Michael J. Radke

Taking images of a total solar eclipse

Taking images of a total solar eclipse can be challenging. Some say the eclipsed Sun is the most difficult astrophotography target.

For the rest of this post, I’ll be assuming you’re using a modern DSLR/mirrorless camera, but the same advice probably applies for dedicated astrophotography cameras and maybe even film cameras. Some hardcore eclipse photographers take photos with multiple different cameras and composite them together, but that’s outside the scope of this post.

(This post is a little bit ~stream of consciousness~, sorry. There are lots of other resources about how to take eclipse photos. I’m just including this for completeness.)

Lens selection

You can take spectacular images of a total solar eclipse at any focal length. But for this process, we’ll be focusing on the middle/outer corona, so I’d recommend a lens with a focal length of 400-500 mm (with a crop sensor DSLR; for a full frame this would be 600-750 mm). This results in an image size of about 2.5° to 4.0° on the long edge. This is my recommendation to get a good amount of detail in both the inner prominences and the outer corona, but the lens choice is definitely up to the photographer here! A wide range is possible.

Because a TSE is so bright, the focal ratio of your setup isn’t particuarly important (so long as you have a tracking mount), but definitely play around with play around with Xavier Jubier’s Solar Eclipse Exposure Time Calculator to see what settings and lenses might work well for your camera.

Finding and tracking the Sun

The eclipsed Sun moves approximately 1° over the course of the 4 minutes of totality. By comparison, the typical field of view of a DSLR with a 500mm lens is only about 2.6°x 1.8°. So in order to keep the Sun centered in your camera’s field of view, you’ll need some sort of tracking mount—a star tracker or equatorial mount—otherwise you’ll be limited to short exposures, and you’ll have to guide the camera by hand to keep the Sun centered in frame. Besides, you should be spending most of your time enjoying totality with your human eyes, not fiddling with a sensor!

If you do have a tracking mount, it’s a good idea to get your camera pointed towards the Sun during or before the partial phases, instead of wasting time doing it during totality. That said, it’s surprisingly difficult to do this! You obviously can’t look at the Sun as you’re aiming your camera towards it, so how are you supposed to find the Sun? Shadows. Move your camera around such that you minimize the size of your camera’s shadow on the ground below it. If you have a solar filter for your camera, you can then look through the filtered camera to fine tune your alignment. If you’re doing this with a telescope you could obviouly just use a (filtered!!!) finder scope. You can also purchase “Sun finders” which project a small image of the Sun or use small shadow spots to assist with finding the Sun.

It’s also difficult to polar align a tracking mount during the day. There are lots of online resources to help with this. I won’t discuss it here (mostly because I am bad at it and don’t really have any tips LOL).

Taking photos

First (and perhaps foremost?), you need to make sure your camera is saving the images in RAW format (*.CR2, *.NEF, *.RAF, *.ARW, etc., depending on your camera brand). RAW files are basically just the unprocessed data from your camera sensor (this is an oversimplification, but that’s ok). PNGs or TIFs might be acceptable depending on what automatic conversion your camera applies to them. Just make sure they are 16 bit format; 8 bit images do not have the required precision for this work, and you’ll end up with strong banding in your final images due to rounding errors. n Next, you’ll need to somehow capture the full dynamic range of the eclipsed Sun. Our eyes are great at showing us both the faint details in the outer corona and the bright inner corona and prominences… but a camera is terrible at this. So you’ll need to take multiple images with different exposure times. This is called exposure bracketing. Most modern digital cameras have a setting to do this automatically. Again, play aroud with the Solar Eclipse Exposure Time Calculator to find an appropriate range of exposure times for your camera and lens combination in order to capture everything from the chromosphere/prominences to the outer corona.

You will also want a remote shutter release, intervalometer, or some other sort of remote camera control so that you can take photos continuously without having to manually hold down the shutter button, which will introduce vibrations and otherwise be annoying. You want to take as many photos as possible during totality, ideally at least 10 sets of bracketed images, so you can stack them together to reduce noise.

If your camera supports tethering (i.e., camera control from a computer via USB), you can use something like the Eclipse Orchestrator app in order to take a set of automated exposures with a variety of settings. If your camera does not support this, I would recommend taking auto-bracketed exposures and not changing your settings during totality. It’s too much of a risk. And, again, you should spend time enjoying the sights and sounds of totality and not just messing with your camera!

Ideally you will also have a set of calibration images (flats, darks, and biases) for your eclipse images. But this isn’t required. Your final images will just be noisier. If you don’t know how to take these calibration images, this is a good starting point.

Some notes about my set up, specifically

The lens/reducer combination I used has a f-ratio of ~5.6 and I shot all the images at ISO 200. The Fuji X-T30 II has a BKT setting on the mode dial, which made the bracketing very simple. You can fine tune the number of exposures and their spacing in the settings menu. I used the Eclipse Calculator to estimate the range of exposures I wanted, and I ended up doing 9 exposures with a step of 1-1/3 EV, centered on 1/30 s. This produced a set of images with exposure times of 1/3200, 1/1000, 1/320, 1/100, 1/30, 1/10, 1/3, 1, and 3 seconds. If I did this again, I would maybe only go out to exposures of 1 second. I’m not sure much is gained with the 3 second exposure, and such a long exposure dramatically decreases the total number of images you can take during totality! I might do some testing at some point to determine exactly what data the 3 second exposure is providing to the composite.

Not sure if this is common with other camera brands/models, but one quirk with the XT-30II is that you can’t do continuous bracketed shooting. A long shutter press only takes a single set of bracketed exposures. In order to get continuous exposures, I used an intervalometer set to a short interval (1 second) to get ~continuous shots.

Additionally, the Fuji X-T series cameras do not support USB tethering, which could have bypassed this issue. If on the off chance anyone from Fujifilm is reading this, please enable tethered shooting on the X-T series!! It seems like more of a firmware limitation than a hardware limitation, given that you can use XT cameras in pass-through mode as a webcam and control some shooting settings using the Fuji X phone app!