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Thread: Aperture of lenses

  1. #1

    Default Aperture of lenses

    Hi,

    I have a question about understanding the model names of lenses.

    For example, comparing Tamron AF 17-50mm F/2.8 XR Di II LD , and Sigma17-70mm f/2.8-4.5 DC Macro.

    The Tamron model refers to F2.8, does that mean that whether i am at 17mm or 50mm, i will still be able to use F2.8, and for the Sigma one, the F stop number will automatically increase from 2.8 to 4.5 as I zoom from 17mm to 70mm, meaning i am forced to use a smaller aperture at the longer zoom.

    I just got my DSLR not long and i notice that with my kit lens. So just like to clarify, so that i know what I am buying when i get other lenses in the future.

    Pls kindly correct me if i am wrong.

    And if i am right, then the Tamron in this case should be a better lens compared to the Sigma, except for the shorter zoom?

    Thank you for you input.

  2. #2
    Senior Member Galdor's Avatar
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    Default Re: Aperture of lenses

    Yes, you are absolutely right.
    Minolta. Konica Minolta. Sony

  3. #3

    Default Re: Aperture of lenses

    yup...no doubt about that...
    D80|Tamron 17-50mm f/2.8|Nikon 50mm f/1.8D|80-200mm f/2.8D
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  4. #4

    Default Re: Aperture of lenses

    yeap thats right. spot on! =)

  5. #5

    Default Re: Aperture of lenses

    Thank you everyone for confirmation!

  6. #6

    Default Re: Aperture of lenses

    Quote Originally Posted by pigletnpiggy View Post
    Hi,

    I have a question about understanding the model names of lenses.

    For example, comparing Tamron AF 17-50mm F/2.8 XR Di II LD , and Sigma17-70mm f/2.8-4.5 DC Macro.

    The Tamron model refers to F2.8, does that mean that whether i am at 17mm or 50mm, i will still be able to use F2.8, and for the Sigma one, the F stop number will automatically increase from 2.8 to 4.5 as I zoom from 17mm to 70mm, meaning i am forced to use a smaller aperture at the longer zoom.

    I just got my DSLR not long and i notice that with my kit lens. So just like to clarify, so that i know what I am buying when i get other lenses in the future.

    Pls kindly correct me if i am wrong.

    And if i am right, then the Tamron in this case should be a better lens compared to the Sigma, except for the shorter zoom?

    Thank you for you input.
    Hello!

    I had posted the above question earlier and got confirmation answers, which was great.

    Then I have been reading a few other threads which confused me again, so need to ask again..

    In this thread below..

    http://www.clubsnap.com/forums/showthread.php?t=378873

    They are discussing about what is the shapest aperture for this particular Tamron lens and most feedback is that the sharpest is at about F4 or f8 or F11.

    My question is, if the lens is not sharpest at F2.8, then (in my 1st qn regarding the Sigma vs. Tamron), how is the Tamron F2.8 lens better than the Sigma F2.8-4.5?

    I am confused because I assume most pple would pay more for a fixed aperture lens, but how come its not sharp at F2.8? If thats the case, would it be better to just save some $ and buy a lens like Sigma which does not have the fixed aperture?

    Pls bear with me if my qn is elementary, perhaps there some other things which i am not aware of.. so need your input.

    Thank you.

  7. #7

    Default Re: Aperture of lenses

    based on my understand is that despite the specifications saying that the the lens maximum aperture is f2.8, it may performs the best (sharpest) at another aperture eg f4. Of course you wont find this mentioned in the technical specs. Most of the time you find this out based on your usage experience of the lens itself. Don't get too worried by such details. As most your basic techniques are sound, then it just just a matter of which photo is the sharpest.
    :)

  8. #8
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    Default Re: Aperture of lenses

    The Tamron is in a sense a better lens than the Sigma, as it allows you to be shooting at F/2.8 along all focal lengths - this is particularly important if you are shooting at low light (no doubt f/2.8 is not as sharp as when the lens is stopped down, but still it should be sufficiently sharp enough to get you a decent picture).

    The thing is that such a phenomenon (as in requiring the apertured to be stopped down for sharper results) occurs across all lens, fixed aperture or not. There are lens that offer little improvement when stopped down for shooting at smaller apertures, but such lens are few. The main thing is to consider what your needs are. After all, f/4.5 is slightly more than one stop away from f/2.8 and would hence require slower shutter speeds or a higher iso - not particularly desirable for shooting unless intended.
    1D3, EF 16-35mm F2.8L II, EF 24-70mm F2.8L, EF 70-200mm F2.8L IS, Speedlite 580EX II, 420EX

  9. #9

    Default Re: Aperture of lenses

    people buy large aperture lenses for the faster shutter speeds, shallower DOF and because those lenses are usually of a higher quality. That being said, NO LENS is at it's 100% best when at it's extreme setting, i.e., widest zoom at biggest aperture.

    In your example, if you zoom a 70-200mm f/2.8 lens to 200mm and do the same with a 70-300 f/4.5-5.6 (and set it to 200), then your max. aperture will mean that on he f/2.8 you could probably shoot with 2-3 stops faster shutter speed than on the "cheaper" lens. Also, if I set both lenses to f/5.6, the 2.8 lense wil give me much sharper pictures because on the 2.8 I'm not "pushing" the limits of the lens, but on the cheaper 4.5-5.6 I am.
    Alpha

  10. #10
    Moderator Octarine's Avatar
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    Default Re: Aperture of lenses

    Quote Originally Posted by pigletnpiggy View Post
    In this thread below..
    http://www.clubsnap.com/forums/showthread.php?t=378873
    They are discussing about what is the shapest aperture for this particular Tamron lens and most feedback is that the sharpest is at about F4 or f8 or F11.
    My question is, if the lens is not sharpest at F2.8, then (in my 1st qn regarding the Sigma vs. Tamron), how is the Tamron F2.8 lens better than the Sigma F2.8-4.5?
    I am confused because I assume most pple would pay more for a fixed aperture lens, but how come its not sharp at F2.8? If thats the case, would it be better to just save some $ and buy a lens like Sigma which does not have the fixed aperture?
    Thank you.
    The discussion is subjective and some people in the mentioned thread also recommended (and did) a test shooting. Also mentioned: there is a difference between "center sharpness" and "edge to edge sharpness". Usually, all lenses used wide open (maximum aperture) are not fully sharp edge to edge. That goes for the Tamron as well as for the Sigma. But once thing to keep in mind here: At f/2.8 the Depth of Field (DOF) is very shallow. So you need a flat object to test the edge sharpness, otherwise the object is just simply Our of Focus (OOF).
    You see already how tricky it could be to say whether the lens is sharp or not. You can search for lens reviews at the common places (Bob Atkins: Canon EOS Lens Reviews or Photozone: Canon EOS (APS-C) Lens Tests). Those guys are familiar with testing lenses and the reviews are very helpful. It's up to you to decide then what fits your needs. Most commonly all lens become sharp (nearly) edge to edge if you step down one or two stops. Two full stops for Tamron would be f/5.6 for 50mm whereas the Sigma lens is already at f/8 for 50mm.

    Saying this we can focus back on the question "what is better?" or "what are your needs?" Many people consider a fixed aperture lens as better because you always know what your maximum aperture is. That means exposure is constant throughout the whole zoom range. So just because you change the zoom from 20 to 30mm means for the Sigma lens that your shutter speed becomes slower. This can be very important in cases where the object is moving. You could counter that with increasing ISO speed but higher ISO speed can result in higher picture noise.
    A constant aperture also helps to keep the DOF shallow. You can check this with this Depth of Field Calculator here (scroll down the page a bit). The Tamron lens maintains a shallower DOF than the Sigma lens at 50mm. Depending on the focusing distance and the your intention regarding DOF / composition this can make a big difference.

  11. #11

    Default Re: Aperture of lenses

    Thank you everyone who took the time to share, really appreciate it

    I am quite interested in the Tamron and have read in the threads that its recommended by many who have used it before.

    I was hoping to find a 2nd hand one but no one seems to be selling.. so i guess its really quite good.

    I read on the Canon thread that its abt $600 from orient photo with intrnational warranty.

    Anyone knows if this is a good place to buy or what is the current price like?

  12. #12

    Default Re: Aperture of lenses

    Quote Originally Posted by pigletnpiggy View Post
    Thank you everyone who took the time to share, really appreciate it

    I am quite interested in the Tamron and have read in the threads that its recommended by many who have used it before.

    I was hoping to find a 2nd hand one but no one seems to be selling.. so i guess its really quite good.

    I read on the Canon thread that its abt $600 from orient photo with intrnational warranty.

    Anyone knows if this is a good place to buy or what is the current price like?

    Any info on this?

    Thanks!

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