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Thread: Lens Ratios

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    Lens Ratios

    Can someone please exlain the math behind macro ratios? For example, I have a Vivitar 100mm macro lens that shoots 1:2 without the diopter on the front. Now lets say instead of the diopter I use a 1.4x telecoverter. What is the lens actually shooting at now?

    Then lets say I have a 21mm extension tube coupled with the 1.4x teleconverter, where am I at now?

    If someone could please explain the math and give some examples that would be awesome!! Thanks!



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    Have a look here: Calculating magnification with extension tubes - as well as other maths

    The thread contains links to an online calculator (and series of them) that gives results and math behind the magnification factors for the different kinds of macro setup.
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    All I can say is that you magnification ramps up quick when you start using a combo of TC's and tubes.

    On my 180mm 1:1...adding the 1.4tc get's me around 1.475:1. Using 68mm of tubes gets me around 1.4:1.....logically you would think that would mean the combo of both would put me at around 1.9:1, but in reality the full set of both puts me between 2.5:1 and 2.7:1. So basically the combo of those really increases mag a lot quicker.

    I can't say for sure, but I would guess on a 2:1 lens that the 1.4TC and 21mm tube would put you at least 1:1 if not a bit beyond.

    I actually have a 1:2 faux-macro that I can try to test out if I can find the time and see what the combo of a 20ish mm tube and a 1.4TC puts the mag at.....of course it's a 300mm lens instead of a 100mm so the tube won't have as much effect on mine as it will your 100mm.
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