[MF3D.FORUM:508] Re: Exact fl match for paired lenses.

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>Where I differ from Greg is that I would not even think of putting one of
>the lenses out of focus to get the same image size. One only uses medium
>format if one wants absolutely sharp images, and while depth of focus
>(similar to, but not exactly the same as, depth of field) will cover it to
>some degree, I can't imagine that you would find that satisfactory after
>spending some $2000 dollars for the pair of lenses. And while one might
>reasonably shim an old Ricoh or  Yashicamat lens, I can't imagine trying
>that with a Mamiya 7 lens.

  In an ideal world you get the factory
to match a pair of lenses for you, or
you buy a bunch and do it yourself (to
0.1% or better).

  In the real world, if your lenses don't
match by 0.5% or whatever I think the
lesser of two evils is to have the focus
points slightly different, rather than
an image size difference. Just my opinion
of course.

  FYI, with an 80mm lens and a COC of 0.06mm
the DOF at f4 when focused at 7 feet is 1.1
feet. So my 3" focus missmatch is well within
that. At f8 the DOF is 2.2'.

  At a 10' focus distance f4 gives you 2.25'
DOF and f8 gives you 4.6'

  For tripod shooting at f11 or f22 or f32
the focus point difference is completely
hidden. Also the further away you focus
the smaller the effect due to the DOF getting
bigger for a given F-stop.

Greg E.

DOF calculator at:
http://members.home.net/gillettm/DOF.html