The lens blur filter for Affinity Photo can be found in the blur category of the blur menu in Affinity Photo. You can also find the filter via the live filters in the layers menu.
It is to mimic a lens in a real camera, wide aperture etc with depth of field and can be used to blur the background. The Bokeh effect with Colors. As I am not a Photography expert, I will leave it at that and go through the effect as a visual effect more than its relationship to cameras. As with all the effects, it requires a layer to work with. Once the panel has appeared, you can modify the radius, blades and curvature as well as the three bloom settings. The effect is very much an average effect if you use the top three settings but the bloom adds to image by brightening the brighter parts of the image and to see the additional lighting, set the threshold to less than 100% as well as increase the bloom factor. The color changes the value from white to adding a little color such as greens and yellows into the image.
You can set the radius etc to high values, the only one that works in the opposite way is the threshold and it is more effective as you reduce the value. Set to the maximum, the filter can infuse color throughout the image
Duplicate the layer and perhaps apply a different effect such as a Gaussian to the lower layer and then use the effect on the top layer and also combining with the blending modes such as color burn etc via the layers panel. You can also reduce the size of the layer and then apply the effect to that
It is great but you can combine it in multiple ways with other filters such as lighting found in the main filter menu. You can also add noise and other effects and then apply the effect
You can apply the effect multiple times to an image as well as combine with other filters but you can also record all these actions via the view menu and studio and macro panel. Click the record button and then record all the steps such as adding a boom to a picture and then stop and playback the result. You can also click the plus button on the macro panel and store this in the library for future use.
You can use it with channels, display the channels panel via the view menu and studio and then select the red channel and apply the effect with radius etc set to different values from the green and blue channels, go to the green and apply and the blue channel and apply. You can, of course, combine this with other effects as well so instead of applying the effect to the blue channel, use the Gaussian blur filter instead. Once you are happy with the color changes, click the little return to RGB at the top of the panel. The navigator is useful to see the changes to the images while using the channels.
You can create a selection in a number of ways, you can apply the effect to the selection or perhaps the invert of the selection. You can also add feathering etc to the selection and apply the effect.
The live feature means you can apply an effect to the image with out it being a destructive effect. You can apply the effect and then change your mind and go back to it later and tweak the settings by double clicking the entry in the layers panel and changing the radius, bloom etc settings. You can also combine multiple live layers as well as combining the layers with adjustments that also can be modified in the same way. You can also modify the result by changing the opacity and blending mode
It can be modified by using the layer menu and fade command. The fade allows for you to reduce the effect as well as how it blends so you can set the effect to a difference or darken blend.
You can apply the effect multiple times with the same setting or change the settings, the end result will end up filling the image with white though the speed of the change depends on the settings.. You can apply the effect with low settings as well. If you want to just use the same settings over and over, use the repeat feature at the top of the filters menu
You can create an intense whitening of the image by using the bloom by pushing it very low (going high reverses it) and then tweaking the factor such as having it quite high. You will end up with a very white image with some parts of the image still showing through.
You can create some seriously unusual color effects by changing the bloom threshold and factor etc for individual channels so you can apply it with one set of values to red and then another to the green by selecting the channel entry in the panel. To see the effect clearly it is always a good idea to have the navigator displayed and you can see the result of the individual channels.
With the most recent release of Affinity Photo, you can now add pattern layers and you can use the filter before you generate the pattern layer from the current selection but you can also apply the filter afterwards, you can also add on top of the pattern layer, the live layer version.
Create a shape using the rectangle tool or ellipse etc and then apply the visual effect to that shape. If you are using a solid color then the blur will have no highlights etc so the bloom will have no use. You can always fill the layer with patterns and also gradients and that will generate intense lighting effects. If you have an even more colorful shape as well as a slightly more interesting shape than a rectangle, all kinds of colorful effects can be generated from the shape
You can do exactly the same with text shapes in Affinity Photo. You can fill the text with gradients or patterns via a selection and then use the filter on that text (remove the selection)