Another cheap option for macro is a reversing ring. These allow you to turn the lens around, which gives amazing magnification. You'll need a 46mm one for the Sweet 35. I have one for my Composer (via a 37/52mm step-up ring), and it's quite amazing. The one problem is there is no means of focusing with a Lensbaby optic as there is only one set of elements and you can't move it relative to the sensor/film. So you have to focus by moving the whole camera.
And a good alternative to extension tubes is a set of bellows. They're a bit more expensive, but older second hand sets can be pretty reasonable (and some even have replaceable lens mountings so you can use different lens and body fitments). They give a range of extension from a few mms to a few inches, whereas extension tubes are limited to a few discreet lengths. The major advantage of extension tubes over bellows is they are simpler and more robust, handy if you shoot out in the field. For studio work bellows are best IMHO.
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