[filmscanners] Re: Nikon LS-4000ED Depth of Field Revisited

["Mats Petersson" <mats.petersson@btconnect.com>]

Julian,

Interesting way of determing DOF. I wonder if it works with Vuescan and a
Canon FS2710??

[snip long description of method of determining DOF on scanner]


>The first time you do step 5, I suggest you choose an outlandish figure
>like X + 50 just to check that the method is working.  If the resulting
>test image is not way our of focus then there is a problem with my
>description.
>
>Hope this helps, because it is not much use knowing the curviness of your
>images if you don't know the scanner DOF.  I look fwd to your results.  If
>any other LS4000 user has done this measurement can you tell us your
>results pls?  (Or LS2000, 30, 8000 for that matter).

I don't know much about the Nikon scanners (I have a Canon FS 2710). But I
think there MAY be a flaw in the above method of determining DOF.

I just think that it may actually be that the "Nikon units" are not the
same size on two different models of scanner, because I have a feeling that
they may be stepper motor steps from some point (or something along those
lines).

Of course, if it's a different stepper motor in the newer scanner, or a
different gear-ratio between the stepper motor and the focusing element
(lens, mirror or CCD or whatever moves), the Nikon units would quite
possibly do different size steps on the different models of scanners.

I'm possibly wrong here, but I just want to point out this possibility, as
I see no reason for Nikon to standardize the unit's used for focusing in
the scanner software, unless they are actually in millimeters/inches (or
some unit related to this).

If the Nikon Unit is not standardized to a set size, then you can't compare
the DOF, since the unit that you're comparing is different. If they haven't
taken the above approach, they can't improve the scanners minimal focusing
step from an older model to a newer one, which could prevent future
improvements on the scanner.

And this of course also means that the "outlandish" value of for instance
50, may not at all be outlandish, it may mean the same as 5, 10 or 25 on an
older model of the scanner.

Now, I can't really say that I have a solution to this possible problem.
Perhaps manual focusing and padding the carrier with some fixed thickness
material (not sure what you'd use...) and fix the focus on that distance,
then add/remove padding to move the film away from or towards the CCD. But
it would require a very precise amount of padding to be used, that is of
known thickness in millimeters (inches or something else universally known
is also possible, not the thickness of 80 g/m2 paper folded over three
times, for instance!). Maybe the little blades (I beleive they are called
Thickness Gauge) that are used to check valve clearances in engines would
be suitable, or very thin fishing line, perhaps. I don't know how many
hundreds of a millimeter we're talking about here, but I'm sure it's not a
whole lot... If using fishing line, it would be possible to cross-check the
actual thickness (as opposed to the stated on the roll) using a micrometer,
as I'm sure it MAY vary in thickness...

I'm just thinking out loud here, so I'm sure someone with more knowledge
will come forward and correct my ramblings in a short while. There seem to
be some pretty knowledgable people on this list.

--
Mats



>Julian

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