I Want to See the Sun III (Not) Unfiltered

I Want to See the Sun III (Not) Unfiltered

Here Phaeton lies, in Phoebus' car...

-Ovid

Here is a photo I took of the solar flares (upper right) shooting off the sun and into space. I used a cheap cellphone held up to the eyepiece of a Coronado PST...but we'll get to that later in this post.

We're going to explore the methods I've used over the past couple years to stare directly at the sun. We'll start with the simplest and cheapest and work our way up.

The easiest is to just look up and stare at the sun with bare eyes. This is a fantastically bad idea invented by the ancients. Galileo went blind from doing this.

Here is a picture of a sun dog (aka parhelion) false sun I took on 5/11/2017 in Michigan. Somewhere on this blog I have a better, earlier photo.

This particular sun dog looks like a rainbow. One time I saw a sun dog (aka False Sun) in which there appeared to be 3 suns in a row! The middle sun was the real one. All three suns were identical in shape (round) and brightness (bright as the sun). It was very weird and made me research what the heck was happening: sun dog aka false sun(s) aka parhelion aka mock sun(s).

Another terrible idea: Above is a green glass "Sun" filter. It screws onto the end of the eyepiece that goes into the telescope and gives nice crisp images of the sun that are tinted green. This will  only let you see sunspots, like in the photo below:

The photo is a tag blurry, but that's not the sun filter's fault, just bad focus. The little dot is a sunspot. The edge of the sun on the left side is crisp. These filters are really cool and come free with many old Tasco garage sale telescopes, but they have some serious drawbacks.

Walking around a church widdershins (against the sun / counterclockwise is considered unlucky or dangerous in Britain, but not in Eastern Orthodoxy.

They are usually found to fit small, 0.965" cheap eyepieces. A couple posts ago I detailed the problem with using these smaller, not so great eyepieces. Because this filter screws onto the eyepiece the burning hot sunlight has to enter your telescope Unfiltered until it hits this filter, which is about an inch from your eyeball. This works ok with really small (weaker) telescopes, but larger telescopes or any telescope using a mirror (reflector) will burst into flames if you point it at the sun, no matter of you have this filter in place or not! The sunlight is only filters for the last inch before it hits your eye, the rest of the time it's melting things in your telescope.

Another problem is that these glass filters have a habit of heating up and shattering! You'll be treated to flying glass and full, magnified sunlight blasting into your eye. They don't seem to sell these anymore, i got mine free from a friend. If you're smart you can use them relatively safely...except that they are not labeled as to manufacturer so they're mystery material. Some are 13 welder's glass but some might be a different version, some are just green glass, some are even cheap plastic. Never use these!

Beyond catastrophic failure of the glass, the most common injury is that while the light coming through the eyepiece is filtered, the light going through your little aiming/spotting scope isn't. People routinely burn their cheeks or set the shoulder of their shirts on fire. The spotting scope magnifies the sunlight. Leave the cap on the front of your spotting scope! Or take it off entirely.

Smaller telescopes and binoculars can be pointed at the sun and instead of shoving you're eye up to the eyepiece you can hold a piece of paper a few inches away from where your eye would normally be. This will project an image of the sun onto the paper. However, you can end up overheating and melting parts of the telescope or binoculars. Some cheap (and some super expensive) telescope eyepieces are epoxied together and may come unglued from the heat-and I wouldn't want to try this with and nice eyepieces. Strictly garage sale finds for the solar projection method.

The next step up in price (less than $30) is solar film i picked up cheap online from Draco Productions. It's made by Baader (make sure you get the film for in front of telescopes and NOT the naked eye version). It's available elsewhere, but Draco was cheap and shipped fast:

The tiny dot showing through the film is the sun...but this is NOT made for naked eye viewing.  If you hold this up to one side of a pair of binoculars (left eye side, held in front of the binoculars) remember to leave the cap on the other (right eye side) or else your left eye will be treated to a beautiful view of the sun while your right eyeball/eye-lid will be melted off your face! People forget, think before you do-your eyes depend on it!

In the above photos you can see the silvery solar film. It's over the objective end of the telescope which gets pointed at the sky: all of the sunlight has to pass through the filter before entering the telescope. It comes in squares and you make a round cardboard frame to stick on the end of your telescope or camera or binoculars. Everything is nice and cool and safe, just as long as you secure it strongly so the wind doesn't blow it off.

So, your can use this on bigger/better telescopes with any eyepiece that fits the telescope (1.25" and 2" eyepieces), not just the puny 0.965 eyepieces. Solar film can be held up to your camera, binoculars, cellphone or camera.. The green glass filter only screws onto toy-quality 0.965" eyepieces and is off unknown safety. Solar film is safer, and more versatile with slightly more surface detail.

As you can see, the silver foil is almost as wide as the opening of the telescope. This is actually too much. There should be a wider cardboard frame and less silver. That's a 3.5" diameter silver circle, or should be 2". This will let less light into the telescope which means less internal glare and less heat. If your telescope has a secondary mirror centered in the objective end, make the hole in the cardboard off-center. You'll have a big cardboard circle with a small silver circle not centered.

The photo below shows my bigger telescope with a bigger mask (and smaller filter letting in less light). To the extreme left edge there is a big plastic cover over the 8" telescope with a tiny cut out showing silver. Ignore the silver camera and lens at the center of the photo, it's the little circle on the budget one almost touching the middle of the left edge of the photo:

Your Reflector mirror telescope won't mind an off-center hole, because the spider 90 degree mirror blocks the center of the telescope. Your view will also have more contrast! With the light gathering power of my 8" telescope I used the plastic end cap with a small hole cut in it (as shown in the above photo) which tones down the internal light reflections. This beast of a telescope is made to grab all the light it can from dim deep-space objects-firehosing (even the filtered) fury of the sun down it is a case of less is more!

So, what do you see? Again, only sunspots and associated phenomena.

Here's a picture using the above telescope with solar film, set up just light it's shown. You can see 9 sunspots. Sunspots are almost always in pairs and have magnetic interactions with each other, but as you can see the highest one near the center of the sun is all alone! Neat.

You'll also notice the sun is white, not green. That's less annoying and also let's more fine detail be resolved by the human eye.

What else can you see with these simple two filter systems? Well, if you pop in more powerful (smaller number in millimeters) eyepieces you can zoom in and see light and dark structures in and around the sunspots and of you get the size of the filter (smaller is better) just right some orange-peel solar surface may be visible. Light grey surface with slightly lighter grey wisps. Anything else? Oh, you better believe it! How about the silhouette of anything that gets between your telescope and the sun: airplanes, satellites, the International Space Station and even planets like Venus. Venus? Yep, here's my photo of the planet Venus passing between the sun and the earth:

Venus is the big dot at the bottom. I took this photo of the Transit of Venus on June 5th, 2012 (my best friend's birthday-the same friend who gave me the green glass filter and a pile of telescopes). Toward the top you can see some sunspots too. Venus is about 84% the size of earth, the only reason it looks even as big as it does is because it's close to us-like how you can take your tiny thumb and block the sun with it.

While tracking Venus moving across the sun I also did my first act of "sidewalk astronomy". This is where astronomers set up a telescope in a weird place, like the middle of the sidewalk and give free views to anyone passing by. It's usually at night of course. I had my solar freak-show set up obviously while the sun was out on the middle of the afternoon, one of my neighbors came by and I gave an explanation and a free peak at a cool event. I'm extremely shy, but I was happy for the company while self-consciously operating this weird silver foil contraption.


What's the next method? Well, you can get a 90° eyepiece holder with a fancy (super expensive) glass filter called a Herschel Wedge. In addition to practically inventing or vastly improving many forms of photography (including astrophotography) he was a great astronomer not only on observing (he named a bunch of moons of Uranus and Saturn) he solved technical problems such as: how can we stare at the sun without going blind like Galileo did? He made a special prism (wedge) and added polarizing filters around it. They're cool (but blast out heat by diverting around 95% of the sunlight), pricey and only good for use with refractor (lenses, not mirrors) telescopes. The glass of the prism messes with the light waves and as mentioned in my previous post, reflector telescope mirrors focus all light at the same point, not different points like lenses.

I opted not to go the Herschel Wedge route since my best telescopes are not refractors. So, what did I do? I bought a really expensive refractors telescope-that can only be pointed at the sun! Didn't expect that did you?

I had been thinking for about a year over a solar telescope. I noticed that at almost all the websites the price of the model I wanted jumped up by more than $100! It was now or never, so clicked over to Amazon, which hadn't raised their price yet and I purchased my very own Coronado PST (personal telescope):

It's a strange beast indeed. My new solar telescope, was worth the wait and expense. Its manufacturing tolerances are 4 times tighter than the Hubble telescope's were. It uses a Fabry–Pérot interferometer / etalon to dump out light and get only 656nm wavelength light to the eye, which is the hydrogen-alpha band of the sun. It's plus or minus 1/10 of a nanometer. The upgrade to make it plus or minus 5/100 of a nanometer would have added almost $2000 to the price (I'm happy with what I got).

So, what does this method do? In addition to sunspots, surface orange-peel wisps and other details the Coronado PST let's you see huge solar flares blasting off the surface of the sun into space. You can also refocus and see an extremely pronounced alligator-skin surface which also shows black lines of cooler areas of the sun. Here's some of my quick snapshots (the real view is much crisper):

That little spike shooting up off the upper right edge of the sun is actually a geyser of fire as tall as two planet earths stacked on top of each other!!!!

These are probably the worst photos I've taken in my life, but when I'm using my PST I just can't be bothered with taking photos. I just get memorized by the awesomeness! 

Here's a review I wrote for the Coronado PST:


THE SHORTER REVIEW/QUICK SETUP GUIDE

Mount on camera tripod. 

Aim at sun.

Lefty-loosey the big tuning ring where the gold tube attaches to the black box until the sun looks like a reasonably crisp circle and not fuzzy.

Adjust the little focus knob at the back bottom of the black box until you can see details (either sunspots, orange peel surface of sun or huge spikey solar flare prominences).

Then slightly adjust the big ring again until you can SEE THEM ALL AT THE SAME TIME.

Yes, using the this scope you can see sunspots, flares and surface detail all at once. There was even a crazy `fault line' of dark red running almost the entire diameter of the sun's surface.

Fiddle with the little focus knob if needed. That's it!

THE LONGER REVIEW
Unboxing must be done carefully since the foam grabs this telescope insanely tight. Be careful you don't break the plastic (nylon) eyepiece thumbscrew. Some people complained that this screw was plastic-but that's a good design feature since it won't scratch, ding or dent your eyepieces. In fact an upgrade on some telescopes costing way more is to throw out the metal thumbscrew and put in a plastic one. It's a good thing to have. Some people have five or six hundred dollar eyepieces that they don't want marred by metal-on-metal contact.

The telescope is extremely heavy compared to its size. The black box is only two pieces: a milled out brick and a cover milled from the same brick of metal. This is very solid and nicely done.

Mounting is easy since there are two holes in the bottom of the black box that can each accept a standard camera tripod screw. Easy.
The eyepiece that comes with the telescope is just a silver plossl, nothing special. It's actually not bad at all except for the fact that it's a relatively weak (magnification-wise) 20mm which gives you a view of the entire disk of the sun and lots of black space around it. I suppose this low power makes it easier to find the sun.

Finding the sun: if you put your hand near the front of the telescope (like when you're adjusting the big ring) you can block the solar sun-finder. You can waste a lot of time panning around with the sun finder blocked. The sun finder uses a hole in the front of the black box--it doesn't use actual telescope to get the image of the sun. If you block the whole with your hand (or part of your tripod) you will never see the sun in the sun finder. ALSO, since the sun finder uses a small hole and not the main telescope-it works EVEN WHEN THE DUST CAP is on the main telescope. I have to admit that was pretty embarrassing. A perfectly centered bright sun dot in the sun finder on the top of the black box just gets you close, you'll still have to center the sun by panning the scope a little.

Focusing: this telescope has a big ring (tuning ring that is between the black box and the gold tube) and a small focus knob. The eyepieces don't rack in or out like on most telescopes. Because of this can supposedly make getting some eyepieces to focus hard or even impossible. I had no trouble using three different eyepieces before the clouds came out and ruined my fun. At first I was scared because the sun just looked like a dark red blurry blob: just like those awful youtube videos that don't do this telescope justice.

Lefty-loosey almost to where the big tuning ring stops is where I ened up. That gives a solar disk that is red and pretty crisp at the edge. Then I turned the little knob sorta in the middle? Not sure but keep at it, it was like 10 turns and then a sun spot seemed to appear and darken out of nowhere, I turned a little more and the sunspot resolved into light and dark portions with fine detail while at the same time prominences (spikes) appeared and lots and lots of surface orange peel, crackle-effect and even a long `fault-line' looking thing that was almost the entire diameter of the sun!!!!!!!! The longest part was dialing the telescope in using the ring and the knob--after that it was smooth sailing.

Eyepieces: the included 20mm plossl isn't bad at all. It's just low power. I could see sunspots which showed black and lighter grey areas. This was the same but crisper than what I could see using Baader Solar film. I could see an incredibly sharp orange peel effect all over the surface of the sun that looked like alligator skin! The photos online that you find do not do the orange peel effect any justice at all: it is insanely cool to look at and very well defined, like a crackle-paint effect. Prominences on the limb looked like geysers of flames spitting out into the black of space. There were four or five on 10/24/2014 that were awesome. There wasn't too much detail using the included 20mm eyepiece for the prominences but only because the magnification was low. So I popped in a higher magnification eyepiece.

I tried a 9mm plossl eyepiece that came free with my Zhumell Z8 reflector telescope. The lower the mm number the higher the magnification is in telescopes. The 9mm no-name brand gave better magnification and maintained almost all the brightness and all detail of the 20mm eyepiece. Awesome, I didn't view too long because I wanted to try another eyepiece. I was really just testing whether they'd come to focus or not, but the views remained awesome. Also, I believe I still had a view of the entire disk of the sun: only with a lot less black space around it and more `zoomed' in.

UPDATE: I also tried a Zhumell 9mm Planetary eyepiece. With its 55 degree field of view the entire sun was still visible (just barely). I then added a 1.25" 2x Barlow (a celestron #93640) which makes this eyepiece into a 4.5mm eyepiece. This made me have to re-focus using the little knob on the bottom/rear of the black box. It took about 8 or 10 turns of the knob to bring to focus and the view was more magnified ("more zoomed in" as newbies say). It was much crisper in focus and brighter than the 3mm (see below) that I tried. BTW: if you click "see my other reviews" on page 5 is my review of the Celestron T Adapter/2x Barlow, which is a pretty useful piece of equipment to have for various reasons besides just 2x your eyepiece collection.

At 40mm aperture the PST only can take about 94x magnification {40mm = 1.5748" x 60 = 94x useful magnification in perfect conditions. 400mm f/length pst + 4.5mm eyepiece = 88x magnification so this is pretty close).
It's a balancing act on the higher powered eyepieces before everything is just "more zoomed in blurry dark garbage", at any rate a 4.5mm will always look better than a 3mm all things being equal. The 4.5mm was a lot better than the 3mm (below) so if you have a 9mm maybe try a 2x barlow than buying another eyepiece.

I tried a 3mm Zhumell Planetary eyepiece. These are long and heavy, not like the cheap plossls. The view was dimmer and I felt that I could focus okay--but the view was dimmer and softer (blurrier) but THAT IS THE EYEPIECE and what happens when you put in higher magnification eyepieces in any telescope. The lower the Xmm number the: higher the magnification but the blurrier and darker the image. Fact of physics, but also the fact that it is a forty dollar eyepiece and not a six hundred dollar one. Anyway, I was pleased with these three eyepieces. It was here that the clouds rolled in-while I was fiddling with the little focus knob trying to get the 3mm sharper. In the PST (400mm f/length) the 3mm eyepiece yeields 133x magnification which is way more than the theoretical limit of 94x for this telescope. It's "empty magnification" which means darker and blurrier, but it still was neat. The point here is: if you have no other eyepieces, a 4mm would be a much better buy than a 3mm for THIS particular telescope. A 4mm eyepiece would produce 100x in this telescope--close enough to the 94x limit.

I suppose one might fiddle with the little focus knob AND the big tuning ring when changing from eyepiece to eyepiece.

What do you see? A deep red sun disk with lighter red crackle effect and black and grey sunspots surrounded by the jet black of space being pierced by deep red spikey prominences spouting off the surface.
Totally worth it! All you need is this telescope and a photographic tripod. You might want more powerful eyepieces to zoom in more. Possibly a 4mm / 5mm and maybe a 9mm / 10mm would give you a nice range of low (20mm that comes with this scope), medium and high power magnification.

Also, anything you can stick your eyeball up to and see through you can stick a camera or cell phone up to and photograph. Search "afocal astrophotography" for various cheap and easy methods. I took no photos because I was so happy and stunned at what I saw that the clouds rolled in on me. Forecast is for clouds and rain.

The sunspots looked much like when using my Baader solar film. The surface detail is way more than I expected. The prominences are awesome as well: they only way to see 99% of the surface detail and any prominences are to use a Hydrogen-Alpha telescope like this. Solar films don't let you prominences at all and only a vague hint at the insane orange-peel effect and what I call "fault-line" activity of the surface.
After researching this product for over a year, I have never been so nervous ordering and so happily surprised (immense surface detail and prominences and all at same time.

So, in summary:

Glass Filter: sunspots
Solar Film: more detailed sunspots and slight surface detail
Coronado PST: detailed sunspots, immensely detailed surface and solar flares shooting into space!

Glass Filter: leaves telescope unprotected, only fits some eyepieces, green sun, can shatter, might not filter UV! Don't use.

Solar Film: can fall off if windy, have to mount yourself. Buy the telescope version, not naked eye version. 

Coronado PST: expensive.

Here are some photos I took of the Transit of Mercury on May 9, 2016:

At some point I'll post about some devices I made myself that allow me to see the sunlight that cannot be seen: infrared!

Alright, you've convinced me to spend some of the two hours a day I'm awake staring at the sun...after my nap. Now go away. Meow.

See the Sun (Chromatically Abberated) Part II

I Want to See the Sun (Chromatically Abberated) Part II 

There is more to seeing than what meets the eyeball.

N. R. Hanson

Speaking of reducing chromatic abberation (in my last post) there is a device that actually increases it...on purpose! It's called a prism. We'll deal with sunlight, rather than the sun itself for now.

Here's a photo of an incredibly awesome prism that really separates the wavelengths of light really well. The craftsman that cut and wet sanded it is an incredible optician: me!

If the glass were perfectly, magically clear it wouldn't work as a prism. The differences in color absorption due to the refractive index, which in turn disperse the colors (breaks white light into a rainbow of its constituent colors). The speed of light changes in different media (air, water, glass) This is a dispersive prism.

If the surfaces are nicely polished and you blast a laser through it, it can act as a simple reflective prism. Lasers are a single wavelength and thus cannot be broken up into rainbows. They are one color only. 

Here's my same prism with a laser blasting through it. No dispersion-no rainbow. It does refract-changes directions at an angle. This is mathematically referred to using Snell's Law and Ray Tracing (computing the angles the laser will exit a prism, or a bunch of prisms and mirrors and lasers in a huge system like a knowing where the ball will go in a pinball machine before you fire it).

So pretty, but useless? Not by a longshot! 

In addition to aiming lasers (boring) you can use knowledge of dispersive refractive indices and wavelengths of light to investigate chemical properties of objects (and stars) you can see but not touch!

Above is a photo I took of a diffraction grating. It's a tiny, cheap $2 piece of plastic that disperses light. The white source light is at the top. The grating has zillions of tiny grooves that act like prisms. 

What is similar to that? A compact disk, which has zillions of pits in it that do the same thing. That's why you see a rainbow on the bottom of music CDs. So I took a CD and put it in a box with a tiny slit to let on light:

This my homemade spectroscope's readout from a fluorescent light bulb. Notice how there are lots of blank spaces in between the color lines? Newer light bulbs are more like the laser than sunlight: way fewer wavelengths to disperse. Here's the cooler part: see the green line? That corresponds to the element Mercury. We now have proven that this fluorescent light bulb contains Mercury in it! We didn't even have to cut it open or touch it at all. 

Astronomers point spectroscopes at stars to learn what elements are burning within them. Same exact principle.

Building a CD Spectroscope is easy. Here's a link to a nice set of instructions: https://www.cs.cmu.edu/~zhuxj/astro/html/spectrometer.html

Is there a way to take what we learned from the last post (PVC Telescope) and use it in spectroscopy? Yes, you can make a Slitless Spectrograph:

However, if you do the Ray Tracing in real life its not a straight line like my drawing above, it's like a downward curved line which is annoying to put into a box and more annoying to hook to a telescope which was my original purpose.

Anyway, I had so much fun with my homemade toys that I ordered a fancy store-bought Spectroscope from Amazon for all of $9 including postage. 

The readout was identical to the ones i made, except that it has a scale to show you the actual wavelengths (in nanometers). Fancy!

On the right you can see the white nanometers scale above the colors. This is pretty even with no black missing lines, so this was probably sunlight on a nice day with no clouds. 

Man has closed himself up till he sees all things

 through the narrow chinks of his cavern.

William Blake

The only difference between my free CD spectroscope, my $2 diffraction grating Spectroscope and my $9 spectroscope is that the $9 one had a nanometer scale. Same readout on all. 

Now, is there a device that melds spectroscopes with prisms? Yes. They're called prism spectrographs. They also make use of Snell's Law and Ray Tracing to get light to pass through a few (usually three) prisms.

In the above pic notice the trapezoid formed by 3 prisms smooshed together. The scribbling is me feebly trying to start figuring out what shape prisms I needed to grind. I wrote "Snell's Law" but it's just part of calculating total internal reflection. I wisely decided manual Ray Tracing would be easier: shine a laser through the prisms and see where it goes, which is what the red laser photo at the beginning of this post shows...so finally, for the first time in human history lasers actually did something useful: lasers kept me from having to calculate inverse trigonomic functions for the angles of incidence. 

As an aside, in not bothering with Snell's Law (named after a guy named Snellius but discovered by Ibn Sahl in the 900s) and playing with Ray Tracing I can also find and deal with any bits of light that doesn't confirm to Snell's Law. Specifically: Newton Rings!

Newton Rings are those weird rainbows that occur when you lay to almost flat pieces of glass on top of each other. They were of course discovered by one of my heroes...Robert Hooke. Isaac Newton played with them over half a century after Hooke wrote about them, so that's where the name comes from. That was almost exactly 300 years ago. The rainbows come from diffraction, not of the glass but because of tiny air pockets between the glass. Shown are two microscope slides I randomly selected: Rings! Actually these look more like wavy lines, but as I squeeze the lines move and change. Interference also plays a role: like throwing two rocks into a pond, the waves from each will eventually touch and mess with the patterns of each alone.

An even weirder aside: Hooke was the first to build a Gregorian Reflector Telescope. It was designed (by James Gregory) before another guy built a reflector telescope, but wasn't made until a little after the other guy did, which is why most reflector telescopes are now called Newtonian Reflectors. Yep, good old Issac cheated Hooke yet again! Gregorian telescopes still mostly survive in very nice, easy to design and build Schmidt-Cassegrain telescopes. Isaac Newton did invent calculus all by himself, or at least he claimed to have done so a few years after Gottfried Leibniz published a paper on the new math of calculus he (Leibniz) invented. In fact we still use Leibniz notations to this day!

Newton is often quoted, "If I have seen further it was because I was standing on the shoulders of giants." This would seem to be a fair acknowlegement and reconciliation-except that he ripped that quote off from Bernardus Carnotensis. Newton: pickpocket of science.

Is that all? Not by a long shot! In addition to identifying burning elements in laboratories and in stars you can do something else with a spectroscope. Calculate Radial Velocity! If an object space shows a slight increase in red wavelengths it is receding away from us, blue means it's floating towards us! Neat. It is the color wavelength version of The Doppler Effect for sound waves.  A passing police car's siren is high pitched when it's coming at you and then goes to a lower pitch (at least it seems to for you) as it passes.

As the car approaches and passes you standing still:
eeeeeeeeee-aaaaaaahhhh. 

To the police officer in the car the siren doesn't change pitch: eeeeeeeeeeeeeeeeeeeeeee.

Shhh...I'm analyzing the sunlight. Ten nanomices and rising-meow!

PVC Telescope: A Modular Optics Lab in a Tube!

PVC Telescope: A Modular Optics Lab in a Tube!

Reflector telescopes use mirrors, refractors use lenses. To make a reflector you precision grind a mirror, for a refractor you need to play with at least two lenses-more of you want color correcting and distortion minimizing qualities.

It's quite simple really. Light gets focused between two lenses: the main objective lens at the end of the tube that gets pointed into the sky and the eyepiece. However different colors of light are different wavelengths. Different wavelengths focus at different places. 

This makes your telescope into a prism: colorfully blurry!

When a nice focused green wavelengths falls perfectly on the eyepiece that means the red and blue waves are a little too in front of and too past the eyepiece to be on focus. This problem is called chromatic abberation and some really expensive refractor telescopes have it. It's something that you can: get used to; hate and buy a reflector (mirror) telescope; or pay even more money to correct. Adding additional lenses can bring the red and blue to the same focus point, this is called an achromatic len(s).

Now, to be clear "blurry" isn't exactly accurate as a description of chromatic abberation. The views is very crisp, but tripled slightly: you'd see the moon with a red moon slightly misaligned with a blue moon slightly misaligned with a yellow moon. All very crisp but distracting.

Many telescopes that are refractors (lenses not mirrors) show this tripled misalignment just along the edges of bright objects as color fringes and flares. Even really, really, really expensive refractors can have a little color fringing from chromatic abberation.

If you want to see chromatic abberation on your own just aim a pair of binoculars at an electrical power line hanging from a telephone pole. Of you hey just the line in focus with a bright, clear sky behind it you'll notice yellow and purple highlights along the edges of the line. Shiny highlights on the line may also have weird color aberrations. The better the optics, the less color fringing.

The glass of the lenses absorbs and passes light waves through at different rates. Reflector telescopes (mirror) bounce light off a mirror-the mirror reflects the light, but doesn't absorbs it. The light bounces and isn't passing through it so reflector telescopes don't have problems with chromatic abberation. 

I wanted to build a refractor of my own design that allowed me to swap different lenses in and out to experiment with correcting various flaws including chromatic abberation. A modular optics laboratory in a tube! I decided to use PVC and headrd to Home Depot with calipers, pad, pencil and a tape measure.

But first I needed a nice lens. I bought a cheap one for $7 on Amazon. It was an Ajax Scientific Polished Glass Bi-Convex Spherical Lens, 100mm Diameter 500mm Focal Length. Nice lens!

1x 3" PVC flat top cap (not the domed/rounded bubble top)

3x 3" PVC 3x3 repair couplings (that are smooth inside, not with an internal ridge)

1x 3" PVC 3"x2 foot foam core pipe

1x 4" PVC 4"x2 foot foam core pipe

A big objective lens

Wood saw to shorten both pipes (hack saws don't cut straight with PVC easily)

Telescope eyepiece or bi-convex lens or eyepiece from binoculars

Black spray paint

A big ring cutter drill bit to cut a hole for eyepiece or lens (.965", or 1.25", or 2" or whatever your focuser needs if you're using a focuser instead of just plunking an eyepiece into the hole in the end cap).

At Home Depot I bought a 4" PVC white pipe and painted the inside black to reduce glare and increase contrast. One insert (repair coupling) with hole in the center pushed in followed by this lens followed by another insert. These trap the lens in the tube.

Another insert with hole at other end of pipe allows a 3" PVC pipe to slide in and out to adjust focus. At the end of the 3" pipe pit a 3" end cap with a hole in it to hold an eyepiece of to fit a telescope rack focuser.

Extend the tubes for close focus like neighbor's house, push them in (shorten) for father focus like the sky, moon and stars. All with so much chromatic abberation they looked like a psychodelic Andy Warhol print! My first view was of a street light a couple blocks away. The abberation was so bad it looked like a bunch of multicolored poles barely touching, not merely "misaligned" slightly. 

Medium distance focus is about 20" from lens to eyepiece (focal length is 500mm f/5). So you'll have to cut the tubes to short lengths. This shows the effects of differing focal lengths on telescope designs: magnification (greater or less zoom with the same eyepiece), brightness (f-stop/speed) and field of view (wide angle).

The magnification (zoom-in) of a telescope equals its focal length divided by the focal length of whatever eyepiece you have in it. Every time you double the magnification you loselose 50% of the sharpness of focus and 25% of the brightness! 

If you're looking at something bright like a planet or the moon that's fine-but for faint nebulae and galaxies it might make you unable to even find your target in the sky. 

Useful magnification is twice the diameter of the objective (lens or mirror) in millimeters. 50mm lens x 2 = 100x top magnification.

1000mm focal length ÷ 100x = 10mm eyepiece needed.

Remember though: my design slides in and out so I can change my focal length slightly, but not my objective diameter (unless I swap out the front lens). I can change my magnification by changing eyepieces.

My telescope has a 100mm diameter objective lens. Twice 100mm equals 200x maximum magnification. 

Its 500mm focal length ÷ 200x desired magnification = 2.5mm eyepiece needed. Those are expensive, but I've got a wonderful 3mm eyepiece that gets me close enough. However, in my larger telescope that same eyepiece will give me 400x magnification! Everything effects everything else in the optical chain.

Too close...zoom out or claws out!

Once you've played with focal length and eyepieces you can add a concave lens in between to try and correct for chromatic aberration, etc. Alternatively you can use a double or bi-concave lens instead of an eyepiece. This is really a telescope laboratory in a conveniently simple modular package!

So less than ten bucks for the lens and about thirty-five for the pvc if you don't have it around the house compared to big bucks for a 4" refractor astrograph telescope (plus you'll have to scrounge up a focuser and maybe some other lenses to experiment with correction).

It's quite a large and heavy beast! 

Here it is mounted on top of a rather long, metal, 1970s Tasco. PVC is incredibly heavy, but if you take care and balance it well it moves easily. Even on a terrible mount. Tasco had the worst mounts in the business, but an even bigger tragedy were their eyepieces. They were the small 0.965" size and atrocious! 

I bought an adapter for $9 on Amazon that is a 90° elbow: one end fits into the 0.965" opening in the telescope; the other side has a 1.25" hole that accepts professional 1.25" eyepieces (but not 2" Diameter ones). If you have an old Tasco buy the adapter and some cheap 1.25" eyepieces and you'll be blown away! A 20mm, 12mm and 9mm are a fine set for most Tascos. The mount will still be criminally terrible: jerky, wobbly, prone to falling, etc.

I also took some old slide and film projector lenses and converted them to use as eyepieces. They have varying outside diameters so some had to be spun up on a metal lathe and smallerized, others were too narrow and needed tubing or duct tape wrapped around them for a snug fit.

You can find old lenses like this cheap or free all over the place. Even if you're using a store bought telescope it's neat to increase your eyepiece collection for free and have fun doing it!

At dead center of the photo above you can see the 90° adapter on the Tasco and upper right is the eyepiece simply stuck into the end of my PVC telescope.

Woah, the colors! Chromatic-Cat says meow!

See The Sun Part I

I Want To See The Sun Part I

Much like my other series of posts about seeing atomic particles, this is the first in a sporadic series of posts about using different devices to "see" the sun. From a simple radio telescope to solar viewing filters to a purpose-made solar telescope I'm going to do what you were always warned not to do: stare at the sun! I'll probably throw in some info about my homemade UV and infrared goggles too.

So, what do you need to make a radio telescope? An old satellite TV dish, 8 AA batteries with holder, an rf choke, a satellite finder, and some other odds and ends like solder, tape, a tripod, coax cable and coax terminators. Less than twenty dollars worth of stuff from Radio Shack (and your neighbor's garbage).

Simple instructions from the NRAO (National Radio Astronomy Observatory) are available here: 

http://www.aoc.nrao.edu/epo/teachers/ittybitty/procedure.html

Big caveat: the 0.1Mhz rf come on all the online plans don't seem to exist. Use any smallish RF choke. They may have meant milli or microHenrys (mH) but not Megahertz (Mhz). It's an honest mistake considering Mr Hertz is the guy that discovered radio waves. He used a spark gapped radio antenna, like a bug zapper for radio waves! So many of the things I experiment with are like bug zappers. Alpha particle on my spark detector-zap! Gamma or X-ray on a Geiger tube: zap! On or off electrically. Zap or no zap. 

With this radio telescope we're dealing with something more subtle: quantity. Not just yes or no, but how much? One decibel or two? A flat or peaked curve? Twenty MHz (yes we actually are taking Hertz now) means a solar flare. Ten to forty MHz and you could be looking at Jupiter, but Jupiter's magnetic storms are best monitored between eighteen and twenty-eight MHz. A wide swath between forty and eighty MHz with a plan around sixty MHz? That's Saturn my friend! Two and a half GHz-that's my Hot Pockets in the microwave oven. Of course you add voltage to the mix when interpreting too: frequency, an amplification, amplitude,  voltages, standing wave ratio...all sorts of things used in everyday devices like stereos, phones, cb radios, etc. It's all just electromagnetic waves. 

Setup is to aim at blue sky, dial decibel knob just barely to zero. Point at sun and itll6read around 6. How to aim at sun? Get the shadow of the LMB (pointy part) just barely onto the disk. Trace shadow on dish with marker once needle jumps up:

I ditched the dangerously unbalanced mounting bracket and spun the dish upside-down. There was a hole there that allowed the standard camera mounting screw to fit through, and as luck would have it the nuts from the dish bracket fit the screw. Mounting was easy!

I'm pondering getting a longer coax cable to attenuate the signal and help the RF smooth noise away. It might be possible to coil it on the tripod to create a balun. A balun is just a coil that helps a system cross from a balanced state to an unbalanced on (such as coax cabling).

Update: I did rearrange everything farther from the dish and coiled up a make-shift balun.

The red plastic cup holds the 8 AA battery pack. The second output from the LNB (low noise block converter) is capped off with a gold-plated coax terminator. The LNB is the brains of the dish which is basically a radio received. The actual dish is just a waveguide-badically an receiver in your car, only this received and translates microwaves from satellites instead of AM/FM waves. Simple!

So what am I looking at? Radio waves from our Sun. It turns out that the huge nuclear inferno above our heads melting 600 million tons of hydrogen into helium every second makes quite a lot of radiowaves! Here's a nice video of me aiming at the Sun and then slightly away a few times.

If I tame all the RF interference (probably by just moving the battery pack away) and plug this into my oscilloscope it should be easy to detect other things: like people walking past the dish or cars driving by. According to the NRAO a cellphone signal is a billion times more powerful than the cosmic rays detected by larger radio telescopes, so a radio-people-detector is very plausible (I've seen it done actually) even though this design is referred to as an Itty Bitty Radio Telescope.

My set up procedure now is to point to clear sky and dial up the gain on the meter until it almost squeals. Then I point out at the sun. If I really crank it up I can tell when the telescope scans past the sun, to the quieter open sky and then much quieter on the neighbor's tall chimney.

With the tripod locked the sun moves out of the dish's narrow focus rather quickly. The moon would do the same as it slides into the path of the sun's light the moon will get brighter in the sky-and on the radio telescope's meter. Think about it, when the moon is dark its surface is -243° Fahrenheit but when the sunlight hits it the surface rapidly heat up to a little over +250° Fahrenheit! Wow! It happens whether we can see the moon or not in the sky, on bright days you could search for the moon in a blue sky. I found it:

I'll revisit this with the oscilloscope data at some point, but lugging this weird device around my neighborhood during the day is embarrassing enough without an additional wheeled cart hauling crazy looking electrical boxes and wires. 

It will give me something more productive to at oscilloscope practice than just trying to write my name with it...cause that's what oscilloscopes are for right? M I K E!

Itty Bitty Radio Telescope? Looks more like an Itty Bitty Kitty Detector to me! I'll just mash my face all over it to be sure. Can it see me? Does it know it's mine now? Meow!