Why are nearby twigs still sharp when I focus on a leaf, and how can I isolate just the leaf?
Asked 1/19/2018
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I wanted only a red leaf to be in focus, not the nearby twigs. I used a Fujifilm S7000 in aperture priority at f/2.8, ISO 200, and used AE/AF lock to focus on the leaf before recomposing. I expected the focus lock to keep only that point sharp.
Why are the twigs still in focus, and what can I do to make only the leaf sharp?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
12
Short answer: as the framing is, you cannot achieve this without post-production. If you do not want to use blur-filters in something like Photoshop, you should try to use another framing.
The twig on the left is as close to the camera as the leaf is - therefore, when you focus on the leaf, the twig will also be in focus, because the focal plane is just that - a vertical (as in: parallel in relation to the camera's sensor, or 90° to the axis of the optical path) plane. If you want to change that, you will have to separate the twig and the leaf distance-wise. Looking at your picture, I'd guess that making one step to the right and then reframing on the leaf would at least improve the situation.
To show you what I mean with the focal plane, here's a stolen picture from Wikipedia's article on focus:
It wouldn't matter if you focussed on "depth" or "field" - both are in the same focal plane - and it is the same with your leaf and twig. However, there would be a difference between focussing on "feet" and "barrel". You can try that out yourself with a ruler (or virtually anything) on a table: focus changes with distance, not from left to the right. (For this assumption, we exclude tilt-shift photography.)
The twigs in the background are another topic: you could try to either frame closer, pushing for stronger background-blurs (and a faster transition between in-focus and out-of-focus), or you could use a wider aperture (if available).
Originally by user69369. Source · Licensed CC BY-SA 4.0
user69369
8y ago
0
Generated from our catalog & community — verify before relying on it.
AF/AE lock does not lock focus to one object only—it locks a focus distance. Anything at roughly the same distance from the camera as the leaf can also appear sharp.
That’s the key issue here: the leaf and some twigs are in the same focus plane (a plane parallel to the sensor), so focusing on the leaf also keeps those twigs in focus.
To isolate the leaf, you need to change the geometry of the shot so the twigs are at a different distance than the leaf—for example, move left/right or change your angle and reframe. A wider aperture helps blur objects in front of or behind the focus plane, but with a small-sensor compact camera like the Fujifilm S7000, f/2.8 usually won’t produce very strong background blur in this kind of scene.
So your practical options are:
- change your shooting position/composition so the twigs are not at the same distance
- use the widest aperture available
- blur the twigs later in post-processing if needed
Your understanding of focus lock was slightly off: it locks distance, not a single isolated spot in space.
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