Re: Exact fl of lenses... 220 VR

[Bill Glickman <bglick@xxxxxxxx>]

Harold

      This link does not give exact fl...at least not for the Mamiya lenses
I looked at.  Am I missing something?

Bill G


----- Original Message -----
From: "Harold Wong" <hgw@xxxxxxxxxxxxx>
To: <panorama-l@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, June 14, 2000 12:55 PM
Subject: Re: Exact fl of lenses... 220 VR


> The fl stated on the lens may not reflect reality. Check out
> www.photodo.com and they will give you and exact fl for the lens they
> tested. Maybe this is the variable you've been missing.
>
> Harold
>
> > ----------
> > From: Bill Glickman <bglick@xxxxxxxx>
> > To: panorama-l@xxxxxxxxxxxxxxxxx
> > Subject: Re: Exact fl of lenses... 220 VR
> > Date: Wed, Jun 14, 2000, 12:13 PM
> >
> >
> > Andrew
> >
> >
> > > I agree. You must know the focal length but this is not a factor that
> > changes
> > > with the exposure time you use on the camera, ... is it?
> >
> >       That was my unfortunate discovery, and it makes sense.  I can nail
> > down a fl to .1mm at a given shutter speed.  Works perfect every test...
> > aspect ratio is dead on.  However, when using the same fl, but change
the
> > shutter speed from 1/125 to 1/15, I can not reproduce the same aspect
ratio.
> > All other test variables remained constant.  It makes sense... because
> > unless the motor speed is in sync at exactly every shutter speed,  you
will
> > not be using the optimum fl.  For the random checks I did, none worked
out.
> > :-(
> >
> > In a previous post a gave exact examples of this.  But this new found
> > knowledge puts me in a quandray..... all 50 rolls of my testing were
> > practically useless, unless I always shoot at the ss I tested at.
Otherwise
> > I must test each of my 4 lenses at every ss to find the exact. fl
setting.
> > If not, one might as well just throw an educated guess in and hope for
the
> > best.  For now, I will try my hardest to use the ss where my test
results
> > were perfect.... if not, I'll just take my chances.  The amont of
testing to
> > determine all this information is time and cost prohibitive for me right
> > now.....
> >
> > Regards
> > Bill G
> >
> > That is my
> > > "objection". The focal length of a given lens is not a variable. To
determine
> > > the focal length of a lens precisely one uses a nodal slide generally.
Most
> > > lenses are stamped with approximations to their actual focal length.
For
> > > precision panoramic work you should go to the trouble of determining
the
> > actual
> > > focal length of the lens.
> > >
> > >
> > > Andrew  o o  0 0 o . o  Davidhazy, Imaging and Photo Tech
> > >          \/\/\/\/\/\/          http://www.rit.edu/~andpph
> > > __________|        |_____________________________________
> > >
> >
> >
> >
> >
> >
>