constant f vs not (e.g. f2.8 vs f2.8-4)


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Jun 1, 2006
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#1
want to know the differences and pros & cons...

what you would prefer and why.
 

fireframe

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#2
Cons: Usually more expensive and heavier
Pro: More flexibility in aperture settings. Lens will be more useful in more situations.

Money aside, of course it's better to have the fixed maximum aperture. But then if you find yourself shooting at much smaller apertures (to get wider DOF, for example) most of the time, then it's a darn good waste of money. :p

Of course, there's always the better build, as these 'fixed' lenses are usually in the more 'pro' category.
 

westwest1

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#3
Benjymocha said:
want to know the differences and pros & cons...

what you would prefer and why.
constant aperature feel better...f2.8 mean its f2.8 all the way...dun need to worry...

these lens got higher resales value too...:thumbsup:
 

kcuf2

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#4
lets say a 70-200 f2.8 lens and another lens 70-200 f2.8-4

For the 1st lens 70-200 f2.8, from the range of 70mm to 200 mm, u can shoot it at f2.8, meaning u can maintain a constant speed of 1/200s for example...

but for the other 70-200 f2.8-f4 lens, at 70mm u can shoot at 1/200s, but at 200mm, u can only shoot at 1/100s.

this difference in speed can mean a blur and sharp picture..
 

Apr 12, 2005
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#6
Benjymocha said:
want to know the differences and pros & cons...

what you would prefer and why.
The differance is in the largest aperture you can use for the short or long end of the zoom.

For a F/2.8 lens, the largest aperture you still can use is F/2.8 whether you're shooting at the short or long end of the zoom. For e.g. a 70-200mm lens, the largest aperture you can use is F2.8 when you shoot at any focal length (70mm to 200mm).

For a F/2.8-F/4 70-200mm lens, if you're shooting at 200mm, the largest aperture you can use is only F/4 (which is 1-stop smaller than F/2.8) which means in situations where a proper exposure can be achieved with using F/2.8 aperture size combined with a certain shutter speed and ISO on the F/2.8 lens, you can only use F/4 and then compensate with a higher ISO or slower shutter speed than a F/2.8 70-200mm lens. In some situations, it could mean not getting the depth of field you prefer (F/2.8 vs F/4) or not fast enough shutter speed (to freeze actions) or too much noise from using a higher ISO.

Of course, for the F/2.8 lens, you still can use F/4 for whatever focal length and so it can do whatever the F/2.8-F/4 lens can do and then more.

So the choice is clear. As aperture size in terms of F-stops is a relative number between the actual aperture size and focal length, a long focal length means that a good sharp F/2.8 lens has much more glass and also much more difficult to manufacture than a F/2.8-F/4 lens. Thus, a F/2.8 lens is much more expensive than a F/2.8-F/4 lens, everything else constant.
 

Artosoft

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#7
+evenstar said:
and it can mean a correctly exposed vs underexposed image if you're shooting M mode..
You can always put your attention on your camera light meter and adjust aperture/shutter speed properly...

Regards,
Arto.
 

Jun 1, 2006
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#8
kcuf2 said:
lets say a 70-200 f2.8 lens and another lens 70-200 f2.8-4

For the 1st lens 70-200 f2.8, from the range of 70mm to 200 mm, u can shoot it at f2.8, meaning u can maintain a constant speed of 1/200s for example...

but for the other 70-200 f2.8-f4 lens, at 70mm u can shoot at 1/200s, but at 200mm, u can only shoot at 1/100s.

this difference in speed can mean a blur and sharp picture..
sorry for the stupid qn, could be that i'm not awake yet but how do u correlate the 1/100s and 1/200s with the f-stop? :dunno:
 

Jun 1, 2006
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#10
Clockunder said:
For a F/2.8-F/4 70-200mm lens, if you're shooting at 200mm, the largest aperture you can use is only F/4 (which is 1-stop smaller than F/2.8) which means in situations where a proper exposure can be achieved with using F/2.8 aperture size combined with a certain shutter speed and ISO on the F/2.8 lens, you can only use F/4 and then compensate with a higher ISO or slower shutter speed than a F/2.8 70-200mm lens. In some situations, it could mean not getting the depth of field you prefer (F/2.8 vs F/4) or not fast enough shutter speed (to freeze actions) or too much noise from using a higher ISO.
so if F/4 is just 1 stop smaller, would you compromise and get a F4 instead of F2.8 cos of price?
 

jnet6

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#11
Benjymocha said:
so if F/4 is just 1 stop smaller, would you compromise and get a F4 instead of F2.8 cos of price?
For example @ 200mm... yr f-stop @ F4, yr shutter metered @ 1/60.
If you got a F2.8 "constant" 70-200mm, @ 200mm, F2.8, S=1/125, more advantage if you do not want to increase yr ISO. :)
 

zac08

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Feb 21, 2005
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#12
Benjymocha said:
so if F/4 is just 1 stop smaller, would you compromise and get a F4 instead of F2.8 cos of price?
If you shoot in bright light conditions and do not need faster focusing. Then you may wish to compromise and get the cheaper f4 option. But if you need low light capabilities then you may need the f2.8
 

DeSwitch

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#13
if $$$ not issue get f2.8. Its always a better choice. if you get f2.8, you can add 2x TC and still use AF cos it now f5.6 but if you get the f4 and add 2x TC, yr max aperature becomes f8 and unless you have a 1 series body, you cannot use AF.
 

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#14
A f2.8 will also make the viewfinder brighter than a f4.

Not forgetting most lenses are sharper when stopped down. Hence a f2.8 can get great sharpness at f4, while a f4 will need go down to f5.6 for equal sharpness.
 

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