Is lens testing at chart distance really an accurate measure?

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techjedi Veteran Member • Posts: 3,950
Is lens testing at chart distance really an accurate measure?

Whenever we read tests on zoom lenses, there is logically different performance tested/observed over the gradient of focal lengths covered.

However, little is said about performance across the focus distance range from minimum focus distance to infinity.

I am not an expert in testing methodology for companies like DXO, but if you were to fit a MTF chart into frame for a given prime lens, that would imply you were only testing one subject distance within the focusing range for that lens.

This seems reasonable for some focal lengths where most photos would be at or near "chart distance", but I would imagine its a poor test for lenses whose focal length is used generally at focus distances beyond the size of any lab test room.

For example, to properly test a wide angle landscape lens at its primary useful focus distance (infinity), it seems you would need a massive chart on the horizon rather than focusing within a lab controlled room to a piece of paper.

So, maybe my understanding of these tests is flawed and there is some means of testing at all focus distances and not just whatever distance fits a chart into that field of view?

Have there been thoughts on this in past discussed here? Are there maybe any wide angle lenses whose testing scores are invalid because they were tested at an irrelevant focus distance?

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