## [rollei_list] Re: maxwell screen

• From: "Austin Franklin" <austin.franklin@xxxxxxxxxxx>
• To: <rollei_list@xxxxxxxxxxxxx>
• Date: Mon, 11 Feb 2008 09:31:08 -0500

```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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