Re: Exact fl of lenses... 220 VR

[Martin <martinjg@xxxxxxxxxxxxxx>]

Title: 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



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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
> __________|        |_____________________________________
>