Do dichroic enlarger's internal filters get stale?

[tbm]

I just bought a used Saunders/LPL 670MXL dichroic enlarger from a portrait studio that sold it because they switched to digital. I performed several tests with several negatives today by setting the yellow and magenta filters variously from 00 to 1 to 2 to 3 and to 4 and making prints at these settings. I then failed to notice a difference in the tonality compared to that I used to get with my insertable Ilford filters in my standard Saunders/LPL enlarger. Is this possibly due to heavy use by the studio and resulting degradation/ wearing out of the internal dichroic filters or is that not possible? I've never seen an illustration in a book or on the Web of how dichroic enlargers are made, so I don't know if their filters can wear out/fade like the insertable ones. Thanks for responding!

Terry

 

[glbeas]

If you have a color analyzer try reading your Ilford filters and then the dichroics and see what the difference is. You may need to recalibrate the dichroic, I think they do fade after a long while. You also may want to check the bulb, an older bulb will have a lower blue output and will throw the contrast off a bit.

 

[Ed Sukach]

Is this a true "Dichroic" head or a "Multicontrast"?
Dichroic filtration is usually given in increments of (M)agenta, (Y)ellow and (C)yan... from values of 00 to 170 - 200.
Multigrade heads are 00 - 4 or 5 -for corresponding grades, using Multigrade paper.

I don't think "fading" is much of a problem - athough I have heard of filter replacement.

 

[tbm]

It is a true dichroic enlarger. However, it didn't arrive with any instruction booklet and I just discovered the cyan dial is set at zero. Is that zero cyan setting probably the culprit creating little, if any, difference, in print contrast when I change the yellow and magenta dials only?

 

[glbeas]

So were you simply setting the dials to 1, 2, or 3 or were you using a chart to get the equivalent color settings for the contrast grades in VC?

Paul Butzi has an interesting read on the subject:
http://www.butzi.net/articles/vcce.htm

 

[tbm]

I used a chart that Saunders faxed to me which contains settings for the yellow and magenta dials but not the cyan. The settings correlate with standard Ilford drop-in square filters.

 

[glbeas]

Cyan filters are not used in these charts, all they would do is create neutral density. I also have an Ilford chart, they are not alway quite accurate. Like developing film this is a starting guide. Experiment and take notes until you are getting the results you desire and use this as your new calibration. Remember add magenta for higher contrast and add yellow for lower. Some folks advocate having both colors in at the same time for neutral density so going from one grade to another will not change exposure times. If I remember rightly that was the focus of Butzis article.

You might want to doublecheck and be sure the filters are actuating when you turn the knobs, there's always the possibility of damage to used equipment.

 

[geraldatwork]

With only the safe lights on or with the room fairly dark place a negative in the carrier and a white sheet of paper on the easel. Open up the lens all the way and turn the enlarger light on. Set the head height to about an 8X10 enlargement. Set all 3 colors to 0. The Cyan should stay at 0 for the test. Now slowly rotate the magenta to a higher number. You should see the image get redder (pinker) and darker as you rotate to the highest number (170-200) Set the Magenta to 0 and do the same exercise with the yellow filter. As you go higher it should both a deeper yellow and darker. If you don't see a major change from 0 to 170 then the filters may be faded or need some kind of adjustment.

 

[jovo]

one other thing to consider is whether or not you've inadvertently left the focus/filter lever in focus. if that's the case, you're not using the filters at all as they've been bypassed.

 

[b.e.wilson]

By "stale" I presume you mean can a dichroic filter change color, presumably after being heated.

The answer is no. Dichroic filters are made by depositing an inert material (typically a transparently-thin layer of titanium dioxide) onto a glass surface. The color of the filter comes from the interference patterns made by specific colors of white light as it crosses the thin-layer boundries. For example, a magenta filter will pass magenta and reflect green, the cyan filter will pass cyan and reflect red, the yellow filter will pass yellow and reflect blue.

Only by changing the thickness of the layer will the color change, and glass nor TiO2 will evaporate at enlarger-bulb temperatures.

Dust and scratches can obscure the filter, having some effect of the overall color balance of light, but the color of the filters should be quite stable. By the way, never touch a dichroic filter. The materials are very stable and ineret, and can be cleaned with good solvents, but while it may be necessary to dust occasionally with dust-off, the filters are best left undisturbed.

The largest cause of color head trouble is miscalibration of the filter raising mechanism. The more you dial a filter in, the more it is raised into the light path (they follow sequentially). If the mechanism has slack, or if it's received a good bump, it's likely that the color balance of the head set at, say, 20Y20M will look different than another head set similarly.

Of course I can say the same thing about two brand new heads from the same maker, just smaller differences.