Re: Enlarger lens options.

"otzi" <xx@[EMAIL PROTECTED]
> wrote in message 
news:48231a4a$0$30466$afc38c87@[EMAIL PROTECTED]
> Thanks for all the input folks.  I was curious but 
> unconvinced. Just wondered why so much was invested for so 
> little gain. But these responses were very encouraging.
> Thanks.
>
     Lots of snipping here.
     There are a number of reasons for the newer lenses. One 
is simply that lenses have a very long lifetime so buying 
one often takes the buyer out of the market for some time 
unless a "better" replacement can be offered. Another is 
that computer aided design makes it easier to make new 
designs and evaluate them. Before computers the lens design 
procedure could progress only so far through mathematical 
analysis at which point a sample lens had to built and 
evaluated on the optical bench. The computer allows very 
complex analysis to be made quickly so that new designs can 
be brought much closer to optimum before one is made. Often 
the difference between a computer optimized lens and one 
designed by the older methods is slight. I also mentioned in 
an earlier response to this thread that the optical glass 
types available had changed necessitating redesign of many 
existing lenses. Since many of these were designed before 
computer optimization became generally available the 
redisign for new glass types also resulted in either 
improvement in the original design or a completely new 
design.
     Nearly all modern enlarging lenses are based on a 
generic type known as a Plasmat as are many large format 
camera lenses. These have several inherent advantages such 
as low astigmatism which is im****tant for flat field 
applications such as enlarging. They are also have 
relatively wide coverage angles.
     Modern multi-coating also helps performance by 
increasing the image contrast.
     Keep in mind that any lens with fixed position elements 
can be optimized for only one object to image distance. The 
performance at other distances can be good but will not be 
quite up to the optimum distance. Most camera lenses are 
optimized for approximately infinity but enlarger lenses are 
optimized for whatever distance corresponds to the 
magnification the manufacturer thinks it will be used for 
mostly. Some manufacturers, Rodenstock and Schneieder 
particularly, specify the magnification range for their 
lenses. While the lens can give satisfactory performance 
outside of this range special range lenses will do better. 
Both manuacturers offer lenses for relatively large 
magnification, i.e., photomurals, as well as for more usual 
size prints. Since the print size does not vary so much with 
differences in format (one makes 8x10 or 11x14 from all 
common negative sizes) the optimum magnification will vary 
with the lens focal length, that is, it will be greater for 
a lens for 35mm than for a 4x5 lens.
     A  high power grain focuser will often show up 
differences in lenses that are much harder to see in a print 
but may also introduce its own problems, for instance, some 
grain focusers are not very well achromitized and will show 
color fringes due to its own optics which are not present in 
the image from the enlarging lens.


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Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]