The flange to sensor distance of 17.526mm is unique to ensure the correct mounting of this lens for lens and camera bodies associated with a type “c” mount system.
One key point: Where are the measuring points located? Every complex camera lens has two cardinal measuring points. We use these to ascertain focal length and object distance. From the front nodal we measure object distance. From the rear nodal we measure focal length and distance lens to focused image.
These two cardinal points are chosen by the lens designer based on need. They may at the center of the lens array but more likely they are separated. They can actually be inverted. They may fall in air forward or rearward of the barrel. They are not normally published. Their location can be discovered but this will be tricky.
The space between the last lens element and the image sensor is called the “back focus”. The lens maker adjusts the position of the two cardinal points so that clearance is provided for swinging mirror and/or focusing mechanism. The length of the lens barrel can be artificially shortened by the positioning of the cardinal points. This makes the lens less awkward.
The lens acts like a projector lens in that it projects an image of the outside world onto the image imager. You can view this projected image if you hold the lens so that it projects an image of a bright object onto a white paper screen.
Stray light does bath the projected image despite the fact that the camera body is equipped with an image mask and image baffles. This stray light mainly reduces image contrast. This stray light can induce artifacts we call flare and ghost images. The lenses are coated with a thin transparent mineral coat that greatly reduces stray light creation.
You cannot produce an image on the image sensor by holding something in close proximity to it. You can produce vague mages called shadowgrams, and you can see artifacts which are shadows casts by objects on the cover glass of the image senior. Generally, these are nuisances rather than image that are art forms.