Fast Glass? What does that mean?

M

Moab Man

Senior Member
I have read this a few times "fast glass" and I get that it means a lens that brings in enough light so that you can take the picture quickly without having your shutter open too long and you get a blurry picture. Assuming my understanding is correct so far, what makes one lens faster than another. Light still travels at the same speed, and glass is clear, so what makes one lens faster than another.

Thanks and I'm sorry if this was the wrong forum I couldn't find what seemed to be a better place for this question.
 
Pierro

Pierro

Senior Member
Yes your first sentence is about aperture, and fast apertures bring / allow more light and faster shutter speeds. As you suspect, fast f1.2 lenses are pretty darn fast, whereas f8 isnt.

AS for the difference between several f1.2 lenses, then its down to manufacturing. Glass isnt clear like you say - some have coatings to deal with flare and contrast, and also stuff like control of CA. So despite the light being constant in the natural world, it isnt once it meets up with barriers like DSLR lenses.
 
Marcel

Marcel

Happily retired
Staff member
Super Mod
There is also the size of the actual lens to consider. Obviously, the larger lenses are usually faster than the smaller ones. So "fast glass" lenses are usually bigger and heavier than their slower counterpart.
 
S

stmv

Senior Member
so,, for example,, every doubling of number is 1/4 the area,,

F2 -> F4, 1/4 the area, so,, needs 4X more light, or 4X more exposure time. so,, you can see, that well,

or vice versa,, F4 -> F2,, needs 1/4 of the exposure time,, or essentially 4 times faster !

hence the term... fast glass.
 
S

Sambr

Senior Member
Actually don't listen to them - it means " it will take more money out of your wallet faster than other glass." Tust me I know:)
 
M

Moab Man

Senior Member
salvatore said:
Actually don't listen to them - it means " it will take more money out of your wallet faster than other glass." Tust me I know:)
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This is not good for me. My other addiction is:

Just
Empty
Every
Pocket

I will be the guy in the homeless shelter with all the cool toys and no place to live.
 
E

Eye-level

Banned
You just don't need it for 99% of the snaps that you are going to make in your life unless you live in a frigging cave and if that is the case I would hope you would invest in a good set of floodlights and some reflectors...and with the sensors they make nowadays the so called "fast" lenses lose some of their chutzpah IMO. BWTHDIK. haha
 
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