Fullbody person pictures with a nice bokeh?

Started Oct 22, 2012 | Discussions thread
random78
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50-210mm can give higher blur than 50mm 1.8
In reply to Kalainen, Oct 23, 2012

Part of your problem is of course that the 50mm 1.8 on APS-C can't match the shallow DOF capabilities of 85mm @ 1.4 on FF.

However keep in mind that the background blur is not directly determined by the DOF. The 50-210mm can give you smoother background than the 50mm 1.8 even though it looses out on DOF!

To understand that assume that you take the same portrait with 50mm @ 1.8 and 100mm @1.8. If you keep the same framing then the DOF between the two shots will be identical (you will have to go back twice as far with the 100mm to keep the same subject size in the frame). However the 100mm shot will have a narrower FOV so it will have less background in it. So the background will essentially be "magnified" more thus giving larger background blur even though the DOF is same. This effect will be more noticeable when the background is at a distance from the subject.

The general rule is that the background blur for distant backgrounds is determined by the physical aperture size of the lens. The 50mm 1.8 has a physical aperture size of 50/1.8 = 28mm and the 100mm 1.8 will have a physical aperture size of 55mm so it will have more background blur for "distant" backgrounds. Similarly the 210mm @ f6.3 = 33mm. So slightly better than the 50mm 1.8 in terms of background blur of distance backgrounds. Plus you get more isolation due to narrower FOV and not as likely to have cluttered background.

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