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Thread: Need advise on Lens.

  1. #1
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    Default Need advise on Lens.

    I have been reading with great interest on Lenses with constant aperature like f4 etc. It make me a litle confuse here. Lets say we have 2 lenses with the same focal length. example Canon 70-200 f2.8L and another Canon 70-200 f4L, will there be any dofferent if I were to take the same picture with both aperature set to f4.

    The answer may help some newbies like me to decide which lens to buy if future because I know some of us dont really need f2.8. It will save some $$$.


    Thanks.

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    Moderator ortega's Avatar
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    Default Re: Need advise on Lens.

    exposure wise, it will not make a difference

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    Default Re: Need advise on Lens.

    Quote Originally Posted by De'Switch
    I have been reading with great interest on Lenses with constant aperature like f4 etc. It make me a litle confuse here. Lets say we have 2 lenses with the same focal length. example Canon 70-200 f2.8L and another Canon 70-200 f4L, will there be any dofferent if I were to take the same picture with both aperature set to f4.

    The answer may help some newbies like me to decide which lens to buy if future because I know some of us dont really need f2.8. It will save some $$$.


    Thanks.
    I've not used either lens so I can't comment on their quality per se.

    Generally, when you use a lens at its maximum aperture, the result is likely to be not as sharp, and some lenses may exhibit light falloff at the corners. So on that basis, the f/4 lens might not perform as well as the f/2.8 when both are set to f/4.

    In terms of exposure, f/4 is f/4 on any lens, regardless of maximum aperture.

  4. #4

    Default Re: Need advise on Lens.

    To add on... Based on your example, F2.8 will give an additional stop of light (relatively more useful under low light), narrow depth of field (background blur) and lots of extra weight for muscle building.

  5. #5
    Phildate
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    Default Re: Need advise on Lens.

    Yes, there will be a difference because the f2.8 lens is a better quality lens all round. The quality of glass/elements allows it to have a max aperture of 2.8 but you should also see the improvements at every other aperture.

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    Default Re: Need advise on Lens.

    if i'm not wrong, the F2.8 will yield sharper results at F4 as compared.

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    Senior Member jnet6's Avatar
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    Default Re: Need advise on Lens.

    also a big diff for 85mm F1.8/F1.4/F1.2...

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    Default Re: Need advise on Lens.

    Quote Originally Posted by efreedom2001
    I've not used either lens so I can't comment on their quality per se.

    Generally, when you use a lens at its maximum aperture, the result is likely to be not as sharp, and some lenses may exhibit light falloff at the corners. So on that basis, the f/4 lens might not perform as well as the f/2.8 when both are set to f/4.

    In terms of exposure, f/4 is f/4 on any lens, regardless of maximum aperture.

    I'm only using this 2 lens as example becos they have the same focal length. I also believe f4 is f4 on any lens. Of course, the material used on the lens and coatings make some difference in the quality of the photo. What if we assume all other condition are the same any the only difference is the minimum aperature. Will it make a difference in the picture quality? I'm trying to differenciate the must have and the good to have.

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    Default Re: Need advise on Lens.

    Quote Originally Posted by shinken
    To add on... Based on your example, F2.8 will give an additional stop of light (relatively more useful under low light), narrow depth of field (background blur) and lots of extra weight for muscle building.

    This should be the only advantage of the f2.8 over the f4 right?


  10. #10
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    Default Re: Need advise on Lens.

    If you can afford it, get the f2.8 lens. The old adage of 'You get what you pay for' is usually true for photographic equipment.

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    Moderator ortega's Avatar
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    Default Re: Need advise on Lens.

    you must consider if it is a want or a need
    good to have but will not suffer if you don't

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    Default Re: Need advise on Lens.

    f4 is not f4 on any lense, unless they share the same focal lengths and max aperture.

    Technically, shooting the 70-200 f2.8 @f4 will produce a sharper image than to shoot 70-200 f4 @f4. How do I put this.... well think of it like this, 70-200 f2.8 @f2.8 is 'equal' to 70-200 f4 @f4. And if you shoot 70-200 f2.8 @f4 that would be 'equal' to 70-200 f4 @f5.6. You get the idea? Both the lenses are built differently, they may have similiar focal lengths but manufacture problems + physics complicates things.

    In reality when you have the chance, it's always good to go try out for yourself. Shoot both lenses at f4 and compare the shutter speeds at a focal length. What I wrote above might be wrong, it's just what my brain tells me.

    Just curious I see in your signature, why would it be a 'must have/good to have' when you already have the 70-300 sigma macro? Getting a telezoom 70-200 is redundent unless you sacrifice the macro lense?

  13. #13

    Default Re: Need advise on Lens.

    Quote Originally Posted by De'Switch
    This should be the only advantage of the f2.8 over the f4 right?

    Extra stop of light and narrower DOF. Plus what others mentioned and I left out: the F2.8 lens is likely to be sharper at F4 compared to an F4 lens. However, don't take is for a given that any large aperture lens would be sharper than a smaller aperture lens. For the 70-200 lens, the optics of the F2.8 is arguably superior than the F4 to begin with. Another exception to the rule (larger means sharper when stopped down) is that the difference is sharpness is most obvious when stopped down 1 or 2 stops from maximum aperture (not minimum. F2.8 is a larger aperture than F4). Thus, the F2.8 is sharper at F4 than the F4 at F4. However, when stopped down sufficiently, that would no longer be a rule of thumb. The 85 F1.2 and the 85 F1.8 is an example. Stopped down to F11, the sharpess is extremely similar.

    With these info in mind, you can make your decision. The larger aperture lens allow you to shoot at lower F stops, allowing more light and shallower depth of field. This is important because for example, if you bought the 70-200 F4, and decide you need to shoot wide open at F4, the 70-200 F2.8 would yield sharper pictures. The differences in sharpness narrows as you stopped down the aperture further (generally speaking).

    Generally speaking, only very generally, people will opt for the lens with a larger aperture to gain the extra flexibility. But as you rightly considered, this extra flexibility may be a want, not a need. It's possible to use F2.8 for well lit indoor shoots without flash. But F4 would be trickier. Not a whole lot of difference, but some. If you shoot outdoors, and want everything to be in focus, you won't be shooting wide open anyway, so the F4 lens is more than enough. If you want to isolate your subject from the background, a larger aperture, i.e. F2.8 will give you a narrower depth of field. So, end of the day is, what are you going to use the lens for?

    Another issue for consideration is actually not the photos itself. Its the weight. Quite often, the F2.8 lenses tend to be heavier than their F4 counterparts. Initially, I thought, what the heck is 2-300 grams difference gonna make. I regretted my decision when I had to shoot full days with the lens, and ditched all my F2.8 lenses, and kept my large aperture lenses to primes. Some muscle men here in clubsnap feel that the extra weight adds to a better weight distribution though.

  14. #14
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    Default Re: Need advise on Lens.

    Thanks for all the feedbacks and it really give me more understanding of the aperature thing. I'm not thinking of buying these lens yet but like I said earlier, I use these as example because they have similar focal length. So generally a bigger aperature lens should yield a sharper image provider the optics quality are good.

    foxtwo, I'm not thinking of buying a new lens now. I'm just using these 2 lens inorder to put my question correctly. If not there will be a lot of other factors like brand, IS, different focal length etc to confuse the main question on the max aperature of the lens.


    Thanks all.

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