Archived posting to the Leica Users Group, 2000/11/05

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Subject: Re: [Leica] APX25 replacement
From: Walter S Delesandri <walt@jove.acs.unt.edu>
Date: Sun, 5 Nov 2000 08:59:49 -0600 (CST)

I heard last week that APX25 was NOT discontinued?.....of course, 
I heard on here it was....anybody know the poop?..
I can't stand tech pan.....and I did spend lotsa time trying..
I prefer "conventional" slow film with full exposure and 
minimum development...
Walt

On Sun,
5 Nov 2000, Erwin Puts wrote:

> Is there life after APX25? A scientifically conducted study by several
> German authors in 1990 gave these results. Technical Pan had a resolving
> power of 250 lines per mm and APX25 of 180 lines per mm. These were the
> best. A step below these two were almost on equal footing: PanFPlus and
> Tmax100, with a small finegrain edge for PanF. These data in another
> notation. TP and APX could resolve details of a width of  4 to 5 micron.
> That is the maximum definition for a lens like the Apo-Summicron-R 2/180,
> which defines the practical upper limit for the moment. The recently
> designed  Leica lenses however will be slightly below this level (in the
> region of 7 to 10 micron), where the PFP and TMX are located. Older Leica
> lenses have a limit at 20 micron generally speaking.
> My own comparisons (prints at 20x and microscope analysis at 100 and 400
> times enlargement) do indeed show a theoretical advantage of the TP and
> APX25 emulsion.(Both however are challenged by the new BW film, I am
> currently investigating).
> For most situations, the PFP would be a worthy replacement of the APX25 with
> the additional plus of a full stop more speed and it is a true speed of
> ISO50. Because the APX25 has a fairly steep curve, the sharpness impression
> is excellent. The PFP however has a moderately steep curve, giving a
> smoother graded tonality.
> The sharpness impression is a bit less, but even so an enlarger lens like
> the Apo-Rodagon-N 2.8/50 would have to perform at its best to get this level
> of detail on the print at 20x enlargement.
> You could try to do a comparison shooting with some of your APX25 films and
> the PFP to see where the differences are and how important they are.
> For most of my purposes I can easily switch between APX25 and PFP. If the
> problem is demanding I have TP with CC40 filter to compensate for the
> enhanced red sensitivity.
> 
> Erwin
> 
>