Astrophotography is both an art and a science. Photographers capture the same data but process it in different ways. This is the creative part of astrophotography. To excel at this pastime involves hard work and dedication. You’ll need to master science concepts and photographic techniques alike.
In this post, I will explain why in astrophotography, how to do flats is important.
Why Are Flat Frames Important?
Flat frames play an important role in post-image processing. They help fix any light source inconsistencies caused by factors like dust. This can collect on the optics of cameras and telescopes. Certain areas of the photo may show vignetting or irregular brightness spots. Flats make it easier to get beautiful images.
Check out this explanation of flat frames and how they can help you improve your images.
Creating astrophotography images that capture the beauty of our universe is not easy. It’s important to understand all aspects of this craft – including flats! What exactly are they?
Flats are photographs taken with a constant light source throughout the entire frame. They must be taken using the same setup as your astrophotos. The telescope, the lenses and the filters should remain as they were when the photos were taken.
Adding flat frames into your photography workflow helps correct many issues. These include dust particles and uneven lighting which can reduce photo quality.
Why is dust a problem in astrophotography and how can it affect your images?
Sources of Dust
All photographic equipment and lenses are affected by dust. Your telescope or camera may collect dust from the atmosphere depending on where you use it. Windy and dry areas can be a problem. In spring and summer pollen can also get onto your lenses. No matter how careful you are small particles and debris will build up in hidden areas of your optics.
How does dust affect astrophotography?
Dust can affect your astronomy images in several ways. Spots, streaks, dim areas, and dust motes are common. Understand how these happen and you may be able to prevent problems before they occur.
Small particles of dust can reduce the reflected light from your mirrors. This can cause a dimming of the light in certain places of your image. Larger dust particles cause more serious issues. These are more noticeable and can include dust motes. These are often circular, darker areas that can spoil your pictures.
There are several ways to clean your camera or your telescope’s optics.
You can use a blower, a brush, or a microfiber cloth to remove dust particles. Learn more about how to clean your telescope’s mirrors here.
Dust prevention methods
Better to prevent problems with dust before they affect your images. I always try to replace my lens covers and never leave anything open to the elements. Dustproof boxes and covers can help. If you can keep your equipment in a dust-free environment this will also make a big difference.
Sometimes though no matter how hard we try, dust will find a way in! It’s then that your flats will come to your rescue!
It is possible to do without them if you have a clean optical system. But at some point, you’ll need to learn how to take flats.
So how do we do that?
How to Take Flat Frames
To get a consistent and evenly lit image with your telescope or camera, cover the lens with a white T-shirt. It is important to take at least 10-15 flats. Use the same exposure settings as you had when you shot your object in the sky. Additionally, flats should be taken in the same location.
Stacking software uses these flats to create a master flat by calculating an average. The master flat can then correct the final image and remove any defects.
Achieving clear and high-quality images of the night sky can be a challenging task. But, by utilizing a master flat, it’s possible to remove any variations in lighting. Your images will look so much better!
A step-by-step guide to taking flat frames
Here are the steps to follow:
The White T-shirt Method
- You can take flats either before or after your imaging session. Be careful not to change any settings or anything in your setup or optical path. This includes camera settings.
- Point your telescope or camera towards a bright point in the sky. This cannot be done at night because you need a light source.
- Take a few pictures with the aperture of your telescope covered with a white T-shirt.
- Upload your pictures to your laptop or computer.
The Light Panel Method
Follow step 1 as above then:
2. place the light panel in front of your telescope aperture or camera lens
3. take some pictures.
4. Upload the flat frames to your computer or laptop.
You can use a laptop with a bright white screen as your light source. This can be a good alternative to the methods above. The steps would be the same as for the light panel.
Here is another clear explanation of flat frames on Youtube:
How to use the flats
After you have the flats on your computer you can use a program like Deep Sky Stacker. This software will average out the flats and create a master flat.
When you have the master flat you can stack your astrophotography images. I use Siril to stack my images, but there are alternatives. You can use Deep Sky Stacker, Pixinsight, and many more.
The stacking software uses the master flat to correct for problems in your optics. Dust motes and vignetting are removed and your image looks better.
That’s the theory. It seems quite simple though I have found it difficult to take flats. It does need practice.
Calibration Frames for Astrophotography
There are other types of calibration frames we use for astrophotography. These are dark frames and bias frames.
Dark frames remove heat and electronic noise created by the sensor to ensure crisp images. To take things even further, bias frames are helpful for reducing any noise seen in the camera itself.
Flats need to be taken when your optics change. If you use different filters, you must take flats for each. The results will improve the quality of your astrophotos. Flats will give you cleaner images which will be easier to process.
What are the most common problems with taking flats?
There are several problems that may make taking flats for astrophotography difficult.
The first problem is one that I have faced. It can be quite difficult to get even lighting. This can cause vignetting in your image.
The only ways you can correct this are to experiment with different light sources. You may need to move the light source. Light panels are more consistent than aiming at the sky. Test what works best.
Another problem is under or over-exposure. This does need testing.
If the flat is under or over-exposed it will not correct the image as you wish.
Another problem is often the setup. You must use exactly the same setup as you used for your photographs. You cannot change anything or the flats will not work.