Motivation is a photography blog that discusses the creative aspects of photography. The posts will include thoughts about images and their interpretation, photographers and their work, technique, workflow, my ongoing projects, and perhaps even the occasional off topic rant.

Zone Plate And High Pass Filtration

I don't usually write many blog posts about Photoshop techniques, but have been asked a few times about my "Dreamscape" images made using the Lensbaby zone plate optic. The "Dreamscapes" series can be seen here. At any rate, the question I have been asked pertains to the sharpness of the zone plate images, and, specifically, how the images are made to appear sharper than a typical zone plate shot.

First, for those that may not be familiar with the term, zone plate photography is ,in some ways, similar to pinhole imaging. However, instead of using a pinhole to allow light into the camera, a series of clear concentric circles spaced at mathematically determined distances are used for this purpose. What this effectively does is:

i) markedly decrease the shutter speed compared to pinhole imaging, as the zone plate lets in much more light than a pinhole per unit time

ii) impart a unique glowing appearance to the highlights in the image and

iii) make the focus of the image even softer than the same shot made with a pinhole.

For a little more information about zone plates see here.

I very much enjoy the 'dreamy' look that the zone plate imparts, at least for some types of images. However, I have to admit that the images sometime do appear too soft focused for my taste, but, yet, the same image made with a pinhole doesn't quite yield the same effect. For this reason I have often added a 'high pass sharpen' layer to the image in Photoshop.

Here is an example of what it can do to a zone plate photograph (the smallish imagesin the blog make it a bit difficult to see, but I think you can tell if you look is much more apparent on a slightly larger image)

Dreamscapes #1....No High Pass Sharpening
Copyright Howard Grill

Dreamscapes #1...With High Pass Sharpening
Copyright Howard Grill

The method is started by flattening the image. Now the image consists of only a background layer. Duplicate this background layer twice and click the icons to turn these duplicate layers off, making them invisible. Now click back on the background layer to make it active and go to the Photoshop filters and choose High Pass (Filter>Other>High Pass). You get a dialogue box in which you can choose a radius. Choose 75 pixels to start, but this is obviously a ‘jump off’ point for experimentation.

Your image will now look totally disgusting. Don’t worry….just click on the duplicate background layer which is directly above the layer that was just filtered to make it active and then click on the icon to make it visible. The image now returns to the way it looked before starting this whole thing because it is a duplicate of the original at 100% opacity lying on top of the filtered image. Now the fun begins. Change the blending mode of this layer from normal to overlay (or try Soft Light or Hard Light) and the image undergoes an interesting change.

Perhaps the effect is too much? That is why I added the second duplicate layer (which is not visible at this point) on top of the others at the start of the technique. Click on that layer to now make it active and click on the icon to make it visible. The image now appears as it did before starting. But turn down the opacity of this topmost layer to let the filtered look come through and see how you like it.

In this example, I think the technique really 'tightens up' the look and puts the focus squarely on the person without losing that dreamy zone plate look. This works best on simple images with strong graphic lines. But I find that zone plate imaging works best on those types of compositions anyway.