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

["" <golder@netzero.com>]

Julian,

Thanks for your feedback and added instructions.  I will apply your 
instructions for determining my LS4000s critical and acceptable DOF and post 
them here.

Thanks again,

Derek



----- Original Message -----
From: "Julian Robinson" <jrobinso@pcug.org.au>
To: <golder@netzero.com>
Sent: Saturday, January 25, 2003 1:26 PM
Subject: [filmscanners] Re: Nikon LS-4000ED Depth of Field Revisited


Hi Derek,

>In the web site above, critical focus is maintained with a +/-12 Nikon
>unit range, and decent focus within a +/-24 range.  How this translates to
>the LS4000, I don't know.
>
>I have looked at the scans super magnified and tried to discern what makes
>for a critical focus range in the LS4000 and what makes for a decently
>focused range (using NikonScan focus units) by looking at grain structure,
>but I fear I have not been to successful with this method.

I was very interested to read your comments - it is good to hear that at
least some examples of the LS4000 seem to work well re focus.  As Peter
said, the extent of the focus problem definitely varies a lot of between
individual scanners.

But I am bothered that you couldn't determine the critical focus range -
particularly since I have been waiting for a year or so for someone to do
this on an LS4000!!  (it was my page you were looking at).  Can you have
another go?  It would be very instructive for LS4000 owners, of which I am
not one, and also for me to know if the LS4000 is an improvement over the
LS2000 in this respect.

It should be easy to do, unless I am missing something about the LS4000
that interferes with the method.  Let me try another description to see if
it helps. Pls don't be insulted by the level of detail, I am trying to make
sure we are doing the same thing.

1) Use a negative, neg is better because scans have more apparent grain to
play with.
2) Do a preview and crop the image on the preview to be a small area around
some part of the neg with obvious grain
3) Do a "manual autofocus" on that point, read the focus number in Nikon
units - call your reading X.  By "manual autofocus" I mean :

         - hold down on the control or command key and click on
            the focus button (the one like a checkered flag)
         - now click on your test area on the preview (the cursor
            should have changed to a gunsight)

4) Scan, save the scan and enlarge in PS or whatever.  Note that the grain
is sharp.
5) Now, manually set the focus point to X + 5 or 10 units.  To do this,
type the required value directly into the "Manual Focus Adjustment" box on
the Scanner Extras palette.  Repeat the scan and check if the grain is
still sharp.
6) Repeat 5) as often as necessary increasing the focus point value each
time, (moving the lens more and more away from the correct focus point)
until the resulting scan has clearly lost grain sharpness
7) Repeat 5) and 6) but this time setting the focus point to LESS than the
auto-derived focus value (i.e. X-5, X-10 etc), until the image again has
definite soft grain.
8) You should now have a series of little images with names like "+5",
"-20".  Line them up in Photoshop or whatever, in order, and pick the two
(a plus value and a minus value) at which the grain first becomes
definitely soft.  The difference between them is the DOF in Nikon units -
to grain sharpness level.  I did the same exercise again, but looking at
the *image* sharpness disregarding the fact that the grain was obviously
soft and got another figure - a greater range - over which the image was
acceptably sharp for my purposes.  This gave me a kind of "worst case" -
the actual range which I had to keep my film within if the image was to be
usable.

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).

Julian



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