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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Lithium-Ion Batteries Power Your Devboards Easily

March 14, 2024 by Arya Voronova 25 Comments

Last summer, I was hanging out with a friend from Netherlands for a week, and in the middle of that week, we decided to go on a 20 km bike trip to a nearby beach. Problem? We wanted to chat throughout the trip, but the wind noise was loud, and screaming at each other while cycling wouldn’t have been fun. I had some walkie-talkie software in mind, but only a single battery-powered Pi in my possession. So, I went into my workshop room, and half an hour later, walked out with a Pi Zero wrapped in a few cables.

I wish I could tell you that it worked out wonders. The Zero didn’t have enough CPU power, I only had single-core ones spare, and the software I had in mind would start to badly stutter every time we tried to run it in bidirectional mode. But the battery power solution was fantastic. If you need your hack to go mobile, read on.

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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” →

On An Aging Space Station, Air Leaks Become Routine

March 11, 2024 by Tom Nardi 41 Comments

Anyone who’s ever owned an older car will know the feeling: the nagging worry at the back of your mind that today might be the day that something important actually stops working. Oh, it’s not the little problems that bother you: the rips in the seats, the buzz out of the rear speakers, and that slow oil leak that might have annoyed you at first, but eventually just blend into the background. So long as the car starts and can get you from point A to B, you can accept the sub-optimal performance that inevitably comes with age. Someday the day will come when you can no longer ignore the mounting issues and you’ll have to get a new vehicle, but today isn’t that day.

Looking at developments over the last few years one could argue that the International Space Station, while quite a bit more advanced and costly than the old beater parked in your driveway, is entering a similar phase of its lifecycle. The first modules of the sprawling orbital complex were launched all the way back in 1998, and had a design lifetime of just 15 years. But with no major failures and the Station’s overall condition remaining stable, both NASA and Russia’s Roscosmos space agency have agreed to several mission extensions. The current agreement will see crews living and working aboard the Station until 2030, but as recently as January, NASA and Roscosmos officials were quoted as saying a further extension isn’t out of the question.

Still, there’s no debating that the ISS isn’t in the same shape it was when construction was formally completed in 2011. A perfect case in point: the fact that the rate of air leaking out of the Russian side of the complex has recently doubled is being treated as little more than a minor annoyance, as mission planners know what the problem is and how to minimize the impact is has on Station operations.

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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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Dial-Up Is Still, Just Barely, A Thing

March 6, 2024 by Lewin Day 97 Comments

In an era dominated by broadband and wireless cellular networks, it might come as a surprise to many that dial-up internet services still exist in the United States. This persistence is not a mere relic of nostalgia — but a testament to the diverse and uneven nature of internet infrastructure across the country.

Yes, dial-up internet, with those screechy, crackly tones, remains a useful tool in areas where modern, high-speed internet services are either unaffordable or unavailable. Subscriber numbers are tiny, but some plough on and access the Internet by the old ways, not the new.

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