ND filter changes color balance?

[gijsbert]

Hi,
I did my first RA4 color printing last weekend, and noticed that exposure times needed to be very short for the Fujicolor Crystal Archive I have so to not have to close my enlarger lens too much I put a ND0.9 filter on but the result seems to suggest it is far neutral! Here a quick mobile phone picture of some results:


Upper-right is the test print with the ND0.9 filter, lower-right is the same setup without the ND filter but 2 stops closed on the lens (I thought it was a ND0.6, oops) so not quite the same exposure but I did not expect the difference to be so big!

Does anybody use ND filters to get longer exposure times for color printing or is that a big no no? Would a different brand be more neutral, this was a Tiffen?

Thanks,
Gijsbert

 

[btaylor]

I’ve never tried using ND filters, though I don’t know why you would get such a wild color shift. If you’re using a dichroic color enlarger, dial in cyan to reduce exposure and compensate by bumping up yellow and magenta.

 

[wiltw]

Different brands of ND filters have been known to affect the color balance when used over the TAKING lens, so one should not be surprised about color shifts created when the ND filter is used at the enlarger lens! I recall, for example, a test of Mirumi polarizer made the results somewhat bluish compared to no filter. And I have seen a number of past complaints of the resin ND filter causing color shifts.

 

[MattKing]

Adding a filter below the lens may also have introduced some extra flare and reflected light into the light path.
Any chance you have a green enlarger ?

 

[Nodda Duma]

Having characterized absorptive ND filters for work, even really fancy expensive absorptive ND filters are not uniformly transmitting across the visible spectrum. They roll off in blue and/or red slightly. So they do not provide a flat transmission. This is the type that is used for photography

Reflective ND filters (which cut down the light using a silver deposition layer) are spectrally flat transmiitting. They look like shiny mirros.

 

[gijsbert]

No, the enlarger is not green
I've done some tests on digital with and without ND and the difference are quite visible, at least viewing them next to each other. And I did discover the ND had some veiling or bloom (not sure what the term is), cleaning helped with that. I think I have a reflective ND left from last years solar eclipse viewing, but with ND5 it's going to be painfully long exposures.
I'll try adding cmy filters, at least that is before the negative stage. I also have a diffuser but it's probably not neutral either. Perhaps I should get a lower wattage bulb and a sub-second timer!
Lots of stuff to try. I think my main conclusion is that even slight color changes, whatever the source, have significant effect on the final image.

Thanks for the replies!
Gijsbert

 

[pentaxuser]

Hi,

Upper-right is the test print with the ND0.9 filter, lower-right is the same setup without the ND filter but 2 stops closed on the lens (I thought it was a ND0.6, oops) so not quite the same exposure but I did not expect the difference to be so big!

So what are the two on the left. The top left looks the best to my eye.

Thanks

pentaxuser

 

[GLS]

Having characterized absorptive ND filters for work, even really fancy expensive absorptive ND filters are not uniformly transmitting across the visible spectrum. They roll off in blue and/or red slightly. So they do not provide a flat transmission. This is the type that is used for photography

An exception to this would be the Lee IRND proglass range. They were originally designed for the cine industry, and are extremely expensive (£180 each for the 100x100mm size). However, they have an exceptionally flat absorption, even on a 10-stop filter:

I hear the Firecrest filters from Formatt-Hitech are also very good.

 

[gijsbert]

After upper-right I stopped using the ND filter, lower-right was density test and too much magenta, lower-left was another density test with +10M adjustment, upper-right is my current final: 3 seconds F/11 plus another 10M, I'm pretty happy with it, maybe a little bit too blue.

Another realization of these first prints is that the lab gives me fairly high contrast scans (probably sharpened too) and/or I often add more contrast via levels and that those scans are not reproducible, at least not easily, in wet print. Scan of the negative I'm working on:



Of course, I've done just 2 sessions so I need a lot more practice!

 

[halfaman]

I used a B+W 1 stop ND filter recently with a thin underexposed negative (too short times) and I haven't noticed any color shift.

 

[Rudeofus]

Since C-41 process yields rather low contrast negatives, RA-4 process has rather steep contrast to yield normal looking images. That's why even small errors in exposure and/or filtration give you completely off results. These ND filters you use may be adequate for dSLR use, but evidently require some filter correction when used with RA-4. Since these filters can be assumed to be linear, you should be able to determine a filter correction factor when using the ND filter. If you don't do RA-4 that often, adding some constant amount to yellow or magenta filter when using ND might be easier&cheaper than buying some high end ND filter.

 

[Mainecoonmaniac]

I'm not too sure if this is related, but when I printed on RA, I never changed the density of a print with my timer because changing exposure time will cause a shift in color so I always changed density by F stop. If you changed your exposure times, this may cause a shift. But it's been over 20 years since I printed RA.

 

[darkroommike]

ND filters are not completely neutral, especially the sheet goods like Roscolene. So that's one possibility. You may also be experiencing reciprocity, color printing papers are actually optimized for rather short printings as anyone who ever printed using a Kodak S-type printer can testify. We actually used to use the slope adjustment to compensate for reciprocity.