Follow up on Hammerheads lens question

[GTMeyers]

Hey everyone. I have a quick question about the apperture of lenses in general. I understand that the lower the f-stop the wider the apperture, but why do I hear some photographers call lenses with lower f/#'s "fast" or "faster". I thought that the lower the f/# the shallower the depth of field. Personally when I shoot I try to get the higher f/# so that I get a less shallow depth of field.

Am I thinking incorrectly? Why are the prime and low f/# lenses usually more expensive? Thanks for your help in advance.

 

[Johnboy2978]

The lower the f stop the more shallow the depth of field and greater the blur you will see in the background. A higher aperture will yield greater depth of field and more will be in focus. A portrait shot with an aperture of f/2.8 will reduce the BG to a blur while an f/28 will have practically everything in focus which would be used more w/ landscapes for instance.

A lens is referred to as being fast when it allows for a wider aperture (f/1.4, 1.8, 2.8). The terminology comes from the fact that these wider apertures allows for more light to strike the digital sensor or film. Thus, you will be able to shoot with a faster shutter speed thereby reducing camera shake and keeping the ISO rather low also reducing grain or digital noise.

Prime lenses have a fixed focal length such as 50mm, 28mm, 70mm etc. They generally have a much wider aperture like 1.8 or 1.4 and actually are usually cheaper than a "fast" zoom lens. For instance, my 50mm f/1.4 lens cost around $200 while my 70-200mm which has a max aperture of 2.8 throughout the focal range cost around $900. Prime lenses generally yield much sharper pics but the trade off is the fixed focal length. Fast zoom lenses are much more expensive b/c of the increased complexity in making such a lens. "Fast" lenses are generally constructed w/ much more quality.

 

[GTMeyers]

Okay, thanks. I haven't done much up close portrait work before. I am more of a landscape and far away shots kind of guy. I am thinking of getting into wedding photography so I guess I should start investing in a prime lens for the up close shooting.

I appreciate the explination. It definitely helped me out.

 

[Johnboy2978]

For weddings most will recommend a 24-70mm f/2.8, a 70-200mm f/2.8 in addition to a couple of good prime lenses. Prime lenses are great and usually worth every penny.

 

[Mike_E]

Lenses that have a lower aperture also are more expensive to make due to the width of the lens- literally the amount of optical (read that expensive) glass used- and the care needed to accurately grind and coat it.