Will an f/3.5-5.6 zoom on APS-C give strong background blur, or do I need a faster lens?
Asked 10/13/2013
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I shoot a Canon APS-C camera with an 18-135mm f/3.5-5.6 and mostly photograph kids outdoors and casual family portraits. I often want more background blur than I’m getting now.
I understand that background blur depends on focal length, aperture, camera-to-subject distance, and subject-to-background distance. I already try to use longer focal lengths, get close to my subject, and keep the background farther away, but the results still aren’t as soft as I’d like.
Would moving to another superzoom like an 18-200mm f/3.5-5.6 help much, or is the real limitation the relatively slow maximum aperture on APS-C? If I want noticeably stronger subject separation, should I be looking at a faster zoom such as f/2.8, or at primes like 50mm or 85mm?
Originally by user6189. Source · Licensed CC BY-SA 4.0
user6189
12y ago
2 Answers
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To get the result you want, you need a wider aperture or a larger sensor. If you are already separating the subject from the background as much as is practical, shooting at the lens' widest aperture setting and still not seeing what you want to see then you've reached the limits of you current gear.
At the minimum for longer focal lengths you need an aperture in the f/2.8 or lower range. For shorter focal lengths you probably need a prime with an aperture at f/2 or wider. On your APS-C body I would consider the EF 50mm f/1.4, the EF 85mm f/1.8, one of the 100mm primes, or the EF 135mm f/2 L. If you've just got to have a zoom, the EF 24-70mm f/2.8 L II is an excellent choice but it is pricey. Image quality is virtually identical to the much cheaper 50mm f/1.4 when the 24-70 is set at 50mm, but it is also equally good from 24mm to 70mm. The Tamron SP 24-70mm f/2.8 Di VC is not quite as good, but a lot more affordable and also adds Vibration Control, Tamron's IS equivalent. The APS-C only EF-S 17-55mm f/2.8 IS is also an excellent normal zoom lens, but may be a little short on the long end for you unless you get a separate telephoto lens. For a telephoto lens you should consider one of the EF 70-200mm f/2.8 variants.
For how the sensor size affects Depth of Field (DoF) see this answer. For a comparison of the various 70-200mm options for Canon bodies see this answer.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
12y ago
0
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An 18-200mm f/3.5-5.6 won’t make a dramatic difference in background blur versus your 18-135mm. The main limitation is the slow maximum aperture, especially on an APS-C camera.
To get stronger subject separation, you generally need:
- a wider aperture (lower f-number)
- more distance between subject and background
- to be relatively close to your subject
- often a longer focal length
If you’re already using those techniques and still aren’t happy, you’ve likely reached the limits of your current lens. For noticeably more blur, look at lenses around f/2.8 or faster. On APS-C, 50mm f/1.8 or f/1.4, 85mm f/1.8, or similar primes are common choices. If you prefer a zoom, a constant f/2.8 zoom will help more than another f/3.5-5.6 superzoom.
Also, shooting from lower down can help with kids, because it places the background farther behind them instead of including nearby ground, which makes blur more obvious.
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