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


  • To: lexa@lexa.ru
  • Subject: [filmscanners] Re: Nikon LS-4000ED Depth of Field Revisited
  • From: "" <golder@netzero.com>
  • Date: Thu, 6 Feb 2003 07:37:39 GMT
  • Unsubscribe: mailto:listserver@halftone.co.uk

Julian,

I went back and used your methodology described below to determine the critical 
focus range of my LS4000 and my results seem to be generally what you thought 
they might be.

Namely, critical focus is still intact at -5/+5 Nikon Units from focal point 
(0).  Somewhere between -5/5 and -10/10 it softens enough to remain within 
acceptable focus, but by -10/10 it seems to be clearly out of critical focus.  
By -15/15 the focal shift is significant.  However, one caveat:  all my above 
determinations are being made when viewing a very small portion of the total 
24mm x 36mm image and at a highly magnified view.

Given this, I am still hard pressed to say what would really appear as out of 
critical focus when the total image has been printed, at lets say 8x10, 11x14, 
16x20, and viewed in total.  Tough to say.  A bit of a slippery slope, really.

However, if one is going for the most pristine, most ideal scan and one wants 
to make sure that even a small selection of the total image is printed at a 
decent size, I would imagine one would want film curl not to range outside of 
the -5/5 range if possible and definitely not outside the -10/10 range.

To this end, I have been considering using the slide mounts with Anti-Newton 
glass as quite a few posters have mentioned previously.  However, results 
appear mixed.  Some say it works very nicely for them, keeping film flatness 
within a 0-3 Nikon Unit range w/o any loss of image clarity and sharpness.  
Yet, others seem to indicate this is not the case at all, claiming that the 
scanner even picks up the diffused patterns characteristic of the AN glass.

What have your findings been in this area?  I would be very interested to hear.

Lastly, I would like to post my DOF test results as they relate to the FH-3 
manual strip holder vs. the SA-21 auto strip feeder.  And here, I'm afraid my 
findings still tend to stand out as anomalous.

The reason here being that I pretty clearly got better DOF results (in direct 
enlargement to enlargement comparisons) with the SA-21 Auto Strip Feeder than 
with the FH-3 Manual Strip Holder.

I ran the tests on 2 different images: one was on the inside of a film strip 
and the other was on the end of the strip.  Each one was scanned with the SA-21 
and the FH-3 adapters (in both the LS4000 UPRIGHT and SIDE orientations) and 
then compared at various view sizes and at various DOF settings.

Here is the side by side breakdown of the results (granted, this is ultimately 
a subjective determination):

INSIDE IMAGE:

At Focal Point (0): SA21 sharper than FH3
(Side and Upright about the same sharpness; Side perhaps a little sharper).

At (+5): SA21 sharper than FH3
(Side clearly sharper than Upright).

At (-5): SA21 sharper than FH3
(Upright now sharper than Side).

At (+10): SA21 sharper than FH3
(Side especially sharper; Upright closer to FH3)

At (-10): SA21 sharper than FH3
(especially Upright; Side better than FH3, but not as sharp as Upright)

Summary:

SA21 sharper than FH3 at all dofs. Side and Upright alternate; Side sharper at 
focal point and points above; Upright sharper at points below focal point.



OUTSIDE IMAGE:

At Focal Pt (0): FH3 a little sharper than SA21 in some places.

At (+5): SA21 becomes a little sharper than FH3 in some places, otherwise even.

At (-5): FH3 clearly sharper than SA21
(except at lower left corner)

At (+10): SA21 clearly sharper than FH3
(except  at lower left corner)

At (-10): FH3 clearly sharper than SA21
(except  at lower left corner)

Summary: SA21 and FH3 alternate at differing dofs; FH3 sharper at focal pt and 
at points above, while SA21 sharper at points below focal pt.

Regards,

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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