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#AskPS: Do I need to shoot flats for a DSLR and lens?

H asked:

I only have a DSLR, no scope at all yet. Do I still need to take flat frames, and if so, how?


Hi H,

If you’re shooting long exposures for deep-sky images, then yes! It definitely helps the image a lot to use flats no matter what the focal length or FOV of the imaging glass is. To the camera sensor, the focal length does not matter, and most telescopes and lenses will have at least some vignetting or imperfections that shooting flats can fix, dramatically improve the final quality of your image and remove the need for cropping.
For example, see the single exposure below, and then the final processed image, shot with a crop-frame camera and a 200mm lens at f/4. Notice the vignetting and uneven illumination even with a high-quality telephoto lens:
Single 120s f/4 200mm exposure
Final processed stack of 22 exposures, calibrated with flats/darks/bias
The larger the camera sensor, the worse the vignetting is, because it comes closer to the edges of the lens objective. So, a full-frame sensor will suffer from more vignetting that a crop-frame sensor. That being said, some telescopes are built specifically with larger areas of “flatness”, or you can use corrective elements in the imaging train to fix this as well. BUT, even when using extremely “flat” equipment, your images can benefit from shooting flats.
The process in our tutorial, “How to Create DSLR and CCD Flat Frames for Astrophotography,” is the same for lenses as well as telescopes. Remember, telescopes are just really big lenses. Also, see our tutorial on the basics of how you’d get started shooting deep-sky objects without a telescope!
Cheers, and good luck!


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About the author

Cory Schmitz

Co-founder of PhotographingSpace.com, co-owner of several telescopes and mounts, too many cameras, and not enough hard drives, Cory is an American expat living in South Africa with his wife, Tanja Schmitz.

An avid astrophotographer for timelapse, deep-space imaging, lunar, planetary, and star trail imagery, he is an all-around jack-of-most-trades for night-sky photography.

He is also an internationally published and commissioned astrophotographer, where his photos have been used in multiple online and print publications.

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