Short answer: all Sony A7-series cameras have essentially the same type of built-in filter, and it hasn’t fundamentally changed across generations. What has changed is how effective and refined it is.

Here’s a clear breakdown by what’s actually inside the camera.

🔧 The one filter every A7 has

All models from the original Sony A7 through to Sony A7 IV include:

1) UV/IR-cut “hot mirror” filter (built into sensor stack)

• Sits directly in front of the sensor
• Blocks infrared and ultraviolet light
• Ensures correct colour rendering in visible light
• Without it, images would look reddish/muddy because sensors are naturally IR-sensitive

👉 This is the only true “built-in filter” in A7 cameras
👉 It is always present unless the camera is modified

📊 How it differs by generation

🟢 1st generation (A7 / A7R / A7S)

• Basic IR/UV cut filter
• Slight IR leakage possible in extreme cases (long exposures, heavy ND use)
• Astro shooters often noticed:
  • Reduced H-alpha sensitivity (important for nebulae)
  • Some colour shifts with strong ND

👉 Early sensors = less aggressive IR suppression

🔵 2nd generation (A7 II / A7R II / A7S II)

• Improved sensor stack coatings
• Better IR suppression and colour accuracy
• Still blocks most H-alpha (like nearly all stock cameras)

👉 Evolutionary improvement, not a redesign

🟣 3rd generation (A7 III / A7R III / A7S III*)

• Further refined hot mirror + microlens design
• Better control of:
  • IR contamination in video
  • Colour stability with ND filters
• Lower tendency for IR pollution in shadows

👉 Particularly important for video shooters

🔴 4th generation (A7 IV / A7R V / A1 era)

• Most refined sensor stack
• Improved spectral control and coatings
• Better handling of:
  • Strong ND filters
  • Mixed lighting (tungsten + daylight)

👉 Still the same type of filter, just more precise

⚠️ What A7 cameras do NOT have built-in

This is often misunderstood:

❌ No built-in ND filters

• Unlike cinema cameras (e.g. Sony FS series)
• You must use:
  • Lens filters
  • Clip-in filters (aftermarket)

❌ No built-in IR-pass / astro filters

• The internal filter actually blocks IR, not passes it
• For IR or astrophotography:
  • You need external filters
  • Or a full-spectrum conversion (removes the hot mirror)

🔭 Important for astrophotography (your use case)

• The stock A7 filter blocks most H-alpha (~656 nm)
• That’s why emission nebulae look weak
• Modding removes/replaces this filter → huge sensitivity gain

👉 This is consistent across all A7 generations

🧠 Bottom line

• Every Sony A7 camera has:
  • ✅ A UV/IR-cut hot mirror filter
• Across generations:
  • Same concept, incrementally improved performance
• None have:
  • ❌ Built-in ND filters
  • ❌ Built-in astro/IR-pass filters