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

["Tony Terlecki" <ajt@mrps.demon.co.uk>]

On Sun, Jan 26, 2003 at 08:26:26AM +1100, Julian Robinson wrote:
> 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,

I performed these exact experiments about a year ago when the DOF issues
were being discussed at length. My tests were done on a Kodachome 200 slide
which I specificaly used because of the ease with which I could focus on the
grain.

My own personal tests made it evident that anything much outside of -5 and
+10 from critial focus (this is using Nikonscan's focus units) started to
show unacceptable softening. That to me does not give much leeway in
focusing on a pice of film to get the image sharp across the whole length of
the film. Og course other peopple may not be as fussy with sharpness across
a scan but -5 and +10 are my own personal comfort levels. As a result all my
film is now left uncut and stored in negative sheets so it remains perfectly
flat for scanning. Any probematic pieces of film go in a glass slide mount
with anti-newton glass.

I've had a quick look but I think I've deleted all the test images I made. If
there was significant interest I'd be happy to repeat the experiment.

--
Tony Terlecki
ajt@mrps.demon.co.uk

----------------------------------------------------------------------------------------
Unsubscribe by mail to listserver@halftone.co.uk, with 'unsubscribe 
filmscanners'
or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or 
body