Home News Buyers Guide About Advertising
 
 
 
   
Results 1 to 10 of 10
  1. #1
    Join Date
    Oct 2010
    Posts
    25

    Importance of f number

    I wonder if the maximum opening of a lens is still as impotant as it was in the analog era. I realize that a less light-strong lens can be compensated by upping the ISO number, but I know this opens the door for noise. I also know that most lenses are not at their best when not stopped down, but this is not a new factor to the digital era. Since I have no experience with a DSLR, I would like to know if it makes much sense to invest in f2.8 zoomlenses, perhaps a f4-f5.6 zoom is comparable with a 2.8 from 25 years ago. Thanks in advance for your opinions.
    Willy

  2. #2
    Join Date
    Dec 2006
    Location
    So Calif
    Posts
    3,226
    Yes, a fast lens is still important, as a large maximum aperture will give you an advantage even when closed down a couple stops to the sweet spot.

    There are times when the shutter and ISO will not allow the correct exposure without a large aperture.

    And, depth of focus is affected by f-stops.
    Pentax K20D/K5/15/21/40/70/10-17/12-24, Sigma 17-70 2.8-4.5/150-500, Tamron 90 Macro/70-200 2.8, Canon SX20 IS/Elph 500HS
    (formerly Pentax 50 1.4/50-200/55-300/K100D, Sigma 18-50 2.8/70-300 APO, Tamron 28-75, Viv 800, Tele-Tokina 800, Canon S3 IS, Samsung L210)
    http://s133.photobucket.com/albums/q78/KylePix/

  3. #3
    Join Date
    Dec 2006
    Location
    God's Country - Australia
    Posts
    10,424
    Quote Originally Posted by Willy View Post
    perhaps a f4-f5.6 zoom is comparable with a 2.8 from 25 years ago. Thanks in advance for your opinions.
    Willy
    in IQ probably but it will still be 3 stops slower.
    D800e l V3 l AW1 l 16-35 l 35 l 50 l 85 l 105 l EM1 l 7.5 l 12-40 l 14 l 17 l 25 l 45 l 60 l 75
    flickr

  4. #4
    Join Date
    Feb 2007
    Posts
    207
    Quote Originally Posted by Rooz View Post
    in IQ probably but it will still be 3 stops slower.
    1 to 2 stops slower.

  5. #5
    Join Date
    Oct 2010
    Posts
    25
    Quote Originally Posted by SpecialK View Post
    And, depth of focus is affected by f-stops.
    Good point, being able to slect a shallow depth of field is important to me, often it is primary concern. It looks as though there are still no roses without thorns then, these being added weight in the lens and removed weight from the wallet On the other hand, if that is wan't needed, so be it. I have taken a closer look at some standard (eg 18-50mm) and tele zooms (eg 15-150mm) from Tamron and Sigma and they get decent critics while being affordable. I would have thought about the Canon EF-S 18-135mm lens, but having the zoom range split in two seems (still) to be the better option. In that respect, even the Canon "2-kit" lenses (18-55mm and 55-250mm, both IS) seem to be acceptable and they are cheap and lightweight. But although brand lenses, the third-party f2.8 lenses are likely to be better.
    Having to choose can be so hard
    Gaby

  6. #6
    Join Date
    Jan 2008
    Location
    Terra Australis Incognita
    Posts
    3,877
    2.8 lenses are sharper at most F stops you'll use but they are more costly and much heavier/bulkier.

    It depends a bit what you're shooting and how fussy you are about image quality.
    D800, D300, D90, 24-70 f2.8, 70-200VR f2.8, 300 F4, 105 micro, 16-85VR, 50mm 1.8, Tammy 90 macro, 70-300VR, SB900, 2xSB600, MB-D10, 055XPROB 322RC2. New computers to run photoshop faster. C&C always appreciated. PhotoGallery
    Pressing the shutter is the start of the process - Joe McNally ... Buying the body is the start of the process - Dread Pirate

  7. #7
    Join Date
    Oct 2006
    Posts
    461
    At some point, you will have to choose between saving for fast lenses or borrowing to buy the same.
    I've either traded up into fast lenses or saved: there is no better way.... unless you're rich...

    Then there are the exceptions... I bought my f/4 70-200 "L" and purchased the f/2.8 70-200 "L" with my tax refund two years later.
    EOS 1-D, EOS 1Ds, EOS 1n, EOS T2i D-SLR, EOS 1n (HS), EOS A2E(2), Olympus E-3 DSLR, E30 & E-510 DSLRs, Olympus digital FL50 flash, Canon F1 (old) + four interchangeable finders, EOS 28-70 f2.8 "L", EOS 70-200 f2.8 & f4 "Ls", EOS 430EZll digital flash, EOS 540EZ analog flash

  8. #8
    Join Date
    Jan 2008
    Location
    Terra Australis Incognita
    Posts
    3,877
    I missed a subtle point in Willys post. There have been vast improvements in lens design recently and in terms of sharpness alone a modern cheap zoom could be better than an old pro lens. Still a lot slower.

    Even if it's not sharper it would be lighter and could be preferable for hiking (I hate F2.8 lenses foir those).
    D800, D300, D90, 24-70 f2.8, 70-200VR f2.8, 300 F4, 105 micro, 16-85VR, 50mm 1.8, Tammy 90 macro, 70-300VR, SB900, 2xSB600, MB-D10, 055XPROB 322RC2. New computers to run photoshop faster. C&C always appreciated. PhotoGallery
    Pressing the shutter is the start of the process - Joe McNally ... Buying the body is the start of the process - Dread Pirate

  9. #9
    Join Date
    Aug 2005
    Posts
    6,931
    Quote Originally Posted by loristm View Post
    perhaps a f4-f5.6 zoom is comparable with a 2.8 from one.
    No because depth of field is depth of field. A 25 year old f2.8 lens will have f2.8 dof properties which will still be better then a modern f4.4 lens.
    If you are not wanting to use the dof benefits of a fast lens and you only shoot in the f5.6-f11 type range then your argument may have some credibility.

  10. #10
    Join Date
    May 2005
    Posts
    292
    Quote Originally Posted by K1W1 View Post
    No because depth of field is depth of field. A 25 year old f2.8 lens will have f2.8 dof properties which will still be better then a modern f4.4 lens.
    If you are not wanting to use the dof benefits of a fast lens and you only shoot in the f5.6-f11 type range then your argument may have some credibility.
    This is spot on.

    I cannot even remotely imagine trading in my old 85mm f/1.8D lens for something in the 55-200 f/4-5.6 to shoot portraits. The amazingly wonderfully blurry bokeh of a prime far outweighs any possible convenience of the zoom, no matter how modern and light it is. I know, prime vs zoom, not a fair comparison really. But in my limited experience with the Nikon 2.8 pro zooms, the argument is equally valid.

    The principles of light gathering dont really change and all lenses are beholden to those principles.
    Nikon D200 + MBD200
    Nikkor 24mm f/2.8, 50mm f/1.8, 85mm f/1.8,
    300mm f/4.

Posting Permissions

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