[MF3D.FORUM:432] Re: fl/30

["Bill Glickman" <bglick@xxxxxxxx>]

David

       Case closed... I will run some test rolls using a constant
deviation...and yours / John B formula and report back....  thank you.

Bill G

----- Original Message -----
From: David Lee <koganlee@xxxxxxxxxxxxx>
To: Medium Format 3D Photography <MF3D.Forum@xxxxxxxxxxxxx>
Sent: Friday, April 07, 2000 9:08 AM
Subject: [MF3D.FORUM:428] Re: fl/30


> I realized last night after I had sent the last message that I had
neglected
> to state that my intention is to keep the deviation constant (within
> practical and artistic limits), no matter what the focal length of the
> taking lens or the depth of the scene.
>
> > David
> >
> >          I ran your formula side by side with John B formula and
> > surprisingly enough, using a constant deviation in John's formula of
2.7,
> > your answers were extremely close every time, regardless of the, near
> > distance , far distance and focus distance.  So I guess you are both on
> the
> > same page...and when evaluating a scene, you both would use the same
> stereo
> > base.
> >
> >     But the question that arose earlier.....that is still not clear to
me
> is
> > this.... if your formula is accurate than I guess the answer to the
> > deviation question must be..... the deviation does not change even when
> the
> > fl of the camera lens is increased or decreased.  A few posts ago, it
was
> > suggested that when you double the camera  fl, you halve the deviation?
>
> What you halve is not the deviation, but the stereo base you would have
> gotten from using the 1/30th (dare I say) rule.
>
>  But
> > on the other side of the coin, when you go to shorter fl camera lenses
you
> > should never go below 2.7 deviation. When using longer fl lenses this
> logic
> > appealed to me, hence why I am pursuing this one till the bitter end :-)
> >
>
> The deviation would always stay at 2.7mm for medium format film (assuming
a
> constant viewing lens).
>
>
> > Here is Johns formula if you do not have it handy...
> > http://home.mira.net/~kiewavly/bases.html
> >
> >        David you seem to be very experienced at this, and I guess the
> bottom
> > line is this.... if you have very good success with this formula, than
> maybe
> > the deviation should not change at all, regardless of the camera fl lens
> > being used?   Meaning yours or John B's formula (with constant
deviation)
> > would get us to the same stereo base.
> >
>
> This is exactly right.
>
>
> >       Any one else have experience at this.... following the math is one
> > thing, knowing what works is something quite different.  Thanks David...
> > your input is very helpful to us beginners getting a handle on this...
it
> > seems we are now very close... I really look forward to seeing your
paper
> on
> > this subject.
> >
>
> Interchanges like this will help get me inspired to finish it before the
> convention. I think that the math is very straight forward, what I really
> intend to delve into in the paper is how one actually does these things in
> the field, even down to how one estimates how far away something is and
how
> accurate you need to be to get a good result.
>
> David Lee
>