wm700293 said:Well, the immediately previous remarks regarding the effect of filter thickness would make me want to put a micrometer to the four filters to see if the "12" and "16" filters were significantly "thicker" than the others. One easy way to get more density (darkness) in a filter is to make it thicker rather than changing the relative opacity of the material from which the filter is made. Could this be a contributing factor??? Inquiring minds want to know...
If you read the article you'll find that the problem also occurs with the 3-stop and 6-stop - if you add them after focusing. It's just that you never actually need to pre-focus with those filters, whereas with the very dark filters you have no choice.
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