[rollei_list] Re: maxwell screen
- From: chatanooga@xxxxxxxxx
- To: rollei_list@xxxxxxxxxxxxx
- Date: Mon, 11 Feb 2008 15:17:21 +0000
Re doFocus found a very interesting article here:
http://www.dantestella.com/technical/flange.html
* it is verily small...
* Not intuitive (to me anyway): he points out wide-angle set to infinity has
less doF than a tele-up close (for same aperture presumably).
Bottom line: a mechanical focussing error (eg rollei/ tlr focus screen not
in same position as film-plane or film-flatness issue) have a more
noticeable affect on 'way-off' images vs up close ones; or just forget about
it and take some pictures......:-) ?
On Feb 11, 2008 2:31 PM, Austin Franklin <austin.franklin@xxxxxxxxxxx>
wrote:
> Hi Chat,
>
> I found this on wikipedia:
>
> "A rough formula often used to quickly calculate depth of focus is the
> product of the focal length times the f-stop divided by 1000; the formula
> makes most sense in the case of normal lens (as opposed to wide-angle or
> telephoto), where the focal length is a representation of the format size.
> The precise formula for depth of focus is two times the f-number times the
> circle of confusion times the quantity of one plus the magnification
> factor.
> However, the magnification factor depends on the focal length and format
> size and exact focus the lens is set to, which can be difficult to
> calculate. Therefore, the first formula is often used as a guideline, as
> it
> is much easier to calculate. It relies on the historical convention of
> circle of confusion limit equal to focal length divided by 1000, which is
> deprecated in modern photographic teachings, in favor of format size (for
> example, along the diagonal) divided by 1000 or 1500."
>
> Regards,
>
> Austin
>
>
> > -----Original Message-----
> > From: rollei_list-bounce@xxxxxxxxxxxxx
> > [mailto:rollei_list-bounce@xxxxxxxxxxxxx]On Behalf Of
> > chatanooga@xxxxxxxxx
> > Sent: Monday, February 11, 2008 9:13 AM
> > To: rollei_list@xxxxxxxxxxxxx
> > Subject: [rollei_list] Re: maxwell screen
> >
> >
> > Thanks Austin -
> > I actually meant the equivalent to DOF at the film rather than
> > subject end.
> > In other words how much you can push the film plane/ focus screen
> > around and
> > maintain acceptable sharpness. I may have used the wrong term!
> > On Feb 11, 2008 1:52 PM, Austin Franklin <austin.franklin@xxxxxxxxxxx>
> > wrote:
> >
> > > Hi Chat,
> > >
> > > > Anyone know what the depth of focus is at 1m, f2.8/3.5 for the 80mm?
> > >
> > > Using .06mm COC - 0.048 m for f2.8 and 0.06 m for f3.5.
> > >
> > > http://www.darkroom.com/MiscDocs/DOFCalc.html
> > >
> > > Regards,
> > >
> > > Austin
> > >
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