I hate the attention pressure that usually comes with peering by means of a telescope on the night time sky—I’d somewhat let a digicam seize the scene. However I’m too frugal to sink 1000’s of {dollars} into high-quality astrophotography gear. The Goldilocks resolution for me is one thing that goes by the identify of electronically assisted astronomy, or EAA.
EAA occupies a center floor in novice astronomy: extra concerned than gazing by means 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 may get doing EAA on a restricted finances.
Electronically-assisted-astronomy images 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, somewhat than attempting 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 subject. Its optical geometry makes issues which might be out of focus resemble doughnuts. And it will probably’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 alter the concentrate on distant objects precisely, even when the lens expands and contracts with altering temperatures.
Getting the main target proper is likely 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 (based mostly on a design I discovered in a web based 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 buy an sufficient one for lower than $30.
Getting the main target proper is likely 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 regulate the digicam and obtain photos immediately), 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 photos to reinforce the outcomes with out having Earth’s rotation wreck issues.
It was time to get began. However specializing in astronomical objects is tougher than you may assume. The plain technique is to place the digicam in “stay view” mode, purpose it at Jupiter or a shiny star, after which alter the main target till the article is as small as doable. However it will probably nonetheless be exhausting to know if you’ve hit the mark. I received an enormous help from what’s often known as a Bahtinov masks, a display screen with angled slats you quickly stick in entrance of the lens to create a diffraction sample that guides focusing.
Stacking software program takes a sequence 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 straightforward 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 measurement 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 following hurdle was to picture a deep-sky object, or DSO—star clusters, galaxies, and nebulae. To picture these dim objects rather well requires a monitoring mount, which turns the digicam so to take lengthy exposures with out blurring from the movement of the Earth. However I wished to see what I may do with out a tracker.
I first wanted to determine how lengthy of an publicity was doable with my fastened digicam. 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 period in seconds. For my setup, that might be 1 second. A extra subtle method, known as the NPF rule, elements in extra 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 accomplished higher from a darker spot. I used to be conscious, although, to accumulate calibration frames—“flats” and “darks” and “bias photos”—that are used to compensate for imperfections within the imaging system. Darks and bias photos are straightforward 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 examine, after all, with what any person 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 peculiar DSLR, and a classic telephoto lens pointed on the proper spot.
This text seems within the Might 2024 print challenge as “Electronically Assisted Astronomy.”
