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sdai

Cv 35/1.4

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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

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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.

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