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Thread: About F stops

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    Member cubicon's Avatar
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    Default About F stops

    Hi guys, would like to ask on compensating F stop for either using either TC or other forms of tubes.

    for example i have a lense that is f4.0 and i use a TC 2x, what i understand is I lose 2 stops of light and it becomes F8.

    however, how does that translate on to the camera to get the right exposure? Do i have to set to F8 on my dslr myself to start shooting?

    also, if a lense sharpest is 2 stop from its widest aperture, again using the top as reference. The sharpest point then become 2 stops after F8 ? I guess the same will apply to macro setup?

    Thanks for any help.
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    Member Aikiway's Avatar
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    Default

    Quote Originally Posted by cubicon View Post
    Hi guys, would like to ask on compensating F stop for either using either TC or other forms of tubes. for example i have a lense that is f4.0 and i use a TC 2x, what i understand is I lose 2 stops of light and it becomes F8. however, how does that translate on to the camera to get the right exposure? Do i have to set to F8 on my dslr myself to start shooting? also, if a lense sharpest is 2 stop from its widest aperture, again using the top as reference. The sharpest point then become 2 stops after F8 ? I guess the same will apply to macro setup? Thanks for any help.
    Your camera biggest aperture will begin from F8 automatically. I'm not too sure about the latter, but I think it will not apply.
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    Member cubicon's Avatar
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    Default Re: About F stops

    so even thou my dslr display f4 ... it is actually f8. but wouldnt the metering go hay wire in cam ? then how do i get the correct exp ?

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    Moderator Octarine's Avatar
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    Default Re: About F stops

    Quote Originally Posted by cubicon View Post
    so even thou my dslr display f4 ... it is actually f8. but wouldnt the metering go hay wire in cam ? then how do i get the correct exp ?
    If you have a TC that fits to your system electronically, then the chips in the TC will 'tell' the camera that 2 stops come on top. You can try this by just metering with and without TC at the same scene. The resulting values should show a 2 stop difference. Best to use Av, fix the aperture and ISO, watch the resulting shutter speed.
    For TCs that don't come with chips, the entire setup becomes manual. Best to use Manual exposure mode then. If you intend to use the lens at maximum aperture, just set all parameters and watch the exposure meter. The total amount of light coming in will be measured. The effects from TC are included since the sensors sit in the body.
    EOS

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    Moderator catchlights's Avatar
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    Default Re: About F stops

    Quote Originally Posted by cubicon View Post
    Hi guys, would like to ask on compensating F stop for either using either TC or other forms of tubes.

    for example i have a lense that is f4.0 and i use a TC 2x, what i understand is I lose 2 stops of light and it becomes F8.

    however, how does that translate on to the camera to get the right exposure? Do i have to set to F8 on my dslr myself to start shooting?

    also, if a lense sharpest is 2 stop from its widest aperture, again using the top as reference. The sharpest point then become 2 stops after F8 ? I guess the same will apply to macro setup?

    Thanks for any help.
    you just lose 2 stops of light if you use a 2x tele-converter with a lens.

    the camera meter reading will compensate accordingly, since it reads base on the lights enter into the lens.
    if you use auto exposure mode, like A, S, P mode, the camera will just follow the what the camera meter suggests.
    if you use manual exposure mode and follow the camera meter suggests, it will work just as usual.

    you need to compensate for two stops light loss only when you use hand held light meter.


    as for lens sweet spot, most lenses are close down two stops from the widest aperture, but not all lens are the same, best is the do some series of test to find out the sweet spot of your lenses.
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    Member cubicon's Avatar
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    Default Re: About F stops

    thanks all

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