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I am considering moving to a shorter macro lens for it's better optics- Nikkor 40mm micro. I currently own a 70mm Macro lens.

At the same magnification(eg 1:3), does the 40mm grant a greater field of view?

I'm aware of the impact on minimum focus distance and it's fine by me.

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  • In passing: Do remember that at 1:1 your sensor is 4 focal lenghs from your object. That is, from the back of your camera or rather from the plane containing that o with a bar through it, to the object will be 160 (4x40) away. This gives you very little room to light it, and even less if you want to actually magnify it. I have a pretty good tamron 90 mm macro lens. I wouldn't dream of trying to use a shorter one. Jan 18 '18 at 23:48
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It's little rough, but hopefully it illustrates the concept.

enter image description here

The first camera has a longer focal length macro lens that images the green object at the full width of the imaging sensor. The slightly larger orange object behind it is also projected onto the full width of the sensor.

With the second lens, the focal length is shorter, thus the same reproduction ratio requires a much shorter focusing distance. The green object must be closer to the camera to fill the width of the imaging sensor. If the orange object is still the same distance from the camera as before, it will take up much less than the full width of the camera's sensor.

enter image description here

The image from the first lens and distance combination versus the image from the second lens and distance combination.

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  • I think a more practical assumtion would be the camera moving closer to both lines (i.e. shooting the same scene). Geometrically, the effect would be similar but lesser. It would also be interesting to compare depth of field in both cases (in application to the background object), but this broadens the question...
    – Zeus
    Jul 19 at 1:04
  • @Zeus The relationship of each object to the other in terms of size would still change. The wider the angle of view, the faster the field of view increases as distance from the camera increases. Thus objects the same distance behind the subject which is framed the same size with a wider lens will be smaller than when the subject is framed the same size with a narrower lens from further away.
    – Michael C
    Jul 19 at 22:43
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I think that by definition magnification doesn't depend on focal length. 10mm lens with 1:1 magnification has the same FOV at minimal focus distance as the 1000mm lens with same magnification.

What is different is distance at which that magnification will be achieved (same link):

Working distance is defined as the distance from the front of the lens to the subject. A broad generalization is that the more focal length in your macro lens, the larger the working distance. Thus, a 35mm macro lens will get 1:1 at very, very close distances to the subject, while a 200mm macro will be a much greater distance from the subject

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    @ aaaaaa -- A tip of the hat from Alan Marcus -- Field of view is the same at a specific magnification. However shorter lens has reduced lens to object distance. I think, longer lenses with their elongated lens to object distance are best for most applications. Jan 16 '18 at 22:35
  • @AlanMarcus Thanks! it seems like OP knows about working distance/minimal focus distance, so i didn't mention that advantage of longer macro lenses Jan 16 '18 at 23:08
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At the same magnification(eg 1:3), does the 40mm grant a greater field of view?

A 40mm lens takes in light from a wider angle than does a 70mm lens. For the 40mm lens the angle is around 49°, and for the 70mm lens it's about 29°. If you're setting up each lens to get the same magnification, an object in focus should be the same size with either lens. The difference is that in order to get that magnification, the 40mm lens will need to be closer to the object than would the 70mm lens. (This is exactly the same as for non-macro lenses: I can fill my frame with someone's face using a 50mm lens from three feet away, or with a 200mm lens from twelve feet away.)

So let's imagine that the object we're photographing is a metric ruler oriented horizontally. At 1:3 magnification, 30mm on the ruler will cover 10mm on the sensor, for either lens. Let's further imagine that we place two more rulers in the frame: one a bit in front of the first ruler, and another the same distance behind it. Compared to the 70mm lens, the 40mm lens will see less of the front ruler and more of the rear ruler.

The terms field of view and angle of view are often used interchangeably, which is confusing. Just remember that the angles that the two lenses take in are different, yet the area in focus is the same width because the distance between the subject and camera is different.

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  • Okay I think I get it. So basically the shorter minimum focus distance would lead to the same field of view as the longer lens. Additionally you say that focal length is more a measure of the angle visible in a our view- which does not affect me when working with at a set same magnification on both lense? Sorry for the very long-winded question
    – ABCD312
    Jan 17 '18 at 14:26
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    You seem to be confusing minimum focus distance with focal length. They may be related, but they're very different measurements. Focal length isn't a measure of angle of view, but it does determine the AOV. Follow that link for some examples and a definition of the term.
    – Caleb
    Jan 17 '18 at 14:53
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    @Chai once you've moved the camera closer to the subject to account for the new angle of view, the subject will be the same size because that's what you were adjusting for. But the look of the foreground and background will be different - pay attention to the rulers in this answer. Jan 17 '18 at 16:21
  • @Caleb- I'm revisiting this topic, would you say Nasim explains these terms correctly in this post? photographylife.com/equivalent-focal-length-and-field-of-view
    – ABCD312
    May 4 '18 at 8:44
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Magnification is determined by your sensor size and how much fits in the frame. 1:3 is not macro magnification and you don't need a macro lens, any regular lens could give you such ratio.

If you are keeping the same ratio that means that your field of view and how much fits in the frame remains the same.

If you were able to fit more in your frame, then the ratio won't be 1:3 any more, it would be 1:4 etc.

If less and less fits in the frame then your ratio changes to 1:2, and eventually to 1:1 - which is macro, and only beyond that you get macro magnification.

Here is a video on how to measure macro magnification from my personal website which I am affiliated with - https://esteewhite.com/understanding-macro-magnification-and-how-its-calculated/

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  • All lenses magnify. Most magnify fractionally. That is, they make things smaller in the image they project than the objects actually are. But 0.5X or 0.2X or even 0.002X magnification is still a legitimate use of the word when talking about refractive optics. Such fractional amounts are frequently used in formulae that describe how lenses refract light.
    – Michael C
    Jul 18 at 2:41
  • @Michael C Hmm interesting, I never thought of it like that. I've edited my comment because I meant macro magnificion specifically. I guess what you described could be called - negative magnification, or fractional magnification, not sure what would be the correct term for that but it's just not macro magnification. Jul 18 at 15:15
  • It's not negative magnification, it's fractional. Negative exponents result in fractional positive numbers of a positive number, but magnification is linear, not exponential.
    – Michael C
    Jul 19 at 22:46
  • Just a nit, but many non-macro lenses are not capable of 1:3 magnification (1:3 = 0.33X). Almost all of the lenses I own have a MM of around 0.25X (1:4) or less (e.g. EF35/2 0.24X, EF50/1.4 0.15X, EF85/1.8 0.13X, EF135/2 0.19X). Among my zooms the EF24-70/2.8 comes closest at 0.29X. Some very high end telephoto lenses have such long MFDs that they can't do better than around 0.15X, or 1:6.7 (EF 300/2.8 IS II 0.18X, EF 600/4 IS III 0.15X).
    – Michael C
    Jul 19 at 22:56
  • @Michael C Cool, thank you for the information. Yes, true a lot if the lenses probably don't reach 1:3. I honestly haven't taken the time to measure those. Just working with as you explained - fractional magnification, is not something that I'm used to, but it definitely sounds interesting and I am going to look into it more :) Jul 21 at 0:20
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Crop factor and magnification are sufficient for specifying field of view in the focusing plane (namely while the field of view is dependent on focal length and minimum focusing distance, magnification depends on them in the same way).

However, out of focus objects will scale stronger with the distance for shorter focal length, so the field of view behind the focusing plane is larger (magnification smaller) and the field of view before the focusing plane is smaller (magnification larger) when having a shorter focusing distance.

Regarding the bokeh, with equal aperture number the infinite background will have its features smeared in a similar manner. Because the features appear quite smaller with the shorter focal length, the blurring will also appear much smaller, so while the background would be shown with similar detail level, its appearance will be much more that of a "blurred" background with the longer focal length because the background field of view is quite smaller.

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