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Thread: Trouble focusing with a converter....

  1. #1

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    Trouble focusing with a converter....

    I am just wondering if any one else has had the same problem as me. I love nature photography and shoot with a Nikon D80, Sigma 500mm F4.5 EX HSM lens. To get that extra reach (especially for birds) I am trying a 2x converter. I shoot in manual mode most of the time, and usually in early morning or late afternoon and avoid high noon contrast and harsh lighting. When I shoot with just the lens i get great images that are sharp and clean but when i shoot with the 2x converter It seems that when i look through the view finder i can focus fine but when i download the images to my computer the images are no where close to being in sharp focus. I am very frustrated with the 2x converter. Any advise to help me out with this problem or did i waste the money on the converter?

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    Re: Trouble focusing with a converter....

    Chris,

    I've read about this kind of behavior before. The strongest bit of advice I got from reading about is that 'if you can get at least one crisp, in-focus shot with the teleconverter, it is probably user error; however if every single shot you take (and take hundreds to be sure) is blurry, then the teleconverter is probably bad and you should attempt to get a refund'.

    It sounds like you might be in that latter case. What brand is the teleconverter? Quite often, teleconverters are "paired" with specific lenses. I don't know if I believe it 100%, but I definitely do believe that a cheap teleconverter will likely have design flaws that a more expensive one will not.

    I also figure that at some point, Colin will swoop in here with a much more technical and experienced answer.

    - Bill

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    Re: Trouble focusing with a converter....

    I don't know Nikon but with Canon with such cases you have to set the focussing to the center sensor only.

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    Re: Trouble focusing with a converter....

    There are many things to consider here before you blame it on the teleconverter. For instance at what aperture were you shooting, how well focused is the Sigma lens without the teleconverter, what was the lighting situation when you took the photo, how stable was the camera, etc.? I have never used one, but I have used a camera through a telescope and get the same problems with focusing, mainly it has to be done manually and this can be difficult with a moving object, even a tree blowing in the wind.

  5. #5

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    Re: Trouble focusing with a converter....

    It is a Tamron converter but it wasent a cheap one , i know that my 500mm is a sigma but the converter works well with my Nikor lenses. I was told that the converter would work ( by the salesmen, hmmm) that the optics would work fine but i would not be able to use auto focus, that the converter would work but in manual focus only. I will double check the cameras settings and make sure focusing is set to center.......wish me luck.....and thanks for the input Bill and Hans......................

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    Re: Trouble focusing with a converter....

    "center focusing"...what does that have to do with manual focusing?
    Don't be to quick to blame the TC unless it exhibits the problem with all your other glass,
    which you say that it doesn't. Try a work-around...use a longer DOF...larger f/stop number.

    I use a Canon 300 mm f/2.8 with stacked TC's (1.4 & 2.0 X), works well if I'm careful with manual focusing.

  7. #7

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    Re: Trouble focusing with a converter....

    If I understand things correctly, Chris.

    You are manually focusing. A x2 will not auto focus at F4.5.

    But adding a x2 to a 500 mm lens is likely to be fraught with problems due to the extreme magnification. In fact a x2 only works well on a few specific lenses, and even then there is always a risk of some image quality loss.

    What shutter speed and how sturdy is your tripod? With that sort of set up I would be using cable release and mirror lock up.

    In fact with that lens, I wouldn't really want to go larger than a 1.4x and preferably no converter.

    I have occasionally used a 1.4x on my Sigma 150-500 but the results are never as good as I would like.

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    Re: Trouble focusing with a converter....

    Interesting discussion. Have been experimenting and learning with my first DSLR (550D) for the last few months and have started to think about how to expand lens options. I have a 17-55 and 70-300 both of which came as a bundle with the camera body. Was thinking seriously about purchasing a 2x converter as I enjoy shooting nature, well either that or something like an f1.8 / 50mm...either way interesting topic so I will keep an eye out.

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    Re: Trouble focusing with a converter....

    Not shure what the max aperture for auto focus is with nikon, but with canon it is f/5.6. The only canon cameras that will auto focus at f/8 are the 1d series.

    The 2x converter will make your lens loose 2 stops. So if you have a f/4 lens, it will become a f/8 lens with the converter. At f/8, you will loose auto focus. Manual focus is very touchy with an auto focus lens. They are designed to auto focus quickly, so the focus range is very short.(about a 1/4 of a turn on the focus ring) Because of this , you almost 'have' to use live view and a tripod , to focus accurately. I even use the timer and lock the miror to avoid camera shake when i stack converters.

    If you have live view, try that and a tripod and see if that will help. Or you could get a 1.4x converter and then you will still have auto focus.






    Jonathan, the teleconverters are not designed to work on either of the 2 lenses you listed. If you go to the canon web site, they will list the lenses that work with a teleconverter.

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    Moderator Dave Humphries's Avatar
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    Re: Trouble focusing with a converter....

    Quote Originally Posted by jp01 View Post
    Interesting discussion. Have been experimenting and learning with my first DSLR (550D) for the last few months and have started to think about how to expand lens options. I have a 17-55 and 70-300 both of which came as a bundle with the camera body. Was thinking seriously about purchasing a 2x converter as I enjoy shooting nature, well either that or something like an f1.8 / 50mm...either way interesting topic so I will keep an eye out.
    Beware Jonathan, I'm not a Canon man, but it is my belief that a TC may not work with kit lenses. that said, it may depend on whether 1.4 or 2 times and also whether Canon or third party.

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    Re: Trouble focusing with a converter....

    Quote Originally Posted by Dave Humphries View Post
    Beware Jonathan, I'm not a Canon man, but it is my belief that a TC may not work with kit lenses. that said, it may depend on whether 1.4 or 2 times and also whether Canon or third party.
    Converters will only work on L zooms and any prime lens 135mm or larger.

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    Re: Trouble focusing with a converter....

    Quote Originally Posted by Steve S View Post
    Converters will only work on L zooms and any prime lens 135mm or larger.
    L-Primes over 135mm perhaps

    For the full list ...

    1.4x http://www.bhphotovideo.com/FrameWor...xExtender.html

    2.0x http://www.bhphotovideo.com/FrameWor...xExtender.html

  13. #13

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    Re: Trouble focusing with a converter....

    Hi Chris,

    Have you conidered using an extension tube to allow you to get closer?

  14. #14

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    Re: Trouble focusing with a converter....

    Jonathan. There are two issues here regarding converters.

    Firstly, Canon converters will only physically fit a restricted number of lenses; and neither of your lenses are on the list.

    Secondly, third party converters (Canon fit) will work with those lenses but you will lose autofocus with a x2.

    However, I don't recommend using one with those lenses because of the image quality loss.

    Once, I tried a Canon 1.4x with the 70-300 by adding a 12 mm extension tube between the lens and converter. This lost infinity focus but I only wanted it for macro work anyway. It did work but I didn't like the resulting quality loss.

    A 300 or 400 mm lens will work reasonably well with a 1.4x converter and these options are popular with wildlife photographers. The 2x will lose autofocus unless you have a 2.8 lens, which will be expensive.

    I'm afraid that there isn't really much other cheap options if you want to go beyond 300 mm.

    ps. A 25 mm extension tube worked reasonably well with the 70-300 for close up shots but infinity is lost. And we are into tripod only use now.
    Last edited by Geoff F; 6th June 2011 at 08:14 PM. Reason: extra line

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    Re: Trouble focusing with a converter....

    Wow - as normal what a huge amount of info and detail from everyone, thanks...

    I did think there must be a catch otherwise why would the lens manufacturers sell 600mm+ zoom lenses if one could purchase a simple converter. Your comments all make logical sense even with my limited technical knowledge other than "extension tube". What's that and what's the difference btw that and a converter?!

    As for the tripod have just started to experiment properly with it and on the first outing took the same shot twice, once without tripod and once with. The difference when I loaded into pc was astounding even as a thumbnail. I believe!

  16. #16

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    Re: Trouble focusing with a converter....

    Quote Originally Posted by jp01 View Post
    Your comments all make logical sense even with my limited technical knowledge other than "extension tube". What's that and what's the difference btw that and a converter?!
    An extension tube decreases your minimum focusing distance - so you can get closer - and thus magnify the subject more. You lose the ability to focus at infinity though.

  17. #17
    Moderator Dave Humphries's Avatar
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    Re: Trouble focusing with a converter....

    Quote Originally Posted by jp01 View Post
    Your comments all make logical sense even with my limited technical knowledge other than "extension tube". What's that and what's the difference btw that and a converter?
    The purpose of a converter is primarily to magnify a distant image, (by converting the focal length of your lens by typically 1.4x or 2x (i.e. 300 x 1.4 = 420mm or 300 x 2 = 600mm). It consists of glass lenses and (as you also know), fits between camera and lens.

    As does an extension tube, but like the name suggests, it is literally just a tube (no glass) and merely extends the distance between the lens and sensor, this primarily allows closer focusing, hence a larger image on sensor because you have to get closer to subject. Unfortunately, you can no longer focus to infinity, so no good for (distant) birds, but ok for (closer) bugs

    Either will not be using the lens as designed, so will degrade (one way or another) image quality - moreso with the converter because it has its own glass elements introducing more distortions and reflections.

    Do have a look at the tutorials here at CiC for more information, Sean explains the technicalities much better than I

    HTH,

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