Accessories for Soviet MTO-500 Mirror Lens

This project is a collection of useful 3D-printed accessories for the legendary Soviet MTO-500 mirror lens (including models like 3M-5A / ZM-5).

The goal of this project is to create practical upgrades that make this classic 500 mm mirror lens more convenient for astrophotography, solar observation, and general photography.

The project will continue to evolve — new accessories will be added over time.

Included accessories
Lens Cap for the Original Lens Hood

A protective cap designed to fit directly onto the original MTO-500 lens hood.

The inner diameter includes a small tolerance for soft lining material (felt, flocking, velvet, etc.) so the cap can be installed without scratching the vintage lens.

This is especially important for early lenses — the one used for testing was manufactured in 1968.

⚠️ Solar Observation Safety

Never look at or photograph the Sun through this lens without a proper certified solar filter installed in front of the optics.

These aperture masks do NOT protect your eyes or your camera from solar radiation.

Direct solar observation without a proper filter can cause permanent eye damage or destroy camera sensors.

Always use a full-aperture solar filter designed for safe solar observation.

60 mm Aperture Mask

This insert reduces the effective aperture of the MTO-500 to 60 mm.

Why reduce aperture?

Mirror lenses often show strong central obstruction effects and optical imperfections when used wide open.
Stopping down can improve contrast, sharpness, and image stability, which is particularly useful for astrophotography and lunar imaging.

The design includes extra clearance for flocking or felt to improve fit and prevent scratches.

50 mm Aperture Mask

A more aggressive aperture reduction to 50 mm.

This can further improve contrast and reduce aberrations in challenging conditions such as:

high atmospheric turbulence
bright lunar imaging
solar imaging (with proper solar filter)

Just like the 60 mm version, the mask includes tolerance for lining material.

🚧 Work in progress