What are the core features of roof prisms?
Image orthogonality: maintains the left-right and up-down orientation of the image in line with the original.
Compactness: shorten the physical length of the optical system by folding the optical path.
High precision requirement: the 90° angle of the roof surface needs to be extremely precise (error ≤ a few seconds), otherwise it will lead to image dispersion or ghosting.

What are the advantages and disadvantages of roof prisms?
Advantages:
Compact, small instrument size.
Imaging is oriented correctly and requires no additional calibration.

Disadvantages:
Complicated and costly process (especially phase correction coatings).
Strict requirements for cleanliness and vibration resistance.

BK7 Material Properties
Parameter	BK7
Refractive Index (nd)	1.5168 (@587.6nm)
Abbe Number (vd)	64.2
Transmittance	Standard transmittance (~92%)
Critical Angle of Total Reflection	Larger (may cut edges)
Cost	Relatively low