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UltravioletPhotography

Need help with filter problem UV/IR


StephanN

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In the last few months I've made quite a few UV-photos with my EOS 6D, converted by MaxMax to b/w with an internal XNite 330 filter. Maxmax recommends an additional XNite BP1 filter to get rid of the 10% IR-leak. So, yesterday I shot a series of photos of my cemetery hill with plenty of different filters, IR, a few Chinese ZWB, bug-vision, bee-vision, etc. just to get a feeling for them.

 

So far, so good. However, when I did the comparison shots without any filter (i.w. only the 330), and with the BP1, I could not detect any significant difference. Judging from the photos in visible and infrared, there was a tremendous amount of infrared present, which should have killed the UV-look in the photo without the BP1.

 

I am at a loss what went wrong. Either the filter transmission chart from Maxmax is not correct, or I did something really stupid. Any hints welcome :unsure:

 

Here are the photos:

 

First visible (half of the frame is in the sun):

post-176-0-19012700-1600715244.jpg

 

Next, Infrared 700 nm (quite a lot of it):

post-176-0-50763600-1600715251.jpg

 

330 + BP1 (supposed to be ultraviolett):

post-176-0-99862600-1600715259.jpg

 

330 (supposed to be some ultraviolett and huge amounts of infrared):

post-176-0-51687000-1600715265.jpg

 

For completeness sake, BP1 only (taken with my full-spectrum 6D):

post-176-0-40075100-1600715271.jpg

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What lens was used?

 

I used the Soligor 21mm f/3.8. Actually, for yesterday's IR photos I used a different lens, but I repeated the test today at a different place, and used the Soligor for all filters. Same effect. IR-photo with 1/100s, and UV one with 1s, and with and without BP1 no difference.

 

[Edit: added today's photos]

post-176-0-55486400-1600718126.jpg

post-176-0-31200300-1600718132.jpg

post-176-0-16675800-1600718137.jpg

post-176-0-23220900-1600718144.jpg

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Is your UV filter already stacked? Can you see it from the side, removing it from the frame? If not, are both sides black? That's so strange.

 

The UV filter is a two-part filter, one is mounted inside the camera, the other one is a screw-on filter. But I just realised one mistake: I didn't take the UV photo with the Maxmax-camera, but with the full-spectrum one.

 

So, just did a quick IR-test (700nm) in my flat, and the two cameras give photos with about the same exposure with the following settings:

 

Full spectrum (only 700nm-filter): 1/40s, ISO 1600

MaxMax (XN330 + 700nm-filter): 4s, ISO 25600

 

So, the amount of IR-light passing the XNite 330 is about 11 stops less than for the full-spectrum camera, if I am not mistaken. Apparently the IR-leak plays no role when taking photos of landscape.

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Is your UV filter already stacked? Can you see it from the side, removing it from the frame? If not, are both sides black? That's so strange.

 

Sorry, misread your question. The (almost) UV-filter is mounted inside the camera, the screw-on is the one which blocks the IR-leak.

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Can it be that they left the original hot mirror in place and mounted the X-Nite 330 on top?

 

But wouldn't the hot-mirror also block the UV? Or are there two hot-mirrors, one for UV and one for IR?

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But wouldn't the hot-mirror also block the UV? Or are there two hot-mirrors, one for UV and one for IR?

Dichroic ones should block both (UV/IR cut), while BG glass filters only block IR. If your camera had such a filter, and they left it there and put their X-Nite 330 on top, they basically made a stack. They may have done it on purpose to make your camera UV-only. That's just my hypothesis, I may be wrong.
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Dichroic ones should block both (UV/IR cut), while BG glass filters only block IR. If your camera had such a filter, and they left it there and put their X-Nite 330 on top, they basically made a stack. They may have done it on purpose to make your camera UV-only. That's just my hypothesis, I may be wrong.

 

I see, thanks. I've sent an EMail to Dan from Maxmax, let's see what he can tell me. If they made a stack, all the better, then I don't have to bother with the extra filter and could use all sorts of lenses for UV-photos.

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Confused, when you type "300" did you mean 330?

 

Also, the thing about the BP-1 is that it is dichroic, so it will have the "rings" look, and also the inconsistent color from center to sides especially when used for wide angles.

 

I don't understand. So you aren't shooting all these photos above with the same camera?

One camera has U-330 installed, then another camera for the visual (stock perhaps, or what filter for that)?

A little confusing...

 

However, your basic question is, "why doesn't the BP-1 change the look of the photo shot with the internal U-330 camera", correct?

 

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Confused, when you type "300" did you mean 330?

 

Yes, right, thanks, typo (went back and fixed it). I mean the XNite330, do they even make a 300?

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Their graph for U-330 should work about the same as U-340/UG11. So there should be ample IR (about 10%), enough to make the shoot look QUITE different.

Seems to me the only way you can get that look is if the camera has more than just the U-330 in it, because the IR appears to be already blocked.

 

Also I might add, and this has nothing to do with your question, but the BP-1 doesn't really suppress IR that well, it apparently leaks IR above an adequate OD level.

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However, your basic question is, "why doesn't the BP-1 change the look of the photo shot with the internal U-330 camera", correct?

 

Correct. The filter specification from MaxMax for the XNite-330 has an IR-leak with a transmittance of about 0.1 (see https://www.maxmax.com/filters for details), and I am not seeing it. If I look very closely I might think that I see the rings a bit (when used with the BP1), but that might be imagination.

 

However, I've sent the inquiry to Maxmax, and I hope they have some explanation for me.

 

Apologies for the confusion, sometimes I really ought to formulate my problems in word and read them through a couple of hours later before posting them :rolleyes:

 

For the record: I have got the Maxmax 6D (Bayer-filter removed and internal XNite330), and also got some time before that a full-spectrum conversion on my old 6D. So, when I walk around somewhere, I can carry one camera for UV and one for IR, or one for UV and one for VIS, etc., enabling me to do quick comparison-shots in two different frequency-regions.

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I can see a slight amount more IR in your U-330 shot alone, but no where near what it should be. You should have green/brown/white foliage (depending on WB) and violet/blue skies... not black and white at all.

Is the camera sensor also converted to monochrome too?

Seems strange.

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You know what? Just a guess, but he sometimes likes to put BG38 in the monochrome conversions to tone down the IR so it doesn't blur up the image.

So I am just wondering if he put both BG38 and U-330 in there. Never heard of that, but... Bob has a MaxMax monochrome conversion with BG38 in it, but he puts his UV-pass filter on the front (Baader U),

but remove his Baader U and the camera becomes a 320nm to 720+nm monochrome camera, The "+" meaning that it has 'some' minor amount of IR, but well look at the BG38 graph. Max calls BG38 = CC1, by the way.

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You should test leak-sensitive subjects, like dandelions and polycarbonate goggles (better if you have those Steve adviced me to get, so that if you see through them you can be 100% sure it is IR). Foliage seems a little brighter in the X-Nite330 only shot to me too, but without colors leaks are more difficult to detect. It can also help that your sensor is significantly more sensitive to UV, being de-Bayered, but trees should look different. Can you still find flowers around?
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You should test leak-sensitive subjects, like dandelions and polycarbonate goggles (better if you have those Steve adviced me to get, so that if you see through them you can be 100% sure it is IR). Foliage seems a little brighter in the X-Nite330 only shot to me too, but without colors leaks are more difficult to detect. It can also help that your sensor is significantly more sensitive to UV, being de-Bayered, but trees should look different. Can you still find flowers around?

 

I've got the 3M-googles marked "3M 1 F 2C-1.2", and will try to find some flowers. There are still some around but not sure if they're the kind which give conclusive results.

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Steve, that would explain it, and seems convincing. If the BG38 glass is on top, you should see it, even on top of the black X-Nite330 filter. If it is hidden below, than you can't see it.
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I think it has something in it other than just their U-330 glass.

See this stack, U-340 2.2mm + BG38 2.2mm, it touches the OD3 line, that is where things start to become visible. Adding the 'leaky' BP-1 to that stack would reduce the IR slightly more, depending, but it seems to add up and make sense to me.

Anyway, it is a wild guess, but I can't think of anything else that would explain the absence of IR in the U-330 shot alone.

 

By the way, I used 2.2mm thick glass in that graph because I seem to remember that MaxMax uses 2.2mm to 2.5mm thick glass for the filters I got from them years ago.

I just measured my CC1 a minute ago, and it is actually 2.5mm thick, so my graph is slightly off, but that is assuming they use 2.5mm thick glass now.

Regardless, it is just a wild guess anyway, so the graph is a close enough example of what I am talking about, and... who knows.

 

Hmm, another thought is that 'IF' there is both U-330 and BG38 in the camera, then it is very possible that the BG38 is not as thick as 2mm even.

I would ask them what all filters are in there, AND what thicknesses the filter(s) are. Filter thickness is essential when determining any kind of transmission.

 

 

post-87-0-89200600-1600725158.jpg

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