Fast Glass and Stopping(?)

Discussion in 'Lens Lust' started by Little Cub, Jul 28, 2008.

  1. Little Cub

    Little Cub

    311
    Feb 13, 2007
    Vegas, baby!
    Hi Cafe!

    Can anyone tell me exactly what the term "fast-glass" means? I have a Tokina 12-24, a Tamron AF70-300 F/4-5.6, and a Tamron 28-80 F/3.5-5.6, and a Sigma 18-55(?). Funny thing, I have been shooting for a while and never understood this.
    I guess while I am on the question train, can anyone explain to me what stopping down or up means in easy terms? How do I figure if I need to stop down or up? :confused:
    One last one...I promise! How do I determine what F/Stop to use on what? I have a couple of books that talk about the "whatever F/11," but they never goes into detail of how to capture the intense colors of a sunset. I try to set my exposure to where it reads "correct" through my viewfinder, and my photos still come out dull and mostly colorless in comparison to the stark colors I see in other photos.
    Thank you all for you help! I know these may be photography 101 questions :redface:

    Sincerely,
    Little Cub
     
  2. rotxlk82

    rotxlk82

    Jul 20, 2007
    UK
    Fast glass implies that a lens has a very wide apeture, as photographers we express apeture using F numbers e.g. F/5.6

    A fast lens can be shown by a small number after the F, i.e. F/1.8 or F/1.4
    As such none of your lenses can really be thought of as fast

    The main effect of the F stop on your image is the amount of depth of field that will be produced, if you use a wide apeture e.g. F/1.8 you will have a little depth of field which is good for isolating something like a portrait. If you use a small one like F/11 then you will get a lot of depth which would be good for when you want to show all of a landscape or something. The F stop used has nothing to do will the colour produced, that is determined by your exposure and processing.

    I hope this makes sense, I can understand why it is complicated for a beginner.
     
  3. It took me the longest time for this to click....

    wide open is the smallest f/number your lens will reach, but means MORE light coming into the lens

    stopped down is moving up to larger numbers, but LESS light and MORE depth of field

    Fast (at least in my opinion) means that your lens can reach f/2.8 or lower. I have an addiction to 1.4 lenses....
     
  4. rotxlk82

    rotxlk82

    Jul 20, 2007
    UK
  5. Little Cub

    Little Cub

    311
    Feb 13, 2007
    Vegas, baby!
    Wow! Thank you Robert and Sonya for the quick responses! I understand now what this all means. Sonya, you are right when you say it takes a long time to click. Sheesh! I have been trying to wrap my brain around this for a while. So am I correct to assume that a fast lens is used primarily for sports photography? And the lenses that I have would be used primarily for portraits and studio work? Thank you again for all your help!

    Little Cub
     
  6. A fast lens is not NECESSARILY for sports photography. They're for low light photography, because they let in more light. If you don't want to bump ISO way up or use flash, faster is better. You can *almost* use any lens for studio work since most shoot at f/7 or f/10 in the studio. I specialize in candid portraiture, and most of the time I shoot at f/2 or wider. I don't use flash often, and also love the dreamy effect that shallow dof gives at wide apertures.
     
  7. genera

    genera

    Oct 6, 2005
    California
    All this confusion just to save "1:". :eek:
     
  8. 1:1.8 isn't as accurate as saying f/1.8
    1:1.8 is a ratio, but it doesn't say what. The F-Number is the diameter of the apeture, where f = focal length. So on a 50mm 1.8, f/1.8 would be 50/(divided)1.8 = 27.78mm

    So f/2 @ 200m = 100mm but f/2 at 500 is 250mm.


    1 FULL Stop is a doubling or halving of light. ISO 100 to 200 is a full stop. 200 to 400 etc 400 to 800.

    With shutter speeds 1/60 to 1/120 is 1 stop faster, 1/30 is 1 stop slower than 1/60 and 2 stops slower than 1/120.

    Aperture is a little more confusing, as the doubling or halfing is based on area pi(r^2).
    so it's f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 /f22 Each has 1 stop between them, f/1.4 lets double the light of f/2 and so forth.

    Knowing this can mean that if you want more motion blur than 1/60 @ f/5.6 you can shoot 1/30 @ f/8 which will give you the same exposure. Or you could go the other way1/120 @ f/4
     
  9. Nikkor AIS

    Nikkor AIS

    Jun 5, 2008
    Alberta
    Little Cub: Not trying to confuse you. but, "fast glass" is a term that can also be used for lens that have a large aperture realitive to the focal length. For instance, A F/stop "4" isnt considered fast untill you put it on a Nikkor 600 F4 ED-IF AIS. Than its not just fast, but long. Or long and fast:biggrin:. That term can be applied to other Nikkor supertelephoto's. Like the Nikkor 800 5.6 ED-IF AIS:. Again a 5.6 f/stop isnt generally thought of as particulally fast, but on a 800 mm it's falls into the realm of "long and fast" IMO.

    Gregory
     
  10. and the Sigma 200-500 2.8 is stupendously fast
     
  11. Thanks for the explicit explanation.
     
  12. Little Cub

    Little Cub

    311
    Feb 13, 2007
    Vegas, baby!
    Thanks Cafe!

    This is all making so much more sense to me. I understand how stops work and what "fast glass" is. I would like to shoot low light photos, but all my lenses are around F/3.5-5. Any suggestions on how to use these lenses for that type of photo? Thank you again for all your help!!!

    Little Cub
     
  13. rotxlk82

    rotxlk82

    Jul 20, 2007
    UK
    Well because you're lenses are typically in the 'slow' F3.5 range you'll need to make up for the lost light in other ways.

    1. You could put up your ISO senstivity (but get noise)
    2. Use a flash, built in is ok, external e.g. SB600 is better
    3. Practice handholding/use a tripod/get VR in conjunction with longer exposure times
    4. Shoot in generally better light

    Which body are you using?? If it's a D50 or something lenses like the 35/2 or 50/1.8 are pretty cheap and have a lot of light collecting abilty.
     
  14. Little Cub

    Little Cub

    311
    Feb 13, 2007
    Vegas, baby!
    Hi Robert,

    Thank you for the info. I am using a Nikon D70s and Nikon D200 with these lenses.
     
  15. rotxlk82

    rotxlk82

    Jul 20, 2007
    UK
    Ok, well in that case because both of these cameras support the 'screw drive' AF type lenses there are a number of cheap primes with fast apetures that you could use.

    The 50mm F1.8 lens is very cheap it can be had for about $110 in your part of the world. This will give 10x more light than the kit 18-55mm lens when they're set at the same focal lenght. Other options include the 35mm F2 lens I mentioned or the more expensive Sigma 30mm F1.4 or Nikon 50mm F1.4. All of these will give you loads of light to work with.

    Also you could use the D200's support of older AI and AIS lenses to pick up an old model for even less money, however you will have to focus manually.
     
  16. Little Cub

    Little Cub

    311
    Feb 13, 2007
    Vegas, baby!
    That makes sense. Thanks Robert!
     
  17. genera

    genera

    Oct 6, 2005
    California
    5. Embrace the blur. Don't just tolerate it. Use it as an element of the photo.