Will an 85mm prime give me more background blur than a 50mm f/1.8 on a Nikon D3100?
Asked 10/14/2016
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I shoot with a Nikon D3100 and currently have a 50mm f/1.8. I want stronger background blur for portraits and candid photos, but sometimes I can’t move closer because I need to keep the full subject in frame. For example, I wanted to photograph my child with a sleeping dog, but the background cars were still too distracting even at a wide aperture.
If I buy an 85mm prime mainly for more background blur, will it make a meaningful difference compared with my 50mm f/1.8? Or is software background blur a better solution?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
6
You will get a bit more and smoother blur. If it's worth the Investment is up to you. But be adivsed that the smoothness of the blur is highly depending on the lens-construction itself, so the numbers only say so much
Calculating the DoF, and the Bokeh.In this Screenshot of the Software cBlur (a german online version exists here), you can see the Sharpness-curves for a 50 and a respective 85mm lens, set at the same aperture (f/1.8) and focused on a distance which covers the approximate same object height in the image (190cm, which is roughly a full body portrait).
As you can see, the circles of confusion are higher for the 85mm (blue line), which basically means more blur. In the online version, you can also get example image of the approximate blur. (Which does NOT equal a higher bokeh quality, because that also depends on contstruction details of the lens).
Personal experience
From my personal experience with a 35mm and a 56mm prime on a Camera with Crop Factor 1.5 (which equals your Nikon DX) set to the same aperture (1.4), for Portraits with only head or head and shoulders it's irrelevant (though the 56 has less perspective distortion and makes "nicer" faces), but on a full body portrait, the 56 has more blur. But you also need a lot more space, which may not always be available.
A note on artifical bokeh
Creating a Bokeh in Photoshop or "Blurring Backgrounds" is not an easy Task and requires Depth-Information, which you don't have in a 2D Image (that's why e. g. the iPhone 7 uses two cameras to create an artifical DOF effect, and event this doesn't work perfectly).
Originally by user26144. Source · Licensed CC BY-SA 4.0
user26144
9y ago
0
Generated from our catalog & community — verify before relying on it.
An 85mm prime can give you somewhat more and often smoother background blur, but the improvement over a 50mm f/1.8 is usually incremental if you keep the same framing by stepping farther back.
That’s because depth of field stays roughly similar when framing and aperture stay the same. So simply switching from 50mm to 85mm at f/1.8 won’t be a dramatic change if you compose the shot the same way.
Where an 85mm may still help is rendering: many 85mm lenses are designed for portraits and can produce smoother-looking blur (bokeh), especially wide open. Lens design matters, not just focal length and f-number.
If your main goal is much shallower depth of field, a faster lens is the bigger change—such as an 85mm f/1.4 or a fast lens in the 100–135mm range. Software blur can help, but it is not the same as optical blur from the lens.
So: yes, an 85mm can be worth it for portraits and nicer bokeh, but don’t expect a huge blur increase over your 50mm f/1.8 unless you also gain a wider aperture or much more subject-background separation.
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