Fast Glass

[three_eyed_otter]

Let's See! If you have a fast glass lens (f/2.8) will it be faster at all f-stops?

have a good one
3Eo

 

[Andreal]

Hey there, im new to photography, but I believe that when people refer to "fast glass" they are talking about the fact that the apeture can go very large and hence have the option of using a faster shutter speed. So the answer I believe would be no, it will not be faster at higher f-stops.

 

[Meysha]

simply put... no it won't be. Fast just refers to the fact that f/2.8 is fast compared to the rest of the f stops.

Fast glass = fast lens = the fastest possible speed it can achieve = the largest aperture it has.

You've got three things that control your exposure... and changing any one of them will change your exposure.

Aperture, ISO, and Shutter Speed.

Let's say you have your camera set to ISO: 100, Shutter speed 1/200 and aperture f/2.8.

The ISO 100 always has the same effect on the camera no matter what the others are set at. the Aperture f/2.8 always opens to the same amount of light - no matter what the other controls are set to. The Shutter speed stays open for 1/200.

and now is when I realise it's harder to explain exposure than it should be. Read a lot about how exposure works and you'll understand.

 

[three_eyed_otter]

Hey, thanks for the replies. They both make alot of sense.

have a good one
3Eo

 

[DSLR noob]

Typically faster glass looks better stopped down to an aperture that another lens is fully opened up to.

For example Canon's 50mm f/1.4 is sharper @ f/1.8 than Canon's 50mm f/1.8. strangly enough the 1.8 is sharper @ f/2.8 and above, but like I said, as a general rule, faster glas is sharper at certain apertures than slower glass.

 

[Garbz]

Actually all lenses have a sweet spot. This is because the edges of a lens has irregularities in the way it bends light. Of course a camera lens is a very intricate system of multiple lenses designed to counteract this effect, but generally there's always a sweet spot, and this is generally not at wide open since stopping down the lens reduces the irregularities caused by the edges of a lens element.