Filter Size (Lens Diameter) and Exposure

frXnz kafka

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Been looking to upgrade my walk-about lens lately, and I've been trying to wrap my head around filter sizes. Google was no help, so I thought I'd bring it here.

What is the difference, in terms of the amount of light coming in, between say a lens with a 58mm filter size and a lens with a 77mm filter size? Does the 77mm let in more light, allowing for a faster exposure? Or is there some other advantage I'm missing?
 

Big Mike

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You are sort of on the right track...but looking at the wrong thing and putting the cart before the horse.

A lens with a bigger maximum aperture will let in more light...and that will be in the name of the lens as an F number.

Now, in order to get that larger maximum aperture, lenses often have to be designed with a larger front element and therefore a larger filter diameter.
 

brileyphotog

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Often is the key word...the Nikon 50mm f/1.8, for instance, has a 52mm filter size.

Little number behind the "f/" = big aperture = faster lens...easy as pie
 

AndrewG

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Been looking to upgrade my walk-about lens lately, and I've been trying to wrap my head around filter sizes. Google was no help, so I thought I'd bring it here.

What is the difference, in terms of the amount of light coming in, between say a lens with a 58mm filter size and a lens with a 77mm filter size? Does the 77mm let in more light, allowing for a faster exposure? Or is there some other advantage I'm missing?

The amount of light a lens will admit is governed by its maximum aperture given by the f number. The filter size (diameter across the filter thread) has no influence on exposure. Thus an exposure of, say, 125th and f8 will be the same whether the lens has a filter diameter of 39mm or 77mm.
 
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astrostu

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Math-wise, the amount of light that comes through the lens goes as the diameter-squared. The f/number is directly related to the aperture (aperture/focal length or vice versa, can't remember off-hand).

So, if you have an f/2.8 lens vs. an f/4.0 lens, then you could feasibly take photographs that are (2.8/4.0)^2 = (0.7)^2 = 0.49 => 49% as long with the f/2.8 lens vs. the f/4.0 lens and still get the same amount of light. This becomes very important when shooting in low-light situations where you need a faster shutter speed.

As a rule of thumb, ever successively smaller aperture (so like 6.3 -> 5.4, or 1.6 -> 1.4) will allow you to capture the same amount of light in approximately 73% of the amount of time.
 
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frXnz kafka

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I know all about aperture and F-stops, but surely there is a difference between an f/4 lens with a 58mm filter and an f/4 with a 77mm filter, right?
 

Big Mike

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I know all about aperture and F-stops, but surely there is a difference between an f/4 lens with a 58mm filter and an f/4 with a 77mm filter, right?
Not in terms of light gathering ability or exposure. F4 is F4.

Sometimes, the choice of filter size is more of a convenience. I believe that most of Nikon's pro level lenses are 77mm, even though some of them might not need to be that wide. This is good because the filters and lens caps are interchangeable between them.
 
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astrostu

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I know all about aperture and F-stops, but surely there is a difference between an f/4 lens with a 58mm filter and an f/4 with a 77mm filter, right?

What Big Mike said. I would also think that the smaller filter lens would be poorer quality, just 'cause if you're going to make big glass, usually it's higher quality.

Do you have an example ofan f/4 58mm aperture vs. f/4 77mm aperture? If you have a specific example, we might be able to tell you better why that may be the case.
 

christopher walrath

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The 77 is probably on something like an UBER-zoom (28-200 or more). But beware, the front element sticks out far enough that you may need a spacer for a thread on lens. A filter threaded right on the front might make contact with the front glass causing scratching, a fault that the chap who sold me my 28-200 apparently didn't know before he shipped it out. Lesson learned and all . . .
 
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frXnz kafka

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The 77 is probably on something like an UBER-zoom (28-200 or more). But beware, the front element sticks out far enough that you may need a spacer for a thread on lens. A filter threaded right on the front might make contact with the front glass causing scratching, a fault that the chap who sold me my 28-200 apparently didn't know before he shipped it out. Lesson learned and all . . .
Huh? 77mm is the standard for most pro glass, it's not just for super-zooms.
 

ann

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i have several lenses that take 77mm filters., all are 2.8 lens either film or digital makes no differences 77mm is 77mm
 

Samriel

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There is also the matter of the sweet spot on a lens. The bit in the middle is the best for taking photos. So, the more in the middle the better the lens. ;)

Not sure if this statement is a joke or for real. It does make sense to me though. Else I don't get why the Nikkor 50mm F/1.4 has a 52mm filter and the Sigma 50mm F/1.4 has a 77mm filter. Trying to use the advantage of this sweet spot?
 

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It may seem like the diameter of the front of a lens ought to be related to its
light transmission but it isn't. It all depends on the lens design. For example,
some wide angle lenses have quite large front elements but their light
transmission may be relatively low. The same with some zooms that have long
focal length ranges, like 28-200mm, etc. They can have very large front
elements but a relatively small max aperture.

Also, manufacturers try to keep filter size the same as much as possible for
their lenses so they may design them with the same front dimensions when
they can, even though these lenses may have differing maximum apertures.
This saves the owner from having to buy many sizes of filters.
 

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