I hate the attention pressure that usually comes with peering by means of a telescope on the night time sky—I’d slightly let a digicam seize the scene. However I’m too frugal to sink hundreds 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 newbie astronomy: extra concerned than gazing by means of binoculars or a telescope, however not as sophisticated 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 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 no lens, it value simply US $100. Subsequent, slightly 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 area. Its optical geometry makes issues which might be out of focus resemble doughnuts. And it might probably’t be autofocused. However these shortcomings aren’t drawbacks for astrophotography. And the lens has the large benefit that it may be targeted past infinity. This lets you regulate the concentrate on distant objects precisely, even when the lens expands and contracts with altering temperatures.
Getting the main target proper is among 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 target ring and permits exact changes utilizing a small knob.
My subsequent buy was a modified gun sight to make it simpler to intention the digicam. The model I purchased (for $30 on Amazon) included an adapter that allow me mount it to my digicam’s sizzling shoe. You’ll additionally want a tripod, however you should purchase an sufficient one for lower than $30.
Getting the main target proper is among 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 digicam and obtain pictures immediately), Canon’s Digital Photograph 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 pictures to boost the outcomes with out having Earth’s rotation break issues.
It was time to get began. However specializing in astronomical objects is tougher than you would possibly assume. The apparent technique is to place the digicam in “stay view” mode, intention it at Jupiter or a vibrant star, after which regulate the main target till the item is as small as attainable. However it might probably nonetheless be arduous to know once you’ve hit the mark. I obtained an enormous help from what’s often known as a Bahtinov masks, a display 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 pictures 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 photographs 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 lower right into a circle and glued to a sweet tin from which I had lower 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 pictures 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 with the intention to take lengthy exposures with out blurring from the movement of the Earth. However I needed to see what I may do with no tracker.
I first wanted to determine how lengthy of an publicity was attainable with my fastened 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 length in seconds. For my setup, that will be 1 second. A extra refined strategy, known as the NPF rule, components 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 pictures from my suburban driveway. Little question, I might have performed higher from a darker spot. I used to be aware, although, to accumulate calibration frames—“flats” and “darks” and “bias pictures”—that are used to compensate for imperfections within the imaging system. Darks and bias pictures are simple sufficient to acquire by leaving the lens cap on. Taking flats, nonetheless, requires a good, diffuse mild supply. For that I used a $17 A5-size LED tracing pad positioned on a white T-shirt masking the lens.
With all these pictures 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 individual can do with a greater gear. Nevertheless it does present the sorts of fascinating pictures you may generate with some free software program, an atypical DSLR, and a classic telephoto lens pointed on the proper spot.
This text seems within the Could 2024 print challenge as “Electronically Assisted Astronomy.”