[Leica] exploring the limits (part 3)

["Erwin Puts" <imxputs@knoware.nl>]

The results?
The best resolution I could get (averaged over some observations to account
for eye fatigue and some unavoidable subjectivity when deceiding if a
certain pattern is just resolvable or not):
90  lp/mm in Gigabit with Rodinal (both Agfa products).
90 lp/mm with TechPan in  FX39
80 lp/mm with TechPan in Technidol LC (both Kodak products)
80 lp/mm in APX25 and TX39
70 to 80 lp/mm in Tmax100 in FX39.
.
Every film/developer  combination could easily produce 60 lp/mm IF and WHEN
deveoped and exposed and focused accurately. If any of the three variables
is off the optimum value, results drop to 40 lp/mm or even worse.
Of course you need to address the issue of grain and tonal range and dynamic
range etc and here we see that best are TechPan and Gigabit (but only
whenexposed/developed correctly!), with APX and TMax100 (ex equo) and just a
small step behind the hi-res films.
If you do realise that Tmax100 has a speed of ISO100 and the others barely
get ISO25, that the tonal rendition of Tmax is excellent and that it has a
dynamic range of 7 to 8 stops, when developed appropriately, the overall
winner should be Tmax100!
.
The startling conclusion for me is that there sems to be a threshold of
useable resolution of about 60 lp/mm. This value is attainable when using
outstanding equipment in the right combination of all elements of the
imaging chain.
The use of hi-res films will give you an advantage in grain when enlarging
beyond 15 times, but you will hardly get better useable resolution.
To move beyond this threshold to values of 80 or 90 lp/mm, can be done, but
the additional care, accuracy and control over all parameters is extremely
demanding and you may question if this additional amount of control and
energy is worth the effort.
To be realistic: a true 60 lp/mm with high contrast (high MTF values) on the
35mm negative will deliver a 15 times print with a print resolution of 4
lp/mm, which is exremely high and needs a very attentive eye to detect.
.
I have to withdraw my previous conclusion that the film is the limiting
value in the imaging chain. More study and calculations and these results
with several lenses at seveal distances do indicate that the optical quality
of the lens  is the limiting factor and even more so the user capability and
accuracy of his control over the imaging chain.
The Kodak people do agree that there is not that much practical difference
in 35mm photography between TP and TM100, when used to its full
capabilities.
There is an emperical equation to find the system resolution of lens and
film resolution. This calculation shows that a film resolution of 200 lp/mm
and a lens resolution of 100 lp/mm (like apo 90 or apo 135)gives a system
resolution of 90 lp/mm!! Precisely the result I get experimentally. That
shows that my rsults are close to what can be done, using the equations that
Kodak and others use, based on their experiments and esting.
Feed into the equation a film resolution of 400 lp/mm and you get a system
resolution of 100 lp/mm, agian within the bounderies of my results.
Use a lens with a useable resolution of 50 lp/mm (like the Canon or
Summicron 50) and you get a system resolution of 50 lp/mm again a
confirmation of my previuos testing results and why I changed from Summicron
50 to apo90 for this type of testing.
The equation tells you that for a lens with a resolution of about 50 lp/mm
the resolution of the film is irrelevant! Film resolution becomes an
important  topic when using high quality lenses and being able to use the
optical capabilities of the system!
This conclusion will have strong imapct on the domain of handheld
photography and it also explains why Tri-X and handheld shooting  is such a
happy and impressive combo.
.
The next stage will be the test of the apo 280 and the R8. Here I have the
absolute pinnacle of lens quality and resolution.
Next part will discuss the implications: so do not rush to hasty conclusions
and let the results as they stand, sink in and reflect a bit on what is
being unveiled here.
Erwin