P3D Re: DOF Table on Realist lens cover varies among samples!

[Paul Talbot <ptww@xxxxxxxxx>]

Greg Wageman wrote:
> 
> From: Michael Kersenbrock <michaelk@xxxxxxxxxxxxxxxxxx>
> >Maybe only the lid is older?  Or maybe it's newer
> >and they "improved" DOF for competitive marketting reasons?
> 
> Perhaps they changed the size of the Circle of Confusion.  This is a key factor
> in DOF scales, and you're comparing apples to oranges unless you know this
> parameter.

Greg, do you mean "changed the parameter for purposes of the
calculations" or that the CoC of the lenses actually changed?
(I don't understand CoC in the first place--makes my head spin
in confused circles ;) --, so I don't know whether it is a lens
spec or an assumption used to come up with DOF.)
 
> The CoF indicates how sharp their definition of "in-focus" really is.

Is this a typo or something new you're springing on us?  ;)

> I suspect you're correct that marketeers may have insisted they
> relax this parameter, based on what the competition was doing.

I would hate to think of David White doing something down and dirty
like that!  ;)  It occurred to me to compare the DOF scales between
my retrofitted early Realist and my later Realist.  The dials are the
same!  (The later Realist has an exposure guide instead of a hyperfocal
table inside the lens cover; I compared the markings on the dial.)

My Sherlock attempt:  My early Realist, retrofitted with DOF scale,
and later Realist have identical, conservative DOF scales.  The DOF
scales both match the hyperfocal table on the inside cover of the
early Realist.  Mike K's non-retrofitted early Realist, apparently
of later vintage than my early Realist, has a "little fib" in the
hyperfocal table.  Ergo, I surmise that in the process of retrofitting
the DOF scale to the early Realists, David White also replaced the
hyperfocal table on the inside of the lens cover with the more
conservative version they had adopted.  So Mike's speculation
that "Maybe only the lid is older?" could still be on target.

I received a note from P3D chief detective Gabriel that he recalled
noticing the different hyperfocal tables long before this discussion
came up.  A follow up message listed the values from two samples, a
2.8 Realist and a 3.5 Realist.  The table for the 2.8 Realist matches
Mike K's table; the table from the 3.5 Realist matches mine.  So
other possibilities are that Mike's Realist is a 2.8 with the lenses
downgraded to 3.5s :( , Mike's lens cover, or hyperfocal table
sticker was replaced at some time with one that doesn't match his
lenses; or what appear to be "bread and butter" David White 3.5
lenses are not all the same, and David White knew that.  It is
intriguing to speculate how this all ties in with reported perceived
differences in sharpness of Realist lenses from sample to sample.

There must be Realist gurus out there who have the real answer.
Please speak up to spare the list my rambling musings!  ;)

Paul Talbot


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