On 10 Jul 99, at 10:09, Jan Steinman <olympus@xxxxxxxxxxxxxxx> wrote:
> >From: "Terry and Tracey" <foxcroft@xxxxxxxxxxxxxxxxxxxxxx>
> >
> >In a John Shaw book, he says a 90mm lens has the same DOF whether it is
> >mounted on a 35mm, 6*6 or a 5 *4. I'm so confused.
>
> Yes, it has the same DOF *on the imaging medium.* Now blow that 4" x 5",
> 6cm x 6cm, 35mm, and 4mm x 6mm CCD sensor image up to an 8" x 10", and the
> DOF will be different in proportion to the print size.
>
> Say for illustration purposes that the circle of confusion from this lens
> is 2mm on the imaging medium. That is about 1/6th the area of the CCD
> sensor, but less than 0.40f the 35mm frame, and less than 0.010f the
> 4x5 frame. So the end-print DOF is better the larger the imaging medium
> for a given focal length and aperture. (Please forgive minor inaccuracies
> in this "back of napkin" analysis... feel free to flame me for gross
> inaccuracies... :-)
The circle of confusion would be the same *for a given focal length
lens at a given distance and aperture*, but a 50 mm lens would be a
very wide angle for a 4"x5", wide angle for a 6x6, normal for 35mm,
telephoto for 110 and long telefoto for 4mmx6mm CCD.
The degree of enlargement would also differ from medium to medium.
It all works out that the smaller the image size, the more DOF for a
given view angle and aperture.
> So if I screwed up here, please correct me, but it doesn't make sense that
> you could dramatically increase your end-print DOF simply by using smaller
> film. Otherwise, we'd all be using 110 film, and 8x10 view-camera
> landscapes would simply not be possible! (Yea, I'm ignoring tilt for the
> sake of simplicity...)
The 8x10 has much better grain structure and resolution than the 110
and is the tool of choice for mucho detail. Landscapes are possible for
the 8x10 because small apertures are used and the DOF easily covers
stuff from 20 metres out. (The 110 would cover from 20" out at the
same aperture.)
>
>
> : Jan Steinman <mailto:jans@xxxxxxxxxxx>
> : 19280 Rydman Court, West Linn, OR 97068-1331 USA
> : +1.503.635.3229
------------------
From: Tom Trottier, President, ACT Productions Inc.
infoanim@xxxxxx http://www.act.ca
+1 613 594-4829 fax +1 613 594-8944
199 Holmwood Ave, Ottawa, Ontario, Canada K1S 2P3
"Make it as simple as possible, but no simpler" - Einstein
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|