What does 'Fast' mean?

When I see an advert with Fast lens mean. E.g. Fast 200mm.

 

It means a large maximum aperture - which means a large piece of glass in front - which means you pay a lot more.

 

It also means you can take photos in a lower light with a faster shutter speed.

 

A fast 200mm lens would be something like a 200mm lens with a maximum aperture of 2.8.

One that would not be as fast would be one with a maximum aperture of, say, 4.5. As you surely already know, the smaller the aperture number, or F-Stop, the wider open it can get, allowing more light income, thus letting you shoot, as said, with a faster shutter speed, which minimizes motion blur in the image caused from camera shake.

 

How does this affect the other side of the coin? What differences are there between a "fast" and "slow" lens in the very small apertures?

Also, if my camera as an f27 setting, does that mean any lens I attach to the body will shoot at f27?

 

There is usually no difference. A "fast" lens just has a larger max aperture than a "slow" lens.

 

the way i think about it....if you have a lens that has a max aperature of 4.5 it won't perform as well at 4.5 as a lens with a max aperature of 2.8 or so....am i right?

 

It is often said that a lens will be it's sharpest a couple of stops closed down from wide open. That is a popular generalization, but it may or may not be true, depending on the particular lens. There are always exceptions to the rule.

The Nikon 50mm f/1.8 manual focus lens is said to be sharper at f/1.8 than the Nikon 50mm f/1.4 is at f/1.8

There are folks who claim the 75mm f/3.5 planar on a Rollei TLR is sharper at f/3.5 than the 80mm f/2.8 version at f/3.5

I'm sure there are folks who would debate these examples, but there are many, many posts on the internet saying it is so.

 

yes and no.

Generally the fast 2.8's are made of much higher quality glass then their 4.5 brethrin.

 

I think not! If you attach some lens that has minimum aperture at f16, you won't be able to shoot at f27.

So, you have the camera with f setting on it's body? As I know, such setting may work properly only if the lens supports using of that particular feature.

For example, Nikon F-100 has f control on it's body. But if you attach for example Helios lens on F-100 body, the only way to set the aperture would be by operating aperture ring placed on the lens. If you set camera's f setting to f8 while aperture ring on Helios is set to f4, the camera will shoot at f4!

Similar thing is with autofocus - you may use the autofocus feature only if you have an AF lens attached!

 

That is definately what the salepeople are going to tell you Their mantra is more money equals better stuff. Personal testing (or by a friend you trust) is really the only way to tell for sure.

 

Hmm, good point. I just haven't ever noticed a lense advertising its upper f settings. Maybe I better check that out on my lenses.....