Re: Exact fl of lenses... 220 VR

[Harold Wong <hgw@xxxxxxxxxxxxx>]

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
> > __________|        |_____________________________________
> >
> 
> 
> 
> 
>