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I can read the various MTF and other lens-testing charts, but they are only as meaningful in my work as I can implement them in the studio or field. In other words, I am not much of a lens tester myself, except though actually using the lens for my own work. I am certain that any given lens reaches greatest resolution at a certain f/stop, just as the experts tell us. No doubt. However, what I really want to know is about what kind of curve the particular lens creates from its widest to its narrowest aperture and how does that curve affect my particular work. That’s the curve I actually use. In other words, is it “sharp” wide-open or does that sharpness start a couple of stops later, and how long is that sharpness maintained? What kind of curve do we have, sharp or gentle? As someone who stacks focus, I don’t stack focus at the same aperture that I use for taking a traditional single-shot photo. With a one-shot photo I tend to, of course, push the aperture higher (narrower) to get as much depth-of-field as I feel I need for a particular shot, which often is as much as I can get without degradation of the image through diffraction. Yet when I stack focus, I don’t worry about using a narrower aperture to get my depth of field, but rather I use focus stacking to create the apparent depth of field. So, for focus stacking I want a single aperture on the lens-curve that marks the point of greatest resolution for that lens. In summary, I don’t try to stack with narrow apertures, but almost always with a single aperture for the lens that is considered its peak-resolution, what commonly is called “sharpness,” although that is a rather nebulous term. That way every increment of the stacked layers has maximum resolution and therefore the resulting stacked images shares that too. Not to be confusing, but sometimes I stack not at the point (aperture) of greatest resolution, but just a little higher (narrower) if I am trying to create a little additional faux micro-contrast for that image. I take advantage of the greater depth-of-field obtained at a narrower aperture and record the additional depth-of-field as if it were greater acutance – micro-contrast. I am still undecided whether this actually helps, but it is a concept I am playing with. Normally I stack at the aperture that the testers (or my eyes) tell me has the most resolution for that lens and leave it go at that. The point here is that I come up with my own idea of what aperture curve will work for the job at hand, i.e. what I can get away with. All photographs IMO are impressions, our own mental and psychological impressions of what we see out in the world, given the caveat that much of what we see, our impressions, come not from the outside, but from our own mind and approach. Because focus stacking is a form of lossy sampling, a stacked photo is almost an impression of an impression, so to speak. I don’t easily fall into believing that what I am photographing out there in the world has a reality greater than my own impressions and approach. Let’s take the recent Zeiss 135mm APO as an example, and the following are just my thoughts on how I use this lens for close-up photography. The Zeiss 135mm is sharp wide-open, so I don’t have to add a couple of f/stops to achieve better resolution. With this lens wide-open, I get a depth-of-field (DOF) that is razor sharp. With that ultra-thin slice of DOF, I can literally paint focus, layer by layer, until I create what we could call a block of focus that represents what I want in that image to be sharp and in-focus. Because the lens is fast and wide open, whatever I don’t layer-paint is automatically blurred or part of the bokeh of the image. Note that this is the opposite of much traditional advice for focus stackers, i.e. that we push the lens as high as we can without suffering too much diffraction and then stack. I am going against tradition here because I like the results better. Now, back to the Zeiss APO 135mm lens. With traditional one-shot photos, when I am not stacking, I find that from the Zeiss 135 APO I can get usable resolution and acutance all the way to up to something like f/13, which is a long way. Yes, by then I am recording diffraction that bothers me (and way before that), but I often can get by with it. If I don’t need peak sharpness for the particular subject, I can shoot at f/16 and inject some little bit of needed clarity or contrast in post. Beyond f/16 I am getting too much diffraction and image-degradation to venture there. Since I am primarily a close-up photographer (rather than a macro photographer), much less a micro-photographer, the lack of extreme detail at f/16 with the Zeiss 135mm APO is often acceptable, diffraction and all. In fact, I have an ongoing battle going on within me whether to do a lot less stacking and a lot more taking single-shot traditional photos. I am also experimenting with what I call “short-stacks,” where I take two or three shots that capture the particular areas in a photo I want to be in high-focus and stack that. I find that with these new Zeiss APO lenses do actually work much better than I would have guessed for short stacks. Years ago, when I was first starting out with focus-stacking, I did short stacks because I was lazy, and the results were that I had way too many artifacts in the final images. But with, as I have mentioned in many articles now, these three new Zeiss APO lenses (135mm, 55mm, 85mm), this short-stack technique seems to work out very well indeed. And I don’t even stack them in the ordinary way. Yes, I use Zerene Stacker with short stacks, but when retouching I have a different approach. Ordinarily, I retouch artifacts only, but with the short-stack approach I tend to just paint in from each of the layers just the main part that layer has in perfect focus, kind of in a whole-cloth sort of way. Most of us used to this in Photoshop. I do have to pay attention to where these layers overlap, but I have been surprised how successful that has been. Here is a little tableau I have put together. I will have to show a larger view at another time, but I am focusing on the two-dollar bill, but have included some burlap (pleated) so that it rises up and we can see how much depth-of-field is available at the higher apertures. Perhaps some of you reading this will have suggestions for what kinds of objects I could additionally include. These shots are not about color, but about resolution, diffraction, and depth-of-field. I notice that I can get away with f/11 (see the copper tacks), but with f/16 it is more iffy (but often still usable) for close-up, but not for macro. Lately my internal mantra seems to be “I always seem to go for high resolution,” but am interested more in acuity (micro-contrast) in post. And I only do all of this with APO lenses, for the most part. Your thoughts? Are these kind of images useful to anyone by myself?