UR-Pro filters info?

[bghazzal]

SUMMARY

 

Returning to the filtering / transmission info we now have on the UR-Pro Cyan filter, we can try to summarize the data as is:
 
- In terms of spectrum, the UR-Pro Cyan does indeed function like fluorofilter, with a similar profile.
The filter blocks the UV spectrum, and strongly restricts cyan to green transmission, while maintaining a medium transmission of dark/purple blues, and strong transmission of orange/red wavelengths, thus having a marked warming effect and smoothing spectrum alterations of ambient light in blue water (which helps the camera white balance).
Practically, the working result is that UR-Pro Cyan preserves some deep blues for the water column, while nudging the cyan/green cast to a warmer yellow-orange tones, which gives a good base for colour grading to aesthetically pleasing results.
In this, it is not the most colour-accurate (the Keldan Spectrum filter is clearly more accurate), but is nonethless great and very practical for underwater video use (which explains its popularity).

- The UR-Pro Cyan induces a general light loss in the roughly -1.6 to -2 stop / Ev range (being a colour filter, this is also relative to wavelength transmission, as discussed here)

- Physically, the UR-Pro Cyan was made of acrylic or glass (not gel), with an orange to reddish tint, and was the steepness of the curve seems to indicate that it was an optical grade filter.

If we take the available transmission data from the filter patent and order it on the wavelength/colour spectrum, we end up the following:

UR-PRO CYAN FILTER WAVELENGTH TO TRANSMISSION, MAIN DATA POINTS

Below 370 nm:  0%

UV ULTRAVIOLET: BELOW 400 nm
Below 400 nm: 25%
VIOLET: 400-450 nm
Below 410 nm: 27%
Below 450 nm: 12%
BLUE: 450-500 nm
Below 470 nm: 8%
Below 500 nm: 4%
CYAN: 500-550 nm
Below 520 nm: 7%
Below 550 nm: 18%
GREEN: 550-580nm
Below 570 nm: 50%
YELLOW: 580 - 600 nm
Below 600 nm: 87%
ORANGE: 600 - 650 nm
Below 700 nm: 90%
RED: 650 - 700 nm

 

-  We are also given a rough visual representation of the UR-Pro Cyan filter's transmission curve, which can be rendered as is on the wavelength spectrum:

UR-PRO CYAN FILTER SPECTRUM TRANSMISSION CURVE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

- Combining these data sets, we can add the following projections for wavelength transmission cut-off (known data point are in bold type, projections are in italic type)

 

UR-PRO WAVELENGTH TO TRANSMISSION, KNOWN DATA POINTS AND PROJECTIONS

 

 

 

ALTERNATIVES

 

In terms of possible alternatives, there seems to be a marked difference between optical grade photographic filters, which have might tighter, precise cut-off points, and design specificities like fully cutting off the UV spectrum, and lighting filter gels, which have a more sloped curve, with less marked cut-off points.

 

- A relatively cheap and somewhat more accessible option would be to combine existing lighting gels such as fluorescent filters (FL) / orange colour temperature adjustment filters (CTO), or orange to pale red colour conversion filters (CC), with a UV blocking filter to steepen the curve.
This seems promising, as illustrated above.
 

However, one thing to look out for when combining lighting gels would be light exposure / stop loss.

A loss -3 stops / Ev would be a reasonable limit. For smaller sensor cams like action cams, it would be best to stay in the -1.5 to -2 Ev / stop range, as anything stronger would introduce to much noise when shooting in ambient light.

Some options to look into would be Lee and Rosco filters, such as the (discontinued...) Lee Pale Red 166 combined with the Lee 266 UV, or the Rosco Cinegel  3310 Fluorofilter, or other CTO / CC filters of their respective ranges (Rosco 166 Pale Red, Roscolux and Cinegel CTOs, etc.)

- Another option would be to look into existing optical grade filters for photography (color correction, fluorescent filters, such as the Tiffen 47B filter for example) or those designed for other optical applications (microscopy, astronomy...). These would require no additional UV filters, but these will usually be in glass form, so less flexible, and more expensive.

 

- Lastly, there would be the option of trying to tweak existing photo filter gels (Magic Filter or Keldan) to bring them closer to the UR-Pro Cyan, combining them with a minus green lighting gel for instance.

From my tests on grading flat action-cam footage, Magic Filter's handling of magenta (inverted, when to other filters) is problematic at depth for my video grading use (more details here and here) but a filter like the Keldan Spectrum SF-1.5, combined with a gel giving it a bit more "bite" (a minus green gel?) seems like a promising base for experimentation.

 

cheers!

 

ben

 

Edited July 11 by bghazzal

[DreiFish]

Good investigative work and good summary, Ben. I got the CTO and minus green filters in various strengths -- just finding the time and energy to test them is proving challenging 🙂

[bghazzal]

As a follow-up, a very kind soul sent me a bunch of Lee filters samples for further testing.

 

First test was with the Lee Pale Red 166 combined with the Lee 266 UV, combo presented above.
Physically, this dual setup was tricky to setup on my GoPro 7-  the filters are held in place by an o-ring, which vignettes on the image and cuts some light, and they were not in the best shape after setting them up .
And unfortunately, due to human error ISO and lowlight settings were not identical on the two GoPros, but it was enough to see that the filter combo was a little too strong compared to the UR Pro.

The Lee Pale Red combo had a strong pink/red cast in the shallows, but performed really well at depth (10m+), actually better than the UR-PRO cyan...

However, loss of light (and settings?) meant higher ISO, and more noise on the gels (results are blurred by the settings issue and also gel damage while inserting in the housing, which could also explain the loss of sharpness).

Here's and ungraded side-by-side capture from a clip shot at 10m depth:



(one can see that the gel combo actual cuts more greens than the UR-Pro, and lets more blues through, but with a slight magenta hue, meaning it's a little too strong for the depth).
Quickly graded results are similar, and the filter works.

 

And here is a deeper ungraded shot, at 15+m - here again, the Pale Red combo generally outperforms the UR-Pro, and the magenta hue is less present due to red absorption:
 

 

So overall an interesting combo,  definitely less versatile than the UR-Pro in the shallows but pushing the blues over greens, which is interesting, and probably works nice in the 15-20m depth range.

The drop in image quality, due either to ev / absorption, ISO settings I had on the 2nd test cam, gel damage or the fact that the gels are not optical quality (?), would need to be addressed...

An interesting option, but a slightly different beast from the UR-Pro Cyan 😃

Edited September 10 by bghazzal

[bghazzal]

Following up on this, I decided to try another, more hands-on approach and simply selected all the Lee filters I had at my disposal which were visually close in tint to the UR-Pro Cyan, and ran some basic tests on the best results in the Lee range.

.

 

The winner (closest to the UR-Pro Cyan) visually was the Lee 008 Dark Salmon filter.

This similarity was then confirmed by shooting a whibal grey card, and running the results in lightroom.

 

Results where as follows:
 

UR PRO CYAN Temp value -51, MAGENTA -26

LEE DARK SALMON T -60, MAGENTA -28

The temp scale used here (-100 - +100) is what LR uses for non raw files instead of kelvins, but this is very similar to the previous tests with raw files and kelving values.

(please not that the UR-Pro filter used in these tests was half-dry and not the cleanest... 😅)

UR PRO CYAN AS SHOT:


LEE DARK SALMON AS SHOT:


UR PRO CYAN white-balanced:


LEE DARK SALMON white-balanced:

Other Lee filters tested ranked as follows:

PALE RED -68, MAGENTA -43
GOLD AMBER -70, MAGENTA -20
MILLENIUM GOLD -77, MAGENTA -25
 

****

 

Available Lee filter data for the 008 Dark Salmon is as follows:
 

Colour Temperature 6774K (daylight)

Transmission Y:  35.4

This warming value is coherent with the UR Pro Cyan's roughly +3000K warming effect, and a transmission value of 35 is also roughly in the -1.5 / -1.6 exposure range.

 

The Lee Dark Salmon is interesting contender, which would need to be tested in water.

As an important side note to the UR-Pro info posted above, UR-Pro also released, a few years after the original UR-Pro Cyan, a lighter filter called the UR-Pro Cyan SW (shallow water).
I do not know if the UR-Pro cyans I have are standard or SW, but I suspect they might be the latter, which would explain differences with the original curve.

 

*****

Finally, I also tried to select Lee filter gels equivalent for the Keldan Spectrum SF-1.5, but didn't find anything as conclusive - the Keldan gel's dark pink hue is really quite particular (true custom design?), and there was no direct equivalent in the filters I have at my disposal...

cheers!

ben

Edited September 10 by bghazzal

[Davide DB]

1 hour ago, bghazzal said:

The winner visually was the Lee 008 Dark Salmon filter.

This was confirmed by shooting a whibal grey card, and running the results in lightroom.

 

Results where as follows:
 

UR PRO CYAN Temp value -51, MAGENTA -26

LEE DARK SALMON T -60, MAGENTA -28

The LR scale used here (-110 - +100) is what LR uses for non raw files, but previous tests gave the UR-Pro WB 2350K, so very similar.

 

Oh my Gargamel!

You are close to creating the formula for the philosopher's stone!

 

P.S.
the formula for creating the philosopher's stone involves, in addition to mercury and sulfur, six smurfs boiled in snake venom...

[bghazzal]

As yet another follow-up to this fascinating quest for the filter-grail, I tested the Lee 008 Dark Salmon filter in water (depths ranging from 8 to 20m on a tropical morning, slightly overcast day in east Bali) and the results are in...
 

As anticipated (drum roll?), the filter works really well, with a very similar profile to the UR-Pro Cyan (or Cyan SW?), however with one major caveat:

 

it is stronger / darker (and a bit warmer) than the UR-Pro - meaning a little more loss of light / ev, and also a slightly deeper tint in the reds - this is visible when looking at the camera's ISO sensor data, with a higher ISO on the LDS.
Yet what this also means is that, as expected, the Lee gel actually works better than the UR-Pro when going deeper, but this is a give and take, as it means a greater loss of light - could be fine in the tropics, less so elsewhere.
So, the quest is not completely over just yet.

However we can add with confidence that the Lee 008 Dark Salmon is a truly worthy replacement for the UR-Pro cyan, and readily available for very cheap in gel rolls... 😄

But a tad stronger, then...

***

Since the proof usually is in the pudding, here is some test footage, shot on two GoPro7 Black held side by side (no tray, this is quick and dirty handheld, one GP in each hand...), identical settings (flat profile ie. WB native, GoPro colours, ev -0.5, ISO max 1600, 4K 60fps).
If you're fast enough as a click-slinger, you can actually watch both clips at the same time 😉

UR-PRO CYAN FILTER VS. LEE DARK SALMON GEL FILTER, AS SHOT (not white-balanced in post, ungraded)

 

UR-PRO CYAN FILTER VS. LEE DARK SALMON GEL FILTER, WHITE-BALANCED IN POST + QUICKLY GRADED

 

not bad for a commercially available gel, eh?...
(please not that grading adjustments are flexible and subjective choices - there is plenty of room for modifications on both cams - this was just a quick and dirty grade, aiming to bring the cams' footage to similar results)

 

cheers!

ben

Edited September 16 by bghazzal

[Davide DB]

This is it at last! Great achievement Ben.

When the tests are over I want to pin this thread.
A sheet of Lee gel also costs only 10€ and you are basically good for a lifetime. Also many cinema services give away the test swatchbooks and each filter is surely enough for at least two Gopros.

 

It would be interesting to see the results in other seas from other members with GoPros.
I hope to try it with my GH5 as well.

 

Edit: the lee 008 Dark Salmon seems to give its best deeper

[Nikolausz]

It looks great. It would be interesting to try out also with larger sensor cameras.

[Davide DB]

5 minutes ago, Nikolausz said:

It looks great. It would be interesting to try out also with larger sensor cameras.

 

Or lakes 😈

[Nikolausz]

21 hours ago, Davide DB said:

 

Or lakes 😈

Challenge accepted. But it will take time.

[bghazzal]

Looking forward to some lake action then! 😄

If we take a look into other filters in the Lee range and compare curves, the LEE 008 Dark Salmon actually comes out as really close to the UR-PRO Cyan (if the spectrum reconstruction is correct, which it seems to be empirical tests).
Both filter material's colour is also nearly identical





To address the exposure issue, here is the Dark Salmon and a few other (lighter) potential contenders, superimposed on the UR-Pro spectrum/transmission reconstruction data posted a few posts above:

 

 

 

delete me
please

 

Main transmission differences are highlighted in red:
 

violet	blue	cyan	green	yellow	orange	red
400 nm UR PRO  = 25% LDS = 17% 410 nm UR PRO  = 27% LDS  = 17%	450nm UR PRO  = 12% LDS = 13% 470nm UR PRO  = 8% LDS = 8%	500nm UR PRO  = 4% LDS = 6% 520nm UR PRO  = 7% LDS = 8%	550nm UR PRO  = 18% LDS = 21% 570nm UR PRO  = 50% LDS = 36%	580nm UR PRO  = 65% LDS = 48%	600nm UR PRO = 87% LDS = 75%	700nm UR PRO  = 90% LDS = 88%

Assuming the UR-Pro filter reconstruction data  is correct, to summarise:

• UR-Pro lets more violet/deep blue than the Lee Dark Salmon, 27% vs 17% at 410nm - the UR-Pro curve goes up at this point a sort camel hump in violet/deep blues.

• UR-Pro lets more green through, 50% vs LDS 36% at 570nm, and also more yellow 60% vs LDS 48% at 580nm and orange 87% vs LDS 75% at 600nm, so a steeper steeper curve from green to orange.

These transmission differences likely explain exposure differences between the UR-Pro and LDS, especially the 570nm to 600nm points.

The rest of the two filters' transmission is actually almost identical, only a few % difference, which is rather impressive and explains why the results are so similar....

This is going to be hard to beat I think...


****

For lighter alternatives, quick and dirty colour/exposure test on land (placing gels on the gopro lens, sorry for the fingertips 😅) gives the following results:

 

 

It seems "107 light rose" is the most solid contender for a similar but lighter filter, though I'm a little concerned that the curve from green to orange is much flatter in this case...

cheers

Edited September 17 by bghazzal