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What is the minimum sensor size need to get a separation between the subject and the background (bokeh) ? Print size A5

Not using a DSLR . Assuming max aperture is f/2.8 at wide end.

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    Depends on aperture, focus distance, focal length, and what "decent" really means to you. Therefore: Could you be a bit more specific? – flolilo Jan 28 '18 at 16:38
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    I think the question would have more merit if it asked for the bokeh differences for portrait photography for all sensor sizes, so an 85mm (or equivalent) lens shot at f/2.8 at a subject distance of ~10ft. Somehow, please add a viable experiment to the question that helps us understand what you're going for. – Hueco Jan 28 '18 at 16:55
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    "Assuming max aperture is f/2.8 at wide end." 2.8 is an f-number, not an aperture (or more precisely an entrance pupil) measurement. Many variable aperture zoom lenses will blur the background more at, say 55m and f/5.6 than at 18mm an f/3.5, because the entrance pupil for 55mm @ f/5.6 is 9.8mm wide, whereas the e.p. for 18mm @ f/3.5 is only 5.42mm wide. – Michael C Jan 28 '18 at 18:58
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    Related: How do I find a point-and-shoot camera specifically for bokeh / a very shallow depth of field? – Michael C Jan 28 '18 at 18:59
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    The question as asked is not answerable because it has not defined the following: 1) the camera to subject and camera to background distance (and thus the ratio between the two). 2) The acceptable amount of blur needed to qualify as "getting separation." 3) the desired focal length/angle of view provided by the lens with a specific sensor. – Michael C Jan 28 '18 at 19:07
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You get it a little bit backwards. Sensor size itself has nothing to do with background-subject separation, it is only question of the depth of field.

Sensor size comes into play when you consider same field of view. You will need wider (shorter focal length) lens to capture same field of view on smaller sensor, than on larger sensor. So, to some degree, same picture shot on camera with smaller sensor will have larger depth of field, than on camera with larger sensor.

There are a lot of parameters involved in definition of depth of field, so you should read question linked above. For most practical purposes, sensor size is not what defining quality of artistic content of the image anyways, so don't worry about it too much, but you might wanna consult this question on sensor size differences.

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  • Is this applicable for compact camera too ? Seem like most of them have good focal length but very small sensors – nish1013 Jan 28 '18 at 19:20
  • @nish1013 it is camera-independent. "compact camera" is small because -- in part -- of smaller sensor – aaaaa says reinstate Monica Jan 28 '18 at 19:31

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