A newbie-esque Question: Why do low aperture lenses cost more?

[PhotoJunkieJen]

So I've noticed, all else being equal, low aperture lenses cost most. For instance, Sigma's 10-20 comes in a 4-5.6 model... and now a 3.5 which costs much more. Canon's 50 mm lens at 1.4 costs more than the 2.5.
And I've noticed everyone in wedding photography tends to use 2.8 lenses. Why is that?
It stands to reason in my mind that you'd want more of an aperture range for a greater dof. What am I missing here?

[RexK_Cozumel]

There is a lot more engineering that goes into making a large aperture lens. Also the lens itself uses a lot more glass. Pick up a kit lens 18-55 and then pick up a 24-70 f2.8 and you will instantly know the difference.

In wedding photography you are generally going to run into a lot of low light situations so having a large aperture is important. as for why 2.8 and not something larger.. Well 2.8 is the largest aperture you can buy zoom lenses in right now. And a lot of wedding photographers like zoom lenses because it is easier/faster to compose shots by turning the zoom ring instead of changing position.

You have a larger aperture range with f2.8 glass. Just because the maximum aperture of the glass is f2.8 through out the zoom range does not mean that you have to use f2.8 all the time. you can just stop it down to 3.5 or 5.6 or whatever you want.

[PhotoJunkieJen]

That makes a lot of sense. Low lighting is something I've worried about as I've done my homework over what it takes to shoot a wedding. I guess I'm also worried about the focus at 2.8... would it be good enough to please a client (considering I'd be photographing people who move... and not a rock that I could put a 12 minute open shutter on )

Anyway, just trying to get as informed as I can before I venture into this whole new realm of high stress photography

[LoveDSLR]

Originally Posted by PhotoJunkieJen

I guess I'm also worried about the focus at 2.8... would it be good enough to please a client (considering I'd be photographing people who move... and not a rock that I could put a 12 minute open shutter on )

A lot of us shoot at f/1.2 to f/2.8 without focusing a problem. Focusing with f/1.2 - f/1.4 lenses may require some practices and shooting at f/2.8 is normal for pros.

That's why we use DSLR that is capable of low noise at ISO 6400. Other techniques such as pre-focus can be used.

[RexK_Cozumel]

If you are really worried about focusing issues shooting at 2.8 then you can bump your iso up and use 5.6 or so. That should give you enough depth to get your focus.

anyways I vary from 2.8 to 5.6 depends on the situation. I rarely ever shoot portraits at anything above f5.6 unless I am trying to knock out mid day sun.

[wulf]

It's the options that a wide aperture opens up (and DoF is not so much of a problem if you can get some distance between you and the subject).

It is also that many lenses are a bit soft wide open but perform best two or three stops in. On my 50mm lens, I can be at f/4, which I find a very useful aperture, and get very sharp results; I'd be at about f/8 two or three stops in on the kit lens at 50mm zoom, needing slower shutter speeds or higher ISO.

I certainly think every DSLR photographer should try to get some experience using "fast glass" even if they ultimately decide to invest in lenses based on different criteria.

Wulf

[MatthewBotos]

Here's a video that gives you an idea of what goes into making lenses: