Quote Originally Posted by Reinhold View Post
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Another reason for using a focusing sheet instead of focusing directly on the easel surface: if you use a precision grain magnifier you need a piece of paper of the same thickness as your printing paper under the magnifier. Otherwise your plane of focus will not coincide with the papers surface...
No real need. There is plenty of DoF around your paper plane, several mm in fact. The thickness of the paper lifts the grain magnifier to the theoretical correct plane, but not having it creates a focusing mistake to small to make any difference. Having said that, if using black easels (which is a good idea), you need a white focusing sheet anyway.