Results 1 to 14 of 14

Thread: constant f vs not (e.g. f2.8 vs f2.8-4)

  1. #1

    Default constant f vs not (e.g. f2.8 vs f2.8-4)

    want to know the differences and pros & cons...

    what you would prefer and why.
    I go by feel... Never followed the rules.
    www.photosbymarbles.com

  2. #2

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Cons: Usually more expensive and heavier
    Pro: More flexibility in aperture settings. Lens will be more useful in more situations.

    Money aside, of course it's better to have the fixed maximum aperture. But then if you find yourself shooting at much smaller apertures (to get wider DOF, for example) most of the time, then it's a darn good waste of money.

    Of course, there's always the better build, as these 'fixed' lenses are usually in the more 'pro' category.

  3. #3
    Deregistered
    Join Date
    Feb 2006
    Location
    @ AMK
    Posts
    2,616

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by Benjymocha
    want to know the differences and pros & cons...

    what you would prefer and why.
    constant aperature feel better...f2.8 mean its f2.8 all the way...dun need to worry...

    these lens got higher resales value too...

  4. #4
    Senior Member
    Join Date
    Dec 2005
    Location
    KFC
    Posts
    1,777

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    lets say a 70-200 f2.8 lens and another lens 70-200 f2.8-4

    For the 1st lens 70-200 f2.8, from the range of 70mm to 200 mm, u can shoot it at f2.8, meaning u can maintain a constant speed of 1/200s for example...

    but for the other 70-200 f2.8-f4 lens, at 70mm u can shoot at 1/200s, but at 200mm, u can only shoot at 1/100s.

    this difference in speed can mean a blur and sharp picture..
    09 Oct 09 officially marks the date I become a canon convert.

  5. #5
    Senior Member +evenstar's Avatar
    Join Date
    Jan 2004
    Location
    Singapore / United Kingdom
    Posts
    5,655

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    and it can mean a correctly exposed vs underexposed image if you're shooting M mode..
    eat. drink. shoot

  6. #6

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by Benjymocha
    want to know the differences and pros & cons...

    what you would prefer and why.
    The differance is in the largest aperture you can use for the short or long end of the zoom.

    For a F/2.8 lens, the largest aperture you still can use is F/2.8 whether you're shooting at the short or long end of the zoom. For e.g. a 70-200mm lens, the largest aperture you can use is F2.8 when you shoot at any focal length (70mm to 200mm).

    For a F/2.8-F/4 70-200mm lens, if you're shooting at 200mm, the largest aperture you can use is only F/4 (which is 1-stop smaller than F/2.8) which means in situations where a proper exposure can be achieved with using F/2.8 aperture size combined with a certain shutter speed and ISO on the F/2.8 lens, you can only use F/4 and then compensate with a higher ISO or slower shutter speed than a F/2.8 70-200mm lens. In some situations, it could mean not getting the depth of field you prefer (F/2.8 vs F/4) or not fast enough shutter speed (to freeze actions) or too much noise from using a higher ISO.

    Of course, for the F/2.8 lens, you still can use F/4 for whatever focal length and so it can do whatever the F/2.8-F/4 lens can do and then more.

    So the choice is clear. As aperture size in terms of F-stops is a relative number between the actual aperture size and focal length, a long focal length means that a good sharp F/2.8 lens has much more glass and also much more difficult to manufacture than a F/2.8-F/4 lens. Thus, a F/2.8 lens is much more expensive than a F/2.8-F/4 lens, everything else constant.
    Last edited by Clockunder; 13th August 2006 at 06:03 PM.

  7. #7
    Senior Member
    Join Date
    Aug 2005
    Location
    Tanjong Katong
    Posts
    3,710

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by +evenstar
    and it can mean a correctly exposed vs underexposed image if you're shooting M mode..
    You can always put your attention on your camera light meter and adjust aperture/shutter speed properly...

    Regards,
    Arto.

  8. #8

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by kcuf2
    lets say a 70-200 f2.8 lens and another lens 70-200 f2.8-4

    For the 1st lens 70-200 f2.8, from the range of 70mm to 200 mm, u can shoot it at f2.8, meaning u can maintain a constant speed of 1/200s for example...

    but for the other 70-200 f2.8-f4 lens, at 70mm u can shoot at 1/200s, but at 200mm, u can only shoot at 1/100s.

    this difference in speed can mean a blur and sharp picture..
    sorry for the stupid qn, could be that i'm not awake yet but how do u correlate the 1/100s and 1/200s with the f-stop?
    I go by feel... Never followed the rules.
    www.photosbymarbles.com

  9. #9
    Senior Member
    Join Date
    Feb 2003
    Location
    Outside the Dry Box.
    Posts
    16,268

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    OT abit...

    which is better? f3.5 constant or f2.8-4?
    Logging Off. "You have 2,631 messages stored, of a total 400 allowed." don't PM me.

  10. #10

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by Clockunder
    For a F/2.8-F/4 70-200mm lens, if you're shooting at 200mm, the largest aperture you can use is only F/4 (which is 1-stop smaller than F/2.8) which means in situations where a proper exposure can be achieved with using F/2.8 aperture size combined with a certain shutter speed and ISO on the F/2.8 lens, you can only use F/4 and then compensate with a higher ISO or slower shutter speed than a F/2.8 70-200mm lens. In some situations, it could mean not getting the depth of field you prefer (F/2.8 vs F/4) or not fast enough shutter speed (to freeze actions) or too much noise from using a higher ISO.
    so if F/4 is just 1 stop smaller, would you compromise and get a F4 instead of F2.8 cos of price?
    I go by feel... Never followed the rules.
    www.photosbymarbles.com

  11. #11
    Senior Member jnet6's Avatar
    Join Date
    Apr 2004
    Location
    not here often anymore
    Posts
    8,170

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by Benjymocha
    so if F/4 is just 1 stop smaller, would you compromise and get a F4 instead of F2.8 cos of price?
    For example @ 200mm... yr f-stop @ F4, yr shutter metered @ 1/60.
    If you got a F2.8 "constant" 70-200mm, @ 200mm, F2.8, S=1/125, more advantage if you do not want to increase yr ISO.

  12. #12
    Senior Member zac08's Avatar
    Join Date
    Feb 2005
    Location
    East
    Posts
    11,755

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    Quote Originally Posted by Benjymocha
    so if F/4 is just 1 stop smaller, would you compromise and get a F4 instead of F2.8 cos of price?
    If you shoot in bright light conditions and do not need faster focusing. Then you may wish to compromise and get the cheaper f4 option. But if you need low light capabilities then you may need the f2.8
    Michael Lim
    My Flickr Site

  13. #13
    Senior Member
    Join Date
    Oct 2005
    Location
    1.45N 103.83E
    Posts
    3,202

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    if $$$ not issue get f2.8. Its always a better choice. if you get f2.8, you can add 2x TC and still use AF cos it now f5.6 but if you get the f4 and add 2x TC, yr max aperature becomes f8 and unless you have a 1 series body, you cannot use AF.

  14. #14

    Default Re: constant f vs not (e.g. f2.8 vs f2.8-4)

    A f2.8 will also make the viewfinder brighter than a f4.

    Not forgetting most lenses are sharper when stopped down. Hence a f2.8 can get great sharpness at f4, while a f4 will need go down to f5.6 for equal sharpness.
    Videographer @ A Merry Moment

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •