Q&A: Solar Time-Lapse Basics

Question: I have an 80mm equatorial refractor and I’d like to use it to take photos of the Sun. I saw the Great American Eclipse with eclipse glasses and thought it would be cool to photograph the next one. Any tips about how to do that? I’m a newbie amateur astronomer and haven’t done any astrophotography yet, but I’m willing to invest some time and money into this hobby. Many thanks for any advice you can provide! — JS, Oshkosh, Wisconsin

Answer: Well you’ll have plenty of eclipses to choose from, especially if you’re willing to travel. Here’s the link I posted last week to data for all solar eclipses between now and 2030.

To answer your question, the equipment needed depends on what type of telescope you have. Some scopes are better at this task than others. An 80mm refractor works well for astrophotography so you’re all set on that front. The next question is what type of imaging system you want to use: eyepiece CCD, DSLR, or smartphone?

The trend these days is toward direct CCD imaging with an eyepiece adapter. But many still use DSLR (or film) cameras, both of which can produce excellent results. The cheapest way to go is with a smartphone (or point & shoot) camera and an inexpensive mechanical adapter that holds the camera above the eyepiece where you’d normally position your eye. This method is called afocal astrophotography. You can try just holding the camera with your hand but it’s tricky to get it aligned and focused properly.

I use a 128mm refractor with a DSLR attached to an eyepiece projection T-adapter. The top image shows the individual optical components I need to assemble for solar astrophotography (time-lapse or not). Component J (TC-80N3 intervalometer) is attached to automatically trigger my camera at regular intervals. Newer DSLRs have this function built in. Below is the full list of components. Depending your scope’s focal length, and the eyepiece used, the lengths of extension tubes and spacers will vary.

A: 2″ back for Takahashi FS-128
B: 2″ x 2.375″ extension tube
C: 2″ to 1.25″ adapter
D: female section of 2.5X Barlow used as 2.5″ spacer
E: Coronado BF15 15mm solar blocking filter (more on this below)
F: 40mm Orion-Sirius Plossl eyepiece
G: UT2 eyepiece projection adapter
H: Canon T-adapter
I: Canon EOS 20D
J: Canon TC-80N3 intervalometer

One absolutely essential component for photographing (or viewing) the Sun is a filter that reduces the intensity of sunlight. If all you want to see are sunspots, or the phases of a partial eclipse, a cheaper neutral-density filter can be used. If you want to see more detail, including solar flares, you’ll need a more expensive band-pass filter. I use a Coronado Hα (hydrogen alpha wavelength 652.28 nm) filter that can produce results like this. Unlike a neutral-density filter, which simply covers the front aperture of your scope, the Coronado is a two-piece system that uses a tunable filter up front as well as a blocking filter just before the eyepiece. The two components not only protect your eyes and camera, they also reduce heating of the optical components.

One other component I find useful is a “shadow aiming sight” (shown below) to help point the scope at the Sun without having to look in that direction with my eyes. You can buy similar devices, but I fabricated mine from a piece of white cardboard and a small metal clip. Most scopes have protrusions that, when aimed at the Sun, will cast shadows at specific locations. In my case it’s the two clamp knobs that hold my scope to the mount. When the two shadows align, I know the scope is pointed at the Sun. The image below shows the shadow of the front knob higher than that of the rear — tilting the scope downward slightly will align them.

Once you have the proper components assembled, spend some time experimenting with the camera settings. Every combination of optical components has its own exposure “sweet spot” that can best be found by trial and error. My time-lapse of last week’s eclipse was shot at 1/400 second using ISO 1600 at an optical magnification of 40X. The effective focal length was 1123 mm and the aperture (Coronado SM40) was 40 mm, yielding f/28 for the filter-scope-eyepiece-camera system.

You can find a lot of info about how to do astrophotography online. What you see here is what works for me. Good luck with your venture, clear skies, and if you have any more questions you know where to find me.

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