Re: Exact fl of lenses... 220 VR

[Bill Glickman <bglick@xxxxxxxx>]

Marty

     Excellent suggestion, I think that should work, would save some
time...thank you...

Bill  G



----- Original Message -----
From: "Martin" <martinjg@xxxxxxxxxxxxxx>
To: <panorama-l@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, June 14, 2000 12:47 PM
Subject: Re: Exact fl of lenses... 220 VR


> Instead of testing each lens why don't you try this:
>
> first find out on every one of your lenses the perfect manually inputted
> variance in focal length for the same shutter speed on every lens, say
30th
> of a second.  then test one lens on all the shutter speeds (preferably the
> one you will use the most often), and figure out what the different
> variations in focal length are needed for each shutter speed and describe
> each change for every shutter speed as a percentage of the 30th of a
second
> focal length setting and then using a calculator apply the percentage to
all
> the other lenses focal lengths for each shutter speed in relation to a
30th
> of a second.  if this works you will save a lot of film and time.  if it
> does not, you will have all the settings for your favorite lens.
>
> marty
>
>
>
> ----------
> 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
> > __________|        |_____________________________________
> >
>
>
>
>
>