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Off-axis Three Mirrors Anastigmats (TMA) are a particularly interesting type of instrument for applications in the field of Earth observation. Compact and light weight, TMA can be designed over a wide field-of-view with excellent correction of aberrations. Hence, they can be used for various applications requiring a high revisit time with a small payload. In the frame of the Proba-Evo mission, we have worked on the stray light control of a wide-field TMA operating in the VNIR range. Stray light indeed represents a critical aspect for Earth observation, in particular in the case of wide-field instruments. This paper intend to describe the guidelines to follow for designing the opto-mechanical components of a TMA, as well as the different steps to perform for the stray light analysis specifically of this kind of instrument. We also show that numerical tricks can be employed for TMA to perform the analysis efficiently. The aperture stop is an example of critical element for stray light, for which black treatment is not enough and specific light traps need to be designed. Also, we discuss the placement of baffles for blocking straight shots and avoiding out-of-field illumination on the detector. The scattering of the mechanical structure can be avoided by placing vanes, also we show that specular coatings can be used to completely suppress certain stray light paths. Another contributor is the scattering from the mirrors, whose analysis is performed based on experimental characterization of the surface roughness as well as BSDF measurements.
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