When it comes to astrophotography, using a prime lens with a maximum aperture of f/1.4 set to f/2.8 can offer significant advantages over using a zoom lens at its widest aperture of f/2.8. Here’s why:

Superior Sharpness and Clarity
When you stop down a prime lens from f/1.4 to f/2.8, you’re working within the lens’s “sweet spot,” where image sharpness and clarity are at their peak. Prime lenses are typically designed to perform exceptionally well when slightly stopped down from their maximum aperture. At f/2.8, a prime lens that can open up to f/1.4 will generally produce sharper images with better detail across the frame, including the corners. In contrast, a zoom lens at its maximum aperture of f/2.8 is often working at its optical limits, which can result in softer images, especially around the edges of the frame.

Reduced Aberrations
Stopping down a prime lens from f/1.4 to f/2.8 also helps to reduce optical aberrations such as chromatic aberration, coma, and vignetting. These issues are less pronounced at f/2.8 on a prime lens that can go wider, leading to cleaner, more accurate images. On the other hand, a zoom lens operating at its widest aperture of f/2.8 is more likely to exhibit these aberrations, which can distort star shapes and introduce unwanted colour fringing—factors that can detract from the overall quality of your astrophotography.

Better Star Definition
One of the most crucial aspects of astrophotography is capturing pinpoint star details. A prime lens stopped down to f/2.8 often provides better star definition with reduced coma, leading to sharp, round stars even at the edges of your frame. In contrast, a zoom lens at f/2.8 might struggle with star sharpness, particularly in the corners, where stars can appear elongated or smeared.

Consistency Across the Frame
When using a prime lens at f/2.8, you can expect more consistent image quality across the entire frame. This means that not only the centre but also the corners of your image will be sharp and well-defined. Zoom lenses, particularly when used at their maximum aperture, can exhibit variations in sharpness and clarity across the frame, which is less ideal when you’re aiming for a uniformly sharp night sky.

Less Vignetting in Stitched Panoramas with Prime Lenses
One of the challenges in astrophotography, especially when creating panoramic images, is dealing with vignetting—those darkened edges that can appear in your photos. Vignetting is more pronounced when using wide apertures, and it can become particularly problematic when stitching multiple images together to form a panorama.
Prime lenses, however, typically exhibit less vignetting compared to zoom lenses, particularly when stopped down to f/2.8. This is due to their simpler optical design, which helps to reduce the light falloff at the edges of the frame. When you stitch multiple images taken with a prime lens into a panorama, the reduced vignetting means there’s less noticeable darkening at the edges of each frame. As a result, your final stitched panorama will look more seamless and uniform, without visible lines or abrupt transitions between the individual frames.

This advantage is especially important in astrophotography, where consistent brightness across the entire image is crucial for maintaining the natural look of the night sky. By using a prime lens, you can avoid the distracting lines and uneven lighting that can sometimes mar a panoramic shot taken with a zoom lens. The result is a smoother, more cohesive image that beautifully captures the expansive view of the night sky.

Conclusion
While zoom lenses offer versatility and convenience, they often come with trade-offs that can impact the quality of your astrophotography. Using a prime lens with a maximum aperture of f/1.4 set to f/2.8 offers several advantages, including sharper images, reduced aberrations, better light transmission, improved star definition, and less vignetting in stitched panoramas. These factors collectively make prime lenses the preferred choice for capturing the night sky with greater detail and precision.

That said, zoom lenses can still work and are perfectly okay for astrophotography, especially if you’re just starting out or need the flexibility of multiple focal lengths in a single lens. However, as a general rule, if you’re aiming for the best possible results—whether it’s sharpness, clarity, or overall image quality—a prime lens will give you the edge you need to take your astrophotography to the next level.

Some Prime Lenses for Sony:

1. Sony FE 24mm f/1.4 GM (G Master)

2. Sony FE 14mm f/1.8 GM (G Master)

3. Sony FE 35mm f/1.4 GM (G Master)

4. Sigma 14mm f/1.8 DG HSM Art

5. Sigma 28mm f/1.4 DG HSM Art

6. Sigma 40mm f/1.4 DG HSM Art

Some Prime Lenses for Nikon:

1. Nikon AF-S NIKKOR 20mm f/1.8G ED

2. Nikon AF-S NIKKOR 24mm f/1.4G ED

3. Nikon AF-S NIKKOR 35mm f/1.4G

4. Sigma 14mm f/1.8 DG HSM Art (Nikon F-mount)

5. Sigma 28mm f/1.4 DG HSM Art (Nikon F-mount)

6. Sigma 40mm f/1.4 DG HSM Art (Nikon F-mount)

Some Prime Lenses for Canon:

1. Canon RF 24mm f/1.4L USM

2. Canon RF 35mm f/1.8 IS Macro STM

3. Sigma 14mm f/1.8 DG HSM Art (Canon EF-mount)

4. Sigma 28mm f/1.4 DG HSM Art (Canon EF-mount)

5. Sigma 40mm f/1.4 DG HSM Art (Canon EF-mount)