The Sun on August 29, 2024

When I image the Sun in white light, my practice has been to use my Canon EOS M200 mirrorless camera adapted to my 102mm Orion Maksutov-Cassegrain telescope equipped with a glass white light filter. The image quality I’ve gotten with this setup has been okay. Not spectacular but just okay.

For visual work, my 90mm Meade Series 390 achromatic refractor coupled with a Lunt Herschel wedge at the back of the scope delivers far superior results. It’s really quite astounding how much cleaner and contrasty the view of the Sun is through a refractor and Herschel wedge compared to what a glass white light solar filter can do.

For imaging, however, the main problem with using my 90mm Meade with a Herschel wedge has always been one of achieving focus. With the camera coupled to the Herschel wedge, I need more length toward the front of the scope in order to hit the focal plane. But the focuser’s draw tube meets up with the telescope and runs out of play before I can get to that point.

My workaround has been to unscrew the lens cell from my 2x Orion Shorty Barlow lens, which turns it into a 1.5x Barlow lens, and attach it to the 1.25" nosepiece that I use between my T2 adapter and the telescope. This bends the light in such a way as to position the focal plane further back, which is exactly what I need.

But with a cropped-sensor camera like my M200, that creates another problem: being able to fit the entire solar disk in the frame. Using a Barlow lens increases the effective focal length and focal ratio by whatever factor it’s rated at. In this case, using a 1.5x Barlow turns my 1000mm f/11 refractor into a 1500mm f/16.5 refractor. The image is larger and dimmer, and my M200’s sensor just isn’t big enough to get all of it.

Now that I have my full-frame Canon EOS R8, however, I have always been curious to see if the sensor is big enough to accommodate the entire solar disk in a way that I haven’t been able to do with my Canon EOS M200.

At the same time that I got an M42-to-RF adapter to attach my R8 to my Questar, I also got a T2-to-RF adapter. It’s taken me this long to try out that camera on my Herschel wedge-equipped refractor.

I picked an awful time to try this out today. It was almost solar noon, when the Sun is at its highest and most intense. With the bright glare of the Sun reflecting off the concrete I was set up on, I had a tough time seeing whether I was in or out of focus on my camera’s back monitor screen. The poor midday seeing wasn’t helping matters, either.

But getting focus aside, the main thing I discovered is that, yes, the entire Sun does fit in the frame on my R8, which is awesome. But it’s a tight fit.

After I got as close as I could with my focus, I fired off 15 exposures. This is the best one, which I resized into a more pleasing square:

What I see here is an image of the Sun that is much truer to what the Sun actually looks like: a pale orangish-yellow disk that pops with contrast especially when sunspots are present. Glass white light filters cast the Sun in more of a burnt orange color, which isn’t a faithful indication of the Sun’s true color if you could look at it with your naked eye—which of course you should never do.

Today’s sunspot activity is not by any means overwhelming, but there’s enough going on to show what they look like in a Herschel wedge. I especially like the solar faculae that surrounds the sunspot regions and that are more visible near the Sun’s limb (see the upper left and lower right sides of the Sun in the image above). These structures are much easier to see when I use a Herschel wedge compared to what a glass filter-equipped scope can show.