Biscuit head refers to the SLR lenses, the length of a very short (that is, very thin) class of lenses, due to the look similar to a cookie, and thus gained the nickname of cookie head.

This type of lens in order to pursue the ultimate compact size, at the expense of the size ratio of the maximum aperture, and even the image quality of the lens. The maximum aperture of the cookie head is generally only F2.4-2.8.

2, the origin

Pentax DA 40mm F2.8 Limited lens was listed at the end of 2004, due to the lens thickness of only 15mm, so it has gained the reputation of the world's smallest DSLR automatic lenses in one fell swoop. Although more thin and light lenses have emerged since then, but so far there is still no rival that can surpass it, Pentax DA 40mm F2.8 Limited can be said to stand the test. The Pentax DA 40mm F2.8 Limited has also been nicknamed the "cookie cutter lens" because of its ultra-thin profile.

3. Advantages

(1) Small, so the entire lens fits easily in your pocket;

(2) Fast, focusing speed is unmatched by zoom heads;

(3) "Fast" large-diameter aperture, allowing for much faster shutter speeds and the ability to capture moments;

(4) Viewing angle: the Pentax DA 40mm F2.8Limited has been recognized as a "biscuit lens" due to its ultra-thin stature.

(4) fixed perspective, use skilled, you can blind shoot (do not look at the viewfinder) can also be carried around, in the moment of pulling out the camera to complete the shooting preparation, can be frozen moments, will not attract attention, do not need to take a view of the camera, is a humanities photographic tool, some of the masters of the work, is the masterpiece of this type of camera.