Saturday, January 24, 2009

Focus Charts

Since I was having trouble focusing my manual focus Takumar, I thought I'd check whether my camera was front- or back-focusing, i.e., the focus point was in front of or behind where it was supposed to be.

(This applies even with MF lenses because my camera has "focus confirm", where it uses the autofocus sensors to show when you're in focus, even if you have to turn the focus ring yourself. It's pretty handy when you have a smaller viewfinder and no split prism, as is typical for APS-C DSLRs like my K200d.)

Casual testing using a magazine revealed an apparent front focus of ~10mm on both the Takumar and the modern 18-250 zoom. Yipes! What a bummer when the zoom already needs warranty repair for asymmetric vignetting (see shadow in upper-right corner of previous two posts).

However, use of an actual focus test chart in good light (above) shows that the zoom has no focus problems. It seems to autofocus within +/- 2mm, randomly distributed, which is just fine. The Takumar does have a front focus of ~6mm, but that's easy to compensate for by approaching focus from the far side and backing off slightly after confirm.

Both lenses are plenty sharp, and the Takumar very much so when stopped down. They sure make my point and shoot look like a dog, which is the point I suppose. :)

Project 100, #11.

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