Can I use just two ±3 EV bracketed shots for HDR instead of smaller or more numerous brackets?
Asked 6/19/2014
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I use a Sony NEX-5R and sometimes bracket exposures for HDR/exposure fusion in Photomatix. Since the camera’s sensor dynamic range is greater than the 6 EV gap between a -3 EV and +3 EV exposure, it seems like two frames at the widest bracket would always be enough, with any closer spacing or extra frames just adding redundant overlap. Is that reasoning sound, or are there situations where smaller steps or more frames produce a better result?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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You are incorrect in the assumption that redundancy is a bad thing. A good HDR tool will be able to average the results of many images to reduce noise. Having more images also reduces the chance that there is movement in one of the images that will impact the result.
A few points, DXO also measures dynamic range at each ISO setting. The NEX 5R has 13.1 EVs at ISO100, which doesn't fall to 7 EV until ISO 12800!
Finally I would question the benefits of HDR at all with a Sony Exmor sensor. At ISO100 you are already getting 13 stops, if you do +-3EV that's 19 stops, which is almost certainly greater than the lens is capable of delivering. All lenses suffer from veiling flare to a certain degree which will prevent you digging too far into the shadows.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
12y ago
0
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Not always. Two frames at -3 EV and +3 EV can work, but the overlap is not just “redundant.” In HDR/fusion, overlap is useful because:
- it gives the software more well-exposed data to blend
- multiple frames can reduce noise by averaging
- more overlap can preserve better midtone/highlight/shadow detail
- extra frames can help if one exposure is affected by motion or other issues
Wider spacing is less ideal when the scene’s dynamic range is lower than your total bracketed range. Then you may be spreading exposures too far apart and relying more on the weaker ends of each file instead of using stronger midrange tonal data.
Also, sensor dynamic range figures are typically best-case at base ISO; usable range changes with ISO and real-world conditions. Lens flare and scene contrast can also limit how much practical shadow detail you can recover.
So: two ±3 EV frames are sometimes enough, especially with a high-dynamic-range sensor, but they are not universally optimal. Smaller steps or more frames can improve noise, blending, and tonal quality depending on the scene.
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