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This question IS about:

  • Does a macro lens have a shallower DOF at the same settings and focal length as another prime?
  • If so, what in the optics is responsible for this?
  • Using a Macro lens as a street photography lens.

This question is not about:

  • Basics of aperture and Depth of field
  • Macro subject distances- this question is about 'real world distances'

Most answers to previous questions either went down this road or did not focus enough optics, which is why I'm asking it again.

EDIT: I agree with all the evidence based arguments provided here. Although based on anecdotal experiences I still remain convinced there is a problem. I do believe flatness of the depth of field is likely the most plausible answer. As I have noticed that I have 'slices' of in-focus areas.

Sample 1 Shot on Sigma 17-70 Contemporary at 70mm, f4 17-70 Pic

Sample 2 Shot on Sigma 70mm EX DG Macro at f4 70mm

Evidently, the second image is at a closer subject distance. But the depth of field is quite different. And It was shot at 1/1250 second.

  • If you were panning with car motion for the second shot, that could be contributing to the foreground blur. At 1/1250 it probably wouldn't contribute much, but if the car was moving fast enough, the effect could be visible. – junkyardsparkle May 12 '18 at 19:40
  • It wasn't a pan. I pre-focused the spot and fired a burst. The car was going uphill and also coming from a previous ascent. So I think it's not a contributing factor here – Chai May 12 '18 at 21:57
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The term 'Macro' means that the lens allows to focus on short distances. This is accomplished by allowing the internal elements to move farther or differently, or sometimes by a switch that moves an additional element that is normally not movable.

Therefore, the macro capability has no effect on DOF.

Of course, as the positioning and count of elements is different, there might be a difference from another lens, but it is very small, and can go either way (more or less DOF).
DOF is mostly defined by the distance to the object, the size of the sensor, and by what is still qualitatively considered 'in focus'. Technically, the DOF is always 0; even a micron off the focus plane the picture is 'out of focus'. But if the fuzzyness is less than a pixel wide, or its amplitude is small enough, so you can't see it, we consider it still 'in focus'.

  • Standard DoF charts use 0.030mm for FF and 0.019mm or 0.020mm for APS-C sensors when calculating for a display size of 8x10" viewed from a distance of 12", which means that at that display size the circle of confusion can be around 5-7 pixels wide (most digital cameras in the FF to APS-C range have pixels around 0.004mm wide) before we notice the blur. – Michael C May 12 '18 at 16:46
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As mentioned in the other answers, the general case is that a similar focal length and aperture will give you a similar DOF at a given focus distance. There is one thing about many macro lenses, though, that could impact the perception of DOF in certain cases - the fact that they tend to have very flat planes of focus, where lenses designed for portraiture often don't. This could actually cause backgrounds to be more "in focus" towards the edges of the image.

As an example, here's a shot from a 60mm f/2.8 macro lens showing even sharpness across the target:

enter image description here

This shot, on the other hand, is from an old 63mm f/2.7 Kodak cine lens, a fairly extreme example of field curvature:

enter image description here

You can see that there is a change in focus distance as you move from the center of the frame, blurring the plane but keeping the ruler, which is tilted towards the camera, relatively in focus. This field curvature can exagerate the shallow DOF effect in many settings, and might be completely absent in many macro lenses.

  • While all the answers are factually sound, this is the one that explains my problem accurately. Similar to your image, I might have focus on cheeks but not the tip of the nose etc. Or just a slice of focus on road that I am photographing at f/4. However, could you elaborate the advantages of a curved DOF ? because I believe it's only a draw back due to the flatness of the chart in your image. For faces- animal faces, it should prove to advantageous- am I understanding it right? – Chai May 12 '18 at 17:49
  • 1
    Exactly, field curvature is good or bad depending on how it suits your purpose. For scenes involving something wall-like that goes from close at one side of the frame to further at the other, it can give more in-focus foreground, with a more dramatic focus drop-off in the background (imagine the ruler in above shots extending through the center of the frame)... for more about this, check out this answer and the links within it. – junkyardsparkle May 12 '18 at 19:24
  • @Chai Typically, field curvature moves the point of focus towards the camera at the edges of the frame. Since most animals' faces when seen head on have the middle of the face (i.e. nose) nearest the camera and the edges of the face (i.e. ears) further from the camera, uncorrected field curvature would make the parts of the face behind the nose/eyes blurrier, not sharper. It is possible to 'overcorrect' for FC that would make the point of focus further from the camera at the edges. In reality, lenses with the flattest field tend to have a field of focus shaped sort of like a lasagna noodle. – Michael C May 13 '18 at 1:09
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There is no more difference in depth of field when using a macro lens at "normal" distances as compared to using a "non-macro" lens than there would be if comparing two "non-macro" lenses of different design approaches to one another. What makes a macro lens "macro" is the ability to focus closer than other lenses. The closer focus distance allows the image of the object to be larger as it is projected onto the camera's imaging plane (sensor or film).

Depth of field (DoF) is determined primarily by aperture and magnification. Factors that affect magnification include: focal length, display size, and viewing distance. The sensor size affects DoF as it is directly related to the enlargement ratio between the size of the image projected onto the sensor when compared to the size of the image as it is viewed. One must enlarge an APS-C image more to view it at the same size compared to a FF image. But this "theoretical" DoF for a particular aperture, focal length, sensor size, and display size is rarely achieved. The imperfections of our lenses mean that there is more actual blur than the theoretical amount of blur we would expect if our lenses perfectly matched their designed optical formulae.

That is not to say that there is no effect on image quality when comparing a typical macro lens to a typical non-macro lens used at distances not considered "macro":

  • Most macro lenses are highly corrected for field curvature. This means the field of focus is usually flatter for most macro lenses than for many non-macro lenses. On the edges of the frame this could make it look like the macro provides greater depth of field when photographing objects that are all arranged in a plane more or less parallel to the camera's imaging plane. But what is really happening is that a less corrected 'non-macro' lens renders a curved field of focus so that most of the DoF on the edges of the frame is closer to the camera that the DoF region in the center of the frame.¹ Sometimes the effect of uncorrected field curvature is a highly desired quality, particularly for portrait work. Sometimes the flat field of focus is more desired, such as for art reproduction or landscape work.
  • Macro lenses tend to be "tuned" so that they are at their optimal performance at very close focus distances. Their design is intended to make the "sweet spot" of the lens when it is being used for macro type work. Because a lens well suited for macro work needs to be highly corrected for most of the optical aberrations, such a lens that performs well at macro distances usually tends to perform well at other distances as well, even compared to "non-macro" lenses, but it is usually at its best when focused on very short distances.

¹ Even many of the earliest photographers realized this. Group portraits of military officers taken during the American Civil War (1861-65) almost universally have the group posed in a loose semi-circle so that the officers on both ends are as in-focus as those in the middle. If they had been arranged in a straight line parallel to the film plane, the officers on the ends would have been behind the curved field of focus rendered by the lenses used at that time.

2

Depth of field is determined by:

  • Aperture
  • Focal length
  • Focus distance
  • Circle of confusion

It may be slightly affected by various aberrations in complex lenses (diffraction, TCA, etc.), but those are not generally considered part of the equation because they're, well, complex...

Outside of those factors, though, other than a closer minimum focus difference, a 100mm macro lens is pretty much equivalent to a 100mm prime lens or a 24-300mm zoom lens with its focal length set to 100mm. Different builds might have differing image quality due to the above as well as other factors that affect resolution and distortion, but the depth of field should be nearly identical for any particular exposure.

I often use my EF 100mm f/2.8L Macro as a mid-telephoto prime on my EOS 7D Mark II .

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