm gives 42.7 - 47.5 cm for near and far focus distance with a DOF of 4.77 cm. That is very shallow. You are photographing a plane but the points at 45 cm are on a sphere from the focal point. So obviously the corners will be farther than 45 cm, and so they will get more and more blurry. You can try this: manually focus on the corner (e.g. in LiveView) and you will see that the center is blurry, so focusing is the issue, not the lens) \$\endgroup\$
    – TFuto
    Jan 8, 2015 at 15:10
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    \$\begingroup\$ I've just tested the lens on another scene (kitchen tabletop, strongly top view) and made two shots: one focused on the center, and second is focused on the corner. Absolutely no difference, the center is sharper, the corners are softer. It seems to be that there should be another reason of bad sharpness in the corners. Is it possible that 50/1.4 lens cannot give good results when we shot on its minimal focusing distance? For example, because macro is not this lens was intended for. \$\endgroup\$
    – Sunny Reborn Pony
    Jan 8, 2015 at 18:08
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Here is an example from dxomark: enter image description here you can look at details for specific lens and camera, and how it performs at different apetures.

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  • \$\begingroup\$ the most curious thing here is that my lens (Canon EF 50/1.4) and the popular Canon EF 100/2.8 Macro have nearly the same sharpness at closed apertures. You can see this if you go to Measurements -> Sharpness -> Field Map and choose f/11 on both lenses: dxomark.com/Lenses/Compare/Side-by-side/… \$\endgroup\$
    – Sunny Reborn Pony
    Jan 8, 2015 at 14:45
  • \$\begingroup\$ @SunnyRebornPony that's because at f/11 you are diffraction limited. \$\endgroup\$
    – JDługosz
    May 12, 2017 at 9:08
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Yeah you are Right but I think I have shot with both Lenes 50mm and 75 to 300mm.In my Point of view the Pics that I have taken from the Lens 75 to 300mm is best for Photography

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  • \$\begingroup\$ The Canon 75-300 is unquestionably an awful lens in every possible way; it's soft at just about every aperture and focal length. Try an actually good lens and you'll see the difference. \$\endgroup\$
    – Philip Kendall ♦
    Jan 9, 2018 at 15:34
  • \$\begingroup\$ I agree with you that a lens designed for photography is best suited for photography. Having a 75-300 is perhaps better than nothing - but it is arguable not going to fit OP's need for a lens with corner to corner performance. \$\endgroup\$
    – OnBreak.
    Jan 9, 2018 at 16:25

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