The F Number On A Lens Means Something? Who Knew!

March 18, 2024 by Jenny List 59 Comments

The Raspberry Pi has provided experimenters with many channels of enquiry, and for me perhaps the furthest into uncharted waters it has led me has come through its camera interface. At a superficial level I can plug in one of the ready-made modules with a built-in tiny lens, but as I experiment with the naked sensors of the HD module and a deconstructed Chinese miniature sensor it’s taken me further into camera design than I’d expected.

I’m using them with extra lenses to make full-frame captures of vintage film cameras, in the first instance 8 mm movie cameras but as I experiment more, even 35 mm still cameras. As I’m now channeling the light-gathering ability of a relatively huge area of 1970s glass into a tiny sensor designed for a miniature lens, I’m discovering that maybe too much light is not a good thing. At this point instead of winging it I found it was maybe a good idea to learn a bit about lenses, and that’s how I started to understand what those F-numbers mean.

More Than The Ring You Twiddle To Get The Exposure Right

lose-up of the end of a lens, showing the F-number range — The F-number range of a 1990s Sigma consumer-grade zoom lens.

I’m not a photographer, instead I’m an engineer who likes tinkering with cameras and who takes photographs as part of her work but using the camera as a tool. Thus the f-stop ring has always been for me simply the thing you twiddle when you want to bring the exposure into range, and which has an effect on depth of field.

The numbers were always just numbers, until suddenly I had to understand them for my projects to work. So the first number I had to learn about was the F-number of the lens itself. It’s usually printed on the front next to the focal length and expressed as a ratio of the diameter of the light entrance to the lens focal length. Looking around my bench I see numbers ranging from 1:1 for a Canon 8mm camera to 1:2.8 for a 1950s Braun Paxette 35 mm camera, but it seems that around 1:1.2 is where most 8 mm cameras sit and 1:2 is around where I’m seeing 35 mm kit lenses. The F-stop ring controls an adjustable aperture, and the numbers correspond to that ratio. So that 1:2 kit lens is only 1:2 at the F2 setting, and becomes 1:16 at the F16 setting.

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The Short Workbench

March 13, 2024 by Al Williams 36 Comments

Imagine an electronics lab. If you grew up in the age of tubes, you might envision a room full of heavy large equipment. Even if you grew up in the latter part of the last century, your idea might be a fairly large workbench with giant boxes full of blinking lights. These days, you can do everything in one little box connected to a PC. Somehow, though, it doesn’t quite feel right. Besides, you might be using your computer for something else.

I’m fortunate in that I have a good-sized workspace in a separate building. My main bench has an oscilloscope, several power supplies, a function generator, a bench meter, and at least two counters. But I also have an office in the house, and sometimes I just want to do something there, but I don’t have a lot of space. I finally found a very workable solution that fits on a credenza and takes just around 14 inches of linear space.

How?

How can I pack the whole thing in 14 inches? The trick is to use only two boxes, but they need to be devices that can do a lot. The latest generation of oscilloscopes are quite small. My scope of choice is a Rigol DHO900, although there are other similar-sized scopes out there.

If you’ve only seen these in pictures, it is hard to realize how much smaller they are than the usual scopes. They should put a banana in the pictures for scale. The scope is about 10.5″ wide (265 mm and change). It is also razor thin: 3″ or 77 mm. For comparison, that’s about an inch and a half narrower and nearly half the width of a DS1052E, which has a smaller screen and only two channels.

If you get the scope tricked out, you’ve just crammed a bunch of features into that small space. Of course, you have a scope and a spectrum analyzer. You can use the thing as a voltmeter, but it isn’t the primary meter on the bench. If you spend a few extra dollars, you can also get a function generator and logic analyzer built-in. Tip: the scope doesn’t come with the logic analyzer probes, and they are pricey. However, you can find clones of them in the usual places that are very inexpensive and work fine.

There are plenty of reviews of this and similar scopes around, so I won’t talk anymore about it. The biggest problem is where to park all the probes. Continue reading “The Short Workbench” →

Retro Gadgets: Pay TV In The 1960s

March 8, 2024 by Al Williams 20 Comments

These days, paying for TV programming is a fact of life. You pay your cable company or some streaming service and the only question is do you want Apple TV and Hulu or would you rather switch one out for NetFlix? But back in the 1960s, paying for TV seemed unthinkable and was quite controversial. Cable TV systems were rare, and the airwaves were a public resource, so allowing someone to charge to watch TV on the public airwaves was hard to imagine. That was the backdrop behind the Telemeter — an early attempt to monetize TV programming that was more like a pay phone than a modern streaming service.

[Lothar Stern] wrote about the device in the November 1959 issue of Popular Mechanics (see page 220). The device looked like a radio that sat on top of your TV. It added a whopping three pay-TV channels, and inside was a coin box, and — no kidding — a tape punch or recorder. These three channels were carried from a Telemeter studio over what appears to be a dedicated cable strung on existing phone poles.

Of course, TVs with coin boxes were nothing new. But those TVs were found in public places, airports, and hotels. The money was simply to turn the TV on for a set amount of time. This was different. A set-top box unscrambled channels delivered over a dedicated cable. Seems like old hat today, but a revolutionary idea in 1959.

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Stacking Solar Cells Is A Neat Trick To Maximise Efficiency

March 7, 2024 by Lewin Day 51 Comments

Solar power is already cheap and effective, and it’s taking on a larger role in supplying energy needs all over the world. The thing about humanity, though, is that we always want more! Too much, you say? It’s never enough!

The problem is that the sun only outputs so much energy per unit of area on Earth, and solar cells can only be so efficient thanks to some fundamental physical limits. However, there’s a way to get around that—with the magic of tandem solar cells!

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Walking And Talking Through The UK National Museum Of Computing

March 5, 2024 by Dave Rowntree 17 Comments

I found myself in Milton Keynes, UK, a little while ago, with a few hours to spare. What could I do but rock over to the National Museum of Computing and make a nuisance of myself? I have visited many times, but this time, I was armed with a voice recorder and a mission to talk to everybody who didn’t run away fast enough. There is so much to see and do, that what follows is a somewhat truncated whistle-stop tour to give you, the dear readers, a flavour of what other exhibits you can find once you’ve taken in the usual sights of the Colossus and the other famous early machines.

A VT01 terminal showing "the adventure" game running — Click this image to play in your browser.

We expect you’ve heard of the classic text adventure game Zork. Well before that, there was the ingeniously titled “Adventure”, which is reported to be the first ‘interactive fiction’ text adventure game. Created initially by [Will Crowther], who at the time was a keen cave explorer and D & D player, and also the guy responsible for the firmware of the original Arpanet routers, the game contains details of the cave systems of Mammoth and Flint Ridge in Kentucky.

The first version was a text-based simulation of moving around the cave system, and after a while of its release onto the fledgling internet, it was picked up and extended by [Don Woods], and the rest is history. If you want to read more, the excellent site by [Rick Adams] is a great resource that lets you play along in your browser. Just watch out for the dwarfs. (Editor’s note: “plugh“.) During my visit, I believe the software was running on the room-sized ICL2966 via a VT01 terminal, but feel free to correct me, as I can’t find any information to the contrary.

A little further around the same room as the ICL system, there is a real rarity: a Marconi TAC or Transistorised Automatic Computer. This four-cabinet minicomputer was designed in the late 1950s as a ‘fast real-time computer’, is one of only five made, and this example was initially installed at Wylfa nuclear power station in Anglesey, intended as a monitoring and alarm system controller. These two machines were spare units for the three built for the Swedish air defence system, which were no longer required. Commissioned in 1968, this TAC ran continuously until 2004, which could make it one the longest continuously running computers in the world. The TAC has 4 kwords of 20-bit core memory, a paper tape reader for program loading and a magnetic drum storage memory. Unusually, for this period, the TAC has a micro-coded CISC architecture, utilising a whole cabinet worth of diode-matrix ROM boards to code the instruction set. This enabled the TAC to have a customizable instruction set. As standard, the TAC shipped with trigonometric and other transcendental functions as individual instructions. This strategy minimized the program size and allowed more complex programs to fit in the memory.

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Big Chemistry: Hydrofluoric Acid

February 27, 2024 by Dan Maloney 32 Comments

For all of the semiconductor industry’s legendary reputation for cleanliness, the actual processes that go into making chips use some of the nastiest stuff imaginable. Silicon ~~oxide is~~ comes from nothing but boring old sand, and once it’s turned into ultrapure crystals and sliced into wafers, it still doesn’t do much. Making it into working circuits requires dopants like phosphorous and boron to give the silicon the proper semiconductor properties. But even then, a doped wafer doesn’t do much until an insulating layer of silicon dioxide is added and the unwanted bits are etched away. That’s a tall order, though; silicon dioxide is notoriously tough stuff, largely unreactive and therefore resistant to most chemicals. Only one substance will do the job: hydrofluoric acid, or HFA.

HFA has a bad reputation, and deservedly so, notwithstanding its somewhat overwrought treatment by Hollywood. It’s corrosive to just about everything, it’s extremely toxic, and if enough of it gets on your skin it’ll kill you slowly and leave you in agony the entire time. But it’s also absolutely necessary to make everything from pharmaceuticals to cookware, and it takes some big chemistry to do it safely and cheaply.

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Ask Hackaday: What If You Did Have A Room Temperature Superconductor?

February 26, 2024 by Al Williams 80 Comments

The news doesn’t go long without some kind of superconductor announcement these days. Unfortunately, these come in several categories: materials that require warmer temperatures than previous materials but still require cryogenic cooling, materials that require very high pressures, or materials that, on closer examination, aren’t really superconductors. But it is clear the holy grail is a superconducting material that works at reasonable temperatures in ambient temperature. Most people call that a room-temperature superconductor, but the reality is you really want an “ordinary temperature and pressure superconductor,” but that’s a mouthful.

In the Hackaday bunker, we’ve been kicking around what we will do when the day comes that someone nails it. It isn’t like we have a bunch of unfinished projects that we need superconductors to complete. Other than making it easier to float magnets, what are we going to do with a room-temperature superconductor? Continue reading “Ask Hackaday: What If You Did Have A Room Temperature Superconductor?” →