I hate the attention pressure that usually comes with peering by way of a telescope on the night time sky—I’d slightly let a digital camera 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 identify of electronically assisted astronomy, or EAA.
EAA occupies a center floor in beginner 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 price range.
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, slightly than attempting to marry this digital camera 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 regardless 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 discipline. Its optical geometry makes issues which might be out of focus resemble doughnuts. And it could’t be autofocused. However these shortcomings aren’t drawbacks for astrophotography. And the lens has the large benefit that it may be centered past infinity. This lets you alter the concentrate on distant objects precisely, even when the lens expands and contracts with altering temperatures.
Getting the main focus proper is without doubt one of the bugaboos of utilizing a telephoto lens for astrophotography, as a result of the concentrate on such lenses is sensitive and simply will get knocked off kilter. To keep away from that, I constructed one thing (primarily based on a design I discovered in a web-based astronomy discussion board) that clamps to the main focus ring and permits exact changes utilizing a small knob.
My subsequent buy was a modified gun sight to make it simpler to goal the digital camera. The model I purchased (for $30 on Amazon) included an adapter that allow me mount it to my digital camera’s scorching shoe. You’ll additionally want a tripod, however you should purchase an enough one for lower than $30.
Getting the main focus 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 packages: Canon’s EOS Utility (which permits me to manage the digital camera and obtain photos instantly), Canon’s Digital Picture Skilled (for managing the digital camera’sRAW format picture information), the GNU Picture Manipulation Program (GIMP) picture editor, and a program known asDeep Sky Stacker, which lets me mix short-exposure photos to reinforce the outcomes with out having Earth’s rotation smash issues.
It was time to get began. However specializing in astronomical objects is tougher than you may assume. The apparent technique is to place the digital camera in “stay view” mode, goal it at Jupiter or a brilliant star, after which alter the main focus till the thing is as small as doable. However it could nonetheless be arduous to know while you’ve hit the mark. I received a giant help from what’s often known 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 collection of photos of the sky, compensates for the movement of the celebs, and combines the pictures to simulate lengthy exposures with out blurring.
After getting some good pictures of the moon, I turned to a different simple goal: the solar. That required a photo voltaic filter, after all. Ibought one for $9 , which I minimize right into a circle and glued to a sweet tin from which I had minimize out the underside. My tin is of a dimension that slips completely over my lens. With this filter, I used to be in a position to take good photos 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 digital camera 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 doable with my mounted digital camera. A standard rule of thumb is to take the focal size of your telescope in millimeters and divide by 500 to provide the most publicity length in seconds. For my setup, that may be 1 second. A extra refined strategy, known as the NPF rule, elements in further particulars relating to 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 photos from my suburban driveway. Little doubt, I might have executed higher from a darker spot. I used to be aware, although, to amass calibration frames—“flats” and “darks” and “bias photos”—that are used to compensate for imperfections within the imaging system. Darks and bias photos are simple sufficient to acquire by leaving the lens cap on. Taking flats, nonetheless, requires a fair, 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 photos 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, after all, with what anyone can do with a greater gear. However it does present the sorts of fascinating photos you’ll be able to generate with some free software program, an atypical DSLR, and a classic telephoto lens pointed on the proper spot.
This text seems within the Might 2024 print problem as “Electronically Assisted Astronomy.”
