Enlarger Head: Magenta Problems...

[KidA]

I have a Rollei 6x7 CX L colour enlarger and recently I noticed the magenta colour dial is not giving me accurate readings of the true amount of colour it adds. To make this simpler: the cyan and yellow filter reach a certain maximum number in the display window (I can't remember exactly, but I think it's 200). For some reason the maximum displayed value I can reach on my magenta dial is 170. In the little window in which the numbers are displayed, I see that there are more numbers past the 170 value. Magenta does start at 0 (not some 'negative' value). I opened the head to check that all the colours work... they do - the magenta filter travels up as far as the other two, giving full true magenta values.


It's not the end of the world, but I would like to know a) if this can be easily adjusted, and b) if not, would it be correct to assume that I must multiply the 'window' value shown, by a factor of 0.85 (170/200) to find out what actual value is going on in the head?


Example: I want an actual value of M->50

50 x 0.85 = 42.5 <- number to set in the display window should be M->42.5

*Obviously, this is just an example and I would find out, as precisely as I can, the correct factor number*


My main concern is the fact that the dials are not linear; a level 2 1/2 variable contrast value is M->5 but half step up to VC 3 jumps to M->25 (not M->10, the double of 5).

Basically, if I cannot fix this problem by adjusting the values shown, is there a proper way to ensure accurate values? Say, in the event of having to use another enlarger, or to truly be able to compare variable contrast filters values to my faulty head.

Anyone experience something like this before? Anyone know if this simple formula would be accurate?

 

[mklw1954]

I think as a practical matter, trying to establish standard M and Y settings, especially with a view to using them on other enlargers, isn't useful as filtration settings for each combination of enlarger, film (and the way it was developed), and paper are different. Enlarger filters fade with time even though the dichroic filters are not supposed to. Just find the settings that work for the films you are using. Therefore, there's an incentive to stick with one or a couple of films and to use the same paper.

 

[ic-racer]

Was it like this when you got it? What does the manual say about it?
Many color heads are made in a manner that they show different maximum numbers for the colors.
Check to see that the magenta filter covers the light completely at the maximum setting.
The numbers are arbitrary in many cases, but some enlargers are set up so 15cc = 0.15 log d = 1/2 stop
I believe the Rollei 6x7 CXL is similar to the Saunders 670 DXL. The Saunders has M=200, Y=200 and C=170.

 

[RobC]

enlarger Y and M filters are not set/calibrated in density/time factor units.

Yellow filtration adds density in the low values upto approx 60 units and then levels off so that additional density/time factor changes very little as you add/subtract Yellow.

Magenta filtration adds density much more steeply to begin with and then settles down to be fairly linear continuing to add density all the way to maximum Magenta.

This is the case for Durst 130 unit enalrgers. The enlargers that use 200 units of filtration may be different but the fact is that Y and M are very different in the amount of density they add and so you can not expect the dialed in/out filtration units to correspond to a linear time/exposure factor increase/decrease.

If you have a ND dial on your enalrger then they it may be calibrated to time/density log units. My L1200 has this which is accurate but the Y and M filters are not in exposure/log/time units.

 

[cliveh]

Basically, if I cannot fix this problem by adjusting the values shown, is there a proper way to ensure accurate values? Say, in the event of having to use another enlarger, or to truly be able to compare variable contrast filters values to my faulty head.Anyone experience something like this before? Anyone know if this simple formula would be accurate?

Look at the print and not the filter values.