For years and years, I've used neutral density filters on the front of my camera lenses to get long exposures. More than a decade ago I bought a Big Stopper 10-stop Lee plastic filter to get exposures up to about a minute in daylight; this smooths out water and provides a slightly surrealistic look. It is so old that it has changed colour, going more and more blue over the years, till today it is completely unusable for colour photographs and cannot be corrected in Lightroom.

About four years ago, I bought a 15-stop Lee IRND glass filter, and I use this to get exposures around 6 minutes in daylight. The great advantage of this is that you get a completely flat effect with pictures of the sea. Especially around the Thames Estuary, there can be standing waves of low-frequency swell that seem not to even out in a 30-second exposure; 6 minutes is enough to get a completely smooth sea and a very surreal look. Unlike my original Big Stopper, this filter is completely colour neutral.

But all this means using a big camera and a tripod. How about doing this on your smartphone instead? This is what the Even Longer app does.

Even Longer is an app that came to my attention because of the YouTube algorithm. It recommended a video by Glyn Dewis who is a fan of Even Longer and gave a very nice explanation of how to use the app.

I downloaded it and had a little play. It looked good, but, in basic mode, it didn't offer RAW capture, so I decided to pay for that. It is not overly expensive, and, as it turned out, well worth the price. You need to use it on some form of stand so that it stays still during the exposure. My preference is to use it on a Platypod.

As far as I can tell, the app takes huge numbers of images over a time period that the user specifies; it then processes them within the phone to give a synthetic long exposure. There are three modes, of which I've used two. The most approachable is Frame Averaging. In this, multiple frames are averaged, and the result is effectively a long exposure. As more frames are added they contribute to the average, increasing the effective exposure length. Another mode is "Light Trails". In this, rather than simply averaging the images, it uses a kind of overlay (lighten) mode. It records areas of a new image that are brighter than anything that went before. With multiple images of, say, a car going along a road at night with its lights on, the effect will be to generate a light trail. As shown in some of these images, it works fine in daylight as well if something goes through the frame which has higher luminosity than what was there before.

The images shown here should indicate it works really well. These are just my first goes. I'm sure I'll use it, and refine its use for my purposes, much more in the future.

But why bother with a phone to do this when the filters on a "proper" camera are the gold standard? I think there are three things.

First, no futz. It is an awful lot of futzing around to set up a long exposure on a big camera: filter rings, the right size thread adapter, putting everything together and so on. Even determining the exposure and setting bulb mode (possibly with an external timer) is all a futz. With an app, put the phone on a stand of some sort, open up the app, frame the picture, choose your time and mode and press go.

Second, people don't seem to notice. When I was in Llandudno in March trying the make some abstract pictures of the lido using 6-minute exposures, my tripod, camera and filter attachment seemed to attract the attention of passers-by who want to talk. They were fascinated by what I was doing and wanted to know all about it. That is fine. I'm always happy to talk to anyone who might be interested. But I can either engage in conversation or I can make pictures: realistically, I can't do both. So I chatted away. But while chatting, more people came around the lido and hung about exactly where I wanted to go next. People static in the frame were not my idea, so once the conversation was over, I gave up any idea of making further long exposures. Something to go back to another time.

I also wanted to make some long exposures along the front of the shelters that are characteristic of the place. Rather than set up the big camera, with all that would entail, I just popped the phone on the Platypod mount and set that beside me on a bench facing the subject. Two-minute exposure dialled in and off we go. And no-one noticed and wanted to chat. Lots of people went through the frame and were averaged out — or, and this amazed me, contributed their luminosity in Light Trails mode.

Third, simultaneous modes. Following on from the previous point, Even Longer records both Frane Averaging and Light Trails simultaneously, and can write a raw file for each. Oh my goodness! Two images in the time of one. After a single exposure, you can choose whether the LT or FA works best for that picture. And my top-of-the-range Sony cannot do Light Trails-type overlays, only time averaging using ND filters. (An Olympus camera like the EM-1 mk2 I tried ages ago will do Live Composite, which is very like Light Trails - a distinct selling point for the OMDS cameras. The new OM-1 has a synthetic ND filter as well.)

Even Longer can produce a RAW DNG file, which can be edited in Lightroom. The file goes straight into the iPhone Photos app. There are two simple ways to get this into Lightroom for processing. Either let it sync with the desktop version of Apple Photos and then export the original unmodified file, saving it onto your local file storage for import into Lightroom. Alternatively, import it into Lightroom on the phone and let it sync across into desktop Lightroom. The files process very nicely in Lightroom. Raw files from the big camera (my Sony Alpha 1) have more dynamic range and resolution, but iPhone DNGs are pretty good anyhow.

I found it surprisingly rewarding to make pictures from this app, and, for me, it is well worth the price.