Earlier this summer, Comet Neowise passed by, giving me a glimpse of the second comet I’ve seen in my lifetime. The previous sighting was the amazing Hale-Bopp in the 90s. Although I am old enough for Halley’s 1986 visit, I couldn’t see it at all from my location in the northern hemisphere. Comet Neowise was visible to the naked eye once dark-adapted, and its tail spanned a large swathe of sky. My one regret is not having a decent telescope for its viewing.

If there’s one thing about the house-arrest experience of 2020’s pandemic, it’s that it encourages you to take up new hobbies. Astronomy was always one of my hobbies, but, like many, it had been back-burned as I got older. Newly-motivated, I purchased a Nexstar 8SE. Since one of my other hobbies is photography, it seemed inevitable that I would delve into astrophotography.

So, I think my biggest misconception about astrophotography was that all of those amazing internet photos were taken with giant telescopes. Bigger must be better for astrophotography, right? Well, I think I was surprised to learn that most photos I viewed were taken with relatively small (80 mm - 100 mm aperture) telescopes. The Nexstar 8SE has an 8” (203 mm) aperture. Many of these smaller scopes had modest focal lengths in the 250 mm - 450 mm range, compared to the Nextstar 8SE’s 2032 mm. So what gives?

I wrote a separate blog post about what to consider when buying a telescope. The things to keep in mind are:

• Focal length directly affects magnification. Divide your eyepiece into your focal length for magnification. So, a 400 mm telescope with a 10 mm eyepiece magnifies 40 times.

• Aperture directly affects brightness and detail. The dimmest object you can see is determined by aperture.

• Focal Ratio (f/stop) directly affects how long of an exposure you will need to take to photograph a given object. Divide aperture into focal length to get focal ratio. Camera owners are very familiar with f/stops and know that “fast’ lenses will let a lot of light in, allowing shorter exposure times..

So the desired combination of these elements depends upon your stargazing targets. For example, most people don’t realize how big the Andromeda Galaxy is in the sky because you generally can’t see it with your naked eye. Imagine a full moon, then copy and paste that moon six times wide and three times tall. The Andromeda Galaxy is a little bit bigger than that in our sky! So, if you want to photograph it, and your telescope has so much magnification that it can’t even fit the entire full moon into a single frame, it has zero chance of capturing the Andromeda Galaxy. The Nexstar 8SE cannot fit an entire full moon in frame. I took this daytime photo of the moon by stitching together six photos:

So, if you want to photograph Andromeda-Galaxy-sized things, a smaller focal length telescope, like one of those 200 mm scopes I mentioned earlier, will work better than the Nexstar’s 2032 mm focal length.

Now the next part is a little tricky. As much as you may try, your eyes cannot take long-exposure images. So if you want to see dim things, you’ll want a larger aperture telescope. But if you want to photograph dim things, you want a telescope with a fast focal ratio, since focal ratio affects exposure time.

Those small scopes make a little more sense now. They all have very fast lens with medium focal lengths and are built for astrophotography. Could you use them for visual astronomy? You could, but for eyeballs the big guys like the Nexstar 8SE will do a much better job.

The other thing the small scopes have in common is a tracking equatorial mount. The Nexstar 8SE has a tracking altitude-azimuth mount. In theory, if you wanted a one hour time-lapse camera exposure, both telescopes should be able to keep everything motionless and centered due to their tracking capability, right? Well, no, not for an alt-az mount, and this is the part that confused me at first.

To understand why, let’s do a quick exercise. Make a fist and stick your arm straight out. I’ll wait…okay, I see you’re not doing it, c’mon…that’s better. Now, rotate your arm so that your fist turns clockwise. We’re going to call the axis that your arm is rotating the z-axis. Now lift your arm up as if pointing to the moon and bring it back down. The up-and-down motion of your arm is the y-axis, or altitude axis. Now swing your arm to the left and right. The left-right motion is the x-axis, or azimuth axis. An altitude-azimuth mount can move in the left-right and up-down directions, but can’t rotate in the z-axis.

An equatorial mount rotates in the z-axis, or right ascension axis. Stick your fist back out. Now, imagine an arrow coming up off the top of your hand. Move your hand up six inches in the direction of the arrow and bring it back down. By doing this you’ve added a second axis. The up-down motion is the declination axis.

Now, rotate your wrist 90-degrees clockwise. The imaginary arrow coming off the top of your hand rotates with it and is now pointing to the right. Swing your arm in the direction of the arrow. This is still the declination axis. It’s always in the direction the top of your hand is pointing, regardless of how you rotate it.

I found right ascension, declination, altitude and azimuth thoroughly confusing, but the arm exercise helped me understand it. So, why on earth would you want to use the complicated equatorial mount? The answer is because you are on Earth, and Earth has this inconvenient feature of constantly rotating. Because of the Earth’s rotation, stars travel in arcs across the sky. Like an archer’s arrow, they rise, peak, then fall below the horizon. If you remember your geometry days, trying to draw a circle using (x, y) coordinates is complicated. But drawing it in polar coordinates is mindlessly easy. Alt-az is x,y and equatorial is polar.

It’s not just that it’s harder. Imagine your archery friend wants you to take a video of him shooting an arrow. You zoom in on the arrow as it shoots 45 degrees up into the sky and you perfectly track it as it reaches its apex, tilts down, and descends, sticking in the ground. When you play back the video, the arrow is perfectly centered in frame, but it rotates, initially pointing up, flattening, then pointing down. That’s because you are tracking it in the x-y (alt-az) axis. You’d need to add a third axis, rotation of your wrist, to compensate for the rotation of the arrow.

Get it? The Nexstar 8SE will perfectly track Saturn across the sky, keeping it centered in frame, but, like the arrow, Saturn’s rings will start pointing up at 45 degrees, flatten, and then point down over time. The only way to fix that is to add a z-rotational axis to your telescope. If I were to do a long-exposure of Saturn, the disc of Saturn would stay centered but, like a snow-angel’s wings, Saturn’s rings would fan out into blurry arcs and its moons would trace star trails.

The answer to “how long of an exposure can you take with the Nexstar 8SE before getting star trails” is complicated, but in general, probably about 30 seconds. Things close to the North Star trace smaller arc than things further away, so the amount of blurring you get depends on where the object is in the sky. I usually limit exposures to 15 seconds.

The other issue is that the tracking control software drifts over time and makes a correction every 30 seconds or so. In the 360-photo sequence of the Orion Nebula, below, you can see the nebula drift up and then back down. If I tried to do 60-second exposures, it would have been a blur. But as 5 second exposures it was fine. The photo stacking software re-aligned all the images in post-processing:

This is a good segue into the next misconception I had for astrophotography: what you see in the telescope doesn’t remotely look like the Hubble-telescope-type photos posted on the internet. First, your eye can’t take 15 second exposures, so even bright objects like the Hercules Cluster look like milky, faint cotton balls and colorful objects like the Orion Nebula look like milky, faint wedges. Second, 15 seconds isn’t enough even for a camera. To get those amazing photos, you need to stack hundreds of images. Imagine you’re using an old film camera and a 15 second exposure would blur due to movement. Instead, you do 15 one-second exposures, all on the same piece of film. The end result is 15 seconds of exposure without the blurring. This is key: even though I am limited to short timeframes for my exposures, there’s no limit to the number of exposures I can take, other than my time. So, if I want a one-hour exposure of a faint galaxy, I can take 360 ten-second exposures.*

Now that I’ve got you grounded, here’s the equipment and software:

These are my tools, now a quick primer on how they work. Stacking software aligns your hundreds of photos by matching up stars, then it reinforces the repeating elements and discards the anomalies. When you take your photos, you’ll take up to four sets:

• LIGHTS: The normal-exposure photos of the thing you’re photographing. Usually I take at least 25 lights at ISO 1200 - 3200 with exposure times of 5 seconds - 15 seconds

• DARKS: Dark photos are taken with the telescope’s lens cap on, so they are black. They need to be taken at the same ISO and exposure time as the Lights and the camera should be at the same temperature as the Lights. I usually take 25 - 50 darks. Your camera produces inherent noise in low-light which will show up in the dark photos. The noise will then be subtracted from the Lights in your stacking software.

• BIAS: Bias photos are taken with the telescope’s lens cap on at the same ISO as the Lights but with the fastest exposure your camera has. My T5i can do 1/4000 second. I’ll take 25-50 bias photos. The electronics of your camera produce inherent noise in the sensor, which shows up in the bias photos. This noise is then subtracted from the Lights in the stacking software.

• FLATS: You can make flats anytime by putting a diffuse, even, white light source over your telescope and photographing it. Some people use an iPad with a white screen and a t-shirt over it. Your camera’s sensor sensitivity is probably uneven and this will produce stripes or gradients that are noticeable when you boost low-light photographs. These will be subtracted from the Lights in the stacking software.

• DARK FLATS: After you take your flats, put the lens cap on to take your dark flats. I was a bit perplexed how these were different than Darks, but Darks at taken at the same temperature and exposure as Lights, while Dark Flats are taken at the same temperature and exposure as Flats.

You feed your lights, darks, bias, and flats into Astro Pixel Processor (or another freeware program like Deep Sky Stacker) and it does the rest. Depending on the number of images you give it, it may take most of the day to process them. The image that you get out of stacking is surprisingly dark, but the image data is there hidden in the pixels. The next step is to make the data visible, a process called stretching. Astro Pixel Processor will do some of this for you, but I prefer Photoshop. During stretching, you adjust the curves of the photo to make the data fall into the visible range. If there are other issues, like the red-green-blue channels being misaligned due to aberrations, you align them to fix the color. It’s interesting that your telescope picked up all this data but it was just too dim to see.

Here’s what the unedited 5-second exposure of the Orion Nebula looked like coming straight from my camera at ISO 3200:

I took that picture 360 times, along with darks and bias photos, and fed it into Astro Pixel Processor. Here’s the Astro Pixel Processor output:

I then stretched it in Photoshop. Here’s what the final photo looked like:

Just a little different than the original! It’s crazy that all of that was in the top photo to start. I didn’t add anything in Photoshop. I just reset where the white and black points were to straddle the wavelengths of the Orion Nebula. I’m still in awe that I took that from my deck.

Here’s the Orion Nebula taken a few months later with an f/6.3 focal reducer and dual bandpass clip-in UHC filter. Note the difference in colors. (The focal reducer is one of the best additions I’ve purchased and the UHC filter is great for emission nebula like M42):

Hopefully this was helpful. Incidentally, the Cloudy Nights forums are filled with opinions stating that the 8SE is only good for visual astronomy and planetary imaging. I disagree. All of my pictures are taken with the default alt-az mount and a DLSR (and a focal reducer for some), so you definitely can enjoy both visual and astrophotography out-of-the-box. I agree that the 8SE is designed to be a visual astronomy scope, but that doesn’t mean you can’t take some nice astropics with it. A couple of opinions:

• Generally, I’ve been successful imaging things in the Messier catalog, although it depends on the color of the target (I don’t have a modded camera and targets with deep reds are harder to photograph than targets with greens). Targets up to 6.5 magnitude can usually be imaged, although I can certainly image fainter magnitudes depending upon the color.

• If you envision a time lapse with star trails spinning around Polaris, the ones closest trace small arcs and the furthest large. Same deal when imaging, so the length of an exposure you can take without star trails depends on where an object is in the sky. It’s why there’s no single answer to “how long of an exposure can you take with the Nexstar 8SE?”

• There is no reason you can’t piggyback mount a camera to your scope and take wide-field astropics. When you do this, you get all the benefits of the Goto mount and Starsense setup.

• Keep in mind that the trade-off for upgrading to a more expensive mount is that you will either need a helper to set up your scope or you’ll need extra time to carry it out piecemeal and assembly it. It’s definitely a plus that I can carry the entire assembled scope onto the deck by myself. The typical EQ mounts people direct 8SE owners to on the forum weigh in at 76 pounds, excluding the telescope and accessories, so your total kit weight will exceed 100 pounds with these.

• I may upgrade to an EQ mount for longer exposures, or I may get a lightweight camera-only EQ setup, such as a Star Adventurer. I’m leaning towards the Celestron AVX, since weight is important to me. I realize guiding will be trickier with the AVX than a higher-payload scope such as the CGEM, but I just don’t think I’ll use my scope as often if I need to assemble it each time.

• You can use light pollution or ultra-high contrast filters, but these further eat into your exposure time because they block not only the bad light but also a little of the good light, so these work best with brighter objects such as the Orion Nebula and/or a focal reducer (although if the target’s color is right, such as the Dumbell Nebula, these have helped me with faint objects).

Here’s a few other (less dramatic) photos I’ve taken in the months leading up to the Orion pic. These all have much less exposure time but were fun none-the-less:

While you’re here, if you enjoy sci-fi stories with a classic exploration theme, why not check out my series, Hayden’s World, available on Amazon and Audible? You can listen to a clip below:

Listen to my author interview with series narrator Shamaan Casey: