How big is f/1?


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yaoxing

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#1
We all know how big f/1.4 is compared to f/1, f/1.8 compared to f/1.4, etc... (relative sizes), but does anyone knows how big exactly is f/1? What's the diameter of the f/1 aperture? :embrass:
 

Ansel

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#2
The same as the focal length? If focal length is 50mm then the aperture is 50mm too. Have to confirm. This is just a guess. Now if you look at a 300mm f2.8, it's looks much bigger than a 35mm f2.8 right? It's got to do with the focal length, that's for sure. My guess is that f2.8 means that the aperture is 1/2.8 of the focal length. So, 1/2.8 of 300mm is much bigger than 1/2.8 of 35mm. So, f1.0 on a 50mm lens is 1/1.0 of 50mm = 50mm. Wah, 5cm wide man! :bigeyes:
 

showtime

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#3
ok so i have a 24-85 f3.5-4.5
thus the apperture size at the wide end is 1/3.5 of 24mm, which is 6.8mm? not even 1 cm?

that seems EXTREMELY small and i think visualy, the apperture seems bigger than that... maybe the theory is wrong? can anyone confirm?
 

#4
Yes, at the 24mm end, it's 24/3.5 = 6.8mm. Visually it seems bigger coz you're viewing it through a series of lens elements, which have a magnifying effect.

And yes, a 50/1.0 will have an aperture of 50mm. Which is why a 50/1.0 is so big.

Regards
CK
 

Ansel

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#5
showtime said:
ok so i have a 24-85 f3.5-4.5
thus the apperture size at the wide end is 1/3.5 of 24mm, which is 6.8mm? not even 1 cm?

that seems EXTREMELY small and i think visualy, the apperture seems bigger than that... maybe the theory is wrong? can anyone confirm?
Yes, I might be wrong, but don't forget you are looking thru a glass, ie, your lens, it may give you the impression it is bigger or smaller than it actually is.

I will do some research and get back.
 

blurblock

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#8
yaoxing said:
We all know how big f/1.4 is compared to f/1, f/1.8 compared to f/1.4, etc... (relative sizes), but does anyone knows how big exactly is f/1? What's the diameter of the f/1 aperture? :embrass:

I think the f-stop is in relevance to the focal length of the lens.

For example, a 50mm lens with an aperture of 50mm will give you a f/1 f-stop. The 50mm lens with an aperture of 38mm will give you a f/1.4, 50mm lens with an aperture of 28mm gives you f/1.8, 50mm lens with 18mm aperture gives you f/2.8...etc etc ....

Basic theory, fstop = focal length / aperture ....... of course, newer technology allows multiple lenses within a camera lens to produce focal length effect, making the camera lens shorter then the actual length, for example a Sigma 28-300mm is not 300mm long ;).

Just my 2cts ;).....
 

sehsuan

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#12
to add on to ckiang's answer... do note the nikon 70-200 VR. its aperture diameter ranges from 25mm to 71+mm, of which is house somewhere in the lens body. of course, needless to say, the filter is a 77mm :)

typically screw-in filters are a little larger than the largest aperture of a lens (or quite a bit more especially for variable aperture lens) since there has to be some leeway to account for vignetting. :)
 

blurblock

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#15
yaoxing said:
No wonder the 200-400mm f/2.8 looks like a flower pot! :bigeyes:
200-400mm at f/2.8? Is there such a lens? at 400mm the aperture size of the lens will be around 142mm :bigeyes: ..... adding another 54% for the angle of view, the filter size will be around 220mm :bigeyes:
 

Watcher

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#16
ckiang said:
Yes, at the 24mm end, it's 24/3.5 = 6.8mm. Visually it seems bigger coz you're viewing it through a series of lens elements, which have a magnifying effect.

And yes, a 50/1.0 will have an aperture of 50mm. Which is why a 50/1.0 is so big.

Regards
CK
The actual aperture diaphram (sp) can be bigger than say 6.8mm, however, the diameter of the rays of light passing through the diaphram is at guranteed to be at least 6.8mm. That is why at the other end of the lens (85mm), due to the focusing and zooming lens elements, the diameter has increased to 18.9mm. The diaphram does not change at all, but the circle of light does...
 

Watcher

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#17
sehsuan said:
to add on to ckiang's answer... do note the nikon 70-200 VR. its aperture diameter ranges from 25mm to 71+mm, of which is house somewhere in the lens body. of course, needless to say, the filter is a 77mm :)

typically screw-in filters are a little larger than the largest aperture of a lens (or quite a bit more especially for variable aperture lens) since there has to be some leeway to account for vignetting. :)
That is why the high cost of this pro lens, with a f/2.8 constant aperture. The design of the lens is very tricky...
 

Watcher

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#18
yaoxing said:
No wonder the 200-400mm f/2.8 looks like a flower pot! :bigeyes:
Or are you talking about the 400 f/2.8? That one is large... The 200-400 f/4 is already 124mm. I seem not to be able to find the diameter of the 400 f/2.8 out from Nikon's SG and US website... :dunno:

The AF Nikkor 300mm f/2.8 (non AF-S) is hmmm 133mm! :bigeyes: :bsmilie:
 

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