Sigma 10-20 f4-5.6 DC question

[Blind Bruce]

Why does this lens have so large a front lens or filter ring when the lens just back of it is so small? Ir looks like the filter could have been half the size.

 

[ethanbt]

It's in ultra wide angle range.

 

[Ido]

There could be several reasons, and the only way to know for sure is to ask the engineers (or anyone who's seen its internals). There are three reasons I can think of:

1. Vignetting: Ultra-wide-angle lenses have, of course, a very wide field of view. It's possible that the optical designers found the distance between the front element and the filter thread that they chose is the minimal distance where the filter thread isn't in the field of view of the lens. There's an easy way to test that: hold your finger right outside the lens barrel, and slowly move it closer and closer to the front element of the lens (without touching it, obviously), until you see it, or any shading it causes, in the viewfinder. If your camera's viewfinder isn't rated for 100% coverage, use the Live View mode.
   
2. Bigger elements inside: It could be that inside the barrel of the lens, there are lens elements that are bigger than the front element. That doesn't sound quite right to me, but maybe if someone who is more knowledgeable about optics thinks it's possible, they can chime in with an explanation.
3. Focusing motors / electronics: There may be something occupying that added space in the barrel, perhaps having to do with focusing or any electronics.

 

[480sparky40 39]

Physics.

You are creating a product that uses physics, and your product must conform to the laws thereof.

This is the same reason we don't have a 5-2000mm f/0.8 pancake lens.