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How to WB this (or maybe the filter I have is bad)


bsas

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I got this filter to test and it has a "custom" stack that in theory is an UG11 and BG40 (no idea the thickness).

I think it is "kind of working" but I have no idea how to basically test it. I tried a basic "sun scream" test but maybe the one I have wasn't "strong enough" because it turns out yellowish/orange instead of black.

Or maybe it is an WB issue... no idea... can you guys tell me what I am doing wrong, or maybe the filter is bad?

 

Thanks!

 

post-268-0-05518000-1567463827.jpg

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The BG40 is not completely blocking IR. It is not the best for IR-blocking. I'll go find the link to a some charts.

 

Here is a chart for two thicknesses of UG11 dual bandpass filter glass. You can see that considerable IR-blocking is required around 700 nm.

post-4-0-05173700-1428604078.jpg

 

 

Here is a chart for 4 different IR-blockers in 2.0 mm thicknesses. You can see that for a 2.0 mm thickness only the S8612 and the BG39 can block IR at/below OD 4.0 (with the cut to the left side of 700 nm.) But the S8612 has a higher transmittance for 2.0 mm thickness and so becomes the more desireable IR-blocker. How thick an IR-blocker to choose depends on knowing the thickness of the U or UG glass. The top charts are "diabatic" and illustrate better the blocking differences than do the second set of linear charts.

I'll note in passing that the purists amongst us like blocking at better than OD 4.0.

post-4-0-04354500-1473031788.jpg

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Aha! So basically that stack is supposed to leak some colors and it’s working as intended? Interesting.

Can you take this color off in post? If so, how?

 

A bigger question would be: what is the best thing or color to point the camera to WB for UV? In my case I was pointing to the sky (don’t know why, I thought it made sense).

 

Thanks!

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I don't know what the thicknesses are of the two filters you are stacking, so I cannot say what it is "supposed" to do. :lol: :lol: :lol: Alls I can tell you is that your stack is passing* some IR which contaminates the reflected UV you are trying to record.

 

If you simply desaturate the photo, you will see that the sunscreen is grey in tonality. If you try to process that grey into black, you will be wreaking havoc on the tonalities of your photo and possibly destroying its actual UV-signature.

 

Similarly if you attempt to process that greyish-yellow sunscreen into black within a color photo, you will wreck everything else. (Some other parts of the photo will become too dark.)

 

Under a UV-pass filter or stack which is properly IR-blocked to OD 4.0 or more, that sunscreen will be black or a very very very dark false colour.

 

 

*or "leaking some IR" as we often say around here.

 


 

I'm worried that someone sold you that stack as a legitimate UV-pass filter stack. BG40 is *not* recommended as an IR blocker. Use S8612 for best results. Or BG 39 for good enough results. And, again, you cannot add an IR-blocker until you know the thickness of the U/UG glass so that a proper thickness can be chosen for the IR blocker.

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Don't use BG40 or BG38 for UV stacking.

Thickness is important, no way to calculate without that info.

We don't know what thicknesses you are using, but assuming you are using 2mm thick for each of those two glass types, then the stack is borderline for sure, OD3, not enough,

although it looks worse than I would expect for OD3 even.

Regardless. You need to get the OD down to under 4.

Also, Are you sure this is actual UG11, and BG40?

Here is a graph of that stack assuming 2mm for each, but you may have thinner versions of one or the other or both.

 

post-87-0-39334600-1567126038.jpg

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...although it looks worse than I would expect for OD3 even.

 

Yes, that photo is not OD 3.0, imho.

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Well, "a "custom" stack that in theory is an UG11 and BG40 (no idea the thickness)", is not too defined.

The "in theory" part is too vague. Why do you say "in theory"?

Skin color has partial natural skin color, not what skin looks like in UV. So there is some amount of visible/IR in the mix looks like.

If you want to test it, stack it with some UV blocking filter, some longpass filter, yellow, etc., I don't know what you might have that would work.

Any yellow, orange, red (even) filters? Try stacking with one, and see if you get any image at all.

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To get to your other non filter questions.

I like to photograph a dandelion, but there are not back yet. A dandelion will give a very distinct black center and yellow outside. Great for tests as if it fails a dandelion test, what you are testing will be bad for uv as this is high contrast test.

Andrea seems to like sunflowers. You may be able to buy some at the store now or see them in fields. They too will give a distinct dark center like pattern. You will see them a lot in the test links to get an idea what it should look like.

 

I used to always white balance off black Asphalt, while walking around. But recently have been using a block of PTFE. You can buy a chunk off ebay. Or if you have a roll of "plumber tape", its very thin white plastic like stuff used to lubricate fixtures when tightening. Its the same thing. Just wrap 5 to 10 layers around and old credit card and keep it in your pocket. You want a fresh white surface when WB, so just back roll a little and roll back up when ready in restore it in your wallet. I still carry a white, black, and grey card in my wallet. Not sure if I still have my periodic table card.

 

I like the idea of a sun scream test. Do you yell when the filter doesn't work?

 

The issue with sunscreen is there are 2 types. Absorbing, looks black on you when imaging UV and reflecting. I seem to buy the reflective kind, so you don't see a strong contrast on the skin, it just looks shinny glossy.

 

Hope that helps.

 

Why the others are jumping on your IR leak, is look at your thumb and thumb nail in that photo. Its pasty, ghost like white. That either means you are in the soft IR reflective light zone. Or you have never left your dark enclosed thermal insulation bunker deep 30 feet under the ground. So your skin has no melatin in it. Most likely your looking at IR.

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Some people like to play with deliberately leaky stacks. There's nothing wrong with that, but just don't call it a UV photo, call it a UV+ photo or something. If you are intending to take a UV only photo, you need to get some S8612 to block the IR, as previously discussed. BG40 won't do it well. Post processing can't turn a non-UV photo into a UV one, or we wouldn't even bother buying converted cameras.

 

That is a nifty photo, though, on its own merits. Orange sunscreen! Coool.

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Some people like to play with deliberately leaky stacks. There's nothing wrong with that, but just don't call it a UV photo, call it a UV+ photo or something. If you are intending to take a UV only photo, you need to get some S8612 to block the IR, as previously discussed. BG40 won't do it well. Post processing can't turn a non-UV photo into a UV one, or we wouldn't even bother buying converted cameras.

 

That is a nifty photo, though, on its own merits. Orange sunscreen! Coool.

Yes it is an interesting photo.

 

I also like the UV+ designation, indicating a photo with some visual or IR-leakage.

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Yeah, well that is not what he is asking. He wants to know if it is working. He wants to know if the issue is white balanced related or is the filter is bad. The filter is 'bad', meaning not UV only.

Here is his question:

"Or maybe it is an WB issue... no idea... can you guys tell me what I am doing wrong, or maybe the filter is bad?"

 

Skin is not pink in UV and sunscreen is not yellow in UV. You could not make that happen with white balance. The filter is not UV only, not even close.

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Bernardo, I forgot to mention earlier......

 

I'm always happy to convert and white balance a raw reflected UV or IR photo for anyone who may not have a converter which does well at UV conversion. And, I'm also always ready to run a file through Raw Digger for a look at the raw colours or raw RGB channels. Just upload your raw photo to Dropbox or some similar app and provide me with the download location.


 

In the Reference section is lots of info about white balancing in UV.

 

Sticky :: White Balance in UV/IR Photography

 

How to make UV colours reproducible

 

White Balance Search tag for topics/posts about white balance in UV/IR photos.

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Guys, I am super impressed how supportive you all are, thank you very much, I am learning A LOT.

 

So, the story goes like this: before I joined the group I found this auction for this "stack" on eBay for cheap and I went for it. I didn't like the results or the cut of the glass and I asked to return but the seller offered me even a 50% refund to keep it and I thought "screw it, it is cheap, I will keep it for that".

 

But, because the seller is "weird" (to say the least) I cannot know if the glass is what it claims. He was clearly claiming it was an "custom" stack made by BG40 and UG11 glass (never specified the thickness of them). If I believe him and I measure it (I just did), here are the results:

 

The black part (supposedly UG11) is around 2.25mm (very thick). The blue part (supposedly BG40) is around 1.75mm. But in total the stack measures 4.67mm. Here are some pictures:

 

post-268-0-73531800-1567463955.jpg

 

post-268-0-81212200-1567464011.jpg

 

post-268-0-12900700-1567464024.jpg

 

So, after all the talk on my other post everyone convinced me and I bought the 58mm S8612 (2mm) from UVIR Optics eBay store (he just shipped today, so, super excited to get it). Andy, no worries, I will get the "proper" glass soon :D

I am waiting to find an 58mm U-360 to get the full stack (Cadmium... blink blink ;D).

 

But, since I have this "weird" stack with me, why not test it right?

 

By the way, I would love for you to run your WB tests on my RAW files Andrea! Thanks a lot. Here are the links for them:

https://www.dropbox....C01390.ARW?dl=0

https://www.dropbox....C01391.ARW?dl=0

 

And debateman, you are right. My wife has some "fancy" sun scream that are reflective instead of blocking. I must get some strong chemical blocking ones to test my UV stuff.

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EDITOR'S NOTE: I entered this comment in the wrong topic! Apologies.

 

Andy, I was thinking some more about the BaaderU and U-360 photos. I was worried about reading too much into the tonalities because I did not supply the calibrated reflectivity standards in those photos. If those were present, then we could make better judgements about differences in tonalities. Granted, we *do* know that the BaaderU can have a bit of IR leak if forced. But I'm simply hoping that anyone making comparative photos for which tonalities are to be judged or for which some kind of IR leak is to be judged uses some kind of standard so that processing of the two photos is comparable. Ok, that's all. :grin:

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Andy, I was thinking some more about the BaaderU and U-360 photos. I was worried about reading too much into the tonalities because I did not supply the calibrated reflectivity standards in those photos. If those were present, then we could make better judgements about differences in tonalities. Granted, we *do* know that the BaaderU can have a bit of IR leak if forced. But I'm simply hoping that anyone making comparative photos for which tonalities are to be judged or for which some kind of IR leak is to be judged uses some kind of standard so that processing of the two photos is comparable. Ok, that's all. :grin:

[This is in the wrong thread, by the way!] You did use calibrated reflectivity standards, though? You did two tests, one on Spectralon and one an "off the cuff" WB off the sunflower disc. The former is presumably calibrated, so someone could get the same Spectralon target and do a formal test.

 

That stack works out to have the same exact OD 3 suppression, but it looks hotter than that.

 

post-87-0-51463900-1567214865.jpg

Cadmium, this may be why OD3 is just not good enough. We should put the line at OD3.5 or 4.

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Maybe because I am doing a "kind of long" exposure and high ISO shot the OD3 becomes "hotter"? That shot (as you can see on the RAW files) is ISO 1600, F1.8, 1/20.

 

Maybe the lens I am using (Sony FE 50mm f1.8) is blocking so much UV that I am forced to use such a high ISO that is making all leak pop? (no idea, just guessing here).

 

But I also tried with my Takumar 35mm f4 and it still look yellow :(

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Nah, exposure won’t change the hue really. And Sony FE 50mm was tested on here just recently and found to be moderately okay for UV transmission.
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The line It is an absolute. :-) It is where things will definitely show up. Many times stacks work rather well just under that line,

not that I recommend anything higher than OD4, but it can work, and it can depend on other factors in the stack.

However in this case, it is not about the line, what I am seeing in the photo is something that looks much stronger than OD3, so in this case I tend to mistrust the glass in the stack that is used.

In my opinion, UG11 2.25mm + BG40 1.75 would not look quite that hot.

It is true that OD3 will show some leak. That is why the line is there, it is a line, you stay back and under it.

Like you say, OD 3.5 can work, but I recommend OD 4 or under, and of course OD 5 is stainless steal.

 

Your photo is not over exposed, so it doesn't look like you are doing anything wrong.

1/20s is fast for UV, but given the IR content... I can't really judge.

However, it is not unusual to use 200 to 400 ISO, f/8+, for 1s, 2s... etc..

You are basically shooting with hand held UV settings, but again, it is hard for me to judge given the mixed content.

I usually use Aperture Priority, set the aperture and ISO for what I want, and let the camera decide what exposure time is best.

That seems to work 99% of the time for UV shots for me.

 

I am not really familiar with either of those lenses, but I know there are plenty or people here that would be.

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Maybe because I am doing a "kind of long" exposure and high ISO shot the OD3 becomes "hotter"? That shot (as you can see on the RAW files) is ISO 1600, F1.8, 1/20.

 

Maybe the lens I am using (Sony FE 50mm f1.8) is blocking so much UV that I am forced to use such a high ISO that is making all leak pop? (no idea, just guessing here).

 

But I also tried with my Takumar 35mm f4 and it still look yellow :(

 

I would bet that this lens is a 375nm or 380nm+ lens. So will work for UV. But not best with a UG11/U340 stack. Would be better with a UG1/U360 stack. I also bet that the BG40 is not and maybe The knock off QB21 or Qb23, I can't remember all the Chinese codes.

So I would say keep the UG or whatever that is part and use it with you S8612 when it arrives. That may be a good deep UV stack for you.

Also where the glass elements directly on top of each other? That is bad as can cause Newton rings. Should be a spacer.

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I would bet that this lens is a 375nm or 380nm+ lens. So will work for UV. But not best with a UG11/U340 stack. Would be better with a UG1/U360 stack. I also bet that the BG40 is not and maybe The knock off QB21 or Qb23, I can't remember all the Chinese codes.

So I would say keep the UG or whatever that is part and use it with you S8612 when it arrives. That may be a good deep UV stack for you.

Also where the glass elements directly on top of each other? That is bad as can cause Newton rings. Should be a spacer.

A spacer could be rather thin, like one or two layers of tape at some points close o the edge.

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So the conclusions so far seem to be:

 

- stack is probably not even OD3, and leaking like crazy

- therefore the IR blocking glass is probably counterfeit Chinese glass mislabeled as BG40

- the lens is known to be okay for UV (Timber tested it recently)

- we cant judge if the exposure is reasonable since we don’t really know what glasses we have. But that shouldn’t alter the colors anyway.

 

Remaining question: is the “UG11” also counterfeit relabeled Chinese glass?

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- I think it is higher than OD3, yes, but it doesn't really matter, because it doesn't work for UV.

- again, who knows.

-

- I judge the exposure by how it looks, over/under exposed, it looks about right to me.

 

You will never know what the glass is, and It doesn't matter, the filter is not UV only and can't be used for that. If it were me, I would try to send it back for a refund if it is still under the eBay (if it was eBay) return time limit.

It seems worthless to me. My opinion. It might be worth more if a real plot could be generated for it, but short of a spectrometer, forget it, and still what can it really be used for.

It isn't worth keeping. My opinion.

 

By the way, it looks glued to me.

I guess I could ask, who/where did you buy it from?

 

Regardless, the problem will be resolved next week.

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Well if glued he could still stack it with the good S8612 for UV and see what exposure time he gets.

 

Compare it to your ZWB glass alone when stacked with the good S8612. Maybe you will have a fun UV or UV+ filter.

 

If your not intended to publish science on spectral analysis. Then just have fun with the artsy color you will get.

 

If you setup a basement work area for UV work and get 365nm LED lights. Then this will work. There is no IR out of most good UV LEDs. This may also be good enough for a black BLB compact fluorescent black light if used as a light source.

 

Or place it on a weaker flash with low IR. You maybe able to tape it to a Canon 199A flash to get mostly UV.

 

I don't see it as useless for you. Just don't buy it again as you may need to find a use for it.

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Both filters are glued :(... I even thought about getting some kind of dissolvent to try to unglued them but I have no idea what can I use that will not destroy the chemicals on the glass.

 

The vendor on ebay was the guy called “image-laboratory” that people here in the forum told me to not trust, and clearly you were right :(

 

Anyway, if anyone has any idea how to unglue those so I can test them separate with the S8612 glass I am up for it. I don’t care if it doesn’t work and one of them gets destroyed, I am fully open for suggestions :)

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