Using camera lens as a hand lens

Robin Leech releech at TELUSPLANET.NET
Mon Jul 9 12:25:55 CDT 2001


Hello Dave,
Changing the focus by turning the outer ring on the lens system should not
in any way affect your use of the lens.  Most older lens systems moved the
whole lens unit closer or farther away from the camera - this is how one
focussed the lens for different distances.
If you set the lens for infinity, then it should be the smallest and most
compact.  There is no difference to you, the user, if you change from
infinity to the closest point the lens will focus.  That is, there is no
optimum because the lens unit moves as one.
Many of the older lenses, such as the Tessars made by Carl Zeiss, have
identical formulas front to back to front.  Typically, there were 4 lenses
in the Tessar formula.  This formula was copied by the Japanese in many of
their 50s era lenses, mainly because it gives high resolution.  I believe
that the first Micro-Nikkor 55 mm used this formula.
The Japanese, in using the old Tessar formula, improved it simply by using
the special glass made from the sand in Japan.  The Japanese lenses had no
bubbles or other flaws which were so evident in the earlier German lenses.
It should be high resolution as it is color corrected and such.
You may find it better to have the front of the lens towards you, as then
the back of the lens has little, if any, housing to disturb or cast shadows
on the subject being examined.
A wide angle lens may give higher power, but then you have to be closer to
the subject, and with all the lens housing and such, you may find they
interfere with your work.
You will find that many of the newer lenses, and especially the multi-focus
and zoom (i.e., 28-85 mm) lenses have many mobile lens units within the
lens.  You can observe this when you turn the focus ring.
Hope this helps.
Robin Leech
Edmonton
----- Original Message -----
From: "Dave Carmean" <carmean at SFU.CA>
To: <TAXACOM at USOBI.ORG>
Sent: Monday, July 09, 2001 11:12 AM
Subject: Using camera lens as a hand lens


> Recently someone gave me an old normal (50mm) SLR camera lens which I
> have started using as a wide field, low power, hand lens.  It is a
> high quality substitute for the cheap hand lenses I have been using.
>
> I was wondering if other people have experience with this:
> How should I set the focus for the optimum image?  I don't see a
> difference.  Is there an easy way to calculate what magnification the
> optimum image is?  By changing distances I can change the
> magnification, but there is there an optimum?  Should I place the
> camera mounting bracket towards my eye?
>
> Second hand normal lenses are widely and cheaply available as people
> often buy zoom or macro lenses to replace the normal lens the camera
> came with.
> A wide angle lens will give a higher magnification.
>
> Cheers,
> Dave Carmean
> Biology Computer Systems Consultant
> Biological Sciences
> Simon Fraser University
> Burnaby, British Columbia V5A 1S6
> CANADA
> http://www.sfu.ca/biology/qk   (Quick Reference)
> http://herbarium.botany.ubc.ca/  (UBC herbarium Databases)
> http://www.sfu.ca/~carmean/trig/ (Trigonalidae Wasps)




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