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I am interested in taking pictures with a very shallow depth of field, and also willing to have the option to have the bokeh effect,

I'm not an expert in photography so I'm really confused about what I'm supposed to look for in a camera,

I did read that one of the things I need to look for is a large sensor, I found a few cameras that have a 22.2 x 14.8 mm sensor, Is that enough for my needs? or do I also need to look for a certain size of lens and stuff like that?

Thanks

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4 Answers 4

Firstly I'm not sure what you mean by the "bokeh effect". The term bokeh refers to the aesthetic quality of the out of focus area of an image, but it sounds very much like you want to achieve highly blurred backgrounds.

In principal what you want is a camera system that provides a large sensor and the option of large aperture lenses. When I say large aperture I'm taking about the physical opening, not just the f/stop (more on this later).

Ideally then sensor would be 36x24mm, you don't mention a budget but the much more common size of 22.2x14.8mm will provide far better value for money. Focusing close will give you shallow depth of field, but it's not always practical, for example if your subject is bigger than a mouse.

The amount of background blur is also related to the physical size of the aperture. This is given by the focal length (the number in millimetres) divided by the f-number (the number that follows "f/"), so a 50 f/1.8 lens has an aperture that is 50/1.8 = 27.7mm in diameter.

Focal length is important - you have to look past the f/number. Here's an example, the following was shot at f/1.4 at 50mm. Depth of field is shallow, and so the background is blurred:

But now look at this shot, which was taken with a different lens at f/5.6, which is a slow as most lenses go:

The background is not just blurred it's completely obliterated! What's different? The focal length. The first shot was taken with at 50mm f/1.4, so the opening was 36mm across. The second shot was taken at 800mm f/5.6, with an opening a whopping 143mm across!

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"f/5.6, which is a slow as most lenses go" You mean as fast as most lenses go, surely? And even that's a dubious statement: even among cheap zoom lenses, there are many that will go to f/3.5 or f/4 at the wide end of the zoom range. –  David Richerby Jul 5 at 15:50

"Bokeh" is a feature of the lens used and its adjustment, not of the camera directly.

Bokeh is generally improved by:

  • More rather than less aperture blades in a lens and

  • More rounded aperture blades
    (eg Tamron 18-250 and Sonly SAL18250 are optically identical lenses (both made by Tamron) except Sony chose to round the aperture blades more to improve bokeh.)

Reduced depth of field is with resultant "blurred" background is generally a prerequisite to visible bokeh.

DOF decreases with

  • increasing aperture,

  • increasing focal length and

  • decreasing distance to point of focus.


Special case - the mirror lens.

For a given focal length a mirror lens is low cost, compact and low weight. The disadvantages are fixed aperture, fixed focal length, and an "interesting" bokeh effect.

Mirror lenses are generally considered to have poor bokeh due to out of focus points forming "donut" shapes. This can be controlled but often not fully eliminated. Donut snobs hate them.

500mm mirror lens - donuts are visible but average viewer is unlikely to find them objectionable - a donut snob will hate this effect:

enter image description here

500mm mirror lens forming very bad donuts in background. You don't have to be a donut snob to see these, but the picture is probably still acceptable to many "ordinary people" :-)

enter image description here


Extremely low depth of field example:

Use of a reversed lens on the front of the main lens, to provide a "macro" closeup capability, will result in an extremely shallow depth of field causing the background to lose all features. Whether the resultant bokeh is pleasing in a given case is in the mind/eye/brain of the beholder.

Grass seed head using reversed lens macro. Sensor needs cleaning.

enter image description here

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Good explanation of some factors other than aperture shape here: photo.stackexchange.com/questions/12098/… –  mattdm Aug 4 '12 at 15:16

Firstly, there is nothing like a specific camera for bokeh. Bokeh is basically formed by a light source in the out of focus area of the image. But there are factors in camera and lens kit that affect the bokeh or the DOF.

The main necessity for getting shallow DOF is a lens with large aperture such as f1.8.

As you can understand from the exposure triangle, the swallow depth of field is directly proportional to the larger aperture. ie. larger the aperture shallower the depth-of-field.

A 22.2 x 14.8 mm (APS-C) image sensor would be satisfying for getting a nice bokeh effect in the image. Although a Full frame sensor(36×24 mm) would be much better.

Other than this Focal length of the lens, distance of the subject in focus also affects a fine bokeh.

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Yes, bokeh is actually proportional to the physical width of the lens opening.

Say you focus on a near-field object at a finite distance = Z and have a camera/lens combo that gives you a field of view (FOV) with angular half-width = Q degrees. If you define bokeh as the ratio of the diameter of the blur circle B (blurred image of a background point at infinity) to the width of the image frame W, then

                     bokeh   =   B / W    ~    R / ( Z  * tanQ )

where R is the radius of the lens opening - ie half the diameter (Note: In the above equation, Z should technically be Z - F, where F is the lens focal length, but you can usually ignore the F when looking at a far-away object).

So if you have two cameras, a large DSLR and a small point-and-shoot, both with the same angular FOV (ie, lenses are same 35mm-equivalent), then the camera with the larger diameter lens will give you more bokeh. This is independent of the camera sensor size.

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