Andrew Dacey wrote:
>Wow, an actual on-topic post that's not digital to boot, will wonders
>never cease?
>
>
Probably not.
>I'm wondering about how to go about calculating the reproduction ratio
>when combining a macro lens with a teleconverter.
>
>Specifically, I have a Tamron 90/2.5 macro (the 2nd version) which
>goes to 1:2 on it's own. If I attach my Vivitar macro focusing
>teleconverter that would take me to 1:1 (it's a 2x converter) right?
>But, then I can also focus the converter to get extra extension. How
>do I calculate what the total ratio would be? Do I calculate the total
>extension and then multiply by 2 or is there another way to work this
>out?
>
<SNIP>
I like the empirical method where you just bolt it all together and measure
it.
I make that comment mainly because I can?t figure it out :-)
I made a series of rectangles in a CAD package that represented the various
ratios, printed it out and just point and look. And yes I know that the
viewfinder isn?t 100% of the total size (but we chose OM?s because the do
show a lot ? right?) It?s close enough for government work.
If you look at John Shaw?s Closeups in Nature on the chapter on
teleconverters:
50 mm lens with 50 mm extension ? 1:1 with 4? working distance and 2 stop
loss
50 mm lens with 2x and 100mm extension - 1:1 with 8? working distance and 4
stop loss
50mm lens with 25mm extension and 2x converter ? 1:1 with 6? working
distance and 3 stop loss
50 mm lens with 17mm extension, 2x converter, 25mm extension ? 1:1 with 7?
working distance and 3 ½ stop loss.
Jay
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