Decentered lens, anything i could do?

Started Jun 10, 2014 | Discussions thread
BobORama Senior Member • Posts: 2,382
Re: Decentered lens, anything i could do?

A ( much ) better test is a star field test. Go out on a clear night, place camera on tripod, turn off SR, use higher ISO ( 1600 is fine ) to reduce the star trails, use high magnification LIVE VIEW to focus a bright star ( not planet, UFO, airplane, Sasquatch ) in the center of the frame to as small a point as you can, take an exposure that shows several bight stars across the frame.

Then defocus the image slightly so the bright stars almost disappear in the live view, and show up as tiny discs.  We want to see the structure of the little discs.  Post full resolution pictures some place where we can all see it, and we'll take a look. This tests for almost all pertinent aspects of lens performance: CA, coma, collimation ( including centration ). Many words, but less than 5 minutes of actual work.

In sum, two images of the stars one in focus the other slightly OOF.   Its really that easy.

This test is definitive, shows almost all possible optical defects, and eliminates most of the experimental errors one can make - its hard to move the stars.

 BobORama's gear list:BobORama's gear list
Pentax K-5 Pentax K-1 Sigma 10mm F2.8 EX DC HSM Diagonal Fisheye Pentax smc DA 18-55mm F3.5-5.6 AL WR Samyang 14mm F2.8 IF ED MC Aspherical +9 more
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