Re: Enlarger lens options.

"Martin J" <maja@[EMAIL PROTECTED]
> wrote in message 
news:g010f5$2it9$1@[EMAIL PROTECTED]
> Richard Knoppow <dickburk@[EMAIL PROTECTED]
> wrote:
>>     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.
>
> I made a comparison between some better enlarging lenses 
> for 24x36mm
> (Apo-Rodagon 2.8/50, Componon-S 2.8/50, Focotar 4.5/50, 
> Focotar 2.8/40
> and Rodagon 4/60) and compared them at about 8x 
> enlargement (20x30cm
> paper size). Each was perfectly adjusted using a Peak #1, 
> a glass carrier
> and all enlarger planes were adjusted parallel using a 
> laser tool. All
> lenses were closed 2 stops from wide open.
>
> The result: The only one you could distinguish from the 
> others was the old
> Focotar 4.5/50. It had a little curvature of field visible 
> at the extreme
> edges. That's all... no visible difference for the other 
> lenses.
>
> You can see the differences between the lenses with the 
> Peak #1. The curvature
> of field is readily visible for the two Focotars. The two 
> Rodagon
> and the Componon-S were much better and nearly identical. 
> The Apo-Rodagon was
> a little better wide open than the others, but all 2.8 
> lenses were unuseable
> with this opening (for my view of quality...). Stopped 
> down, all
> were excellent.
>
> Martin

    That's quite interesting. I suspect the Rodagon and 
Componon designs are quite similar although I don't have the 
actual prescriptions. Since its likely all the relatively 
modern lenses were designed with the aid of computers I 
suspect the performance should be much alike. I think the 
Focotar is an older design. One of the characteristics of 
the generic Plasmat type, which is what the Rodagon and 
Componon are, is that they can be unusually well corrected 
for astigmatism. Forgoing an explanation of what exactly 
that is (different in a camera lens than in opthalmic 
lenses) it leads to being able to get a very flat field. 
While both manufacturers claim superiority I suspect its 
pretty much a draw. Some think the Rodagon is mechanically 
superior to the Componon. Do your lenses have metal or 
plastic iris blades?


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