hello guys.

newbie Q uli ... what's the difference between having a zoom with range max aperture versus one with a fixed one?

SAMPLE
[Brand Name] 18-50mm f/2.8
[Brand Name] 18-50mm f/3.5-5.6

thanks!

the aperture stays constant throughout the range of the lens...

following your example sir

18-50mm f/2.8
regardless if you are on the 18mm end or the the 50mm the max aperture is constant at 2.8


18-50mm f/3.5-5.6
on the wide of of 18 your max aperture is 3.5 as you zoom in to the 50mm end your max aperture becomes 5.6

fixed aperture, maximum aperture can be used on all focal length. the other one means your maximum aperture in the wide end of lens in eg f3.5 and max aperture for the long end is f5.6.

hth and i hope u understand.:)

Aperture setting is used to control the depth of field and the amount of light coming through the camera. The lower the aperture number, the wider the opening. Confusing, isn't it?


The aperture of a 80-200 mm/f2.8 lens means that the aperture is set at f2.8 at the 80 mm end or the 200 mm. This is especially useful for fast-paced photography like shooting indoor sports (volleyball or basketball) because indoor lighting will not produce bright sharp images (read: properly exposed) as good as daylighting

However for a 18-55 mm/f3.5 - 5.6 lens, the maximum opening at the 18 mm end is f3.5 while the maximum opening at the 55 mm end is f5.6. When you are at the end 18 mm end, you can set the aperture at f3.5 or narrower. When you are at the 55 mm end, you can only set the aperture at f5.6 or narrower.

lets not forget to mention the price difference which is HUGE!:Grin:
also the zoom with constant aperture is always bigger than its conterpart with variable aperture.
the other differene is build and optical quality. manufacturers tend to build into their more expensive model their latest technological innovation. having said that, their are variable aperture zooms with cheap plastic mounting that delivers fine, sharp images like the D40's kit lens.

ah i see.

so a constant low-numbered max aperture for a zoom (say 2.8) provides more aperture flexibility to the photographer since at all focal lengths he can start from a wide opening.

hmm ..interesting... but, yeah, i guess the constant max aperture zooms tend to be more expensive.

thanks guys!

ah i see.

so a constant low-numbered max aperture for a zoom (say 2.8) provides more aperture flexibility to the photographer since at all focal lengths he can start from a wide opening.



Not neccesarily, a lens can only have a number of stops, so if you notice lenses that starts with f/1.8 can only go to f/16 while lenses that starts with f/4 often goes all the way up to f/32



hmm ..interesting... but, yeah, i guess the constant max aperture zooms tend to be more expensive.



They are more expensive because these lenses are often the cream of the crop of the manufacturers and they use their best glass on it. Having a fixed aperture also means bigger glass, making it not just more expensive but also much heavier.

f stops are a measurement of the physical diameter of the aperture diaphragm, so if you notice its useage is f/2.0 where f = focal length, a lens that goes all the way to 100mm with a constant f/2.0 means its diagphram opening must be 50mm (100mm/2), as opposed to a lens that has a f/4.0 aperture that only has a digphram opening of 25mm. So this shows that the lens with f/4.0 can use glass half the size of the f/2.0

Ken

Not neccesarily, a lens can only have a number of stops, so if you notice lenses that starts with f/1.8 can only go to f/16 while lenses that starts with f/4 often goes all the way up to f/32



They are more expensive because these lenses are often the cream of the crop of the manufacturers and they use their best glass on it. Having a fixed aperture also means bigger glass, making it not just more expensive but also much heavier.

f stops are a measurement of the physical diameter of the aperture diaphragm, so if you notice its useage is f/2.0 where f = focal length, a lens that goes all the way to 100mm with a constant f/2.0 means its diagphram opening must be 50mm (100mm/2), as opposed to a lens that has a f/4.0 aperture that only has a digphram opening of 25mm. So this shows that the lens with f/4.0 can use glass half the size of the f/2.0

Ken

This is a very nice explanation sir. You made the explanation very elementary. Those Japanese sites (translated in Engrish) about lens design is simply confusing... :)

f stops are a measurement of the physical diameter of the aperture diaphragm, so if you notice its useage is f/2.0 where f = focal length, a lens that goes all the way to 100mm with a constant f/2.0 means its diagphram opening must be 50mm (100mm/2), as opposed to a lens that has a f/4.0 aperture that only has a digphram opening of 25mm. So this shows that the lens with f/4.0 can use glass half the size of the f/2.0

Ken

thanks for the simple yet useful illustration. i'll keep this in mind as i read more about the science side of photography.

thanks again all!:)

newbie question.. if you have a fix aperture.. then you cannot use the aperture priority settings since its constant???

newbie question.. if you have a fix aperture.. then you cannot use the aperture priority settings since its constant???

Aperture priority lets you set and lock the aperture value (say f/4.0), and the camera automatically chooses the appropriate shutter speed to get a decent exposure.

And yes you can still use it even if you have a fix aperture lens (primes, zoom/primes).

cheers! :)

newbie question.. if you have a fix aperture.. then you cannot use the aperture priority settings since its constant???

There are actually two operations going on here.

First - when you are in Aperture priority mode, what you are doing is presetting your aperture (f/stop) to a value i.e f/5.6 and then letting your camera software find the corresponding shutter speed based on your ISO and most of the time, the average exposure for the scene. It is independent of whether your zoom lens is constant aperture on not.

Second - when a zoom lens has constant aperture, the f/stop value does not change in the full zooming range of your lens. Say you have 15-70mm zoom at f2.8. Using Aperture priority mode, your f/top (f/2.8) will be the same from 15 to 70mm.

On the other hand, if the zoom lens is variable, again using 15-70mm as example with f/stop range from f/2.8 to f/4, your f/stop at 15mm will be f/2.8 and f/4 at 70mm. A loss of one f.stop.

got it guys...

Not neccesarily, a lens can only have a number of stops, so if you notice lenses that starts with f/1.8 can only go to f/16 while lenses that starts with f/4 often goes all the way up to f/32



They are more expensive because these lenses are often the cream of the crop of the manufacturers and they use their best glass on it. Having a fixed aperture also means bigger glass, making it not just more expensive but also much heavier.

f stops are a measurement of the physical diameter of the aperture diaphragm, so if you notice its useage is f/2.0 where f = focal length, a lens that goes all the way to 100mm with a constant f/2.0 means its diagphram opening must be 50mm (100mm/2), as opposed to a lens that has a f/4.0 aperture that only has a digphram opening of 25mm. So this shows that the lens with f/4.0 can use glass half the size of the f/2.0

Ken

Way to Go Master ken!!! yor expranation is very enrightening! and very rayman.

it does not mean that you cant use a different aperture.... constant aperture just states that you have the largest opening in both ends.... lets say if you have a 24-70 2.8.... if you set the aperture at 2.8 (which is the largest opening)... you can use it at 24mm....35mm.... and up to 70mm. Unlike regular lenses... lets say a kit lens 18mm-55mm F3.5-F5.6.... if you set your aperture to its largest opening to lets say F3.5 at 18mm....but the moment you turn the zoom ring...to 55mm the aperture has no choice but to change to 5.6.

So a constant 2.8 lens is a nice buy when doing events like weddings.... you get to use a 2.8 aperture at the widest focal lenth...and still a 2.8 aperture on the long end.