Current lenses:
- Sigma 14mm f/1.4 DG DN Art
- Sigma 50mm f/1.4 DG DN Art
- Sigma sports lens maybe? Like this one:
Some ideas to consider, and probably the top of the list for getting deep galaxy type shots, would be a 200 mm lens. This could be used for nature photography as well. So, to that end, a Sigma 70-200 may be the way to go. This is from the Sigma Sports lineup.
Below is the Sigma 70-200 f/1.4 DG DN lens.
DG stands for full frame compatibility
DN indicates designed for mirrorless cameras

- Expressive imaging capabilities with latest optical design
- Dual High-response Linear Actuator (HLA) focus system
- Dust and splash-resistant structure
- Latest OS2 Optical Stabilization up to 7.5 stops
- Inner zoom and inner focusing
- Minimized focus breathing at all focal lengths
- Superior build quality of SIGMA Sports line
- Completes F2.8 DG DN full-frame mirrorless trio
For moon photography and moon timelapse, composition will trump must pure moon shots. This blurb says it all:
Composition:The 200mm lens offers a wider field of view than a longer lens, making it easier to incorporate foreground elements like trees, buildings, or landscapes into the image, creating more visually interesting compositions.