From: "Kreig McBride" 
To: "Ellen Mackenzie" 
Cc: 
Reply-To: "Kreig McBride" 


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Although I dont know much about these designs, you will find that the =
lenses are probably designed to have the same back focus no matter what =
the focal length based on design for a particular use.   You might try =
to remove one of the rings and see if you gain more eye relief and also = a
wider field of view.  Also sometimes you can remove either a singlet = or
doublet from the lens to improve the field of view and usage as an =
eyepiece.  The lens you are removing is probably used to reimage for a =
very specific use such as TV videocom tubes.  heligon and heliogon are =
trademarks of Rodenstock Co.

Kreig


    -----Original Message-----
    From: Ellen Mackenzie 
    To: atm{at}shore.net 
    Date: Sunday, June 08, 2003 10:15 AM
    Subject: ATM Heligon Lenses
   =20
   =20
    I picked up a batch of surplus Heligon lenses mostly for the glass =
in them. I discovered a few of them made excellent RFT eyepieces. In =
particular, the 90mm and the 50mm. Surprisingly, the stated focal length =
has little to do with the actual working focal length, with both lenses =
having an apparent working distance of about 25 mm. I have searched the =
web to find out about construction details of these lenses but was = unable
to find much useful information.
        Does anyone out there have patent numbers, glass types etc.

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Although I =
dont know much=20
about these designs, you will find that the lenses are probably designed = to have=20
the same back focus no matter what the focal length based on design for = a=20
particular use.   You might try to remove one of the
rings and = see if=20
you gain more eye relief and also a wider field of view.  Also =
sometimes=20
you can remove either a singlet or doublet from the lens to improve the = field of=20
view and usage as an eyepiece.  The lens you are removing is =
probably used=20
to reimage for a very specific use such as TV videocom tubes.  =
heligon and=20
heliogon are trademarks of Rodenstock Co.
 
Kreig
 
 

    -----Original =
Message-----From:=20
    Ellen Mackenzie <mackenzieconsulting{at}symp=">mailto:mackenzieconsulting{at}sympatico.ca">mackenzieconsulting{at}symp=
atico.ca>To:=20
    atm{at}shore.net">mailto:atm{at}shore.net">atm{at}shore.net
<atm{at}shore.net>Date:">mailto:atm{at}shore.net">atm{at}shore.net>Date:
=
Sunday,=20
    June 08, 2003 10:15 AMSubject: ATM Heligon=20
    Lenses
    I =
picked up a=20
    batch of surplus Heligon lenses mostly for the glass in them. I =
discovered a=20
    few of them made excellent RFT eyepieces. In particular, the 90mm =
and the=20
    50mm. Surprisingly, the stated focal length has little to do with =
the actual=20
    working focal length, with both lenses having an apparent working =
distance=20
    of about 25 mm. I have searched the web to find out about =
construction=20
    details of these lenses but was unable to find much useful=20
    information.
        Does
anyone out there =
have=20
    patent numbers, glass types =
etc.

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