I hate the attention pressure that always 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 answer for me is one thing that goes by the title of electronically assisted astronomy, or EAA.
EAA occupies a middle ground in beginner 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 and not using a lens, it value simply US $100. Subsequent, slightly 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 just 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 possibly’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 give attention to distant objects precisely, even when the lens expands and contracts with altering temperatures.
Getting the main focus proper is among the bugaboos of utilizing a telephoto lens for astrophotography, as a result of the give attention to 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 an online astronomy forum) 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 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 satisfactory one for lower than $30.
Getting the main focus 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 applications: Canon’s EOS Utility (which permits me to regulate 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 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 would possibly assume. The plain technique is to place the digicam in “dwell view” mode, intention it at Jupiter or a shiny star, after which modify the main focus till the item is as small as doable. However it could possibly nonetheless be laborious to know whenever you’ve hit the mark. I obtained a giant help from what’s referred to as a Bahtinov mask, a display screen 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 photographs 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, after all. Ipurchased 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 capable of 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 as a way to take lengthy exposures with out blurring from the movement of the Earth. However I wished to see what I may do and not using a tracker.
I first wanted to determine how lengthy of an publicity was doable 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 subtle method, referred to as the NPF rule, components in extra 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 doubt, I’d have achieved higher from a darker spot. I used to be aware, 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, nevertheless, requires a fair, 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 evaluate, after all, with what someone can do with a greater gear. But it surely does present the sorts of fascinating photos you may 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 concern as “Electronically Assisted Astronomy.”