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 carefully...it 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.

Don't Fight Mother Nature

When out photographing, I have always found working with the prevailing conditions to be a far better idea than stubbornly resisting what is going on around me. Let me be more specific by using an example. If I were to go out with the idea of photographing wildflowers and find that it is a windy day, I am much more likely to return with interesting images if I decide to shoot using long shutter speeds in order to create abstract images than if I decided to 'fight Mother Nature' and insist on trying to get tack sharp images using fast shutter speeds and waiting (and waiting and waiting) for the wind to die down briefly. Sure, I might come back with a sharp image or two after the fight, but I would not have enjoyed myself, would have a feeling of frustration, and would have robbed myself of the opportunity to have tried something new.

Nonetheless, I recently found myself 'fighting Mother Nature' without really knowing that's what I was doing. When I finally realized that I was resisting what nature was giving me I had a much more enjoyable time and came away with a reasonable image or two. Let me explain..... In a park near my house there is a group of three trees. They are special trees, though I don't know what species they are. They are quite short, but have an aged appearance with contorted and twisted limbs. Truth be told, I don't have a very good 'relationship' with these trees. I find them fascinating and intriguing......even a bit mysterious. For a year or two I have intermittently gone to see the trees with my camera but have never taken a single photograph of them! I have never been able to compose an image that I liked despite my feeling that there should be a hundred fascinating images among their twisted and contorted limbs. There has always been a bad background I can't eliminate (the trees are right near a busy street) or the composition doesn't really express what the trees make me feel etc. Sometimes, in situations like this, you are defeated before you even try......having tried so many times you go in with a losing attitude and an adversarial position (yes, I know those trees can't really think....but why won't they let me take their picture???).

Well, on Friday I went back again. There was snow on the ground and I thought that perhaps I could somehow use that as a 'clean' background. Of course, it turned out to be a bright day, something that is a rarity during a Pittsburgh winter (November through March is mostly gray.....if you don't have seasonal affective disorder before you move here you rapidly develop it). Because the sun was shining, there were strong shadows on the snow. I was trying to compose images of the twisted limbs, but every time I thought I was getting something interesting the trees' shadows would clutter the background.

After continuing to circle the trees in order to try to get an interesting composition without a distracting shadow in the background, it occurred to me that I was fighting this way too hard. Why not accept the fact that the sun was there and that unless I came back another time the shadows were simply not going away? Why not work with 'Mama' and use what 'she' was giving me? Why not try to incorporate the shadows into the composition? In fact, why not make the shadow the main subject of the image since, over time, I had been having so much difficulty making an image with the trees themselves as the main subject?

So that is exactly what I did! Once I started accepting the shadows as part of the image instead of trying to eliminate them, compositions became much easier.

Shadow Tree
Copyright Howard Grill

Is this an 'award winning' image?? I think not, but it is the only composition that I felt intrigued enough with to actually make me want to push the shutter button.

After liking the way my prior HDR bare tree image looked, I decided to use the same treatment for this image. The contrast range, given the bright snow and dark tree, lent itself to making an HDR composite of 6 images which was then converted to black and white and toned using SilverEfex Pro.

High Pass Filtration

I usually don’t post information about Photoshop techniques simply because there is an entire universe of websites dedicated to Photoshop that are run by folks who are far more Photoshop savvy than I could ever hope to be. However, every so often I run across a technique that I find really interesting and so, on those occasions, a post about it seems reasonable. Such is the case with High Pass Filtration. Please don’t consider this to be the definitive ‘how to’ regarding this technique but, rather, a jumping off point to look into it in a more sophisticated manner if it seems of interest to you.

The reason I found High Pass filtration interesting is that while ‘surfing the net’ I have occasionally come across images that seem to have a somewhat ‘enhanced’ sense of reality that gives them a very three dimensional appearance. The effect seems somewhat similar to the HDR effect, but tuned down. When I have followed discussions about such images the photographer will often say, when asked, that the image in question was not processed with HDR software.

So, it whet my interest when I ran across a technique which, by description, seemed to be one way to generate this effect. It is done by using the Photoshop High Pass filter to increase contrast. I knew that this filter could be used for sharpening and, of course, contrast enhancement is a form of sharpening.

At any rate, here is a way to use this technique in order to see if it will achieve a desirable effect (plus I made my own little addition to what I read). Once the image you are considering using it on is complete, duplicate the image and flatten it, but don’t sharpen it yet. 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 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.

A few comments:

1) I have only played around with this technique a bit and found that there are some images that it truly enhances and others that it totally destroys.

2) If an image is found that would benefit from this technique, the entire process can obviously be performed within the original file by duplicating the entire image and placing the entire image on a new layer and working from there.

4) It really is difficult to duplicate this effect with curves....I tried.

3) With the image size being so small, and with the effect being toned down with the topmost layer blogs don't really lend themselves to really demonstrating the effect well…..so, if it sounds interesting, play around with it on your own images and see what you think. With that in mind I am posting one example. The only difference between these two images was the High Pass filtration step.

Pre High Pass Filtration
Copyright Howard Grill

Post High Pass Filtration
Copyright Howard Grill

Diffraction In Digital Imaging

In the past, it has often been said that the rules of photography are the same whether one shoots digitally or using film. Certainly this is true when it comes to the art of composition, but when it comes to capturing the image there are certain technical aspects that are not quite the same.

The first one that comes to mind is the so called ‘expose to the right’ issue. Most people doing serious digital capture and that are shooting in RAW format are familiar with this concept. In short, most of the data and, therefore, detail that the digital sensor can capture is ‘located’ in the ‘brightest’ stop or two of the image. Therefore, the image should optimally be exposed such that the histogram is pushed as far to the right as possible, without actually clipping. While the image is now overexposed by conventional standards (and therefore this method will not work acceptably well in jpeg format), by shifting the exposure downward in the RAW processor the correct degree of brightness can be achieved and more detail captured than if the exposure had been ‘correct’ by conventional standards.

But you already knew that. What is more interesting is material that I recently read in the magazine Photo Techniques (which is a small magazine in terms of page numbers, but one that is well worth subscribing to). In the Jan/Feb 2009 issue, I learned that there may be significant differences with current digital capture when it comes to diffraction effects and depth of field.

Without going into detail (for that I strongly recommend getting the issue), I would like to provide a quote to whet your interest. In the conclusion of the article by Lloyd Chambers entitled “Diffraction: Resolution Taxed To Its Limits” Mr. Chambers states:

“As megapixels increase, diffraction will become the dominant factor limiting image sharpness, unless and until improved optical designs allow near-diffraction-limited imaging at apertures such as f2, f2.8, and f4. Such lenses are feasible, but will be larger, heavier, and much more expensive than today’s optics. When depth of field is a priority, ‘tilt’ lenses should be used in order to evade the diffraction/depth of field conflict.

To paraphrase an old maxim: f8 and stop there. That simple rule will maintain optimal or near-optimal lens performance and image contrast resolution with today’s DSLRs, while offering reasonable depth of field for many subjects. Stopping down to f11 or f16 is warranted with some subjects, but the contrast compromise should be kept in mind.”

Interesting stuff….the idea that with today’s high quality sensors and optics, diffraction plays a role much sooner (in terms of stopping down to achieve greater depth of field) than when using film.

I put some of this information to use with results that surprised me. I have previously mentioned and shown extreme macro-images I have made from slabs of stone. Though these slabs are flat in the general sense, they are cut with a saw and thus in the ‘macro’ sense are not truly flat. In order to maximize depth of field at high magnification (>1:1) I had been shooting at f16 and f 22. I recently tried shooting at f8 and f11 instead and found that the results were, indeed, sharper. And in this case the depth of field was still adequate with enhanced apparent sharpness. I now shoot all these types of images at f8.

Obviously, when shooting landscapes or other scenes where there are near/far objects that one desires to be in focus, there will be trade offs between sharpness and depth of field. However, it is worth experimenting with one’s equipment, or at least taking shots at a variety of apertures since, in many instances, the improved sharpness will be more desirable than increased depth of field with sub-optimal sharpness throughout.

There are definitely some interesting things to ponder here!