scott kirkpatrick Posted April 18, 2008 Share #81 Posted April 18, 2008 Advertisement (gone after registration) Just to provide a little more evidence, I shot a few frames of the focus test chart with my CV 35/1.4 SC Nokton. This is very unscientific; I shot these photos handheld from close to closest lens focus and did not focus bracket any shot. Still, the shift evident in the photos is too large to explain as a result of errors in technique. The first shot shows the full frame; the next four are crops of the center of the focus test chart; in order they were taken at f/1.4, f/2, f/2.8, and f/4. All shot with filter on AWB in DNG at ISO 640 and autoexposure. In order, the point actually in focus looks to me like "Spot on with veiling flare" at f/1.4, "about 14mm behind point of focus, still with veiling flare" at f/2, "about 30mm behind point of focus" at f/2.8, and "about 50mm behind point of focus" at f/4. The mm measurements are read straight off the chart but should not be presumed to be accurate because I wasn't shooting at exactly 45 degrees. Thanks for showing these. Your details were very helpful, and I hope remind people that simple tests of one's own equipment are within the capabilities of any of us, assuming we are willing to take a little care and put in the time to look at the results calmly. Considering how much time seems to go into 100% pixel-peeping, this seems like a better use of that time. Sean can't (and won't) test everything. I've seen that chart before, but can't remember the reference. Can you provide a pointer? It's easy to make your own, but this one is a little nicer and more informative than a hand-drawn vertical line on a sheet of lined paper. Something that i don't know, and will need to read up on, is if you decide to live with a lens which is 4 cm out at f/4 at a focus distance of 1 m, will it still be 4 cm out at 2m, 4m, etc, or will the error increase proportionally to the distance? Would you mind shooting at 2m distance to see what the trend is? thanks, scott Quote Link to post Share on other sites More sharing options...
Advertisement Posted April 18, 2008 Posted April 18, 2008 Hi scott kirkpatrick, Take a look here Cv 35/1.4. I'm sure you'll find what you were looking for!
blakley Posted April 18, 2008 Share #82 Posted April 18, 2008 I've seen that chart before, but can't remember the reference. Can you provide a pointer? It's easy to make your own, but this one is a little nicer and more informative than a hand-drawn vertical line on a sheet of lined paper. You can get the chart here: Nikon D70 Focus Chart Something that i don't know, and will need to read up on, is if you decide to live with a lens which is 4 cm out at f/4 at a focus distance of 1 m, will it still be 4 cm out at 2m, 4m, etc, or will the error increase proportionally to the distance? Would you mind shooting at 2m distance to see what the trend is? Interesting question & I don't know the answer. I may try this but it could be a few days before I get around to it. Quote Link to post Share on other sites More sharing options...
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