calculating extension tube length and focus distance

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Alan
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So I have a macro bellows and I'd like to use it to copy slides with my xt1. Now it occurred to me that I wouldn't need a macro lens for this, since I have the bellows but us there a way I cam work out how much extension I'll need to get the approx 2:1 magnification I'll need and how far away that puts my slide? Assume a 50mm lens
 
maybe 25mm and infinity focus at a guess?
or just play about, but you will likely need something like a ruler to know where your focusing cos you have a *very* shallow dof and its all blur if your off, even just a little bit
 
Mostly I tend to do macro on a set it up and experiment basis however


From Lefkowitz for a lens normally mounted and set to infinity Extention Distance = magnification X focal length

So 100mm with infinity focus set.

I have that book and see it recommended a lot by people who seem to know what they are up to

I could point you in the direction for some simple formulae for Working distance with regard to large format but for your purposes a better bet might be the photonet lens tutorail

LF lenses tend to be simple so cerain assumptions can be made that don't really apply to smaller format lenses.

(M+1)F=bellows extension

((1/M)+1)F=lens to subject

Normal lenses are not optomized for macro and for something that is effectively flat field copying it might really pay to get one.
 
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