Colorchecker Passport in Solar UV

[rfcurry]

Andrea,

 

I am not being defensive. And I provided plenty of info on my site, far more than any other filter providers, including a spectral transmission chart. See http://uvroptics.com/index.php?CopperU

 

I have also done some stack tests. I also have someone (you know who) performing unbiased, independent tests. But as I said above, if I make conservative claims, buyers can be pleasantly surprised when the filter exceeds their expectations. I do not want unhappy customers.

 

Anyone is welcome to do a stack test. Some will anyway. Hey, I would. As for John's questions, they are not questions, they are his notion of what the filter should be. As I noted, the prevailing OD for the bandpass filters we currently enjoy has been met or exceeded by the CopperU. Some astronomers may wish to trade longer exposure time for greater out-of-bandpass OD. I can and might accommodate them. But the design of my filter has been made with the UV photographer in mind. I have chosen what I consider the best EV to OD balance for people who might frequent this forum; those like me who are, as you note, "simply interested in generic UV photographic use."

 

I will continue to work hard to provide the best filters for my customers. The PrecisionU, for example, has gone through numerous changes, each an improvement. Its peak is now higher, it is thinner, and an AR coating has been added. My costs increased, but my prices didn't. I do not simply build the best, I build the best that I can build, within the functional parameters .

 

I am not here plugging my filters. I am interested in finding out why the PrecisionU and CopperU give such a varied UV palette.

[Andrea B.]

I'm not surprised by these varied UV palettes. We do already know that there are false colour variations across all our UV pass filters in fotos made with Bayer-filtered cams. The colour charts made for Lumix cameras by Klaus and Enrico (and others) show us that this can happen.

 

Even though we cannot reliably infer 'backwards' from those charts to correlate what specific wavelength a given colour comes from, the colour charts still do show us that different wavelengths in UV produce different camera false colours. So it seems to me intuitively obvious that we will get false colour variations across all our UV pass filters.

 

Nailing down the specifics of these false colours is probably beyond what one can accomplish with stacking filters unless one has some kind of expensive collection of narrowband filtration. But it is fun to try.

 

As I pointed out somewhere, the transmission of copper sulphate filtration is well know. What remains to be seen is how the eventual product version of the CopperU performs photographically. Which I'm sure we will soon see. :(

[Alaun]

My approach to these questions:

Think of a rainbow.

 

light source > slit > grit > rainbow picture (Color spectrum) > camera

 

This works fine also with UV light and you can get a feeling of the spectrum and what color the different wavelength come up with

 

Problems:

 

you might get several spectra (first and second, third …) and they can overlap

 

reliable light source (maybe a flash as the SB14 is fine)

 

put these thing together, that you have a stable construction (like an optical bank)

 

So far, I have only tested paper constructions without anything to fix positions, you can get something, but nothing repeatable.

 

But the spectra I get go from blue/violet to some kind of mud yellow

 

very primitive version: Use a CD or a DVD as a kind of mirror to look at a light source covered by a little slit. In visible light you can see all the rainbow colours, in UV you get the "UV-Rainbow”.

 

 

Setup:

 

and with UV:

[Alaun]

How to make a good slit:

 

[nfoto]

Little is known of the spectral properties of the patches on a Color Checker Passport or similar devices. We do know a few are UV neutral and thus appear neutral grey, black or (near) white under different filtration incorporating a wide band in the UV below 400 nm. These patches also are Vis neutral; however, inferring backwards that a colour patch neutral in Vis also is neutral in UV is stretching the truth too far.

 

Those patches that for some filters appear blue or for others appear in golden hues are interesting, but I think we only can test whether or not blocking the 380-400 nm band (more or less completely) changes their appearance. If the presence of sub 400 nm band adds these golden hues and the absence removes these hues with say a CopperU filter, we have at least a good explanation why BaaderU and CopperU can be so similar in UV false-colour rendition, yet differ on a few selected subjects. The first assumption, that BaaderU and CopperU give similar output in general is well documented and the evidence will be presented in due time when testing is completed. However, on some subjects such as the anthers of Anemone sp. they do differ markedly. Usually one thinks in terms of IR leakage as the basic explanation, but testing these filters against strong IR sources doesn't make the leakage hypothesis very likely.

 

I'll set up an experiment with the CC Passport and stacks of BaaderU or CopperU with L-37, L-39, or whatever relevant filters I can locate in the piles on my work table. First priority challenge, however, is reassembling my Naim stereo outfit after a major structural change. That probably take a day at least (including listening tests).

 

Werner: a true "knife-edge" filter. A pity I don't shave so razor blades are scarce as hens' teeth over here.

[JCDowdy]

That probably take a day at least (including listening tests).

 

May I propose a stringent test: Pink Floyd, Dark Side of The Moon. :( :) !

 

Werner,

If you like DIY spectrometers check out PublicLab.org, they have some DIY designs you may find interesting.

[nfoto]

Pink Floyd is OK, but perhaps not disclosing the full potential of the change I'm considering (replacing my endearing sweet-sounding NAIM NAP 110s with the beefier NAP 250s, plus change pre-amplifier from NAC 42 to NAC 32.5 and a new set of power supplies).

 

Listening tests always include a range of Bach, Händel, German electronic music, and at least some CDs by the Danish group Savage Rose. Their lead singer Annisette is a combination of Janis Joplin, a vulcanic eruption, a Hoover at full steam, and a few sticks of dynamite throw into the mixture for good measure.

[Andrea B.]

oh cool I need to look up this Annisette singer.

See also Alabama Shakes lead singer Brittany Howard. She'll knock your socks off!!

This link has a video from an appearance on Letterman Show. Awesome!!

http://www.billboard...gs-bette-midler

see also - same song - maybe better this time

https://www.youtube....h?v=feW9Mr2KZT0

 

you have to see this one:

 

love me some pink floyd always.

[nfoto]

Nothing wrong with Pink Floyd, but they aren't the best material for critical evaluation of audio gear because of all the sound effects.

 

Be aware that the Savage lead singer is often misspelled 'Anisette'. Her name is Annisette Hansen and she's truly tiny, merely 1.50 m or so. Usually sings bare feet so no heels to add to the impact :(.

[Andrea B.]

That's about 4' 11" which is very tiny! I found a vid and listened to her. She does indeed have one of "those voices".

[nfoto]

Try "Madhouse Wedding" from the album "Wild Child". Or the title track. Or "Long Before I was Born" or "The Shepherd and Sally" from the album "In the Plain". The list is near endless. By the way, she's still an active performer on stage. Perhaps not with the same enormous dynamic voice, but maybe not expected from someone older than me :(.

 

I need at least one full day more of listening tests before deciding on the new configuration of the Naims. The living room is flooded with all those black boxes of oh so British design and interconnecting cables run everywhere. Well, before the weekend is over I probably have sorted the pending questions and moved the remainder of the gear to another room, where I'll do another test series now pitched again my valve setup. Sometimes it's nice to have an entire house to oneself and whatever indulgences take my fancy.

 

Next week back on track - only UV photography on the agenda ..... I promise.

[Andrea B.]

I wouldn't mind seeing a couple of photos of your Naim gear. Where are you using those boards I sent? I was telling Mike about it and he's curious too.

[nfoto]

They haven't arrived yet. But will wind up replacing phono boards in a NAIM NAC 32.5 preamplifier. I no longer use analogue record players.

 

In direct view now there are 12 of those black NAIM boxes. Pre-amplifiers (3), power supplies (4), electronic cross-over (1), power amplifiers (4) and a gaggle of interconnecting cables. Plus a few other boxes loaned to my children. And a NAIT unit hooked up to my video viewing PC.

 

NAIM never believed in doing anything simple, except for the design of their cases. Are you really sure you want to see all this mess documented? I might haul out some Broncolor flashes and do the shooting in UV perhaps.

[nfoto]

OK Andrea, these are for you :(

 

Naim boxes all over the place.

 

b/w converted from broad-band D600, no filter, 35 NoflexarSoligor, incandescent light.

 

 

b/w converted from UV with CopperU, studio flashes (uncoated xenon tubes)

 

[Andrea B.]

Finally a non-floral UV foto !! (J/K, of course).

 

Wow!! That is really a lot of components. I find it interesting that every function is separately 'boxed' with Naim. This does allow you to be very specific - and modular - in building an audio system.

 

What speakers are those?

[nfoto]

Epos ES 11. Run bi-amped. Unfortunately, I had to forgo my beloved Quad Electrostatics when I moved into this house due to the room layout being in conflict with the requirements set by these speakers. However, the ES 11 is a very good substitute and functions perfectly with Naim amplification.

[Alaun]

John, thanks for the links.

[Andrea B.]

Back to the CopperU - a question for Reed. You mention not to freeze the filter (of course!). How will heat affect it when shooting outdoors in hot summer sun?

Thanks in advance.....

[rfcurry]

Andrea,

 

Sorry for the delayed response. We had to make a quick run to Nova Scotia and this is my first time online in two days.

The CopperU, like all our filters, ships with a complementary 52mm metal lens hood. Heat is not going to be a problem under normal usage. Even your jaunt to Death Valley wouldn't cause undue expansion of the liquid.

 

The front glass on the CopperU is fused quartz, which is very strong, scratch-resistant, and gives excellent transmission in the UV. The actual quantity of CuSO4 is miniscule. The total thickness of the filter is only 4.5mm.

[Andrea B.]

Thanks, Reed. The lens hood is an excellent idea.

[nfoto]

Spring is almost here and the first buds of Tussilago have been spotted in my neighbourhood. A few more days with temperatures above the freezing point (during daytime at least) and UV photography of the classic spring botanicals can commence.

 

I did some preliminary test shooting during the last days when the sun broke though the lead-grey blanket cloud layer. Apparently my field technique is rusty because I had forgot all about viewfinder light leakage with my D600. So, all tests this time were tainted to some extent.

 

My concern is that we should always include a comparison to the IR exposure not only with a UV bandpass filter. The problem we face is with very low incident levels of UV as even OD 4 for IR might be too much to alleviate signs of IR contamination. Remember that the UV sets the basic exposure. What's important is the difference UV vs IR. I'll pursue this aspect more diligently in the near future.

[Andrea B.]

My concern is that we should always include a comparison to the IR exposure not only with a UV bandpass filter.

.....What's important is the difference UV vs IR.

 

I'm sorry, I don't quite understand what you mean? Do you mean make an IR exposure with an IR-pass -- or --

make an IR exposure with an IR-pass stacked on the UV-pass to test it for IR leak?

Thank you in advance for re-explaining.

[nfoto]

Both, actually. We need to evaluate how much IR is present compared to UV.

[rfcurry]

The problem I faced with developing the CopperU was determining the 'acceptable' level of NIR contamination. Is slightly exceeding the NIR blockage of existing UV-bandpass filters enough, or should I severely block the NIR? Since I was often testing with only two halogen light sources, the UV to NIR ratio was very low. Each test included the amount of NIR passed. But using that information is difficult; the UV imaging community varies in its perceived needs. Inevitably, better NIR blocking decreases the EV. and as the exposure time increases, the passed NIR may increase.

 

Finally, I reasoned that to slightly exceed the NIR blocking of conventional UV-bandpass filters is sufficient. Many photographers that frequent this board use abundant artificially generated UV light, so the UV to NIR ratio is high. For those who use low UV to NIR ratios, a deeper CopperU cell, hence longer pathlength, might be appropriate. However, as noted above, if the UV/NIR ratio is very low, the cascade effect of increased exposure time prompting increased NIR passage is very likely. At that point, a jump to higher ISO and lower f-stop might provide some relief. I must test that.

 

What do you think?

[colinbm]

This is really a chicken or the egg question, Reed.......

From my short experience with UV photography & with compromised cameras & lenses, (which I am remedying), has been that these Mercury & Xenon light sources are a pain & a waste of time. The only useful source of UV in the main are the MET U301 365nm LEDs, which have no IR to worry about. Landscape or outdoors close-ups, is of course using the available Sunlight, (with some artificial UV like the MET U301 365nm LEDs), which is in my opinion, is the only IR that needs to be accounted for, with a filter like the CopperU.

So I guess, in this situation, you need to find the balance of UV exposure time versus, suppressing IR contamination.

Col

 

PS. I am taking for granted the blocking of the visible light, it is the IR that is more difficult.