What effect does changing aperture during a single exposure have?
Asked 3/25/2012
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2 answers
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I tried rotating the aperture ring during one long exposure, dividing the total exposure time across several f-stops so the overall exposure stayed about the same. The result looked surprisingly normal, similar to a single exposure at an intermediate aperture. Why doesn’t changing aperture mid-exposure create a dramatic effect in a static scene, and are there any situations where it can produce an interesting artistic result?
Originally by user2910. Source · Licensed CC BY-SA 4.0
user2910
14y ago
2 Answers
19
For a static scene, I'd expect the results to have DOF almost as deep as at the tightest aperture (you do record details at that aperture, but they are somewhat blurred by wider apertures - reducing contrast), with some camera shake mixed in. Indeed, this would give an effect very similar to just using an in-between aperture - not very exciting per se.
To have the method resulting in something more unique, something should change in your scene while you're changing the aperture. For example, you could fire key light with one aperture and fill light with other, making areas lit by different lights have different depth of field. In following example, note how the subject is fully sharp (the rear part would be blurred on a wide aperture shot), while the background is blurred (it would be much sharper on a narrow-aperture shot):

Single exposure, 58mm f/2 lens; focus on lettering of the other 58mm lens. Exposure started with f/11, key light LumoPro LP120 at 1/2 power snooted almost top-down; aperture changed to f/2, fill light LumoPro LP120 at 1/16 power diffused at left of scene.
For comparison, here's the same image taken with only wide aperture...

Single exposure at f/2. Key light at 1/32 power; fill light at 1/16 power.
...and only with narrow aperture:

Single exposure at f/11. Key light at 1/2 power; fill light at 1/1 power.
To reduce camera shake and allow for unexposed scene adjustment, you could shoot the different apertures as separate frames and combine them in post. Combined with repositioning an object, this could result in image where the object is apparently blurrier closer to focus plane and sharper further away.
Originally by user4390. Source · Licensed CC BY-SA 4.0
user4390
14y ago
0
Generated from our catalog & community — verify before relying on it.
In a static scene, changing aperture during one exposure usually just layers multiple versions of the same image with different depth of field and diffraction. Because all those versions are aligned, the result tends to look like a fairly ordinary shot made at some middle aperture, often with slightly reduced contrast or a soft “haze” in out-of-focus areas.
That’s why your image wasn’t very dramatic: aperture mainly changes light level and depth of field, and if nothing in the scene changes, those effects simply blend together.
The effect gets more interesting if something changes during the exposure. Examples from the answers:
- Use different lighting at different apertures so parts of the scene lit at one moment have different depth of field than parts lit later.
- Create a “sharp subject with blurred halo” look: start wide open and deliberately out of focus, then stop down and make the subject sharp for the rest of the exposure. A dark background and bright subject help.
- Motion or changing background detail can make the layered DOF differences more visible.
So: for static subjects, variable aperture is usually subtle. To make it visually distinct, combine it with changing light, motion, or deliberate focus effects.
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