Are the Polycontrast filters the same as Ilford Multigrade filters as far as grade. It seems like I remember that they were a little different. I have a C23IIXL enlarger and it has room for the filters above the condensers and below the lens. The Polycontrast filter set I have is for below the lens and I am concerned about putting anything between the lens and paper. I can get a set for use above the condenser and I think they are 5 1/2 5 1/2 inches. Also for papers other than Ilford do they match the Multigrade system for VC.
Are your filters Polycontrast, or PolyMax?
The most recent Kodak filters are labelled as PolyMax, and they do provide a wider range of contrasts with variable contrast papers.
That being said, just about any set of filters will provide you with a wide range of contrasts. The grades won't match exactly from brand to brand, but they won't match fixed grade paper values either. As long as you work within a particular system, you can get good results.
With respect to whether below lens filters work as well as above condenser filters, I think the best answer is that if they are clean and in good condition, the below lens filters work very well. They also have the advantage, in my experience, of being easier to switch without causing enlarger movement and vibration, which is important for split grade printing.
If I were you, I'd try the set I have. If you see a good response with the contrast choices available to you, and your prints are sharp, then there is no need to change.
One further point though - all filters will fade over time, and exposure to bright light will accentuate that problem. If the filters you have are already faded, you could benefit from new ones.
I agree with Matt. In addition, don't confuse filter numbers with paper grades. Filter numbers are just that, filter numbers. They don't claim to provide a certain paper grade, not do they. Unfortunately, their paper contrast is often not very evenly spaced either. As Matt said, they differ from one manufacturer to the other, but as long as you stay within one system, who cares? The trouble starts when you switch. Then, your printing records (you do have printing records, right?) are no longer valid.
Originally Posted by Marvin
One way to fix that is the use of a color enlarger or split-grade printing with a green and a blue filter. You can calibrate those for ISO grades, and record your printing that way. If you switch from one color enlarger to another, all you need to do is calibrate it again, and... yes, you can trust your printing records again. And if you use f/stop timing, even better, because... that's another thread.