Discoveries in the Physics & Astronomy shop | Science, curiosities, and surprises
It can be a real pleasure to find old objects lying around, with their dates of acquisition marked on the side. January 29th, ’09!
Which ’09, exactly?
Olin Science Building was constructed in 1954, so it’s doubtful this particular post holder dates back to 1909. Especially as the lettering on both sides matches up.
So we were still purchasing equipment for the old, cast-iron optics rails as recently as 15 years ago? Wow.
Much of our day revolves around the Physics and Astronomy labs in Olin Science Building, which was the finest construction the budget could shoulder in 1954.
Which, after 7 decades, some renovations, and who knows what else, means there are a few minor holes here and there.
Holes which act like a pinhole camera in an otherwise dark lab, casting images of the sun and tree branches on the floor.
Simple. Effective. Does what it says on the tin.
Who can argue with that?
For the most part, the light accumulation of dust, pollen, and other stuff on the objective lens of your telescope is a thing you live with and ignore. The damage you can do to the lens and its optical coatings is far more severe than the minor loss of image quality from tiny flecks. Known and accepted trade-off.
Here, however, we have a classic TeleVue Renaissance that’s still in good shape. Aside from the dust and dead spiders, anyway. Exact age is unclear, but we can roughly place it between TeleVue’s founding in 1977 and the construction of the “Halley’s Comet” models in 1985. Serial number 1100, for anyone keeping track at home. Even dust-covered, the optics appear good at a quick glance, and they have a reputation for remaining in good shape for a long time.
There’s a bit of chromatic aberration when you look closely, an issue which has been resolved in their current models. (Optics = hard.) The design type is called a Nagler-Petzval, which uses a pair of lens doublets to correct numerous distortions caused by refraction. Every design has its pros and cons; this one’s quite nice. Our version has – we think – an air-spaced doublet (two lenses utilizing different curvatures) as the objective, and a cemented doublet in the rear.
At least, that how the Halley’s Comet edition was made. The current optics update utilizes two air-spaced doublets – see the diagram for the NP101is – so it’s reassuring to see that the improvements are incremental. Good sign for the one we have.
Okay, the brass could’ve aged better, but it’s got character!
Black on brass looks good.
Even the knurled knobs on the focuser are brass. We don’t want to leave this for display, however. We want to see the stars!
That dust, though.
Yeah, definitely a problem. A cleaning is in order.
Not pictured: the dead spiders removed with air from a bulb blower. Dead spiders do not improve optical quality.
Here, we’re applying a coat of First Contact polymer cleaner, an expensive but effective treatment for safely removing gunk from precision optics. Comes in a wee bottle like it’s nail polish and smell like nail polish remover. Because it’s got acetone and other solvents in it.
Once it dries, that little tab lets us pull away the pink film with all of the dust and debris stuck in it. A good time to wander away from the stink of volatile solvents and get a cup of coffee.
And, well, that’s a substantial improvement.
It’s not perfect. The polymer is very good at removing particulates, but less so at water-soluble stuff. Once we evaluate this with a camera setup, we can see if a follow-up cleaning with deionized water is necessary.
Problem there, of course, is that we run the risk of introducing tiny scratches in the process. Could be worthwhile if the effects are still visible, but we’re still erring on the “do a minimum of harm” side of things.
Will it live up to its potential as an imaging ‘scope? Maybe. There’s a fair chance. If not, we’ll keep it around as a stylish yet usable throwback for visual observation. The best telescope, as they say, is the one you use.
It’s not just telescopes at the Observatory. We also have a spyglass. What’s the difference?
There are a variety of potential optics for a telescope, using reflectors to reflect and focus light, using refractive lenses to bend and focus light, using mirrors to turn a beam around corners, using these in combination. Each has its pros and cons, and careful optical design and precise manufacturing work to gather lots of light, to provide good resolution and magnification, and to correct for optical aberrations.
And in doing all of that, the image reaching your eye or the camera sensor gets flipped upside down. Also in reverse, if you’ve got a mirror in your optical train. When looking at stars and deep sky objects, that’s not a big deal. “Up” is arbitrary in space. For terrestrial viewing, however, up matters. Seeing that incoming pirate ship upside down is disorienting. So a good spyglass keeps up as up.
It does so by using a Galilean refractor design, which has a concave lens in the optical assembly to avoid the upside-down flip. The resulting telescope is necessarily longer than a comparable refractor with convex lenses, and thus heavier. That weight tends to limit the possible objective aperture size, and the practical magnification limits are low. Still: very effective for spotting Edward Teach at a distance, or for identifying the four largest moons of Jupiter.
Binoculars, incidentally, manage to keep the world upright thanks to a set of prisms between the objective lenses and the eyepieces. Yet another handy trick in the optical design toolkit.
Sometimes, we have old equipment which is rarely, if ever used. Case in point: the mid-20th-century spectroscopes which have been supplanted by digital spectrometers. They’re both effective tools for examining a spectrum of light, one by eye and the other fed by a USB cable. Using a diffraction grating, they split light into its constituent spectrum – its rainbow, more or less – and can identify the presence of individual wavelengths. Not something our eyes can do, as they blend everything together, though that’s very helpful in most situations, such as reading this on your screen.
Summing bands of reddish, greenish, and bluish into a broad rainbow of colors is one neat-o trick.
With a diffraction grating, reflection grating, or prism, you can refract light out along a range of angles which correspond to its constituent wavelengths. Put a sensor at a known angle – your eye or a semiconductor exhibiting the photoelectric effect – and you know the wavelength if you sense a photon. It’s a simple piece of information which can be used to unlock a staggering amount of interesting, related information about what you’re observing.
You can also use a diffraction grating to get a quick sense of the entire visible spectrum of a source by holding it off to the side. Remember: the angle of the light’s path change as it refracts, so you’re trying to angle it back to your eye. Hydrogen has a distinctly pinkish-purplish hue when excited at high voltage, and you can see the dominant red and blue lines in its spectrum. With just that one electron to absorb energy and emit photons, the spectrum can only be so complicated.
That’s in contrast to helium, with its two electrons. The spectrum doesn’t look white, per se, but is much more filled out than hydrogen. Look at those spectral lines, and there are so many more! They’re distinct, measurable, and provide a “fingerprint” that can be immensely useful for scientific study. Or for just looking cool.
Our old iron optics rails get very little use anymore, as we phase them and their accessories out. Most of them, that is.
We may not use the old glass lenses much – sometimes, not often – but the spring-loaded holders still come out from time to time. They grip certain oddly-shaped objects well, and their heavy iron bases do an excellent job of keeping things like fiber optic cables upright and in place.
Rapidly approaching 60 years old, lens holder. April 1963, $6.25. That’s $61.31 in today’s dollars.
We field a lot of requests for small objects in the shop these days. It’s not that there aren’t plenty of big/huge/enormous things worthy of serious research and scholarship (see: stars), but physics sometimes gets wild when you go small. And not even quantum mechanics small… that’s where calling physics not intuitive doesn’t even begin to cover it.
We’re talking channels and structures where 100 microns makes a difference. A micron, or micrometer, is one-thousandth of a millimeter; 100 of them is a tenth of a millimeter. In the general ballpark of the width of a human hair. It’s the scale where you learn the finer points of a tool’s tolerances, where you set a machine to do the work and wait until it’s all finished to figure out if it worked.
Mistakes happen.
Very tiny things also defy your eyes’ ability to inspect them, so we rely on microscopes and other optical magnifiers to check on the quality of work. One of the handiest is the magnifier shown above, a Bausch + Lomb Hastings Measuring Magnifier. It uses a Hastings triplet lens system, composed of three separate glass lenses bonded into a single, composite lens. Doing so produces crisp, distinct images without distortion. At the end it has a scale, so that we can press it against an object to inspect and actually measure features less than a millimeter across!
One of the best features of this magnifier is its portability. At 7X magnification, it’s less powerful than a microscope, but its case fits in a pocket, so it can go anywhere. Clear plastic sides admit plenty of ambient light, removing the need for additional illumination that a microscope requires. You simply pick it up, inspect your object, and carry on. Confirm that microfluidics channels are the proper width. Ensure that you’ve cleaned all the swarf away from tiny features. Examine tools up close for minor damage to their edges.
Or check out the tiny world all around you, just because you can. Some of the best science starts with noticing something neat, and just digging deeper.