Basically more yellow equals less contrast. More magenta equals more
contrast. If you're using Ilford papers check the Ilford website for thier
info on contrast. You can dial in filters for different grades. If you're
using different paper then you'll need to check with that company. One more
thing make sure you look for the Durst numbers. Different heads seem to use
slightly different numbers.

    Nick

assuming that you are using the same standard durst max 130 head on
the 605 with 100W bulb and use Ilford MG-IV, maybe you have an
indication to start experimenting with these numbers (taken from the
Ilford manuals btw but quite acurate in my experience)
MG    Y    M
00    120    0
0    88    6
½    78    8
1    64    12
1 ½    53    17
2    45    24
2 ½    35    31
3    24    42
3 ½    17    53
4    10    69
4 ½    6    89
5    0    130

There is also the possibility to use just one filter, either Y or M to
reach the grades but you would have to modify exposure time as well.
Using 2 filters extends the exposure a bit but it reduces corrections
for different filterings.

have fun
Jack
===============

Hi Stefano,

the best thing you can do is buy the book: "Way beyond monochrome".
It's not only one of the best books on B&W printing actually
available, but it also explains in detail how to calibrate your own
Durst M605 colour head to print Variable Contrast B&W papers. This
book is excellent value for money.

Gilbert

Ciao Stefano,

For Ilford Multigrade IV (and probably with all other manufacturers), you
can find the filtration in every box of paper ...
Basically: the more yellow, the softer, the more magenta the harder.

I prefer to use a color head for multigrade because you can adapt the
filtration to the paper in use (grades spacing, filters factors).
A couple of step wedges, one transparent and one reflection are sufficient.
Kodak and Stouffer sell them.
A MG filter set is dedicated to a specific paper (and type of light source)
and although it does work with other papers, it's rarely perfectly
optimized.
And, if you like this technique, a color head can be used for split-grade
printing (two exposures using a hard and soft filter)

With a color head you use both single (only one filter at a time) or double
(a mix of Y and M) filtering method.
- The single filtering method gives you more contrast range and more light
onto the paper but each grade has its own exposure factor.
- The double filtering method lets you have a constant exposure factor at
the cost of a somewhat reduced contrast range and light.
Like for commercial MG filters, you can set up your double-filtering method
so that the harder grades have an exposure factor twice the other grades.
This reduces the mentioned drawbacks.

For the double filtering method: http://www.butzi.net/articles/vcce.htm by
Paul Butzi
For the Split-Grade method an extract of  "Way beyond Monochrome" by Ralph
W. Lambrecht and Christopher Woodhouse:
http://www.users.zetnet.co.uk/ktphotonics/pdf/BasicSplitGradePrinting.pdf
This book has more than that to offer:
http://www.users.zetnet.co.uk/ktphotonics/wbm.html
There was also an article on color head calibration on this website but it
has been removed.

What I use ? The single filtering method coupled with a software that
integrates the filters factors, so I've the full contrast range, always the
maximum light available *and* ease of use ...

Ciao,