[Leica] Exploring the limits (part 1 of several)

[imx <imxputs@knoware.nl>]

I have been testing the new Gigabit high resolution film since several
months and what began as a simple filmtest, has now been expanded into a
fresh exploration of film and lens capabilities. My results surprise me as
much as I hope it will surprise the readers of this report. An open mind is
necessary, however, as many established ideas have to be discarded!
The Gigabit film has been promoted as a new dimenson in Hi-res BW
photography and a useable resolution of 600 to 900 lp/mm (every line pair a
black and a white line or space) has been quoted. In several usergroups this
claim has been discussed to the extreme: could it be possible theoretically
and if so could there be lenses that can use this capability.
First the basic fact: the resolution of the eye: under ideal circumstances
the eye can resolve at a distance of 25cm at most 6 to 10 lp/mm and here we
take the absolute limit, which is reached when the eye is using its vernier
acuity resolving power. Six lp/mm would be according to all ophtalmic
handbooks a good average. This means that any detail which is smaller than 6
lp/mm cannot be detected as separate lines and will be seen as a grey patch.
A simple calculation shows that to be able to see details that on a film are
recorded with 600 lp/mm, we need a magnification factor of 100 times.
I started using a high quality microscope with a magnification of 40, 100
and 400 times. Then I used a testchart with lines and circles (as the
pattern itself will influence the resolution limit). I set up the Leica in
front of the testchart at a distance that gives a negative magnification of
100 times. The idea was that when using the microscope at M=+100, I would be
able to see the resolution pattern that is closest to the 600 lp/mm. I used
the Apo 135 as this one is capable of resolving at least 300 lp/mm at a
acceptable contrast and even 450 lp/mm at a very low contrast (less than
10%). 
To ensure optimum results I used of course the center portion of the
negative and to make sure film flatness and focussing errors are not a
problem Iused the following setup. A Siemens Star was used to check accurate
focusing (a phase shift in the pattern will indicate a focus error) and I
did extensive focussing bracketing by marking the distance on the lens and
taping scaled paper on the mount to accurately make my bracketing.
Result one is that the lens and the camera focussed extremely accurately
even at 13,5 meters with a 135mm lens, which is reassuring in itself.
I shot three films and checked every negative under the microscope to find
the best results. As resolution tests always involve errors in viewing, I
used the best 10 results and averaged the numbers to get a result that is at
least in principle reproduceable by anyone.
To my utter surprise the microscope revealed at most 60 lp/mm!! (IN one
instance I read off 90 lp/mm, but that is the extreme case, which I could
not reproduce later on). So 60 lp/mm is the practical maximum resolution?
But: what is the limiting facor here: lens or film and where are those
mythical 600 lp/mm?
Back again to the testchart, now with a Summicron 50 of latest design.
Repeat the whole procedure and I got somewhat lower figures, around 50
lp/mm. 
Now some people assert (wrongly, but it is common view) that leica lenses
are optimized for contrast and not resolution. To counter this (you see what
you have to do to get a reliable test with meaningful figures) I used a
Canon F1 with a 1.8/50mm lens, reputedly a high res lens. Results did not
differ: no significant and statistically relevent difference in resolution
between the Leica and Canon lens. I used as a third test a TriELmar at the
50 position and got again results around 50 lp/mm. So obviously the lens is
not the limiting factor and so the results found (60 lp/mm) must be film
based. 
Could the spectral composition of the light be a factor.
I used all light sources, flash, daylight sun and tungsten halogen light to
look for differences: none found.
Then we need comparison films to investigate further.
APX 25, APX 100, Delta 100, Pan F, TMax100 and Technical Pan were selected.
As Gigabit film is standard Agfa Copex Microfiche film (no new emulsion this
Gigabit! Only new is the developer, but wait and see later) and TP is also a
micro-film, which are "forced" to go for continious tone negatives, I
wwanted to use films designed form the start as continious tone film as a
comparison.
Surprise two: using the same procedures and testing developer-film combos
with D76, FX39, Rodinal, TMax, the best film combo for resolution is TMax100
in FX39, which even surpasses the APX25!
To be continued!
Erwin
The first check