What is Lucky Imaging And How to Use It Well In Solar Photography?


Lucky imaging is the method that is most often used in many disciplines of astrophotography, as it dramatically enhances the results. Solar photography is almost unimaginable without it. 

In this article, I would like to provide some basic insight into lucky imaging, and share some of my own methods, settings, pieces of hardware I use, et cetera.

So, let's get to it.

What Exactly is Lucky Imaging, and How is it Used?

I dislike the term 'lucky' - this method is about eliminating the role of luck from the process...

But we are getting ahead of ourselves.

Unless you can leave the atmosphere of Earth and photograph from space, the turbulent air above us will always pose some kind of challenge. It distorts the view! 

Everyone can easily experience this while looking at the night sky, even with the naked eye: the stars will often twinkle or flicker.

This is because even when no clouds are visible, the transparency of that thick layer of air above us varies. 

The mass of air is constantly moving, swirling, and flowing a bit above us. That movement itself is distorting our view.

The Problem with Earth's Atmosphere: Describing the challenges of photographing celestial bodies through the Earth's turbulent atmosphere

This phenomenon is very similar to what happens when you look into a shallow creek or lake while hiking in the hills and forests: the water is crystal clear, the mossy stones below are clearly visible, and the image looks sharp, even motionless, if the flow of the water is undisturbed - however, when you reach below the surface to grab the stone, you'll find that it is actually not there. It's a bit mispositioned, but the image itself is stable.

This is called refraction. It happens when you look at something through the water or through the air: just the fact that light travels to your eye through a transparent material has an effect on the path of the photons. Because of this, the object will be slightly 'off' to where it would be if you had the opportunity to look at it through completely empty space, a vacuum. 

As a photographer of celestial objects, this does not bother us at all: the Sun might be a few millimetres off from its 'real' location, but it's the same Sun. 

Going back to the example of the stone in the creek, the image will be clear and sharp only when the water is either completely stable and motionless, or when the flow is totally laminal (the opposite of turbulent).

This is rare. Usually, there will be some waving, some interference which makes the water turbulent, so the image of the stone will not be still: it will be slightly waving as the surface of the water waves, the image loses focus, and it gets distorted. This happens in the air above us as well.

The strangely vague term 'seeing' has been introduced for this phenomenon. 

If you took a photo of a star or any celestial body, you'd need to be really lucky to get a sharp image. So, instead, you take lots of photos in a relatively short time frame. 

None of them will be perfect, but mathematics can help us here. The ones that are blurred or defocused by the seeing effect get discarded, and we only use the sharp ones that are slightly mispositioned because of the atmospheric waving.

These together create the ultimately clean ones, thanks to the helpful software solutions.

How Lucky Imaging Works: Explaining the process of taking multiple photos and using software to create a sharper, cleaner image 

Because you are making photos through the atmosphere (unless you use the James Webb telescope - good for you! But we, Earth-based enthusiasts, have to make it work from down here), you will almost never capture your object's 'real' image. Some parts of the image look blurry, others are clean but slightly misplaced, just like the underwater stone. However, when you take a long series of photos, you can calculate and get a good idea of where every pixel 'should be'. 

The photons are riding the airwaves above us. Still, we can create a mesh network of the pixels comprising the images and move them back to their 'original' location. It's like smoothing out a wavy, crumpled rubber sheet. Usually, I use 1000 to 3000 reference points for a single image.

This is called 'multi-point alignment'.

The result will be a correct image of the Sun. If you did the same process to the stone, you could make it look as clear as it wasn't under the water.

The process is different to averaging: when creating an 'average' of all the photos of the Sun waving in the atmosphere, we just get a blurry image of it. But when the individual images are used 'on top' of each other, each correcting the mistakes of the other, the result will be an image so sharp that it is practically impossible to create with a single shot. The software only uses those shots of the reference points that are sharp and discard the rest. You set the targeted sharpness. 

I usually go for a 0.1 - 0.5 ms exposure, with 20-50 gain, depending on the solar filter used.

How Many Shots Do We Use for Lucky Imaging?

The standard method involves taking 4000 photos in 30 seconds, so a bit more than 133 images are created every second. This number looks quite high. However, this is one of the features of solar photography: light is not something we are short of. There are so many incoming photons that exposure time is not an issue - the image is always bright enough. Thus, we can take the photos at a very high speed.

Do you need to climb up to a mountaintop for best results with lucky imaging?

A common misconception about solar and astrophotography is that you need to conquer the highest mountains available to see through the cleanest air possible. I certainly tried this as well, and I assure you that you can achieve great results on the ground level as well if you find the best spots. 

The reason for this is that we are trying to get away from anything that can cause ground-seeing effects, which means we are looking for places with very stable air masses or a very laminal airflow. We try to avoid buildings, cityscapes, large paved surfaces, - anything that generates heat which causes turbulence.

And, sure enough, the ground itself has its own heat, it warms and cools as the Sun rises and descends. The 'ground seeing' effect is indeed worse closer to the ground. Still, you can find areas with incredibly laminal airflows while being on the plainest, flattest areas.

If you are interested in finding out how, subscribe to our newsletter so we can send you tricks, methods, solutions like how to avoid ground seeing, and exciting stuff we experiment with in the world of solar photography!

What kind of telescope should you use for Lucky Imaging in Solar Photography?

The Soleye 300 is objectively the best choice currently, based on these parameters:

1. Its mirror has the perfect surface for Lucky Imaging

The 'waviness' of the atmosphere can be measured in tenths of seconds. When photographing a faint nebula, 600 seconds of exposition time would be typical. You don't need a powerful focus because the atmosphere will wash the details away. You can't go over a specific resolution. For this kind of task, a medium-quality diffraction limited (0.82% Strehl) mirror will work just fine.

However, with solar photography, we shoot images faster than the rhythm of the atmospheric waving. That means there is no 'motion blur'; the movement doesn't register on the image. The 'only' challenge is that some parts of the image will be affected by ground seeing, as discussed above. Once we can get a sufficient proportion of sharp images, we can get close to the theoretical resolution level that the mirror is capable of - and suddenly, mirror quality becomes a critical factor! 

Our mirror has a 95%+ quality, and that makes a huge difference.

2. The Soleye 300 handles vast amounts of light, enabling a 0,35 ms exposure time. 

Since we are photographing the Sun, the images are always 100% illuminated so we can be fast. As mentioned above, we shoot photos faster than the atmospheric waving, so you can 'freeze' the atmosphere, and your image will be very sharp and high resolution.

What kind of Software Do We Use for Lucky Imaging in Solar Photography?

Processing the digital images to get the desired results is as easy as pie. You connect the camera with a cable to your laptop and fire up the software: you can use Firecapture or Sharpcap. These are the most popular choices. You set gain and exposition time, and you are ready to rock! The programs record the images, in the rhythm, grouping and batching you want, for example, 4000 images in 30 seconds, ten times. 

When you are interested in focusing on a sunspot or an interesting phenomenon, you can crop the image, enabling you to go even faster, doing 300 fps. (Just make sure you don't run out of disk space!)

When photographing objects with still surfaces, like the Moon, you can take as many pictures as you want in one series, taking several minutes.

 But the Sun won't stay the same for long; that's why 30-second stints feel feasible.

So these are the solutions for recording the image: how about stacking? How can we create those extra-sharp images by pulling the pixels to their proper place?

The most popular choice is AutoStakkert!, which is free to use. This handy software will handle the checking and combining process for you. 

I use preliminary analysis software before starting the stacking process. This one is called PIPP (also free), and it offers a pre-selection.

So, now my AutoStakkert! We will only use the best images to create the final one by locking the parts - that is 'moving' due to the seeing effect - firmly in place. The software can enlarge the image to double its pixel count and fit the images with an accuracy smaller than a single pixel. The software will use interpolation to create the new pixels: it knows what was 'between' the pixels of the original image, thanks to having hundreds of different but (almost) identical shots of the same subject.

 Once I get the final image, I open it in PhotoShop to pull up the Contrast and Sharpness levers; some people prefer to use a program called Registax.  

What Kind of Camera Should You Use for Lucky Imaging?

The camera is certainly not the bottleneck for your solar photography setup. I use the most basic camera you can instantly find when looking for suitable models. 

New cameras are hitting the virtual stands every month. Still, they aren't really more capable, only in parameters that are not crucial for solar photography.

As a reminder and sort of a recap, we don't need lots of pixels because the turbulent air above us will blur those. Instead, we need many images with excellent sharpness - the mathematical formulas of the stacking software will handle the rest.

And I think that's all you need to know about lucky imaging in astrophotography. As you can see, a reliable, older camera can do the job, the software is free and easy to use, and you can manage it with a half-decent laptop. 

The real differentiator is the telescope and the required skill set. One of the key reasons we created Soleye is to give real solutions designed especially for the solar photography community - something the market has yet to offer.

With Soleye, you can achieve results that seemed unachievable before. Beyond the tools, we plan on releasing more content and other learning opportunities so everyone can take photos of the Sun that could be considered world-class.