Lens system with master lens system and conversion lens

A lens system comprising:

• a master lens system comprising a first lens, a second lens, a third lens, and a fourth lens, which are sequentially arranged from an object side of said lens system to an image side thereof, and a first diaphragm which is arranged between said third lens and said fourth lens,
• wherein said first lens is a positive meniscus lens having a convex surface toward the object side, said second lens is a negative lens, said third lens is a positive lens, and said fourth lens is a negative meniscus lens having a concave surface toward the object side;
• and
• a conversion lens system,
• wherein said conversion lens system is arranged in such a manner that said conversion lens system can be inserted and removed between said third lens and said fourth lens of the master lens system,
• wherein when said conversion lens system is inserted and removed between said third lens and said fourth lens of the master lens system, relative positions of said respective first, second, third and fourth lenses of the master lens system are fixed, and a focal length of said lens system becomes shorter than a focal length of said master lens system, and
• wherein when said conversion lens system is inserted between said third lens and said fourth lens, a maximum diaphragm diameter of said first diaphragm is reduced.

A lens system comprising:

• a master lens system comprising a first lens, a second lens, a third lens, and a fourth lens, which are sequentially arranged from an object side of said lens system to an image side thereof, and a first diaphragm which is arranged between said third lens and said fourth lens,
• wherein said first lens is a positive meniscus lens having a convex surface toward the object side, said second lens is a negative lens, said third lens is a positive lens, and said fourth lens is a negative meniscus lens having a concave surface toward the object side;
• and
• a conversion lens system,
• wherein said conversion lens system is arranged in such a manner that said conversion lens system can be inserted and removed between said third lens and said fourth lens of the master lens system,
• wherein when said conversion lens system is inserted and removed between said third lens and said fourth lens of the master lens system, relative positions of said respective first, second, third and fourth lenses of the master lens system are fixed, and a focal length of said lens system becomes shorter than a focal length of said master lens system,
• wherein said conversion lens system further comprises a fixed second diaphragm on the object side, and
• wherein a diaphragm diameter of said fixed second diaphragm is smaller than a maximum diaphragm diameter of said first diaphragm.

A lens system comprising:

• a master lens system comprising a first lens, a second lens, a third lens, and a fourth lens, which are sequentially arranged from an object side of said lens system to an image side thereof, and a first diaphragm which is arranged between said third lens and said fourth lens,
• wherein said first lens is a positive meniscus lens having a convex surface toward the object side, said second lens is a negative lens, said third lens is a positive lens, and said fourth lens is a negative meniscus lens having a concave surface toward the object side;
• and
• a conversion lens system,
• wherein said conversion lens system is arranged in such a manner that said conversion lens system can be inserted and removed between said third lens and said fourth lens of the master lens system,
• wherein when said conversion lens system is inserted and removed between said third lens and said fourth lens of the master lens system, relative positions of said respective first, second, third and fourth lenses of the master lens system are fixed, and a focal length of said lens system becomes shorter than a focal length of said master lens system, and
• wherein a cut-out portion outside of a focusing range in said fourth lens of said master lens system is cut-out from said fourth lens, said cut-out portion is provided as a space for inserting and removing said conversion lens system.

A lens system comprising:

• a master lens system comprising a first lens, a second lens, a third lens, and a fourth lens, which are sequentially arranged from an object side of said lens system to an image side thereof, and a first diaphragm which is arranged between said third lens and said fourth lens,
• wherein said first lens is a positive meniscus lens having a convex surface toward the object side, said second lens is a negative lens, said third lens is a positive lens, and said fourth lens is a negative meniscus lens having a concave surface toward the object side;
• and
• a conversion lens system,
• wherein said conversion lens system is arranged in such a manner that said conversion lens system can be inserted and removed between said third lens and said fourth lens of the master lens system,
• wherein when said conversion lens system is inserted and removed between said third lens and said fourth lens of the master lens system, relative positions of said respective first, second, third and fourth lenses of the master lens system are fixed, and a focal length of said lens system becomes shorter than a focal length of said master lens system, and
• wherein at least one surface of said conversion lens system is aspherical.