I hate the attention pressure that always comes with peering by 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 identify of electronically assisted astronomy, or EAA.
EAA occupies a middle ground in newbie astronomy: extra concerned than gazing by 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 price range.
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, 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 although 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 can be out of focus resemble doughnuts. And it may’t be autofocused. However these shortcomings aren’t drawbacks for astrophotography. And the lens has the massive benefit that it may be focused beyond 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 likely 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 online astronomy forum) 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 allow me mount it to my digicam’s scorching shoe. You’ll additionally want a tripod, however you should buy an satisfactory 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 manage the digicam and obtain photos immediately), Canon’s Digital Photo Professional (for managing the digicam’sRAW format picture information), the GNU Image Manipulation Program (GIMP) photograph editor, and a program referred to asDeep Sky Stacker, which lets me mix short-exposure photos to boost 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 digicam in “dwell view” mode, purpose it at Jupiter or a shiny star, after which modify the main target till the article is as small as potential. However it may nonetheless be laborious to know if you’ve hit the mark. I acquired an enormous help from what’s often known as a Bahtinov mask, 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 photos 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 simple goal: the solar. That required a photo voltaic filter, in fact. Ipurchased 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 digicam so as 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 potential 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 length in seconds. For my setup, that will be 1 second. A extra refined method, referred to as the NPF rule, components in further particulars concerning your imaging sensor. Utilizing anonline 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 question, I might have completed higher from a darker spot. I used to be conscious, 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, nevertheless, requires an excellent, 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 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, in fact, with what any individual can do with a greater gear. But it surely does present the sorts of fascinating photos you’ll be able to generate with some free software program, an unusual DSLR, and a classic telephoto lens pointed on the proper spot.
This text seems within the Might 2024 print subject as “Electronically Assisted Astronomy.”