How to Create a motion blur effect
Shoot a burst
In Finder, choose File > New Folder. Import a burst mode photo into Photos for Mac. It’ll appear in the Bursts Album. Hold Opt and drag the photo’s thumbnail to the new folder to export the series of shots as files.
Change stack blend
Go to the Layers panel and open the Live Stack Group to see the aligned shots. By default, the stacked shots are blended using a Median setting. Click the icon to the left of the group’s checkbox and choose Mean.
Add a mask
Click the duplicated layer and choose Layer > New Empty Mask Layer to its contents. Choose the Paint Brush tool from the toolbar. In the Options bar, set Opacity to 20 per cent, then set the foreground color to white.
Import the shots
In Affinity Photo, choose File > New Stack and check the Automatically Align Images box. Click Add and choose Perspective from the alignment pop–up menu. Select the shots in the folder you created, click Open, then OK.
Examine the shots
Mean mode creates a motion– blurred look similar to that created by the iPhone’s Long Exposure effect. Hold Opt and click on the thumbnail of the layer for the last frame in the burst sequence to view it.
Reveal the subject
Click the mask layer to target it. Apply the brush over the subject. The semi–transparent tip reveals pixels from the top layer. Brush over areas a few times to make them more solid, to mimic a burst of flash.
Rotate the canvas
If your burst of source photos was captured with your iPhone in portrait orientation, Affinity Photo may import the images in landscape. To get them the right way up, use 90–degree rotation from the Arrange menu.
Duplicate a layer
Next, Ctrl–click the same layer’s thumbnail and choose Duplicate from the menu to create a copy. Drag the duplicated layer above the Live Stack Group. The duplicated layer will hide the motion–blurred stack below.
Experiment
Live Stack Group has many blend modes. Here we’ve taken a burst of five shots and used the Mid–Range setting to reveal each layer as a sequence of sharp shots. A layer mask helps make one layer more prominent.