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Thread: less than f2.8 vs f4 and above

  1. #1

    Default less than f2.8 vs f4 and above

    hi people always say FASTER the better faster the better etc..

    how much difference is practical terms is there btw f2.8 (and below) and f4? (more specifically, those super exp 2.8 lenses vs the also quite exp f4 ones. namely the 2 versions of 70-200mm L)

    Practical terms meaning :

    1. Since its brighter, HOW MUCH darker or faster are u able to achieve good AF using the 2.8 vs 4.0? Would the fact taht u have a focus assist (or even better external speedlite)
    [im asssuming just just coz it allow twice the light to get in, DOES NOT MEAN u can AF twice as fast, or twice as dark rite? im sure the lower DOF of the 2.8 also affects AF... so its not a linear relationship]

    Anyone have any practical values? (eg. In street lamp light, 2.8 can acheve AF 50% faster, or can af 80% of the time vs f4s 50%)

    2. 2.8 allows DOUBLE the light of the 4.0 right? so basically this would mean shutter speed can be TWICE as fast as if u were to use a 4.0? (correct if im wrong)

    3. Bokeh wise, are both equally good?

    4. distortion wise at full wide, both as good?


    Thanks!!

  2. #2

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    Quote Originally Posted by sprockett
    1. Since its brighter, HOW MUCH darker or faster are u able to achieve good AF using the 2.8 vs 4.0? Would the fact taht u have a focus assist (or even better external speedlite)
    [im asssuming just just coz it allow twice the light to get in, DOES NOT MEAN u can AF twice as fast, or twice as dark rite? im sure the lower DOF of the 2.8 also affects AF... so its not a linear relationship.Anyone have any practical values? (eg. In street lamp light, 2.8 can acheve AF 50% faster, or can af 80% of the time vs f4s 50%)
    AF performance doesn't just depend on aperture but also other factors such as contrast and lens design(number of elements, IF, RF, floating element...etc)

    Generally, speaking a brighter lens will AF faster and hunt less than a darker lens ceteris paribus or all other factors held constant.

    There is no way to quantify the exact values.

    2. 2.8 allows DOUBLE the light of the 4.0 right? so basically this would mean shutter speed can be TWICE as fast as if u were to use a 4.0? (correct if im wrong)
    Yes.

    3. Bokeh wise, are both equally good?
    It depends on the design and optical formula of the lens. Generally the faster lenses have better bokeh, but not always.

    4. distortion wise at full wide, both as good?
    Depends on design.

  3. #3

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    If you want to isolate your subject from the background the f2.8 is better than f4.0.

  4. #4
    Senior Member sykestang's Avatar
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    From my understanding... it is the difference in the optics. Generally speaking, Lens manufacturing process, the most expensive is the lens polishing process. And this not only involve the front piece of glass but to all glass elements found in the lens. Thus this is the main reason why bigger f-stop lens cost more.

    Say for instance a f4 lens, as the apperture is only up to f4, the polishing process may only involved in the center portion of the lens up to diameter for maybe f3.6-f3.8. This is because only this center diameter constributed the maximum of light to enters the lens.

    Now compare to a f2.8, the polishing may involved a diameter of f2.2 or maybe up to the whole diameter of the lens.

    Thus in general we classified this as a 'brighter' lens as it allow more surface area for light to enter through the lens. And this thus produce a more sharper, higher contrast, images.

    The f-stop no. on the lens does really not contribute a very significant in operation performance like faster AF, better AF, etc. However the better term should be the quality of the pictures, ease of using like in dark events, a f1.4 lens might even give you good pictures without flash, and this is quite important as we all know flash in one way or another, do not give the real colors of the object that we are taking.

    Hope this info helps.

  5. #5

  6. #6

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    Quote Originally Posted by sykestang
    The f-stop no. on the lens does really not contribute a very significant in operation performance like faster AF, better AF, etc.
    (1) I presume that before you made this statement, you tested the AF speed of a f/2.8 lens to a f/4 lens? Which body/lens combination did you test?

    Having tried the 300 f/2.8 at the Clubsnap/Canon Zoo outing with D60, I think its AF speed is faster than a 300 f/4.

    also the off-centre cross sensors of eos-1/3 series only operate with f/2.8 or faster lenses.

    Quote Originally Posted by sykestang
    Thus in general we classified this as a 'brighter' lens as it allow more surface area for light to enter through the lens. And this thus produce a more sharper, higher contrast, images.

  7. #7

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    The differences between a 2.8 and 4 lens would be more pronounced at longer focal lengths because you'd be able to see better bokeh effects and shallower DOF.

    However, 2.8 lenses are usually infused with all the goodies a lens mfg can also offer. So regardless of focal length, you usually get a metal construction, better lens coatings and other exotic offerings, all of which translates into pictures with higher contrast, saturated colors, etc etc.

    A 2.8 lens would allow focusing in darker conditions since it lets more light in. Plus if you're using MF, your viewfinder would be brighter as well. Don't think any practical values exist for AF timing, IMO you'd be interested in AF accuracy with limited light and not timing, coz once the camera AF sensors detect the focus correctly, its a matter of turning the AF screw.

    Bokeh wise a faster lens *usually* gives better bokeh but this is not always true. Faster lenses will usually have better control of distortion.

  8. #8

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    wah thaqnks a billion for all the replies!!!

    how much better is a 50 1.4 vs the 1.8?

    in terms of optical quality, coz i've heard glowing reports for all..

    of coz 1.4 has USM which the 1.8 doesnt...so AF speed maybe affected aswell..

    thanks!

  9. #9

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    Quote Originally Posted by sykestang
    Say for instance a f4 lens, as the apperture is only up to f4, the polishing process may only involved in the center portion of the lens up to diameter for maybe f3.6-f3.8. This is because only this center diameter constributed the maximum of light to enters the lens.

    Now compare to a f2.8, the polishing may involved a diameter of f2.2 or maybe up to the whole diameter of the lens.
    You're saying that lenses with smaller apertures have lens elements only polished in the centre?

    But then f2.2 is larger than f2.8 and f3.6-3.8 is larger than f4 as well...wat gives?

    Aperture Diameter=Focal length/F-stop

    Shouldn't it be that f2.8 lenses have much larger front elements to begin with? I'm sure they are polished all round all my lenses whether f2.8 or f5.6 consumer zooms are pretty shiny.

  10. #10

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    To summarize, f2.8 (and below) lenses:

    1. Are usually termed "pro" lenses (as opposed to "consumer" lenses). This is especially so in the case of zooms.

    2. Allow faster AF, because of more light coming through (all other things [eg camera bodies] being equal). Incidentally, a narrower DOF should make it easier to achieve AF lock (and more accurate), since the contrast between in-focus and out-of-focus areas is greater

    3. Allow a faster shutter speed to be used

    4. Have less distortion (since the lens elements are larger)

    5. Are significantly costlier (although a 3rd party f2.8 like Sigma may cost about the same as a branded "consumer" lens). Prime lenses are a good compromise between cost and aperture size

    6. Are significantly bigger and heavier

    7. Give better image quality

  11. #11
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    (more specifically, those super exp 2.8 lenses vs the also quite exp f4 ones. namely the 2 versions of 70-200mm L)
    70-200mm F4 vs F2.8

    Weight
    F4 = 705g
    F2.8 = 1,310g

    Size
    F4 = 76 x 172mm
    F2.8 = 84.6 x 193.6mm

    Cost (w/o gst and IS)
    F4 = $1,250
    F2.8 = $1,925

    Aperture
    F4
    F2.8

    As you see, the only obvious advantage you'll have for the F2.8 is one extra stop of Light and Shallower DOF at wide open.

    Size is around the same.

    However, the penalty for F2.8 is that you'll have to carry double the weight of the F4 around for the whole day.
    Last edited by jasonpgc; 3rd September 2003 at 12:26 PM.

  12. #12

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    Quote Originally Posted by jasonpgc
    As you see, the only obvious advantage you'll have for the F2.8 is one extra stop of Light and Shallower DOF at wide open.
    For me, that makes a lot of difference as I like to shoot in low light without flash.

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    Quote Originally Posted by Newman
    For me, that makes a lot of difference as I like to shoot in low light without flash.
    For me, WEIGHT makes a lot of difference as I like to shoot WITH TRIPOD in low light without flash.

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    Quote Originally Posted by Lennier
    A 2.8 lens would allow focusing in darker conditions since it lets more light in. Plus if you're using MF, your viewfinder would be brighter as well. Don't think any practical values exist for AF timing, IMO you'd be interested in AF accuracy with limited light and not timing, coz once the camera AF sensors detect the focus correctly, its a matter of turning the AF screw.
    this i guess is the main reason why fast lenses are even more appropriate
    for DSLRs'. correct me if i'm mistaken, but with the corresponding smaller viewfinder/CMOS for the DSLRs, it would allow the human eye to see easier with a faster lens in relatively darker places (eg indoor) than say, f/3.5 or f/4 lenses. in other words....

    f/2.8 with the 1.6x crop factor (more light) > f/3.5 OR f/4 with f/1.6x crop factor (lesser light)

    my guess here, nothing scientific...

  15. #15
    Senior Member sykestang's Avatar
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    Quote Originally Posted by erwinx
    (1) I presume that before you made this statement, you tested the AF speed of a f/2.8 lens to a f/4 lens? Which body/lens combination did you test?

    Having tried the 300 f/2.8 at the Clubsnap/Canon Zoo outing with D60, I think its AF speed is faster than a 300 f/4.

    also the off-centre cross sensors of eos-1/3 series only operate with f/2.8 or faster lenses.


    Frankly, I don't own 2 lenses of the same with different f-stop. It would sound so stupid for me to do that anyway.... Unless I am pro enough for the makers to sponsor me

    Anyway, current own a Nikkor Prime AF300ED-IF f4 and a Nikkor Tele-Zoom AF80-200 f2.8ED. The only AF speed I notice is that the f2.8 do not 'hunt' as much as the f4 lens that I own... This is correct as f2.8 lens is brighter than f4 thus it is easier to focus... Notice both my lens are of the upper range and is abt the same class not with those lenses that have a range of f-stop like f4.5-f5.6, etc. Also both lenses is AF not the AF-S version which equip with a silent-wave motor which is more superior in AF speed. Thus I presume both lens have the same motor. As in most cases, the maker of f2.8 lens also equip with better motor and additional stuff and technology, it is hard to compare AF speed. What my previous msg is comparing a make of a f2.8 lens and a f4 lens.

    As for your case with Canon, I can't say much cos I never like Canon to keep an update on their technology. But are you sure the make of the 2 lenses you mention is of the same quality except only for the f-stop of the glass element??? If you would like, I can also compare Nikkor AF-S 300mm f/2.8 with Nikkor AF300mm f/4... then I tells the whole world that f/2.8 lens is faster than f/4... which in this case not true, as now the f/2.8 I mention is equip with a AF-S motor!!! You must compare an apple with another apple... not apple with a water melon then say that the water melon is bigger!!!

    Anyway don't meant to start any flaming wars here, just clearing a point in optics technology and quality in output... not AF speed performance that we are talking.

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    Quote Originally Posted by sprockett
    wah thaqnks a billion for all the replies!!!

    how much better is a 50 1.4 vs the 1.8?

    in terms of optical quality, coz i've heard glowing reports for all..

    of coz 1.4 has USM which the 1.8 doesnt...so AF speed maybe affected aswell..

    thanks!
    For 50 1.4 vs the 1.8 comparison
    http://www.photo.net/equipment/canon/ef50/

    http://cybaea.com/photo/lens-quality-50.html

    http://www.seittipaja.fi/data/pdf/Po...rsus_fifty.pdf
    Last edited by cheechee; 4th September 2003 at 01:14 AM.

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    Just want to contribute a bit.
    Zerstorer > In your first thread, a larger aperture doesn't give a "better"
    bokeh, it just give less depth of field. Bokeh is also determined by a few other factors, like optical purity of the glass and the shape of the aperture ( 5,6,8,11 blades or round aperture) etc etc.

    To some traditionalists, a good bokeh is defined as even blurring, ie a point of light is blurred as a round patch, not hexagonal or what have you.

  18. #18

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    Quote Originally Posted by Prismatic
    Zerstorer > In your first thread, a larger aperture doesn't give a "better"
    bokeh, it just give less depth of field. Bokeh is also determined by a few other factors, like optical purity of the glass and the shape of the aperture ( 5,6,8,11 blades or round aperture) etc etc.

    To some traditionalists, a good bokeh is defined as even blurring, ie a point of light is blurred as a round patch, not hexagonal or what have you.
    Actually, that was what I meant by "not always", without going into detail.

    When comparing the pro version of one lens to another from the same manufacturer, the faster glass almost always comes with rounder aperture, better optical formula and subsequently better bokeh.

  19. #19
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    Quote Originally Posted by erwinx
    Having tried the 300 f/2.8 at the Clubsnap/Canon Zoo outing with D60, I think its AF speed is faster than a 300 f/4.
    So how does the 300/4 compare to your 500/4?

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