Lens Diameter

[Barqs]

Can someone please tell me the difference in the diameter of different lenses?
For example, is it better to have a 55mm or 62mm? Or does it matter at all?

Thanks for the help!

 

[AZ JazzyJ]

I don't know if there is a "magic number" for lens diameter. Typically the diameter of a lens is the product of the amount of light necessary to meet the aperature needs of the lens. Low light lenses typically have a larger diameter than those designed for larger aperatures since they need less light to reach the film or sensor to properly expose the photo. Most of my f/2.8 zoom lenses have a 72mm diameter but I do have one at 62mm. The only plus of having lenses with all the same diameter is that if you use filters you only need to buy one size.

Jeff

 

[0bli0]

diameter does relate to aperture (along with focal length). the longer the lens, and faster the aperture, the larger the diameter.
most of the recent black 'L' lenses are 77mm.

 

[jann1033]

so then even though it's low light my canon 50mm1.8 is 55mm(or 58,now i can't think) due to the 50mm?

 

[seashoreCM]

The larger the lens diameter, the faster the lens is, in a general sense. Faster means admitting more light for a given shutter speed.

Maximum aperture or lens speed, is stated as an f-stop, f/2.8 being common for today's digital point and shoot cameras unzoomed to the widest angle. The smaller the f-stop number, the more light is admitted; the larger the opening in the lens iris relative to the focal length.

"Millimeter Lens" also refers to focal length which has to do with wide angle versus telephoto versus zoom representing field of view. Digital cameras may or may not be described with a 35 mm film camera equivalent for focal length. The only easy way to compare apples with apples is when both cameras you are comparing have focal length stated in 35mm film camera equivalents. Standard angle for most point and shoot cameras made in the last 30 years is between 35 and 38 mm focal length in 35mm film camera equivalent. Traditional 35mm film and larger format film cameras use 50mm lenses as standard angle whereby 35mm lenses are considred wide angle. The typical point and shoot 3x zoom camera goes up to about 105 to 110mm focal length, 4x zoom goes up to about 140 to 150mm focal length (35mm film camera equivalent).

Regardless of the focal length, f/2.8 always means the same amount of light admitted for a given shutter speed, f/4 always means the same amount of light for a given shutter speed, etc. But as the zoom is changed (the focal length is changed) and the lens iris opening stays the same in absolute diameter, the f/stop will change, admitting less light as zoom is increased. A typical camera with an f/2.8 lens and 3x zoom will have at most about f/4.5 in terms of light admittance when zoomed to the maximum.

Approximate focal length versus field of view:
28mm -- 65 degrees side to side
38mm -- 50 degrees
50mm -- 40 degrees
70mm (typical 2x zoom) -- 30 degrees
105mm (typical 3x zoom) -- 20 degrees
140mm (typical 4x zoom) -- 15 degrees

(What is 2x, etc. zoom varies with the widest angle provided on the camera)

 

[boBQuincy]

so then even though it's low light my canon 50mm1.8 is 55mm(or 58,now i can't think) due to the 50mm?

It mostly comes down to the physics of light and glass, most 50mm f/1.8 lenses will have a similar filter diameter, most 50mm f/1.4 lenses will be larger.

The aperture is not totally related to the filter diameter, the aperture is buried deep in the lens. For a 50mm f/1.8 the aperture opens to about 28mm. Because of the physics of lens construction the front element of a 50mm ends up being about twice the aperture size.

In the olden days of manual lenses we could set the aperture and see the circular (sort of) blades chaging the size of the opening. These new-fangled electronic automagic lenses stay wide open until the camera tells them to move. We can still see this by taking a long exposure and staring into the lens, but I wouldn't do it in public!

 

[0bli0]

you can also press the depth of field preview to see the aperture blades close down.

yes i should have been more specific - aperture equals physical opening diameter (the hole the blades make) divided by the focal length. so to get the larger opening for the appropriate focal length, you need to have a wider lens barrel. this is why my 120-300 f2.8 (constant aperture) is 105mm at the lenscap end.

 

[boBQuincy]

you can also press the depth of field preview to see the aperture blades close down.

And you bring up a good point, 0bli0!
How many people even realize our dSLRs have a depth of field preview button, and what it does?

The lens remains wide open until the moment of exposure, so you never see anything but the minimum depth of field. *However*, when the lens closes down for the exposure, what is in focus may change quite a bit and the "surprises" are not always good ones.

If you are going for selective focus, or even if not, press the depth of field button before pressing the shutter button, and see how the scene changes. You may just decide to change the aperture before taking the photo.

 

[Groucho]

And you bring up a good point, 0bli0!
How many people even realize our dSLRs have a depth of field preview button, and what it does?

The Nikon D50 lacks a depth of field preview, and with it being such a common DSLR, lots of people don't have it available.

The D70 does have it - and I think all Canons do as well? On the Pentaxes, it's integrated into the rotating power switch (which surrounds the shutter) - very handy, as your finger can pull the switch for the DOF preview then it's already right on top of the shutter.

 

[Snurk71]

My head hurts...

Okay, I have a pretty elementary question since I don't understand a lot of what is going back and forth here.

If I have an 18-125mm lens and a 50mm prime lens (regardless of the aperature values on either lens), will the field of view/picture taken be the same "width" if I had the 18-125mm zoomed to 50mm? Another way to ask the question, will the 50mm lens already be "zoomed in" closer that where the 18mm would be at its furthest zoom point?

 

[handicap18]

The larger the lens diameter, the faster the lens is, in a general sense. Faster means admitting more light for a given shutter speed.

Maximum aperture or lens speed, is stated as an f-stop, f/2.8 being common for today's digital point and shoot cameras unzoomed to the widest angle. The smaller the f-stop number, the more light is admitted; the larger the opening in the lens iris relative to the focal length.

"Millimeter Lens" also refers to focal length which has to do with wide angle versus telephoto versus zoom representing field of view. Digital cameras may or may not be described with a 35 mm film camera equivalent for focal length. The only easy way to compare apples with apples is when both cameras you are comparing have focal length stated in 35mm film camera equivalents. Standard angle for most point and shoot cameras made in the last 30 years is between 35 and 38 mm focal length in 35mm film camera equivalent. Traditional 35mm film and larger format film cameras use 50mm lenses as standard angle whereby 35mm lenses are considred wide angle. The typical point and shoot 3x zoom camera goes up to about 105 to 110mm focal length, 4x zoom goes up to about 140 to 150mm focal length (35mm film camera equivalent).

Regardless of the focal length, f/2.8 always means the same amount of light admitted for a given shutter speed, f/4 always means the same amount of light for a given shutter speed, etc. But as the zoom is changed (the focal length is changed) and the lens iris opening stays the same in absolute diameter, the f/stop will change, admitting less light as zoom is increased. A typical camera with an f/2.8 lens and 3x zoom will have at most about f/4.5 in terms of light admittance when zoomed to the maximum.

Approximate focal length versus field of view:
28mm -- 65 degrees side to side
38mm -- 50 degrees
50mm -- 40 degrees
70mm (typical 2x zoom) -- 30 degrees
105mm (typical 3x zoom) -- 20 degrees
140mm (typical 4x zoom) -- 15 degrees

(What is 2x, etc. zoom varies with the widest angle provided on the camera)

WOW, that is a LOT of information. Probably a little more than what the OP was looking for.

I think most people answered it pretty much with the wider the aperture of the lens (smaller f/stop number) the greater the physical width of the lens will more than likely be. A 70-300mm f/4-5.6 (@67mm)will have a smaller physical width than a 100-300 f/4 (@82mm). It isn't always the case though. The Nikon 70-200 f/2.8 and the Nikon 80-400 f/4.5-5.6 both take a 77mm filter.

When all is said and done, the size filter a lens takes is about the last thing to really look for in a lens.

For example: Nikon has a 70-300mm f/4-5.6D ED AF (62mm filter size) and a 70-300mm f/4.5-5.6G ED-IF AF-S VR (67mm filter size) and Sigma has a 70-300mm F4-5.6 APO DG MACRO (58mm filter size). Are you going to make your decision on which lens to get based on the filter size?

 

[Groucho]

My head hurts...

Okay, I have a pretty elementary question since I don't understand a lot of what is going back and forth here.

If I have an 18-125mm lens and a 50mm prime lens (regardless of the aperature values on either lens), will the field of view/picture taken be the same "width" if I had the 18-125mm zoomed to 50mm? Another way to ask the question, will the 50mm lens already be "zoomed in" closer that where the 18mm would be at its furthest zoom point?

Yes, on the same sensor (ie, the same camera), the field of view will be identical with a 50mm prime vs an 18-125mm at 50mm. The advantage of the prime is that it's optically designed for 50mm only, so will generally be a bit sharper and have better colors/contrast, it can be faster (much faster, sometimes), and it can be a lot smaller.

 

[MarkBarbieri]

the size filter a lens takes is about the last thing to really look for in a lens

I agree with this. The only time the lens diameter/filter size matters to me is when it exactly matches another one of my lenses. That means that I can share filters for those lenses.