bghazzal

Here is some news -following up on Nick Hope's idea, I ran a patent search for UR-Pro's Kirk Kreutzig in the US. patent data base and got 3 hits for optical filters. Among the 3 three filter patents, 2 actually concerned night-vision devices, but one was of particular interest: patent US-4542959-A "Color correction filter and method of taking underwater photographs therewith", filed on July 25, 1983 and published (patented) on September 24, 1985 Here is the downloadable patent file: 4542959.pdf Not sure if this is UR-Pro Cyan filter patent or not, but maybe there's some related information within. Here is the abstract: 6 pages of rather interesting reading, and while it's difficult to know if it is the UR-Pro Cyan we're familiar with, it does sound like a blue-water/cyan underwater photo filter... To summarize in copy-pastable form, the light wavelength (nm) to % of incident light transmitted is as follows: Below 370 nm: 0% Below 400 nm: 25% Below 410 nm: 27% Below 450 nm: 12% Below 470 nm: 8% Below 500 nm: 4% Below 520 nm: 7% Below 550 nm: 18% Below 570 nm: 50% Below 600 nm: 87% Below 700 nm: 90% EDIT- looking into it, it seems like this is indeed the UR-Pro Cyan, or at least one of its early versions Here is another related patent filed by W TUCKERMAN BIAYS, refering to U.S. Pat. No. 4,542,959 as covering the "UR/Pro Marine CY Filter" https://patents.google.com/patent/US5719715A/en It is well known that light is made up of electromagnetic radiation having a range of wavelengths usually considered to be between 0.4 and 0.7 microns. Underwater color correction is described in U.S. Pat. Nos. 4,542,959; 3,588,215 and 3,929,487. In addition, the following publications discuss the "UR/Pro Marine CY Filter" (which may be described in U.S. Pat. No. 4,542,959) Frink, "Warmer U/W Photos", Skindiver, December 1983; Herbst, "New Filter Banishes the Undersea Blues", May 1986 and Holland, "Filters May Improve your U/W Photography", February 1988. Murphy, in "Shark Eye", appearing in Skindiver, May 1987, apparently describes a filter which may be related to U.S. Pat. Nos. 3,588,215 and 3,929,487. Adams, in "Exposure Control for Underwater Photography", appearing in ElectroOptical System Design Conference, 1971, at page 336, discusses the use of color correcting red filters, as does Rowlands, in The Underwater Photographer's Handbook, pages 74-75, Van Nostrand Reinhold Co. Cardone, in "Clearoptic Lenses", in Skindiver, May 1989, describes a yellow filter, sometimes known as "shooters" glasses. As a bonus, here is a link to a local Chicago Tribune article published in 1999 on Kirk Kreutzig's various filter-related inventions, titled "FILMING 100 FEET UNDER SEA " cheers ben

Thanks for this, interesting product - in the discussions, Craig Jones and Nick Hope also bring up the glass vs plastic issue. To quote Craig's article again: First, your choice of filter depends on whether you are deep or shallow and whether the water is blue or green. The stronger FL-B filters are only suitable for blue water and moderate to deep depths (20-70 feet). Use the FL-D type filters for green water or shallow depths. For any given lens or housing, you may be able to use thread-on filters, rectangular filters (externally) or gels. Some combinations may be supported only by a UR Pro filter in which case your choice is fairly obvious. For those that can use thread-ons I prefer the Singh-Ray FL-B, the Hoya FL-D and the B+W FL-D. I have not used the Hoya FL-W but it may be desirable for very green water. For those who can mount a 4 inch/100mm Lee filter holder externally, the Lee FL-B filters provide essentially a shallow/medium/deep solution. I have also adapted a UR Pro CY resin filter to the Cokin X-Pro filter system. I personally avoid the Tiffen filters and the UR Pro glass filters due to their sandwich glass construction. Sandwich filters have many more light boundries that make them more susceptable to flare. For those lenses that have rear gel holders your choices are more interesting since you can roll your own. First choose your magenta gel. I would use 20 to 50 units depending on depth and clarity of the water. You can then optionally add a warming gel. I would bring an 81C, and 81EF, and a 85 for example. The benefit of the warming gel is that it brings the balance of the light closer to matching the optimal balance of the imaging sensor. The downside is that you give up light sensitivity. On bright days and deep dives use a strong warming gel. Otherwise use a weaker gel or leave it out entirely. Note from the editor - According to Craig, a good starting point is to purchase two strengths of magenta (say, 30 and 50 or 20 and 40), and then add two strengths of warming (81EF and 85). For shallow shots use the weak pair. For deep the strong pair. For green water use the strong magenta with or without the 81EF. You can combine the weak pair or the CC30M alone with strobes if you carefully control strobe power. Reduce strobe power by 1-2 stops to start. Filtering strobes is ideal, but we have some more experimentation to do before anything conclusive can be said.

A little snippet on fluorescent filters (especially the UR-Pro) by Dr. Mustard from this 2005 thread: I have noticed quite a big difference between CC filters and Fluorescent filters is in the cameras ability to auto white balance. Fluor filters (specifically the UR-Pro series that I have used) tend to work really well on AUTO-WB (even when they actually don't look too good on the LCD screen when they are underwater). Whereas CC filters tend to need custom white balancing either in situ with a grey/neutral card or in RAW conversion in post processing. This shot, for example, was shot on Auto WB and can out of the camera looking pretty much like this. The only way I can get such good colour balance straight from the camera with a CC filter is in situ WB. The obvious answer to this is that fluor filters are better. But I am not convinced about this because at certain depths the camera uses more extreme white balance (colour temp and tint) settings for the UR Pro than are needed for the CC filter. It is just that the camera (well my cameras D100 and D70) have found it easy to get the right white balance (in Auto) with the Fluor filter as opposed to the CC filter. And also from this 2006 thread where Nick Hope is pondering UR-Pro vs. Magic for video The Magic Filter does work with Video, but requires manual white balance - which is not always advantageous with moving images. I can only comment on their use on stills, but the Magic filter is actually quite different from the UR Pro. I can tell a UR Pro shot from a Magic shot straight away (on stills). On stills the UR Pro tends to produce more Magenta blue water, while the Magic tends to more to cyany blues. On general reef topography I find the Magic much more neutral coloured (I find the UR Pro CY more muddy looking). The UR Pro also renders Anthias much more red rather than orange (I have just been in the Red Sea shooting them both - hence the Anthias comment). On the plus side for the UR Pro, I think that the UR Pro filter gives more contrasty images than the Magic Filter. Which tends to help moving images. All that said, I am reluctant to persue the video market with the Magic Filter. We set up Magic Filters to provide a solution for photographers than didn't already exist (namely a gel format UW filter). And it is not our intention to take on UR Pro (or others) in the video market. That said we are happy to supply filters to those who want to try them. Alex and also here in 2006 You cannot judge filters just by looking at them. Filters are rather more complicated that the colour that they look. For example UR Pro CY and SW-CY look identical but they are not. It is the details of the transmission spectra that are important. Another example is that the original magic filter looks orangy, but the transmission spectra is nothing like a standard orange filter. http://wetpixel.com/forums/index.php?act=A...pe=post&id=2619 This is the magic transmission spectra and it lets through lots of red, orange and yellow light, some green and very little blue. And orange filter, which may look quite similar, has a much more defined peak in the orange (although I don't have an example). The 2006 UWP article on the inception of Magic Filters is also definitely worth a read: http://www.magic-filters.com/download/UWP26a.pdf Here's an extract I found particularly interesting (highlights by me) : I have used many filters over the last few years and firm favourites have been Kodak’s Wratten CC (Colour Compensation) Red series and UR Pro’s CY and SWCY filters. Both have strengths but neither was the perfect solution for me and this is what started me on the path to Magic. The main limitation of CC Red filters is that only work in very narrow depth range, for example I have found that the CC0R only produces pleasing images between 2 and 6 metres, even with adjustable white balance). This makes them impractical unless we know the exact depth of the subject before we dive. UR Pro’s filters are designed specifically to counteract the filtering effect of seawater and work very well. They are an excellent choice for videographers and work over a wider depth range (I find the CY works best on stills between and 12 metres). Frustratingly, for the still photographer UR Pro filters are only available as glass or thick optical plastic, which means that they cannot be physically fitted on the most popular SLR wide angle lenses such as fisheyes (which can only take gel filters). I designed the Magic Filter to work over as wide a depth range as possible. The Magic filter differs from other UW filters as it is not designed to perfectly counteract the filtering effect of seawater because this is highly variable. Instead it adjusts colours to produce a colour balance that is easily corrected by the camera’s white balance as is this 2007 article And fast-forwarding to a very interesting 2010 thread with a bit of spectrometer action: Nick Hope: The Lee, Rosco etc gel filters are designed to just change the colour of electric lights and are allegedly not "optical" quality (whatever that means), although I have seen point-and-shoot users get away with them. You can get a swatch book from them with loads of samples. Apparently the Magic Filters are somehow different in a way that makes them "optical" quality, but exactly what that is, I have no idea. The archived UR-Pro site (last archived in 2019) is also accessible here: http://web.archive.org/web/20191209011451/http://www.urprofilters.com/content.do?region=FilterInstructions#tips This dive into this pre-Keldan, film to digital, SD to HD history is pretty fascinating - to me anyway 😅 Really worth looking into discussions/input by Craig Jones (author of the "filters and ambient light photography" article I posted extracts of above), Nick Hope and Alex Mustard. We've come a long way but also, in others, full-circle (with non-manually white-balancing cameras like action cams) Technological advances (sensors, RAW, and LED technology, with the availablity of powerful UW light sources) have changed certain aspects (MWB was a hot-topic back in the days, and I hadn't heard of the Expodisc...), but some technical questions remain when it comes to handling the UW colour spectrum, especially for UW video. Just look at Nick Hope's UW-MWB tests in 2007 Trying to figure out what the now extinct UR-Pro CY/ SWCY were feels a little like trying to figure the coca-cola recipe 😝 It's a little sad that such valuable information has seemingly vanished with the company and its patent (?). cheers

Digging into the archives, i found this interesting 2003 article comparing UR-Pro filters to fluorescent filters, and giving "recipes" for some combo filters including the UR Pro ones. https://wetpixel.com/articles/filters-and-ambient-light-photography/ Here is an extract: Color Conversion filters. Color conversion filters come in two varieties, warming and cooling. For this discussion the warming filters are valuable since they can be used to counteract the cooling effects of the water. White light is characterized by its color temperature, specified in Kelvin, where warm light has low values around 3000K and cool light has higher values around 5500K. Although Kelvin is the measure photographers are accustomed to, it is more useful to speak of light in terms of mireds, or micro-reciprocal degrees. You can convert Kelvin to mireds by inverting and mutliplying by 1000000. color temperature equivalent mireds 2800K 357 3000K 333 3200K 313 3800K 263 4100K 244 4700K 213 5500K 182 6500K 154 There are two series of warming filters, the 81 series and the 85 series. They are characterized as follows: filter mireds 81 9 81A 18 81B 27 81C 35 81D 42 81EF 53 85C 81 85 112 85B 131 There are two analogous series of cooling filters, the 80 and 82 series, and they have matching but negative mired values. For our application they are uninteresting but they can be used to adjust the color of strobes or halogen lights. When applying a filter to light simply add the filter value to the light value to get the result. Water generally needs 2-5 mireds per foot to compensate for its cooling effects with turbid water requiring less compensation. Fluorescent Filters. Up until now we've talked about filters that are primarily available as gels that you have to combine and mount yourself. As it turns out, photographers have had to deal with another light source that is overly green and that's fluorescent lighting. Because of that we have at our disposal a limited range of thread-on and rectangular filters that are combinations of the filters that we desire. Additionally, many underwater photographers are familiar with UR Pro, a company that specializes in filters for underwater use. The UR Pro filters are functionally like fluorescent filters. Below is a table that I've compiled characterizing these filters. filter mireds CC M UR Pro glass CY 140 75 UR Pro glass VLF 145 60 UR Pro resin GR 25 30 Tiffen glass FL-B 100 50 Tiffen glass FL-D 40 65 B+W FL-D glass 20 20 Singh-Ray resin FL-B 147 50 HiTech resin FL-B 96 75 HiTech resin FL-D -12 30 Hoya glass FL-D 34 30 Hoya glass FL-W 9 60 Lee resin FL-B 3600K 35 40 Lee resin FL-B 4300K 69 45 Lee resin FL-B 5700K 134 40 Lee resin FL-D 3600K -50 70 Lee resin FL-D 4300K -16 70 Lee resin FL-D 5700K 14 60 ---- This 2007 discussion is also worth a glance: It that the UR-Pros were sold as plastic that you can cut to size or glass, both are exact same underwater but plastic gets scratched really easy. and also describing UR Pro filters as simply FL-B filters repurposed. If you can find FL-B filters in your size they will work well and be much cheaper than UR PRo. UR-Pro was apperently run by Kirk Kreutzig (and were not always easy to reach) It also turns out Nick Hope was looking into the makeup of UR-Pros at the time as well: A few years ago I trashed a big UR-Pro plastic external filter on it's first ever dive (staghorn coral). In subsequent discussions with them about re-polishing etc. I was genuinely interested in what UR-Pro had managed to patent about their filters, and what makes them so unique. I had a search for the patent (was involved with patent stuff in my old career) but couldn't find it, and I could never get a specific answer or a patent number out of them. Just that they "sill hold the patents" and that other filters will not give the same performance. Would still love to know what's so special about them. Other old threads discussing the UR-Pro / Magic filters worth a read include this one here as as well as this one here I'll keep digging around, see if anything else comes up. cheers b 

This is a summary of observations / data gathered from filter tests based on raw files shot on the LX10. Parameters: LX10 raw files, WB set to 6000K (like the theoretical value of the MW4300 light), exposure ISO 125, f/8, 1/60 (some exposure change due to the vignetting caused by the filter mount) - WB point is taken on the same spot on a Whibal calibrated grey card. - Light source is a Backscatter MW4300 video light used in wide mode, theoretically calibrated to 6000K (in reality, seems closer to 5000K), CRI 71.1 - colour data is samled in Lightroom Classic (colour slate used isn't a calibrated colour checker) LX10, unfiltered, WB uncorrected (temp 5350K, tint Magenta +19) wb rebalanced in post to check (temp 5000K, tint Magenta +27) Unfiltered colours observed: LR Histogram: UR-Pro acrylic 55mm filter, WB corrected (temp 2350K, tint Magenta -14 - warms by 3000K) Filtered colour modification observed: LR Histogram: - Known filter light loss values for UR-Pro Cyan (measured by Interceptor121): -1.6 Ev Original Magic filter, WB corrected (temp 2950K, tint Magenta +23 - warms by 2400K) Filtered colour modification observed: LR Histogram: - Known filter light loss values for the Magic Filter (measured by Interceptor121): -1.6 Ev Keldan SF -1.5 gel, WB corrected (temp 3000K, tint Magenta -28 - warms by 2350K) Filtered colour modification observed: LR Histogram: - Known filter light loss values for the Keldan SF -1.5 gel: -1.5 Ev (Keldan SF -2: -2 Ev) UR-Pro glass filter, WB corrected (temp 2250K, tint Magenta -10 - warms by 3100K) (note: filter in better condition than the acrylic UR-Pro) Filtered colour modification observed: LR Histogram: - Known filter light loss values for UR-Pro Cyan (measured by Interceptor121): -1.6 Ev Side-by side filtered colour modifications observed in LR: Unfiltered: Ur-Pro Glass : Ur-Pro Acryl: Orig. Magic: Keldan SF1.5: Based on these observations, most significant variations occur on the yellow (warmer on the UR-Pros), green (stronger filtration by UR-Pro, as expected) and also on the handling of the slate-gray tones by each filter. Magic handles the blue channel quite differently - which probaly relates to the magenta boost when rebalancing the WB. Keldan and Magic are actually quite close, but differ on the cooler end of the spectrum, greens, blues and slate-grey. Temperature-wise, the UR-Pro Cyan has the strongest warming effect (roughly 3000K and 3100K for -1.6 Ev), followed by the original Magic Filter (2400K for -1.6 Ev) whereas the Keldan SF-1.5 has the weakest (2350K for -1.5 Ev, in the same range as the Magic). Only the Magic filter requires boosting the Magenta tint to rebalance the WB, whereas all other filters require a reduction of the Magenta tint to rebalance.

Thanks, that makes total sense, the green to brown conversion of the UR-Pro CY just works as a base for grading. On one hand, a filter like the Keldan spectrum seems more accurate in its colour handling, but on the other, the UR-Pro offers an easy to work with base-colour palette, which just works for grading to visually pleasing results in most blue water situations. The Magic's handling of magenta (+23 on a readjusted WB) also explains the spike I was seeing at depth, and makes it difficult to handle imo - for video at least... Really looking forward to seeing the gel test results! One other thing i've been considering, given that the Keldan gels are -1.5, is to stack two (the standard glass filter is -2, the next strength gel is -3.5) This should give a rough -3, which probably can be handled by the GoPro in sunny tropical conditions, and maybe offer a good base as well, since the Keldan doesn't rebalance with magenta boost like the Magic filter does. I've worked on the LX10 raw files to extract colour data, and will post a summary of the observations for the 3 filters.

Yes definitely -now that the WB is clearer, the idea is just to try to see what parts of the color spectrum are the most affected by each filter, and how. The example you just posted fits nicely with the grading data - as Dreifish noted in his mixed lighting / ambient filter tests, and also as I remarked when grading the footage, the greens are much less affected with the Magic Filter than the UR-Pro. The brownish tint is also consistent, with the look and feel of the ungraded footage posted here For sure, these numbers are difficult to deal with, but they also do show roughly how the filters affect the colour spectrum, beyond the white balance / magenta temperature reading. When grading, the UR-Pro and Magic are really quite different in the rendering of certain parts of the colour spectrum. It would be more accurate if I could work on the raw files instead of the JPGs, and the LX10 test shots are more standardised Better still would be using testing with a standardised colour checker and a 100 CRI strobe, instead of an 70 CRI video light and an AOW slate, but I think there's still workeable data to be gained. These are screeshots of the lightroom WB and histogram data from the LX10 raw files, WB set to 6000K (like the light), exposure ISO 125, f/8, 1/60 (some exposure change due to the vignetting caused by the filter mount) WB is taken on the same spot on the Whibal calibrated grey card - LX10, unfiltered, WB uncorrected (temp 5350K, tint Magenta +19) unfiltered, wb rebalanced in post to check (temp 5000K, tint Magenta +27) UR-Pro acrylic filter, WB uncorrected (temp 5350K, tint Magenta +19) UR-Pro acrylic filter, WB corrected (temp 2350K, tint Magenta -14) Magic filter, WB uncorrected (temp 5350K, tint Magenta +19) Magic filter, WB corrected (temp 2950K, tint Magenta +23) ******* These are extras, but here is an original glass UR-Pro (not damaged like the acrylic UR-Pro), which shows a reading very close reading to the acrylic UR-Pro, and also a Keldan -1.5 Spectrum Filter gel. UR-Pro glass, WB uncorrected (temp 5350K, tint Magenta +19) UR-Pro glass, WB corrected (temp 2250K, tint Magenta -10) Keldan SF -1.5 gel, WB uncorrected (temp 5350K, tint Magenta +19) Keldan SF -1.5 gel, WB corrected (temp 3000K, tint Magenta -28) It would be nice to grab the colour square data from these raw files instead, but I don't know how to do this in the version of lightroom I have (there's no "colour pipette") and my photoshop CS6 is too old to handle Panasonic RW2 files... EDIT - I found a way to display the RGB info in lightroom (switching to "soft proofing"), and will work on the raw files filtered RGB values, which should be more precise.

Yes, there's clearly a lot going on. I couldn't find a way to do this with the raw files in Lightroom, and my Photoshop CS6 can't seem to handle raw files (probably some camera raw issue), but to give an rough idea of what's going on with the colours with the two filters, I worked on the JPGs in Photoshop, and grabbed the colour data from each square, but from the GoPro files set to 6000K WB (theoretical calibration of the video light used) If anyone knows how to do this with raw files (I'm guess my image software is too old), it would be more accurate... The (very rough) data I have is as follows: GOPRO UNFILTERED - WB 6000K RED SQUARE: R187 G100 B93 ORANGE SQUARE: R193 G118 B87 YELLOW SQUARE: R200 G212 B0 GREEN SQUARE: R62 G153 B96 BLUE SQUARE: R105 G110 B168 SLATE-GRAY SQUARE: R111 G100 B117 GOPRO + URPRO - WB 6000K RED SQUARE: R243 G132 B113 ORANGE SQUARE: R244 G149 B117 YELLOW SQUARE: R252 G208 B49 GREEN SQUARE: R171 G144 B91 BLUE SQUARE: R183 G129 B143 SLATE-GRAY SQUARE: R197 G140 B123 GOPRO + MAGIC - WB 6000K RED SQUARE: R229 G125 B96 ORANGE SQUARE: R234 G139 B95 YELLOW SQUARE: R237 G213 B29 GREEN SQUARE: R153 G168 B87 BLUE SQUARE: R168 G142 B127 SLATE-GRAY SQUARE: R176 G142 B117 If we reorder this per square to track the global changes the filtration induces, we get: RED UNFILTERED R187 G100 B93 UR PRO R243 G132 B113 MAGIC. R229 G125 B96 ORANGE UNFILTERED R193 G118 B87 UR PRO R244 G149 B117 MAGIC R234 G139 B95 YELLOW UNFILTERED R200 G212 B0 UR PRO R252 G208 B49 MAGIC R237 G213 B29 GREEN UNFILTERED R62 G153 B96 UR PRO R171 G144 B91 MAGIC R153 G168 B87 BLUE UNFILTERED R105 G110 B168 UR PRO R183 G129 B143 MAGIC. R168 G142 B127 SLATE-GRAY UNFILTERED R111 G100 B117 UR PRO R197 G140 B123 MAGIC R176 G142 B117 This, combined with the histogram and white balance / temp data, should give a rough ideal of how each of the two filters is affecting the colour spectrum (and, hopefully, what needs to be adjusted on the Magic gel to more closely match the UR-Pro).

To develop the comparison between the UR-Pro SW Cyan (55mm acrylic SRP-Blurfix model) and the original Magic filter gel, based on the GoPro raw still files (LX10 raw files gave similar results, we can make the following observations: When it comes to white-balance, other than the UR-Pro being slightly warmer, the main difference between the two filters comes from the handling of magenta. As observed on the GoPro (and the LX10), rebalancing with UR-Pro gives a negative Magenta reading, whereas rebalancing with the Magic gives a positive Magenta reading. GoPro raw files, WB set to Native, 6000K light (results are similar with camera WB set to 6000K) UR-Pro Cy, unbalanced WB UR-Pro Cy, rebalanced WB: 3100K Magenta -44 Original Magic filter gel, unbalanced WB Original Magic filter gel, rebalanced WB: 3500K Magenta +20 *** Based on these readings, there is a 400K warming effect difference between the two filters, which is not much, however when it comes handling of Magenta, the UR-Pro increases magenta by +31 (+13 to -44) whereas the the original Magic decreases Magenta by -31 (+13 to +20) As an experiment, if we try to match the two filters by warming up the Magic filter and boosting the Magenta, we get a very similar result between the unbalanced UR-Pro filter and the modified unbalanced original Magic filter: UR-Pro Cy, unbalanced WB Modified Magic filter gel, unbalanced but with WB warmed to 5900K and Magenta increased to 76: Results are now visually quite close for such rough measurements. But while the results are visually similar, the histogram still shows significant differences in colour distribution. To fine-tune this, it would be interesting to get readings on main individual colour channels (squares) as well, see how both filters affect them, but I'm not sure how to approach this.

I ran the test raw stills again today, testing just the UR-Pro acrylic and the Original Magic filters. White balance was set to 6000K then to NATIVE (flat). Results are pretty much identical on both setting, and as follows: NO FILTER, WB set to NATIVE As shot WB 5500K Magenta +13 Corrected WB 4900K Magenta +11 (for reference NO FILTER, WB set to 6000K, supposed calibrated light output gives: As shot WB 5200K Magenta +6 Corrected WB 4900K Magenta +9 - filtered readings are identical) UR-PRO acrylic, WB set to NATIVE Corrected WB 3100K Magenta -44 Original Magic, WB set to NATIVE Corrected WB 3500K Magenta +20 As observed on the LX10, a major difference is that the rebalancing with UR-Pro gives a negative Magenta reading, whereas rebalancing with the Magic gives a positive Magenta reading. If i'm calculating correctly, based on GoPro raw files readings: - the UR-Pro SW Cyan filter warms the light by 2400K (5500K to 3100K), and increases the magenta by +31 units (+13 to -44) - the original Magic filter warms the light by 2000K (5500K to 3500K so 400K cooler/less warm than the UR-Pro), and decreases the Magenta by -31 units (+13 to +20) There is a 400K warming effect difference between the two filters, which is not much, however for the original Magic to match the UR-Pro's handling of magenta, you would need to boost magenta by +76 (+14 > +62)... At a quick glance in lightroom, setting the original Magic's wb to 5900K and boosting the magenta to +62 gives a very similar result Modified original Magic, with WB set to 5900 and Magenta boosted to +76 I posted more illustrations in this thread Results are now visually quite close for such rough measurements. But while the results are visually similar, the histogram still shows significant differences in colour distribution. To fine-tune this, it would be interesting to get readings on main individual colour channels (squares) as well, see how both filters affect them, but I'm not sure how to approach this. cheers b

Ran the test again on the GoPro raw files to check the difference, testing in WB set to 6000K then to "native" (flat), testing only the UR-Pro acrylic and the Original Magic filters. Results are as follows for GoPro RAW still files WB 6000K NO FILTER, WB set to 6000K As shot WB 5200K Magenta +6 Corrected WB 4900K Magenta +9 UR-PRO acrylic, WB set to 6000K Corrected WB 3100K Magenta -45 Original Magic, WB set to 6000K Corrected WB 3450K Magenta +22 WB NATIVE NO FILTER, WB set to NATIVE As shot WB 5500K Magenta +13 Corrected WB 4900K Magenta +11 UR-PRO acrylic, WB set to NATIVE Corrected WB 3100K Magenta -44 Original Magic, WB set to NATIVE Corrected WB 3500K Magenta +20

rats... realised I only transfered the jpegs for the GoPro tests, and deleted the raw files... But the LX10 raw tests are valid. So, after importing and rebalancing in Llightroom, I'm getting the following white balance values for the LX10 raw stills No filter, raw, camera WB set to 6000K to match light supposed to be 6000K - white balance "as shot" 5300K, +19 Magenta - corrected white balance 5000K, +28 Magenta UR-PRO acrylic corrected WB 2350K, -14 Magenta UR-PRO glass 55mm corrected WB 2250K, -8 Magenta UR-PRO (?) glass 2 corrected WB2300K, -23 Magenta Keldan SF -1.5 corrected WB 3050K, -27 Magenta original Magic filter corrected WB2950K, +24 Magenta Howshot corrected WB2200K, -32 Magenta

The video clips of the filter tests follow the same sequence - idea was to check if there were differences in the way WB was handled when shooting video as well (which is what I do exclusely), maybe grabing some captures to check that as well. Now I'll need to wipe the cobwebs off an old copy of lightroom and see if I can extract some values. Visually, there is a massive difference between Magic and UR-Pro, which is much yellower. As expected, the Keldan SF-1.5 is the weakest - and it seems the 2nd non-branded glass filter (which was sold to me as a UR-Pro) is not the same build, as suspected... Probably not a UR-Pro - Cheeky vendor... The acrylic and glass UR-Pros seem identical at first glance - other than the fact that the acrylic is not in a good state, (it lived mounted on a GoPro in a BCD pocket, albeit with a lens cap on, for thousands of dives over the years...). But I have three acrylic UR-Pro 55mm, including one which is in a much more preserved state...

GO PRO 7 Camera White Balance set to 6000K, GoPro colors photo/4K clip without filter (paper no filter, 6000K) photo/4K clip with UR-PRO acrylic filter (paper UR-PRO ACRY 6000K) photo/4K clip with UR-PRO glass 55mm filter (paper UR-PRO GLASS 6000K) photo/4K clip with UR-PRO (?) glass 2 55mm filter (paper UR-PRO GLASS 2 6000K) photo/4K clip Keldan SF -1.5 (paper Keldan SF-1.5 6000K) photo/4K clip with original Magic filter (paper Magic 6000K) Camera White Balance set to Native, GoPro colors (flat profile) photo/4K clip without filter (paper no filter, Native) photo/4K clip with UR-PRO acrylic filter (paper UR-PRO ACRY Native) photo/4K clip with UR-PRO glass 55mm filter (paper UR-PRO GLASS Native) photo/4K clip with UR-PRO (?) glass 2 55mm filter (paper UR-PRO GLASS 2 Native) photo/4K clip Keldan SF -1.5 (paper Keldan SF-1.5 Native) photo/4K clip with original Magic filter (paper Magic Native)

Following up on the info posted in these two threads 1 & 2, and to try to better understand how UR-Pro filters work, I ran some tests today, both with the GoPro 7 and the Lumix LX10. The test setup isn't as precise as Dreifish's - I don't have a strobe, and no light meter to check the kelvin values of the light used. I also don't have a calibrated colour checker. However what I do have a Whibal calibrated greycard slate, which I used on the tests. I used what I had for the colour references, ie an AOW slate, a printed book cover, but nothing calibrated, all setup against a dirty Balinese grey wall... The light source used is a Backscatter MW4300 video light, which is supposed to be calibrated to 6000K in wide mode (for matching when used as a pair) - I had no way of checking if this was accurate - which was used in a dark room. So nothing too rigourous or fancy, but enough to highlight the differences in behaviour between the filters tested. Tests were as follows: - Light source: 6000K calibrated (?) Backscatter MW4300 video light - Cameras: GoPro7 Black / Lumix LX10 (stills and video clips for both) - Filters: none, UR-Pro 55m acrylic filter (SRP Blurfix convex design), UR-Pro 55m glass filter, UR-Pro 55mm glass filter (no brand markings, so not 100% sure this is a UR-Pro), Keldan Sepctrum Filter SF -1.5 gel, Original Magic Filter Gel For the LX10 tests, I also added a generic Howshot filter I have designed for the Inon UWL-H100 Test sequence: GO PRO 7 Camera White Balance set to 6000K, GoPro colors photo/4K clip without filter (paper no filter, 6000K) photo/4K clip with UR-PRO acrylic filter (paper UR-PRO ACRY 6000K) photo/4K clip with UR-PRO glass 55mm filter (paper UR-PRO GLASS 6000K) photo/4K clip with UR-PRO (?) glass 2 55mm filter (paper UR-PRO GLASS 2 6000K) photo/4K clip Keldan SF -1.5 (paper Keldan SF-1.5 6000K) photo/4K clip with original Magic filter (paper Magic 6000K) Camera White Balance set to Native, GoPro colors (flat profile) photo/4K clip without filter (paper no filter, Native) photo/4K clip with UR-PRO acrylic filter (paper UR-PRO ACRY Native) photo/4K clip with UR-PRO glass 55mm filter (paper UR-PRO GLASS Native) photo/4K clip with UR-PRO (?) glass 2 55mm filter (paper UR-PRO GLASS 2 Native) photo/4K clip Keldan SF -1.5 (paper Keldan SF-1.5 Native) photo/4K clip with original Magic filter (paper Magic Native) Lumix LX10 Camera White Balance set to 6000K raw photo/4K clip without filter (paper no filter, 6000K) raw photo/4K clip clip with UR-PRO acrylic filter (paper UR-PRO ACRY 6000K) raw photo/4K clip with UR-PRO glass 55mm filter (paper UR-PRO GLASS 6000K) raw photo/4K clip with UR-PRO (?) glass 2 55mm filter (paper UR-PRO GLASS 2 6000K) raw photo/4K clip Keldan SF -1.5 (paper Keldan SF-1.5 6000K) raw photo/4K clip with original Magic filter (paper Magic 6000K) raw photo/4K clip with generic Howshot filter (paper Howshot 6000K)

Thanks - I'll try this with GoPro raw stills - I don't have a colour checker or a strobe but do have a calibrated Whibal grey card, and the Backscatter MW4300 video light is supposed to be calibrated to 6000K in wide mode (for pairing) - not sure if the is truly accurate (I do find it quite warm in post...), but it's the best I can do here, since I also don't have a light-meter. I mentioned colour checker more for the colours themselves - my idea was that if it's possible to read colour values in lightroom, then it checking each colour square without then with the two filters, especially the greens and blues, could give an idea how the on-lens filter affects specific ranges in the spectrum. I'll give it a go. EDIT - I ran the test on the GoPro and LX10 - test details are here Working from the LX10 raw files, I get the following data for WB in lightroom, with different filters: No filter, raw, camera WB set to 6000K to match light supposed to be 6000K - white balance "as shot" 5300K, +19 Magenta - corrected white balance 5000K, +28 Magenta UR-PRO acrylic corrected WB 2350K, -14 Magenta UR-PRO glass 55mm corrected WB 2250K, -8 Magenta UR-PRO (?) glass 2 corrected WB2300K, -23 Magenta Keldan SF -1.5 corrected WB 3050K, -27 Magenta original Magic filter corrected WB2950K, +24 Magenta Howshot corrected WB2200K, -32 Magenta However, I'm wondering if there is a way to use LR to measure the impact of the filter on greens/blues? I didn't have a full colour checker but do have a few colour squares in my test picture. Once I'm here: Is there any way to measure the effect of the filter is having on each of the colour squares? Data seems identical when I move the dropper on both images, so I must be doing something wrong. The idea would be to pinpoint broad differences in the way each filter affects a colour range, to highlight differences. Thanks! b

Beautiful - Love Le Grec as well! I still remember the gorgonians and this explosion of life when the wreck comes into view...🥰

Thanks - Backscatter's mount isn't sold in these parts, only the standard AOI, and importing isn't an option - but it could possibly be an option elsewhere. The tricky bit, given the proprietary design, would then be to find a flat acrylic UR-PRO CY somewhere, and one large enough to work with. Most of the ones still on sale are glass, and the acrylic ones I have are slightly convex (SRP's blurfix mount, with 55mm threads directly on the side of the filter) Once the large acrylic UR-Pro filter is found, would then need to cut/machined it to fit in the Backscatter mount... Other options I could see, that would require no machining and standard UR-Pro filters would be buying the AOI 55mm thread adapter. - The mount would then be: GoPro Supersuit > 55mm filter adapter > 55mm UR-Pro Filter > AOI 55mm thread adapter > AOI UWL-03 lens But with the extra weight of the lens it probably wouldn't hold on my 55mm filter adapter, and if I ever upgrade the GoPro, the filter adapter is no longer available for more recent models (one of the reasons I didn't upgrade, as previously discussed) A more stable option would be to get the more sturdy and universal Inon 67mm filter mount for the supersuit - There are no 67mm UR-Pro filters available, so the mount would then be: GoPro Supersuit > Inon 67mm filter mount > 67mm to 55mm stepdown ring > 55mm UR-Pro filter > AOI 55mm thread adapter > AOI UWL-03 lens But clunky as well, and what of vignetting with all those adapters... Not easy, not easy...

Hmmm, logisitics are a tad tricky, my spectrometer is still at the cleaners, all that 😁 😉 Looking at your tests for the ambient filters, I'm wondering if would it make sense to try shooting a still of a colour checker on land, first without, then with the UR-Pro and original Magic filters on. With high CRI strobe and WB set to the strobe's, it should be close to neutral lighting on the raw file, right? Then maybe the individual colour reading differences, especially blues and greens squares, could be measured in software (I'm really bad at image software, but I guess photoshop or lightroom can give such readouts?) Wondering if this could be a quick and dirty way to get a rough curve highlighting the main differences between the two filters, and then seeing what best matches Rosco / Lee graphs in terms of required filtering range.

Yes, the pictures I'd posted are also from their product page, but I don't understand how it's possible unless they moved the lens further away from the supersuit port. It's snug on the original AOI, no room for a piece of plastic as far as i can see, as the back of the lens sits almost touching the supersuit port. Moving it forward seems risky (increasing the risk of vignetting and corner deformation), so not sure how this works. This thread mentioned vignetting with the mount, but then none if cropped to 16/9, so not sure...

I don't really understand how the Backscatter mount modification works. They use an AOI mount, but with a slot on the side to slide the filter in. But looking at my AOI mount and lens, don't really see in what space the filter would fit in, since as far as I can see it sits snug next to the port. So was it moved further away from the port? The other issue is that my acrylic UR-Pro are not flat, but slightly rounded, as per the SRP design...

Digging around, I found these historical documents to add to the pile : a very heated 😅 Polar Pro / UR-Pro comparison with some basic data on the UR-Pro SWCY https://interceptor121.com/2013/01/13/underwater-video-tips-polar-pro-red-filter-for-gopro/ and an 2005 X-Ray article: Photography_UsingFilters_15.pdf Otherwise coordinates for the historical, US-based UR-Pro company here: email no longer works. Checking my emails, in 2016 it was forwarding to SRP...

Yes, that’s exactly it - clearly the same issue, and as you pinpointed it, it's clearly a weaker filtering of the greenish cast in the ambient spectrum... This is actually also an issue I had why I tried the Keldan Spectrum on the GoPro – it was way too weak, even in Palau’s generally blue water. And to add to this, the Keldan Spectrum gels are also slightly weaker than the SF2, as they’re sold as SF -1.5... Interestingly, they worked fine when manually white balancing the Lumix to ambient light at depth, the UR-Pro performing the worst of the 3 (Keldan SF-1.5 gel > Original Magic > Ur-Pro CY), and it’s exactly the opposite ranking on the GoPro (Ur-Pro CY > Original Magic > Keldan SF-1.5 gel ), which clearly needs a more powerful filter. All this highlights the importance of having a good filter to work with, as I was mentioning above – these 3 filters are well-designed specialist products, and yet they behave quite differently, which becomes even clearer when working on the footage in post... While the Magic is useable, I’m also a little worried about the red/magenta/orange boost I saw a little deeper – I’m guessing it’s also an effect of the white balance being thrown further off by blues/greens, leading to overcompensation. This is not good, as needs more work in post and this further degrades image quality… Thanks for the links to gels, it would be great to try to reverse-engineer the UR-PRO SWCY formula – they really had something going with it, it's really a shame to lose such a tool. I have no idea how manufacturers work on designing custom filters – do you think the UR-PRO SWCY was actually a proprietary design (like the Keldans), or based on some pre-existent tone (which could then be source / purchased?). Unfortunately, the Rosco/Lee gels are near impossible to source in Indonesia – there is a distributor in Singapore, but the sample I ordered didn’t make it over the first time, and with custom duties it’s a bit of a nightmare. I think it’ll have to wait a few months, when I’ll be in a place where gels are not accessible... cheers

That’s pretty much it. The Magic Filter footage is definitely useable/workable, but more fiddly, and also I’m a little worried about the red/orange/magenta boost at depth. It’s still possible to find UR-Pros online, especially Ikelite models, but they’re generally in odd sizes. I wonder if it would be possible to DIY it, hole-punch / cut up one of the UR-Pro acrylic filters to make a piece which could slide in the supersuit, or another system which would allow the use of an UR-Pro filter with the lens (as mentioned earlier, I'm not interested in Backscatter's proprietary filter solution). if going the filter + screw on lens (with the 55m adapter for instance, like Inon's), I'm afraid it will induce vignetting / distortion on the UWL-03... Having a slip-in filter in the housing is clearly the best solution in this case...

To follow-up on the subject, did you see this ACE360 review - especially the sequence on colour shifts when using the Ace360 in auto profiles, and the issues with locking said profile? Interesting bit starts here: 5"40 in on a related note, this has just been posted - a bit of Okinawan testing of the "big 3" with the AOI UWL-03 Sounds interesting! cheers b