Higher magnification also increases the apparent size of the aperture relative to the front lens element.
Generally speaking, a larger actual physical aperture diameter will usually translate into a larger entrance pupil, however a longer focal length also helps that, as a longer focal length increases magnification. The size of the entrance pupil is really what determines how blurry OOF content will be, as it is the limiting factor for blur circle size. This is often called the "physical aperture", however it is more appropriately termed the entrance pupil. The background is now so blurred that the mirror box is acting as a second aperture and producing the strange cropped shaped highlights.īackground blur, as an intrinsic element of a lens, is related to the physical diameter of the aperture as observed through the front of the lens.
Bokeh lens kit full#
Just for fun here's what you can expect from a full frame camera and 85mm f/1.2 lens: If you're really into blurred backgrounds and want to push it as far as you can upgrading to a full frame camera is an ever more tempting option as prices come down. You can be assured that any distracting details in the background will be gone when using this lens wide open. Now comparing this to the previous shot, the bars of the chair in the bottom left corner are gone, as are any details in the tree's leaves. The same scene with a 50 f/1.8 would look something like this: All the major manufacturer's offer such a lens and due to it's symmetrical construction they can usually be snapped up for only $100-150. This combines the longer focal length effect seen above with a significantly wider aperture. The best thing you can do for Bokeh is to invest in your system's 50 f/1.8 lens. The background is still recognisable which can be a problem with less attractive settings. So you can get a degree of blur from your kit lens with a real subject, when used relatively close. Not only is the background less cluttered due to the narrower field of view, but the blur is greater if you look at the Christmas tree lights. It could be argued that the camera should have stayed put, but in either case the same number of variables change, this way better reflects actual usage. Here is what our scene would look like with an 18mm lens at f/3.5 on an APS-C sensor:Īnd now here is how the same scene would look with at 55mm f/5.6 when the camera subject distance is changed to maintain subject size. It can be difficult comparing blur at different focal lengths so I have chosen a Christmas scene so the points of light show the blur radius clearly. I will answer this with the help of a giraffe named Sophia who stands about 4 feet tall and has a head roughly the right size for a realistic focus distance. However longer focal lengths enlarge the background blur so which should you use?
Conventional wisdom states a larger aperture will give you shallower depth of field and more blur. With a standard kit zoom your aperture is limited to f/3.5 at the wide end and f/5.6 at the long end. A very common subject for blurred backgrounds is portraits, so this is the case I'm going to consider.
However this approach leaves you only able to shoot very small subjects. Depth of field diminishes very quickly with focus distance, so much so that it becomes a major problem with macro photography getting a non blurred background (or subject!) If you just want bokeh for bokeh's sake then you can achieve this with pretty much any lens and any type of camera, even a tiny sensor compact, by focusing extremely close.
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