# Lens Ratios



## jubbin2001 (Jul 30, 2010)

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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## Overread (Jul 30, 2010)

Have a look here: http://www.thephotoforum.com/forum/...ication-extension-tubes-well-other-maths.html

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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## NateS (Aug 2, 2010)

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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