[LargeFormat] New Member

[Les Newcomer]

the Rapid Rectilinear lens was developed in 1866 and was the next generation
over the single element landscape lens. It offered free or reduced from
distortion, coma and curved field.  It was the common formula from the 1870s
through the '20s. It was not an anastigmat and gains in speeds were at the
expense of angle of coverage.

The RR lens is made of a pair of minscus dublets (two cemented elements) of
old style glass.

the Tessar was the last of the modern (well mid 20th century) lenses such as
the Dagor Protar and Unar.

Von Hoegh of Goerz saw that the Protar was limited in its speed because it
"depended on the front cemented surface was used to correct spherical
aberration, but led to a bad aberration zone if the aperture was raised
above f7" (Kingslake P127 Lenses in Photography) he goes on...

"he then replaced the front elements with a seperated dialyte* leaving the
old cemented combination in the rear."  The dialyte is a combination of a
positive lens in the front with a double concave element behind, it
seperated by a mincus shaped airspace-- in effect the front half of an
Artar.
"the aperture of the Tessar was raised from 5.5 in 1902 to 3.5 in 1910 and
recently (1950) to 2.5"


US stops were one of several attemps at an aperture scale. US stops double
EACH stop were fstop double every OTHER stop.  F16 and US 16 are the same
soooo

4   5.6   8   11   16   22   F stops
1   2     4    8   16   32

If you see a lens on ebay with an "f128" aperture, it's most likely US stops
and is really f90  I've also seen "super fast f1.8 brass lens!"  only to
find out its actually an f4.5


you asked, "what would the differenced between the two? " be

Actually in contact prints for the proper format I don't think you'd see
much of a difference at all, particularly if you stopped down, with a nice
contrasty subject.

Now shooting yours wide open and a 2-4x enlargement, it would, uhhh make a
very nice portrait lens.

Les

> From: "Guy Glorieux" <guy.glorieux@sympatico.ca>
> Reply-To: largeformat@f32.net
> Date: Mon, 25 Feb 2002 12:44:59 -0500
> To: <largeformat@f32.net>
> Subject: Re: [LargeFormat] New Member
> 
> 
> ----- Original Message -----
> From: "Les Newcomer"
> 
>> Boy you got me there!  Is that the name of the shutter or lens? What's
> the
>> fastest aperture and is the scale in fstops or US stops?  If they are
>> Contitnental stops-- same as fstops but shifted ie  9, 12.5 18, 25
> then it
>> might be Kodak of England.
>> 
>> Could it have come from a Kodak folder?
>> 
>> A photo might help.
> 
> Les,
> If my memory serves me well, it comes from a 4A Folder.  Speeds run from
> T, B, 1/25 to 1/100 while the F-stops run from US 4 to 8, 16, 32, 64.
> What is the difference between F-stops and US stops?  Never realized
> that there were different kinds of aperture.
> Actually, I just discovered faint engravings on the side of the lens
> reading Rapid Rectilinear Bausch&Lomb Optical Co..  So this would be
> different from Scot's anastigmat lens.  What would the difference be
> between the two?
> Thanks for your help.
> Guy
> 
> 
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