ND Filters and Long Exposure: Do You Really Need Them?
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Understanding Long Exposure Photography
Capturing long exposure shots with traditional cameras during daylight requires a tripod and a filter, whether it's a polarizer or a Neutral Density (ND) filter. These cameras can maintain the shutter open for an extended period, enabling varied exposure times. In contrast, modern iPhones have limitations; they can only keep the shutter open for a maximum of one second to prevent processor overheating. For exposures longer than this, multiple frames must be combined using a technique known as Frame Averaging. This method gained popularity with the app Slow Shutter Cam, which I first used on my iPhone 4s back in 2012.
Today, various applications, including Apple’s own Camera app, can achieve long exposure shots, with some supporting RAW image formats such as DNG. However, I generally stick to JPG for convenience. My preferred app for this purpose is Reeflex, which offers extensive manual controls for focus, shutter speed, and exposure compensation.
The video titled "Filming with a filter??!! | Filter VS No filter | Demo" provides a demonstration of the impact that filters can have on image quality during long exposure photography.
The Role of ND Filters
When discussing long exposure shots, the effectiveness of using a filter becomes a crucial topic. Achieving the desired results can be challenging due to various factors, including lighting conditions and composition. A popular use case for long exposure photography is capturing flowing water, where the goal is often to create a smooth, ethereal effect. However, if the water is moving quickly, the outcome may appear "braided," which occurs when the individual frame's shutter speed is too fast. This is commonly seen in bright conditions, like midday sun.
To mitigate this issue, one could either take a longer sequence of shots to enhance blending or risk overexposing the highlights, especially where the water is bright. Motion blur from vegetation can also occur due to wind, which is sometimes unavoidable. The two main solutions for avoiding the braiding issue are using an app like Reeflex or employing a Neutral Density filter.
Subsection 1.1.1 Exposure Techniques
When preparing for a long exposure, I always enable the histogram and zebra stripes in Reeflex. Even with a professional camera app, the iPhone will attempt to automatically optimize exposure. The histogram displays exposure latitude, while zebra stripes indicate potential highlight blowouts—critical to monitor since blown highlights cannot be recovered.
To achieve the best image quality, I set the ISO to its minimum and adjust the shutter speed until the zebra stripes appear in the highlights. I then fine-tune the shutter speed until the stripes disappear, ensuring the smoothest water flow while retaining image data.
The Impact of Filters on Long Exposure
Now, you may wonder where filters fit into this workflow. Using a Neutral Density filter reduces the amount of light entering the sensor, allowing for longer shutter speeds without overexposing the image. After attaching the filter, I ensure the ISO remains at its lowest setting, then adjust the shutter speed until the zebra stripes reappear, and fine-tune it once again.
For instance, I took two images over five seconds. The first, without an ND filter, had a shutter speed of 1/177th of a second. While this is relatively fast, it almost freezes the water. When using the ND filter, the shutter speed dropped to 1/22nd of a second. This longer exposure results in richer colors and allows for more movement in the water, ultimately producing a more visually appealing final image.
Conclusion: Mobile Photography with a Serious Approach
My experience with mobile photography has shown me that even without a DSLR, one can achieve serious photographic results. Since selling my DSLR in 2016, I have focused solely on iPhone photography and have no regrets. This article aims to demonstrate that using a smartphone does not diminish one's potential as a serious photographer.
The video titled "Do ND Filters Matter? No filter vs ND vs NDPL Filter" explores the significance of ND filters and compares their effectiveness in various shooting scenarios.