Archived posting to the Leica Users Group, 1999/11/30

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Subject: Re: [Leica] RE: 75mm f1.4 DOF
From: "Tom Schofield" <tdschofield@email.msn.com>
Date: Tue, 30 Nov 1999 17:10:29 -0800

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Sorry, Elisardo, Jim is right!

Depth of field is constant with a given magnification and aperture.  =
Only to the extent that changing focal length changes magnification does =
DOF change.  Likewise, changing distance only changes DOF to the estent =
that magnification changes.  Intuitively, with a longer focal length, =
you are that much further away for the same magnification, so DOF =
remains the same.  Just to confuse you one step further, this is why MF =
or LF are said to have less DOF than 35mm -- they have a larger image =
size on the negative, so magnification is higher.

Thus, if you are using a 60mm, 100mm or 200mm macro set to 1:2, all will =
have the same DOF -- only the back ground changes due to the angle of =
view -- you are much closer with the shorter focal lengths, but DOF =
remains the same.  If the same 2" tall subject takes up 1" on a 35mm =
frame and 1" on a 6x6 frame, both will have the same DOF -- =
magnification is the same; however, if the 2" subject occupies 2" image =
height on the 6x6 filing the frame, there is less DOF because now =
magnification has increase to 1:1.

   I believe this is in AA's The Camera -- I will look up the reference =
when I get home.

Tom Schofield
  ----- Original Message -----=20
  From: elisardo louzan=20
  To: leica-users-digest@mejac.palo-alto.ca.us=20
  Sent: Wednesday, December 01, 1999 3:07 AM
  Subject: [Leica] RE: 75mm f1.4 DOF


  Jim,
  =20
  Sorry, you are wrong!  DOF is affected by the focal length of the lens =
you use.
  =20
  "Everything you know is wrong" by CTEIN
  PhotoPro September/October 1994 pp50-51

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<HTML><HEAD>
<META content=3Dtext/html;charset=3Diso-8859-1 =
http-equiv=3DContent-Type>
<META content=3D"MSHTML 5.00.2722.1300" name=3DGENERATOR>
<STYLE></STYLE>
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<BODY bgColor=3D#b8b8b8>
<DIV><FONT face=3DArial size=3D2>Sorry, Elisardo, Jim is =
right!</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Depth of field is constant with a given =

magnification and aperture.&nbsp; Only to the extent that changing focal =
length=20
changes magnification does DOF change.&nbsp; Likewise, changing distance =
only=20
changes DOF to the estent that magnification changes.&nbsp; Intuitively, =
with a=20
longer focal length, you are that much further away for the same =
magnification,=20
so DOF remains the same.&nbsp; Just to confuse you one step further, =
this is why=20
MF or LF are said to have less DOF than 35mm -- they have a larger image =
size on=20
the negative, so magnification is higher.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Thus, if you are using a 60mm, 100mm or =
200mm macro=20
set to 1:2, all will have the same DOF -- only the back ground changes =
due to=20
the angle of view -- you are much closer with the shorter focal lengths, =
but DOF=20
remains the same.&nbsp; If the same 2" tall subject takes up 1" on a =
35mm frame=20
and 1" on a 6x6 frame, both will have the same DOF -- magnification is =
the same;=20
however, if the 2" subject occupies 2" image height on the 6x6 filing =
the frame,=20
there is less DOF because now magnification has increase to =
1:1.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>&nbsp;&nbsp;&nbsp;I believe this is in =
AA's The=20
Camera -- I will look up the reference when I get home.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Tom Schofield</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
  <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
  <DIV=20
  style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
  <A href=3D"mailto:louzan@worldnet.att.net"=20
  title=3Dlouzan@worldnet.att.net>elisardo louzan</A> </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20
  href=3D"mailto:leica-users-digest@mejac.palo-alto.ca.us"=20
  =
title=3Dleica-users-digest@mejac.palo-alto.ca.us>leica-users-digest@mejac=
.palo-alto.ca.us</A>=20
  </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, December 01, =
1999 3:07=20
  AM</DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [Leica] RE: 75mm f1.4 =
DOF</DIV>
  <DIV><BR></DIV>
  <DIV><FONT color=3D#000000 size=3D2>Jim,</FONT></DIV>
  <DIV><FONT color=3D#000000 size=3D2></FONT>&nbsp;</DIV>
  <DIV><FONT color=3D#000000 size=3D2>Sorry, you are wrong!&nbsp; DOF is =
affected by=20
  the focal length of the lens you use.</FONT></DIV>
  <DIV><FONT color=3D#000000 size=3D2></FONT>&nbsp;</DIV>
  <DIV><FONT color=3D#000000 size=3D2>"Everything you know is wrong" by=20
  CTEIN</FONT></DIV>
  <DIV><FONT color=3D#000000 size=3D2>PhotoPro September/October 1994=20
  pp50-51</FONT></DIV></BLOCKQUOTE></BODY></HTML>

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