I hate the attention pressure that usually comes with peering by way of a telescope on the evening sky—I’d relatively let a digicam seize the scene. However I’m too frugal to sink hundreds of {dollars} into high-quality astrophotography gear. The Goldilocks answer for me is one thing that goes by the title of electronically assisted astronomy, or EAA.
EAA occupies a center floor in newbie astronomy: extra concerned than gazing by way of binoculars or a telescope, however not as difficult as utilizing specialised cameras, costly telescopes, and motorized monitoring mounts. I set about exploring how far I might get doing EAA on a restricted finances.
Electronically-assisted-astronomy pictures captured with my rig: the moon [top], the solar [middle], and the Orion Nebula [bottom] David Schneider
First, I bought a used Canon T6 DSLR on eBay. As a result of it had a broken LCD viewscreen and got here with out a lens, it value simply US $100. Subsequent, relatively than making an attempt to marry this digicam to a telescope, I made a decision to get a telephoto lens: Again to eBay for a 40-year-old Nikon 500-mm F/8 “mirror” telephoto lens for $125. This lens combines mirrors and lenses to create a folded optical path. So despite the fact that the focal size of this telephoto is a whopping 50 centimeters, the lens itself is barely about 15 cm lengthy. A $20 adapter makes it work with the Canon.
The Nikon lens lacks a diaphragm to regulate its aperture and therefore its depth of area. Its optical geometry makes issues which can be out of focus resemble doughnuts. And it could actually’t be autofocused. However these shortcomings aren’t drawbacks for astrophotography. And the lens has the massive benefit that it may be centered past infinity. This lets you modify the deal with distant objects precisely, even when the lens expands and contracts with altering temperatures.
Getting the main target proper is without doubt one of the bugaboos of utilizing a telephoto lens for astrophotography, as a result of the deal with such lenses is sensitive and simply will get knocked off kilter. To keep away from that, I constructed one thing (based mostly on a design I discovered in an internet astronomy discussion board) that clamps to the main target ring and permits exact changes utilizing a small knob.
My subsequent buy was a modified gun sight to make it simpler to purpose the digicam. The model I purchased (for $30 on Amazon) included an adapter that permit me mount it to my digicam’s scorching shoe. You’ll additionally want a tripod, however you should purchase an sufficient one for lower than $30.
Getting the main target proper is without doubt one of the bugaboos of utilizing a telephoto lens
The one different {hardware} you want is a laptop computer. On my Home windows machine, I put in 4 free applications: Canon’s EOS Utility (which permits me to manage the digicam and obtain photographs straight), Canon’s Digital Picture Skilled (for managing the digicam’sRAW format picture recordsdata), the GNU Picture Manipulation Program (GIMP) picture editor, and a program known asDeep Sky Stacker, which lets me mix short-exposure photographs to reinforce the outcomes with out having Earth’s rotation spoil issues.
It was time to get began. However specializing in astronomical objects is more durable than you may assume. The apparent technique is to place the digicam in “stay view” mode, purpose it at Jupiter or a brilliant star, after which modify the main target till the thing is as small as attainable. However it could actually nonetheless be arduous to know if you’ve hit the mark. I obtained an enormous help from what’s referred to as a Bahtinov masks, a display with angled slats you briefly stick in entrance of the lens to create a diffraction sample that guides focusing.
Stacking software program takes a sequence of photographs of the sky, compensates for the movement of the celebrities, and combines the pictures to simulate lengthy exposures with out blurring.
After getting some good photographs of the moon, I turned to a different straightforward goal: the solar. That required a photo voltaic filter, in fact. Ibought one for $9 , which I reduce right into a circle and glued to a sweet tin from which I had reduce out the underside. My tin is of a measurement that slips completely over my lens. With this filter, I used to be capable of take good photographs of sunspots. The problem once more was focusing, which required trial and error, as a result of methods used for stars and planets don’t work for the solar.
With focusing down, the subsequent hurdle was to picture a deep-sky object, or DSO—star clusters, galaxies, and nebulae. To picture these dim objects very well requires a monitoring mount, which turns the digicam so as to take lengthy exposures with out blurring from the movement of the Earth. However I needed to see what I might do with out a tracker.
I first wanted to determine how lengthy of an publicity was attainable with my mounted digicam. A typical rule of thumb is to take the focal size of your telescope in millimeters and divide by 500 to provide the most publicity period in seconds. For my setup, that may be 1 second. A extra refined method, known as the NPF rule, components in further particulars concerning your imaging sensor. Utilizing anon-line NPF-rule calculator gave me a barely decrease quantity: 0.8 seconds. To be much more conservative, I used 0.6-second exposures.
My first DSO goal was the Orion Nebula, of which I shot 100 photographs from my suburban driveway. Little doubt, I might have completed higher from a darker spot. I used to be aware, although, to amass calibration frames—“flats” and “darks” and “bias photographs”—that are used to compensate for imperfections within the imaging system. Darks and bias photographs are straightforward sufficient to acquire by leaving the lens cap on. Taking flats, nevertheless, requires a good, diffuse gentle supply. For that I used a $17 A5-size LED tracing pad positioned on a white T-shirt protecting the lens.
With all these photographs in hand, I fired up the Deep Sky Stacker program and put it to work. The resultant stack didn’t look promising, however postprocessing in GIMP turned it right into a surprisingly detailed rendering of the Orion Nebula. It doesn’t evaluate, in fact, with what any person can do with a greater gear. Nevertheless it does present the sorts of fascinating photographs you’ll be able to generate with some free software program, an extraordinary DSLR, and a classic telephoto lens pointed on the proper spot.
This text seems within the Might 2024 print challenge as “Electronically Assisted Astronomy.”
