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Archive for November 17th, 2011

SX230HS Adapter: Macro Lens Snout

The macro lens adapter took shape around a nice 25 mm doublet lens from the Box o’ Lenses. The Canon SX230HS has a lens opening that’s just about 25 mm in diameter and a larger lens would be better, but at maximum zoom the image pretty much fills the camera’s entrance pupil. I ordered a pair of 50 mm LED ring lights from halfway around the planet and built the snout to hold the ring around the lens:

Macro lens snout with LED ring light

Macro lens snout with LED ring light

That’s the first pass to get the sizes right and work out some details. In particular, that small white ring inside the aperture below the lens didn’t work at all, so I made the main tube opening a bit smaller.

The solid model shows the details a bit better:

Macro adapter snout - solid model - front view

Macro adapter snout - solid model - front view

The inner cone shields the lens edges from (most of the) scattered LED light. I considered angling the side walls to concentrate the ring light, but wasn’t convinced it’d be worth the effort because the LEDs have such a broad beamwidth anyway. The little hole is for the LED power cable, which goes to a 12 V switching wall wart. The 5 strings of 3 LEDs draw about 70 mA, which suggests I should hack the ballast resistors down a bit to boost the current up to 20 mA per string. FWIW, the resistors give 25 mA per string at 13.8 V, so I could probably goose the current a lot higher.

The bottom has four shallow holes for the alignment pegs cut from ABS filament:

Macro adapter snout - solid model - bottom view

Macro adapter snout - solid model - bottom view

The hole in the front end of the main tube is marginally smaller than the lens diameter, as I used the OpenSCAD cylinder primitive instead of the PolyCyl module that slightly enlarges holes to make the answer come out right. The difference is just enough to form a solid stop that aligns the lens and prevents it from sliding into the body before the glue cures.

The whole affair looks pretty scary from the victim’s point of view:

SX230HS macro adapter LED ring light - front view

SX230HS macro adapter LED ring light - front view

But the camera’s view seems OK, albeit with some vignetting:

Canon NB-5L battery through macro lens adapter

Canon NB-5L battery through macro lens adapter

Limited by vignetting & entrance pupil filling, zooming controls the horizontal subject size from 25 mm to about 10 mm. Depth of field is a few mm, at best; the printing on the far end of that battery is fuzzier than it seems.

Best results so far come from:

  • Manual aperture at f/8
  • Manual focus at infinity (move the subject to focus)
  • Shutter delay = 2 seconds to let the camera stop shaking
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