Tuesday, March 20, 2007

Searching for Macros

And so begins the search for a magnifier. The terms Macro, Close-up, and Diopeter get thrown around. The filters that screw on to the lens is usually called a close-up lens. Sometimes a Macro. Diopeter (literally means power of magnification) is rarely seen. But if you get the chance you want an achromatic close-up. The folks at DVInfo.net talk about custom built 72mm achromats for HD work. Others talk about really expensive +7 Century Optics achromatic close up but they're not entirely happy with it. I've heard of Hoya +10 (AC) close ups which some people consider okay for SD work but its not cheap either.

What's all this lingo and how does it matter? First of all lets think of what a macro does. It's a magnifier so the camcorder's lens can focus on a object closer that it normally can. The power has to be high enough so we can get the magnifier closer to the ground glass which is our subject. So we want a +7 or +10 power (or diopeter) magnifier. You can stack magnifiers like a +3 and +4 but this causes recordable light to be lost. We want to keep as much light as possible so I decided on a +10.

Speaking of light, that's what the coatings are for. The better the coating the more light is allowed through the filter. That's why some lenses are cheap and some are very expensive. The expensive ones supposedly let 99% of light to go through. Less expensive multi-coated ones let 97% and so on.

When you magnify an image you multiply flaws. This includes an effect called distortion and chromatic abberation. If you take a regular handheld magnifier you'll notice that the image is sharp in the center and gets stretched out as you get to the edges (distortion). The colors also gets a bit off like a badly tuned TV (ghosting). Now if you have a big enough magnifier you may be able to compensate for distortion by focusing on the center sweet spot. For the ghosting, most recommend to get an achromatic diopeter. This is a two lens magnifier that cancels out this effect. Since those are expensive and we want to experience build it yourself, we're going to have to make compromises.

Just to be able to test, I ordered a +10 Closeup made by Bower. Bower is supposedly at par with Hoya standard coating filters. Since I'm using an SD camera it should be good enough. But for later I really want to try an achromat. So I go buy cheap binoculars.

Say what? Yes, binoculars. The front lenses taken out and facing each other can be used to build an achromat. All you need is a holder and some glue. It'll make a nice challenge. At the end of the day all this experimentation maybe just a bit shy of buying 1 tested commercial product. But that's 1 versus many. And the comparison is great for learning.


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