Seeing Bob's reply quoting Ilford Multigrade dual filltration has given me to opportunity to ask a couple of questions relating to these filtrations.Originally Posted byBob F.

My Durst 605 is 130M max but as there are Durst enlargers with 170M max and both produce grade 5 then am I correct in assuming that each M on a 170 is only a proportion( fixed or otherwise) of an M on a 130. Otherwise the 170 max would not be needed as this is 40 units more than is required for grade 5 which is presumably the max grade possible with Ilford Multigrade.

If this is the case then the ratio between 170M and 130M does not seem to produce the equivalents at less than grade 5 i.e. at grade 41/2 89M(130M max) has an equivalent at 116M(170M max) but the correct filtration is 105M So it would appear that less magenta is required than the fixed ratio would indicate.

On the Y range you'd at least expect the same level of Y would be needed to produce grade 00 on both ranges but in fact the 130Y range requires more Y than the 170Y range which seems contradictory.

It may be that there is not a fixed ratio between the Y's and M's on each range and in fact the Durst Colour Filter circular hand calculator would seem to indicate that higher Y and M content alter the exposure less than lower Y and M. So the first 10 units(0-10) of both M and Y increase exposure more than 10 units between 40 and 50.

I am not sure whether this explains the Ilford Multigrade dual filtration chart. Whether it does or not I cannot see what the explanation is. So there may be more to this than meets my eye.

Can any of you technical buffs explain it in layman's terms?

Of course I could just accept it as a given and it makes no practical difference to my printing skills EXCEPT that understanding the theory stops the distraction of my pondering this forever.

Pentaxuser