Re: Focus shift (was Re: Reciprocity failure)

[boblong@xxxxxxxxxxx (Robert Long)]

On Fri, 4 Apr 1997 17:20:18 +0100 (WET DST), Michel Wurtz wrote:

|I know that a drawing would be better, but I prefer not to put a (small)
|jpeg attachements without asking : does the policy of this list agree ?

Whatever Willem may have to say on the policy issue, your explanation
seemed entirely clear to me, at least, making the diagram unnecessary.

But although I've used the same technique I think it may be fussier
than necessary.  Remember that the human eye resolves finer brightness
detail than color detail.  That's why color TV (NTSC, at least, but I
think it's true of PAL and Secam as well) can get away with something
like half the resolving power in its color signals that it affords in
its brightness (b&w) signals.  So if an object is within the
depth-of-field "window" for the two emulsion layers sensitive to the
longer wavelengths, but just outside it for the IR, the slight
blurring of the IR layer should be unnoticeable given the detail
supplied by the other two.  No?

Or am I opening another of those "angels and pinheads" discussions
that some here may find boring?

Bob Long
(boblong@xxxxxxxxxxx)

------------------------------