NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/rec/photo/20361

Text File | 1992-11-23 | 1.6 KB | 37 lines

Newsgroups: rec.photo
Path: sparky!uunet!zaphod.mps.ohio-state.edu!sdd.hp.com!hpscit.sc.hp.com!scd.hp.com!hpscdm!hplextra!cello!jacobson
From: [e-mail] (David Jacobson)
Subject: Re: Macro depth of field maximum
Message-ID: <[e-mail]>
Date: Mon, 23 Nov 1992 18:55:06 GMT
References: <[e-mail]>
Organization: Hewlett-Packard Laboratories
Lines: 26

In article <[e-mail]> [e-mail] writes:
>What is the best way of achieving high resolution and high
>depth of field at about 3x magnification.  I want to view
>something with a 8x6 mm sensor size CCD camera and a 50mm
>approx lens.
>
>I do not mind a bit of optical hacking.  Are there any
>diffraction limited lenses at this level.
>
>A small lens would be better (ie smaller than a micro
>Nikkor 60mm.

There is no magic.  The only way to get large depth of field for a
given magnification is to use a small aperture.  But there is a rule
of thumb that the achievable lines per mm are roughly 1500/f, where f
is the is the effective f number.  At 3x that is 4 times the labeled f
number.  I've never done anything with video, so I don't know what a
good resoltion is.  I'll guess that 33 lpmm, the same as is standardly
used for 35mm, would be good.  The you could use f/50, effective, or
roughly f/11 on the aperture ring.  But then your depth of field,
again assuming a .03 mm circle of confusion, would be only .15 mm!  If
you go to, say, f/32 on the aperture ring, you depth of field
increases to .42mm, but your resolution drops to 11 lpmm.

  -- David Jacobson