Teleconverters. Explain please

Discussion in 'Photography Equipment & Products' started by DB83, Sep 22, 2009.

  1. DB83

    DB83 TPF Noob!

    Joined:
    Sep 18, 2009
    Messages:
    29
    Likes Received:
    0
    I know that Teleconverters increase reach on a lens but I have a few questions about them. I would look to get the Canon EF 1.4x in the future.

    1. How does it go onto the camera?
    2. Can I mount a EF-S lens on a EF mount on a XSi?
    3. Why does the 2x teleconverter reduce autofocus capabilities?
    4. why do you give up 1 f-stop by using one?
    5. How much would a 55-250mm lens be turned into with a 1.4x?
     
  2. musicaleCA

    musicaleCA TPF Noob!

    Joined:
    May 23, 2009
    Messages:
    2,303
    Likes Received:
    0
    Location:
    Vancouver, BC
    Can others edit my Photos:
    Photos OK to edit
    1. It is attached like a lens to the body, and the lens goes on the front of the teleconverter.

    2. Yes.

    3. Because it's so freaking long, the minimum aperture is significantly reduced, so far less light can reach the AF sensor, reducing AF performance.

    4. Because of the optics involved. By how much the minimum aperture is reduced is dependant on the teleconverter's magnification factor.

    5. Er...well, it'd be turned into a 55x1.4-250x1.4mm lens. That's 77-350. If you then take into account the crop factor of the sensor on your camera, that's 123-490mm equivalent to a 35mm sensor size.

    If you're thinking of slapping a teleconverter on the EF-S 55-250mm f/4.0-5.6 IS USM, I suggest against it. That lens already produces a fair bit of CA and isn't super-sharp (particularly at the long end). If you put a teleconverter in between you're going to see a lot more purple fringing, and there's no guarantee your images will be anywhere near as sharp.
     
  3. CxThree

    CxThree TPF Noob!

    Joined:
    Feb 25, 2009
    Messages:
    505
    Likes Received:
    1
    Can others edit my Photos:
    Photos NOT OK to edit
    I believe the Canon 2x teleconverter only works with L series lenses.
     
  4. Dao

    Dao No longer a newbie, moving up!

    Joined:
    Mar 24, 2008
    Messages:
    6,252
    Likes Received:
    418
    Location:
    St. Louis
  5. epp_b

    epp_b No longer a newbie, moving up!

    Joined:
    Aug 22, 2008
    Messages:
    2,135
    Likes Received:
    12
    Location:
    True North Cold and Freezing
    Can others edit my Photos:
    Photos OK to edit
    Teleconverters are useless on all but fast lenses. Don't even bother with your variable-aperture zoom lenses.

    The only lenses you can properly use them on are fast primes (ie.: 300mm/2.8) or a fast zooms (ie.: 70-200/2.8).
     
  6. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

    Joined:
    Dec 16, 2003
    Messages:
    33,817
    Likes Received:
    1,811
    Location:
    Edmonton
    Can others edit my Photos:
    Photos NOT OK to edit
    I agree with 'epp b'. Unless you have 'fast' (large max aperture) lenses, it's not a great idea to use teleconverters.

    Most cameras need a minimum of F5.6 for the AF to work. That's why most cheap zoom lenses have a max aperture of F5.6 at the long end. When you add a TC into the mix, it steals some light. The 2X takes about two stops of light. So when used with a lens that only has a maximum of F5.6, the camera would only be getting light of an F11 aperture (two stops from F5.6)....and that's not nearly enough for the AF to work.

    If you have a lens with a max aperture of F2.8, then loosing two stops only brings you down to F5.6...which is still OK.
     
  7. djacobox372

    djacobox372 No longer a newbie, moving up!

    Joined:
    May 4, 2008
    Messages:
    2,925
    Likes Received:
    129
    Location:
    Seattle, WA
    Can others edit my Photos:
    Photos NOT OK to edit
    Teleconverters don't make much sense on digital IMO--every test I've done/seen has achieved equal results by cropping/scaling instead of using a teleconverter, and if you crop/scale you aren't reducing the speed of the lens. About the only benefit of a teleconverter is the ability to compose the final shot in the viewfinder.

    For film teleconverters made more sense, film grain is much more coarse then digital noise--so cropping/scaling was not as good of option as a teleconverter.
     
  8. DB83

    DB83 TPF Noob!

    Joined:
    Sep 18, 2009
    Messages:
    29
    Likes Received:
    0
    Hmm. Ok. well, I guess the main reason I was looking at teleconverters is for my future 70-200mm 2.8L. I may have to rethink getting one altogether if it will have significant adverse effects.
     
  9. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

    Joined:
    Dec 16, 2003
    Messages:
    33,817
    Likes Received:
    1,811
    Location:
    Edmonton
    Can others edit my Photos:
    Photos NOT OK to edit
    On a high quality lens like that, a TC isn't as bad of an option as it is with cheaper lenses.

    But as someone mentioned, you might be just as well off by getting a sharp image without the TC and just cropping the image.
     
  10. MrLogic

    MrLogic TPF Noob!

    Joined:
    Mar 27, 2008
    Messages:
    423
    Likes Received:
    0
    Location:
    Rotterdam, Netherlands
    Can others edit my Photos:
    Photos OK to edit
    Interesting. Some people say this logic is fundamentally flawed, but I haven't seen a test so far. Do you have link?
     

Share This Page

Search tags for this page
2x tele converters explained
,

explain teleconverter

,
explain teleconverter f stops
,
explain teleconverters
,
teleconverter canon expalined
,

teleconverter explain

,

teleconverter explained

,

teleconverters explained

,
telephoto converter explained
,
why does a teleconverter reduce maximum aperture