CROSS POLARIZATION with flashes and umbrellas !!!

[ALAIN]

Hello,
I use cross polarization for bright subjects photographed with 2 flashes (D2 Profoto).
I need wide distribution.
I placed the polarized filters on the flashes, which are directed towards umbrellas (indirect lighting standard).
The choice of the angle of these polarized filters seems to me to have a much less detectable effect than in direct lighting! It's very difficult to fine it ! Is the angle offset from that which works in direct lighting? Are there any tips? ...
I would be interested in experiments on this subject
thanks in advance !
Alain from France

[Dicky]

Both the design of the flash unit and its actual positioning of the flash-tube is very important consideration in this scenario 
An exposed u-shaped flash tube or an exposed para-ring-flash is much easier to get wide-distribution light signature from as when compared to that of a receased monolight design flash-unit.

Recall someone attempting to use an indirect focusable parabolic with theses of heads, their complaint was that the profoto head only threw light into the apex (center-curve) of the umbrella/reflector.
Monolights that have exposd flash tube designs, include Briese, Hensel, Visatec (Broncolor) but to name a few!!

Polarised light best works direct, it may not reflect too well off the fabric in the umbrellas especially if its metalic,
Have you got yourself a sunlight attachment?
Would make a amazing creative and fun experiment to play with and see what happens to your light-signature, when you introduce a source of adjustable and controllable polarised light effect?
Could yield superb results!!

Wish you cool creative results 

[JCM-Photos]

Hello Alain

What is important is:
-1- Having no light leak around the light filter

-2- Having the same light polarization orientation on both strobes

I work with Elinchrom lighting gear and they make thick square light pola filters that fits perfectly into the bowl barndoors attachment without any leak. When you don't have a special attachmentyou have to gaffer tape the filter on the bowl to close any light leak.
I only use pola filters on bowls not umbrellas.

To have the correct filter orientation over multiple flashes you have to find it by viewing trough the camera with a pola attached on the the lens. Place the light pola in front of the camera and turn the lens pola until the lighting pola becomes totaly dark, place a mark on the top edge of the light pola.
Place the second lighting pola in front of the camera without changing orientation of the lens pola. Turn the lighting pola until it becomes totally dark and place a mark on the top edge, Now you will have the same polarization orientation on both lights when placing their marks on the top.

[Dicky]

Superb and very kind advice from JCM

[ALAIN]

Hello JMC, hello Dicky,
Thank you very much for these valuable tips!
I'm putting away my umbrellas and I'm looking for a system of bowls (perhaps the traditional Profoto zooms, quite versatile, but a bit expensive...) to easily attach the filters...
My subjects are paintings that have been varnished quite shiny.
Best regards!
Alain

[ALAIN]

I also have 2 Hedler led Fresnel 185W. I wonder if that wouldn't be a cross-polarized idea too...

[sog1927]

Alain,

Diffuse reflection will randomize the polarization of the reflected light.

[ALAIN]

Alain,

Diffuse reflection will randomize the polarization of the reflected light.

Thank you for this information. To be sure, do you want to say "if I use the Hedler LEDs"?

[Dicky]

Bonjour Alain
Pleasure!

Recall that there are hasselbladdigitalforum members ...
Whom are considered to be absolute top-end specialists in lighting and photographing paintings, including entire collections for Galleries and Museums
Wonder if they may kindly, have any "point-in-the-right-direction-tips" for you? 

Best wishes

[ALAIN]

Bonjour Dicky,
Merci pour cette suggestion aux "hasselbladdigitalforum members / top-end specialists in lighting and photographing paintings, including entire collections for Galleries and Museums" !
Best wishes

[ALAIN]

Hello,
I have been using a colorchecker and the profiles very easily made by Phocus for a long time, but for non-reflective paintings (rice paper without varnish and without glass...).
It is only recently that I have to take photos of varnished paintings.
I now have, thanks to the friendly sharing here, elements that I put in place and which bring a lot of improvement (cross polarization...).
I still have to experiment a little more to find the right polarization for a good rendering, aesthetic and realistic.
I noticed that the colorchecker/Phocus profile allows to obtain very similar results, with flashes or Led Hedler Profilux led 1000.
I like the practical side of the Hedlers, in direct lighting with barndoors. I saw an accessory that allows you to mount a polarizer on the Hedler binding, but I couldn't find where to get it! Its only drawback seems to be not being able (without tinkering) to add barndoors. I indicate the link, if the forum knows where to find this wonder...

https://correlatedsolutions.eu/polarization-filter-for-hedler-led-2/

Thank you all once again
Alain from France

[JCM-Photos]

As colors change under polarized light, you should also profile your camera with the same polarized light on The color checker.
This profile should not be used for shootings with other light sources.

[ALAIN]

Oh yes ! In fact, in this case of cross-polarization, we must not modify anything after making the profile, I would even say "neither power nor orientation and nothing...", at the risk of being surprised by false colors (it's is lived ).
It is difficult to see a difference in color richness between flashes (D2 Profoto) and Led (Hedler 1000). I don't know if the Led Hedler spectrum is really as wide as that of the Profoto flashes...?

[docholliday]

Between flash and LED, you also have to be careful of UV contamination of the flashtube. Even "UV Corrected" tubes will drift over time, as they are just a coating and will start putting out excessive UV as time goes on. Some heads use corrected cover/domes instead of tubes. LEDs don't usually have the issue, as they are very, very narrow bandwidth. The UV will make blacks, blues, and violet toned colors "unclean".

The other issue I've run into profiling for accuracy during repro shoots is that the standard ColorChecker doesn't have enough patches to be really accurate. The ColorChecker SG is required to get a really accurate profile. If you really want true accuracy, you'll have to get away from the ColorCheckers as they are "prosumer". You'll need to get into stuff like Avian Rochester targets if you want true, archival accuracy.

As far as colors shifting when power levels change, better light sources have less shift, but even then still can be +/- 25-30K. I have no idea how Profoto reacts on their cheaper line - I'm a Bron shooter. The PRO10 should be better corrected, though.

[ALAIN]

I note these very interesting remarks, thank you Docholliday!
By reading you, I notice that, compared to Profoto D2 flashes, the use of Hedler LED 1000 constant lights does not present any disadvantage in terms of colorimetric rendering.
This added to the practical side of constant lighting, I'm thinking of using Hedlers with cross polarization for small and medium formats, and perhaps reserve flashes for large unvarnished formats, not being able to polarize the lighting with umbrellas.
I don't really know what to do for large formats (approximately 1.5 x 2.5 meters) varnished... Hedlers cross polarized from further away perhaps, to be tested...