For this telescope, the lenses are a concave convex (one side curved out and the other curved in) and a plano concave (one flat side and one side curved in). The plano concave lens is used as the eyepiece with the plano (flat) side facing the eye.
BUN redirects here. For other uses, see Bun (disambiguation). The liver produces urea in the urea cycle as a waste product of the digestion of protein. Normal human adult blood should contain between 6 and 20 mg of urea nitrogen per 100 ml (6â20 mg/dL) of blood.
The BUN is roughly one-half of the blood urea (R). Normal human adult blood should contain between 5 to 20 mg of urea nitrogen per 100 ml (5â20 mg/dL) of blood, or 1.8 to 7.1 mmol urea per liter (R). To convert from mg/dL of blood urea nitrogen to mmol/L of urea, multiply by 0.357.