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Thread: AF searching difficulty

  1. #1

    Default AF searching difficulty

    Hi all
    Got a question to ask about my new toy - Canon EOS 50D with Tamron 18-200 f3.5-6.3 macro lens.
    I find it tends to search quite a bit especially in relatively low lighting (like my room lit by single ceiling light).
    But also sometimes in what seems like pretty adequate lighting - like taking a pair of feet on the ground in a room lit with fluorescent lamp. (Ground and feet color contrast pretty well)
    I also made sure I was taking the pic well farther than the minimum focusing distance (my lens' focusing distance is 0.4m and I was almost a full meter away, zooming to about 150mm). And this was despite trying it at the full auto mode and the macro mode.

    So what is the problem here? And what can I do to make it better?
    Will getting a macro lens with a shorter minimum focusing distance help?
    How about getting a lens with a smaller f value (budget is a problem as always)
    Any setting I can use to make things better? (I cannot afford to use a tripod due to the nature of my work and photos I need to take)
    Or should I get a ring flash or better aftermarket flash to better light up the target when the AF-assist is firing away?

    Please advise!
    Thanks in advance!

  2. #2
    Moderator Octarine's Avatar
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    Default Re: AF searching difficulty

    Fluorescent light only appears bright to the human eye, not to the camera. To cameras it's quite dim. Also, your lens has a very slow aperture at the long end. This makes it even more difficult to the AF system to pick up contrast patterns. Solution here: more light.
    You can support with external flash, especially with a red AF assist beam. The AF sensors are specifically sensitive to the red AF light (and the embedded pattern). 430EX is the smallest Canon flash with red AF assist. 270 doesn't have it, AFAIK.

  3. #3

    Default Re: AF searching difficulty

    Quote Originally Posted by Octarine View Post
    Fluorescent light only appears bright to the human eye, not to the camera. To cameras it's quite dim. Also, your lens has a very slow aperture at the long end. This makes it even more difficult to the AF system to pick up contrast patterns. Solution here: more light.
    You can support with external flash, especially with a red AF assist beam. The AF sensors are specifically sensitive to the red AF light (and the embedded pattern). 430EX is the smallest Canon flash with red AF assist. 270 doesn't have it, AFAIK.
    Thanks for the reply!
    Didn't know fluorescent light appears dim to cameras!
    Thanks for the tip.
    I'm new to photography but I figure from what you say, I have a few choices to allow more light in:
    1. Get macro lens with smaller f value
    2. Use current lens but keep it at short zoom but put on close up filter
    3. Get external flash as you have mentioned

    Does using ring flash help? Do these things have the red AF assist too? (Guess I can go shop to ask and try out but ring flashes are pretty pricey...)

  4. #4

    Default Re: AF searching difficulty

    Canon is well known for struggling with focus under low lighing conditions. Even their higher-end cameras suffer from the same problem.
    Alpha

  5. #5

    Default Re: AF searching difficulty

    Quote Originally Posted by Rashkae View Post
    Canon is well known for struggling with focus under low lighing conditions. Even their higher-end cameras suffer from the same problem.
    Hmm well.
    Too late for that now cos I've already chucked cash into the cam.
    But having said that, I do prefer the images produced by the canon, so I'd still have chosen this cam over others!

  6. #6

    Default Re: AF searching difficulty

    Quote Originally Posted by MolaMola View Post
    Hmm well.
    Too late for that now cos I've already chucked cash into the cam.
    But having said that, I do prefer the images produced by the canon, so I'd still have chosen this cam over others!
    Yup. You'll just need to learn the limitations of the equipment, and work to overcome them.
    Alpha

  7. #7
    Senior Member Galdor's Avatar
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    Default Re: AF searching difficulty

    Congrats on your purchase. Like what bro Rashkae mentioned just used it within it's limitation and it should serve you well.
    Minolta. Konica Minolta. Sony

  8. #8

    Default Re: AF searching difficulty

    i have to fully agree with what bro Rashkae mentioned.

    Know about the limitations of your camera, and work to overcome them.

    You will know the limitations when you shoot more, and know to overcome them when you shoot even more.

  9. #9

    Default Re: AF searching difficulty

    Yes, thanks for the tips.
    But can anyone please advise me on whether or not my deductions are accurate?

    To allow more light in, and hence improve AF:
    1. Get macro lens with smaller f value
    2. Use current lens but keep it at short zoom but put on close up filter
    3. Get external flash as you have mentioned

    Does using ring flash help? Do these things have the red AF assist too?

  10. #10

    Default Re: AF searching difficulty

    The 18-200 tamron doesn't af well even in board daylight.
    Was shooting with a friend using 40D with tamron 18-200mm.
    For what we percieved to be a well lited area under the shade of a tree.....the canon hunt...while pns lx2 manage to focus without any difficultly.
    Once he switch to a better lens 50mm 1.4(usm) no problem
    头可断,血可流,倩女不可不追求 carpe diem,when in doubt, hoot first,apologise later:p GALLERY

  11. #11

    Default Re: AF searching difficulty

    Quote Originally Posted by MolaMola View Post
    Yes, thanks for the tips.
    But can anyone please advise me on whether or not my deductions are accurate?

    To allow more light in, and hence improve AF:
    1. Get macro lens with smaller f value
    2. Use current lens but keep it at short zoom but put on close up filter
    3. Get external flash as you have mentioned

    Does using ring flash help? Do these things have the red AF assist too?
    1. You mean get a real macro lens. Your tamron is not a macro lens,it's just a superzoom with some macro-like abilities. Get a proper macro lens, like a Tamron 90mm.

    2. No no no

    3. That *may* help with focusing (many external flashes have focus-assist lamps) but your best bet is the real macro lens.
    Alpha

  12. #12

    Default Re: AF searching difficulty

    Quote Originally Posted by eow View Post
    The 18-200 tamron doesn't af well even in board daylight.
    Was shooting with a friend using 40D with tamron 18-200mm.
    For what we percieved to be a well lited area under the shade of a tree.....the canon hunt...while pns lx2 manage to focus without any difficultly.
    Once he switch to a better lens 50mm 1.4(usm) no problem
    Ya, it seems kinda capricious.
    Tried to get it to focus on some stuff in my room - hunted back and forth
    Then got it to focus on some other stuff a couple of times, then tried to focus on the same stuff I tried initially - this time locked on AF pretty quickly.

    But otherwise for my purposes, I'm happy with it's quality and performance. You get what you pay for isn't it?

  13. #13

    Default Re: AF searching difficulty

    Quote Originally Posted by Rashkae View Post
    1. You mean get a real macro lens. Your tamron is not a macro lens,it's just a superzoom with some macro-like abilities. Get a proper macro lens, like a Tamron 90mm.
    Ya, then after that I'll just go hunting for grasshoppers and bugs to shoot with my spanking new macro lens - then grab the bug and have it for breakfast cos no more money for meals.

    Quote Originally Posted by Rashkae View Post
    2. No no no
    Ok ok. Have to find a work around then

    Quote Originally Posted by Rashkae View Post
    3. That *may* help with focusing (many external flashes have focus-assist lamps) but your best bet is the real macro lens.
    I guess that may be may most attainable option at this point.

  14. #14
    Senior Member Galdor's Avatar
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    Default Re: AF searching difficulty

    Just get a dedicated macro lens and a flash if you're into Macro photography. The flash is required in Macro too.
    Minolta. Konica Minolta. Sony

  15. #15
    Deregistered marieloves-'s Avatar
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    Default Re: AF searching difficulty

    I have tried the 105mm f/2.8 AI-s Micro.
    I think it's a really good lens especially if you're on a budget.
    Downside is that you do not have Vibration Reduction and Autofocus, which is only available on the current 105mm f/2.8 AF-S VR.
    Maybe an SB-400 should be good for you too, as a first flash.

    Marie

  16. #16
    Senior Member Galdor's Avatar
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    Default Re: AF searching difficulty

    Quote Originally Posted by marieloves- View Post
    I have tried the 105mm f/2.8 AI-s Micro.
    I think it's a really good lens especially if you're on a budget.
    Downside is that you do not have Vibration Reduction and Autofocus, which is only available on the current 105mm f/2.8 AF-S VR.
    Maybe an SB-400 should be good for you too, as a first flash.

    Marie
    Hi Marie, TS is using Canon system. Anyway it's ok to use MF cos most if not all Macro shooters use MF for Macro shoots.
    Minolta. Konica Minolta. Sony

  17. #17
    Deregistered marieloves-'s Avatar
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    Default Re: AF searching difficulty

    Oh didn't exactly read it fully.
    I see, but isn't the AI-s lens able to mount on the EOS?

    Marie

  18. #18
    Senior Member Galdor's Avatar
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    Default Re: AF searching difficulty

    Quote Originally Posted by marieloves- View Post
    Oh didn't exactly read it fully.
    I see, but isn't the AI-s lens able to mount on the EOS?

    Marie
    I think an adapter is required.
    Minolta. Konica Minolta. Sony

  19. #19
    Deregistered marieloves-'s Avatar
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    Default Re: AF searching difficulty

    Oh yes, my bad again!
    I seemed to remember there was one mount that did not require an adaptor.
    May be pre-AI or AI mount.

    Marie

  20. #20
    Member Shin Howard's Avatar
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    Default Re: AF searching difficulty

    Quote Originally Posted by Rashkae View Post
    Canon is well known for struggling with focus under low lighing conditions. Even their higher-end cameras suffer from the same problem.
    I don't agree to the above. As I've both Canon & Sony DSLR.
    Canon Beginner DSLR is slow at focusing, while Sony beginner DSLR is slow and takes forever to focus in low light situations.

    Don't just blame on Canon DSLRs when you are a hi-end Sony user.
    I'm looking at a different perpective of life.

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