The Yongnuo 100mm f/2 (Nikon F mount version) will mount and function on the Nikon D300S, giving you an effective 150mm f/2 equivalent field of view due to the APS‑C crop factor. It’s a budget telephoto prime mainly suited for portraits and shallow‑depth‑of‑field work, though autofocus performance and build quality are not on par with Nikon’s native lenses.

📸 Compatibility & Setup

• Mount: The lens is made for Nikon F mount, so it fits directly on the D300S without adapters.
• Crop factor: On the D300S (DX sensor), the 100mm focal length behaves like ~150mm, giving a tighter telephoto look.
• Aperture: f/2 maximum aperture allows strong subject isolation and low‑light shooting.
• Autofocus: Uses a DC motor — serviceable but slower and noisier than Nikon’s AF‑S lenses.

🌟 Strengths

• Portraits: Flattering compression and shallow depth of field.
• Price: Considerably cheaper than Nikon’s 105mm f/2 DC or 85mm f/1.8 options.
• Optics: Multi‑coated glass reduces flare and ghosting.
• Manual control: AF/MF switch and focus distance indicator included.

⚠️ Limitations & Trade‑offs

• Autofocus speed: Not ideal for fast action; better for posed or slower subjects.
• Build quality: Plastic construction feels less robust than Nikon’s pro primes.
• Sharpness: Acceptable in centre, but edges soften wide open — stopping down improves results.
• Firmware quirks: Some users report occasional compatibility issues; firmware updates may help.

🎯 Practical Use on D300S

• Portraiture: Excellent budget option for headshots and upper‑body framing.
• Street/urban detail: The 150mm equivalent reach isolates architectural or candid details.
• Low‑light: f/2 aperture helps, though ISO performance of the D300S is limited compared to modern bodies.

Bottom line: On the Nikon D300S, the Yongnuo 100mm f/2 is a budget telephoto portrait lens that delivers shallow depth of field and decent optical quality, but with compromises in autofocus speed and build. If you value affordability and don’t mind working around its quirks, it’s a useful addition; if reliability and speed are critical, Nikon’s native primes are stronger choices.

Initial Thoughts.

Had the lens a couple of day and am finding the AF and Exposure both a little inconsistent, I think maybe it is in need of a firmware update but need to find the correct cable to attach to my computer.