Re: Exact fl of lenses... 220 VR

[Bill Glickman <bglick@xxxxxxxx>]

Gene

     I totally agree, if someone has an open line to comm. with the Seitz's,
go for it.

  Unless my camera is unique, everyone should have the same consequence.  If
you wanted a quick reality check for this, shoot a long flat building with
an aspect ratio you can measure.... use a long lens to prevent bending,
shoot at 1/125 and then at 1/15.  Change apt. accordingly.... now compare
aspect ratios on film and see what you get.... you need a good measuring
device.... the longer the building on film the easier it is to get detailed
measurement... In theory they should be identical.  Overlay the chromes on
top of each other on a light box and see if they match up perfectly.

Regards
Bill G


----- Original Message -----
From: "Gene Woolridge" <gene360@xxxxxxxxx>
To: <panorama-l@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, June 14, 2000 4:29 AM
Subject: Re: Exact fl of lenses... 220 VR


> Bill,
>
>         I would love to have Peter Seitz read this post to see if he
agrees
> with your findings. ( Just to have someone give us a definative answer. We
all
> have better things to do than RE-INVENT the wheel!)
>
> No snip intended, in case someone gets offended.
>
> Bill Glickman wrote:
>
> > 220 VR users:
> >
> > Here is the results of my testing....
> >
> > After extensive testing I have concluded the following... I would hate
for
> > anyone to have to go through 60 rolls of film like I just did.
> >
> > Mr. Seitz says that one needs to determine the exact fl down to .05mm
for
> > images to be sharp.  As I mentioned in prior posts, I felt the best way
to
> > accomplish this was shooting a building with a known aspect ratio and
then
> > match this ratio on film.
> >
> >       I succesffuly accomplished this down to .1mm per lens.  However, I
was
> > suspicious if under different rotational speeds the same exact fl would
hold
> > true.  It would take some really precisioned motor gearing for this to
> > occur.    For example, at 1/15 speed, my 150mm lens computed
consistently
> > out to be 146.3mm.   However at 1/125, the lens computes out to be
149.0mm.
> > So, as you can see, to have an exact fl for a lens, one must test this
for
> > each shutter speed.  Then enter into your brain box the fl value that
> > matches the shutter speed selected.  In other words, you would need
about 9
> > exact fl values for each lens to be sure you are accurate, at any
shutter
> > speed.  (to be fair, I did not test at all ss, just a few, but the
pattern
> > was obvious)
> >
> >       So all my testing was in vain, because at different shutter speeds
the
> > exact fl varies ... I can't spare 2 weeks and  200 rolls of film to
figure
> > this out for each shutterspeed.  Therefore, to me, it does not make
sense to
> > try to nail each fl so exact, unless you are willing to do it for every
> > shutter speed you plan to shoot at.
> >
> >          So for me, its boiled down to an estimate....  Sure wish this
was
> > in the manual?  Bottom line, .05mm is a unrealistic goal, and even .1mm
will
> > only reproduce itself at the shutterspeed it was tested at.
> >
> >       Anyone have a different experience?
> >
> >       I also tested different film speeds and the auto exposure... the
auto
> > exposure it apperas requires much tweaking to prevent banding.  As for
the
> > different shutter speeds, at 1/250 and sometimes 1/125, uneven film
uptake
> > can be seen... It seems best to shoot at slower shutter speeds...
> >
> > Hope this can benefit some users....
> >
> > Regards
> > Bill G
>