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This question already has an answer here:

I have the Nikkor 18-55mm f/3.5-5.6g vrii lens using it on the D3300. I have been trying to create some bokeh effect using this lens (I know it isn't a great lens for bokeh). The thing I was wondering was which setting will give me good bokeh.

1). Zooming at 18mm and keeping aperture the widest? (Sacrificing the max zoom for the lens) 2). Zooming at 55mm, this eventually wouldn't have widest aperture.

I know that keeping the aperture the widest and max zooming the lens combined gives you great bokeh. I'd like to know what I could do in my case to achieve the best possible blur.

marked as duplicate by mattdm, scottbb, Olivier, Itai, inkista May 10 '17 at 3:18

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • @Romeo Ninov the suggested answer doesn't say anything about aperture. Whether the user had same aperture for both the zoom settings he used. – samjay May 9 '17 at 11:03
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    Potential duplicate voters: I know we have a number of very similar questions on the site, but I can't find one which actually runs the maths for the very typical 18-55 f/3.5-5.6 kit lens on an APS-C sensor. I'd suggest we leave this one here and try and answer that specific question, possibly with links to the other questions so people can do other cases. – Philip Kendall May 9 '17 at 11:30
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    Clarify: are we talking about taking a picture of the same subject? Are we using the same perspective (camera position & location), or are we also moving closer to or further from the subject to create separation from the background? – scottbb May 9 '17 at 11:46
  • @scottbb you can keep everything the same (object, location, lighting etc). – samjay May 9 '17 at 11:56
  • @Philip The one I just linked covers that very specific question and some of the answers run the numbers. – mattdm May 9 '17 at 12:44
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From this website I see field of view at 55mm 10ft distance to the object is (almost) like at 18mm, 3ft distance.

From this website I calculate

  • at 55mm f5.6, 10ft DoF is 2.27ft
  • at 18mm f3.4, 3ft. distance DoF is 1.16ft

So at the end short focal length will give you shallow depth of field

P.S. The distance above is just example, feel free to select and recalculate the distance of your select

P.P.S. But if you keep the same distance between the camera and the object from second link you can calculate that the DoF will become 20.8 ft. So in this case long focal length win (in sense of bokeh)

  • The math might be right [I can't do math to save my life] but it's readily apparent if you actually try it that you get shallower 'apparent' DoF at max zoom, assuming you frame the subject the same. – Tetsujin May 9 '17 at 13:56
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The zone of depth of field is not split down the middle. As a rule, DOF extends 2/3 further away and 1/3 back towards the camera, measured from the point focused upon. DOF has many ingredients.

  1. Subject distance – When imaging distant objects, the zone of DOF expands. When imaging nearby objects, the zone of DOF is shallow.
  2. Focal length – We maximize the zone of DOF when the lens is set to wide-angle (shortest focal length). We shrink the span of DOF when we zoom to maximum focal length (telephoto).
  3. Aperture – Maximum DOF is obtained when the aperture diameter is small. f/22 yields the greatest DOF, whereas f/3.5 delivers the shallowest DOF.

A setting of 18mm focal length combined with a tiny diameter aperture like f/22 grants maximum DOF. When you zoom to 55mm you are entering into the realm of telephoto. Now the magnification increases (objects appear closer), however the image gets dimmer. As you zoom from a lesser focal length, the mechanics of the lens attempts to compensate. In other words, as you zoom the lens’s apparent diameter increases.

A more costly lens would likely maintain the maximum aperture of f/3.5 as you zoom. However your kit lens runs out of working diameter, and the f/# changes during the zoom. The good news is, the difference between f3.5 and f/5.6 is not significant. Likely you will not notice a significant change in bokeh.

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