fogbound.net




Tue, 23 Jan 2024

The Moon and a Lens

— SjG @ 6:59 pm

From my desk, I could see the the waxing gibbous moon rising. The geometry was such that the moon filled the gap between the open venetian blinds almost exactly. I took a picture with a 300mm lens, focused on the moon.

The moon behind venetian blinds

I was a little surprised how much the venetian blinds in the foreground blurred out over the moon when I did that. When looking through the viewfinder, the image seemed to match what my eye saw: the moon filling the gap between two horizontal lines.

Thinking about it, it made sense. I had the aperture at f/8, so the limits to the depth of field would cause the much closer objects to blur.

I took a few steps closer to the window, so there would be more of a gap between the blinds, and took another picture.

Moon

Although to my eye, the moon was only about 75% of the gap between the venetian blinds, the depth-of-field problem continued to obscure it. So I went even closer.

Moooon

Even though the moon was taking up half the gap (to my eye), the venetian blinds still obscure it. So I went right up to the window, where the view through the lens made it seem like there was no obstruction whatsoever, just a moon floating there.

Moooooooooon

Well, even at this point, the venetian blinds intruded upon the image. Thinking about it more, I realize that the diameter of the lens is bigger than the gap between the venetian blinds. The lens gathers light from all across its diameter, so there’s no way it can see “between” the slats — the light is blocked. Also, as I got closer to the blinds, I was asking the lens for more depth of field (which it could not give me). The slats went further out of the focus and are relatively more blurred. In all likelihood, I didn’t see the effect through the viewfinder because I wasn’t paying sufficient attention.

Back in the day, I probably could have found the right equations to explain this phenomenon. Today, I’m content to notice it and say “Hm. Interesting.”


Sat, 9 Dec 2023

A Dead-Simple Slideshow

— SjG @ 12:30 pm

I have tens of thousands of photos I’ve taken over the years.

I think some of these photos are pretty good, but most are languishing unseen on random hard drives.

To share them, I’ve been a member of Flickr, I’ve posted on the late lamented Twitter, and I post some onto Mastodon. I’ve also created numerous gallery applications/server scripts/web sites (e.g., Statgal), but they’ve generally been clumsy or take too much work to maintain. So I’ve been working on a dumb PHP/JavaScript slideshow thing that will scan directories, cache the details, etc.

Here’s introducing PhotoSpinner. It’s a quick’n’dirty script to provide photos. It’s very simple and allows me to publish categories of pictures without a lot of effort. Source code’s at Codeberg.


Thu, 9 Nov 2023

Winking Hummer

— SjG @ 4:33 pm

I was doing my usual skulking about and chasing the garden hummingbirds, when this one made it clear it knew what was up.

(That’s not CG, AI, or fakery. The image is animated from two successive frames, shooting at 7fps)


Fri, 30 Jun 2023

Perspective correction and uncanny valley

— SjG @ 8:23 am

It’s interesting how optical corrections to “fix perspective” can end up making something look simultaneously “correct” and very, very wrong.

When I say “fix perspective,” I’m talking about the convergence of lines due to perspective. The further something is from your eye, the smaller it appears, so if you’re looking up at a building, the top looks narrower than the bottom. Similarly, if it’s not in the center of the frame, the different vanishing points combine with general lens distortion to make a funny-house mirror image.

This building does not, in fact, get smaller on the higher floors.

Now, optically, your eye sees perspective this way too, but the image-processing in the brain tends to counter it. What you “know” about the building overrides what you’re seeing, and you don’t really notice that it’s going all pointy on top. Weirdly, something that doesn’t bother us when we’re out on the street tends to bother a lot of people when they see it in photography.

In the old days, if you wanted to prevent this perspective narrowing of an architectural feature, you’d use an expensive and somewhat esoteric piece of equipment called a “tilt shift lens.” It would allow you to align the lens with the plane of what you’re photographing, and thereby cancel out some of the distortions. What that means in practical terms is that you can, in a controlled way, counter the convergence of lines due to perspective.

Now we do the same with ordinary lenses and software.

Where the “uncanny valley” comes in is that the convergence due to perspective can be fixed, but the point of view does not actually change. Where you see this dramatically is in something like this tower, where the perspective is telling your eye that you’re seeing it straight on, while the point of view of the constituent beams is from below. It’s mildly Escheresque. Compare the “corrected” and “uncorrected” views below.

I guess the solution is to always photograph everything using remote-controlled drones that sit in the perfect perspective spot, and then fix any lens distortions.


Sun, 3 Apr 2022

Hummingbird Season

— SjG @ 2:10 pm

It’s Springtime in the Quagg Garden, and several hummingbirds have declared it their own exclusive territory. When I take my lunch, I am greeted by spectacular aerial displays: both mating rituals and territorial defense. Less dramatic and yet equally (sonically) expressive, the mocking birds seem to be nesting nearby. Plenty of finches and bushtits and crows come by too.