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ZWB1 (1.5mm): Testing for UV Transmission, Visible Leak & IR Leak

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#1 Andrea B.

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Posted 18 August 2017 - 04:41

Contents: .



General Tests of the ZWB1 (1.5mm)

Background: Many Chinese companies are now manufacturing inexpensive optical UV + IR dual bandpass filters with a ZWB designation. It has flooded the Ebay market. The low price is an attraction to the amateur UV photographer or for the researcher on a strict budget.

However, charts from Optima (linked below) indicate visible leakage of some ZBW glass of certain thicknesses. And, of course, any UV + IR dual bandpass filter requires a good IR-blocker to prevent the Infrared from contaminating a UV photograph. We have also had some informal reports of lack of manufacturing quality control resulting in waves, pits or striations in the glass. So the pros and cons of ZWB glass must be considered.

There is also a very, very strong concern here at UltravioletPhotography.com that some unscrupulous Ebay sellers are selling ZWB glass mis-labeled with the Schott or Hoya brand name.

ZWB Transmission Chart References: .
My ZWB1 Filter: With a recent order Uviroptics (Ebay) kindly sent me a ZWB1 (1.5mm) dual bandpass filter to use in various tests. I wanted to test for visible light leak, IR leak and UV-pass worthiness when stacked with a good IR-blocker.

Camera: D610 full spectrum conversion

Lens: Nikon 105/4.5 UV-Nikkor

Exposure: f/8 @ ISO-400 with various exposure times as needed.

Other Settings:
  • Nikon in-camera Active D-Lighting was turned OFF.
  • Nikon in-camera Picture Control was set to Neutral with 0 settings for Contrast and Saturation
    with a +4 setting for Sharpness.
    This helps while shooting to reach the best exposure without oversaturating any channel and also helps to see detail and focus.
  • Nikon in-camera Preset White Balance was a near-UniWB.
    This also helps to determine oversaturation of any single channel to avoid unrecoverable highlight blowouts.
  • Exposure time was increased to push exposure to the right but not against the wall in any channel. Such exposures are the best to work with in UV, imho.
Conversion:
Photo Ninja was used to convert raw NEFs to TIFs.
Adobe Photoshop Elements 11 was used to label photos.
Photo Mechanic was used to resize and convert TIFs to JPGs for display here.

Unless otherwise noted, the editing steps are as follows:
  • D610 visible color profile made from a CC Passport under the Baader UViR-Cut filter was applied to all visible and false color files.
  • White balance was determined for all filters or filter stacks using a Spectralon rectangle.
  • White and black points were adjusted with the Exposure and Black sliders, respectively.
  • A shadow lift of 30-50 points was applied to certain photos to lift the shadows a bit for presentation of detail. Strictly speaking, the shadow lift is not a necessary edit and in certain cases not a desireable edit, but it does improve the visual qualities of a dark UV photo without seriously affecting the presentation of a subject's UV-signature.
.
Remark on Abbreviated Notation: Filtername-N
The number N denotes the thickness of the filter in millimeters.


Visible Reference Photo
f/8 for 1/2000" @ ISO-400 in Sunlight with Baader UVIR-Cut Filter
Attached Image: visible_sun_20170817wf_5230pnShad50Ill1002.jpg


Ultraviolet Reference Photo #1
f/8 for 1/2" @ ISO-400 in Sunlight with BaaderU UV-Pass Filter
The dichroic BaaderU has a UG11 substrate and thus is not directly comparable to the ZWB1 which appears to have a U-340 type substrate. My purpose here was simply to illustrate a commonly used UV-pass filter.
Attached Image: uvBaaderU_sun_20170817wf_5244pnShad50Ill1001.jpg


Ultraviolet Reference Photo #2
f/8 for 1.6" @ ISO-400 in Sunlight with U-360 (2mm) + S8612 (2mm) UV-Pass Filter Stack
The U-360 filter stack is not directly comparable to the ZWB1 which appears to have a U-340 type substrate. My purpose here was simply to illustrate a commonly used UV-pass filter stack.
Attached Image: uvU360-2+s8612-2_sun_20170817wf_5278pnShad50Ill1001.jpg


ZWB1 (1.5mm) Solo in Dual Bandpass Mode
f/8 for 1/30" @ ISO-400 in Sunlight with No IR-Blocker
Like any other dual bandpass glass, the ZWB1 (1.5mm) filter cannot be used alone for reflected UV photography. More so than most such glass, this ZWB1 (1.5mm) by itself quite clearly produces an Infrared photograph. There may also be some contribution from its small Visible light leakage.
Attached Image: uvZbw1-1.5mmSolo_sun_20170817wf_5252pn01.jpg


ZWB1 (1.5mm) + S8612 (2.0mm) as a UV-Pass Filter Stack
f/8 for 1.6" @ ISO-400 in Sunlight with S8612 IR-Blocker
The IR-blocker considerably cuts the transmission of the ZWB1, but now we can see the UV floral signatures. So we have hope that the ZWB1 might be useable as a UV-pass filter if the IR leak is blocked and the exposures are short enough to keep visible light leak from contaminating the photo.
Attached Image: uvZbw1-1.5+s8612-2_sun_20170817wf_5267pnShad50Ill1001.jpg
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 Andrea B.

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Posted 18 August 2017 - 04:52

Testing for Visible Leak in the ZWB1 (1.5mm)


Baader UV/IR-Cut Filter over ZWB1 (1.5mm) Solo as Dual Bandpass Mode
f/8 for 1/6" @ ISO-400 in Sunlight with No IR-Blocker
Blocking both UV and IR over the solo ZWB1-1.5 filter induces it to behave basically as a Visible filter. I'm not sure how much IR leakage there is at the end of the Baader UV/IR-Cut filter, but there may be a small amount. Remember that the false color here has been white balanced. The raw composite of this frame follows.
Attached Image: buvirCut+uvZbw1-15solo_1-6sec_sun_20170817wf_5311pnShad50Ill1002.jpg

This is the raw composite (before application of white balance) of the preceding frame. The ZBW1-1.5 Visible leakage seems to be mostly recorded in the red and green channels. There is some in the blue channel too.
Attached Image: buvirCut+uvZbw1-15solo_1-6sec_sun_20170817wf_5311rawComp01.jpg



Baader UV/IR-Cut Filter over ZWB1 (1.5mm) + S8612 (2.0mm) as UV-Pass Filter Stack
SHORT: f/8 for 3" @ ISO-400 in Sunlight with IR-Blocker
Conversion only, no other adjustments.
When UV+IR is blocked over a proper ZWB1+S8612 UV-pass filter stack, the stack already has Visible light leak in a 3" exposure. This Visible leakage becomes stronger with increased exposure length. See the next 15" exposure.
Attached Image: buvirCut+uvZbw1-15+s8612-2_3sec_sun_20170817wf_5321.jpg


Baader UV/IR-Cut Filter over ZWB1 (1.5mm) + S8612 (2.0mm) as UV-Pass Filter Stack
LONG: f/8 for 15" @ ISO-400 in Sunlight with IR-Blocker
Conversion only, no other adjustments.
When UV+IR is blocked over a proper ZWB1+S8612 UV-pass filter stack, the stack exhibits even more Visible light leak in the 15" exposure. And some D610 upper LCD light leak is beginning to appear. That is my fault for not covering the upper LCD on my camera. Sorry 'bout that!
Please refer back to the ZWB1 + S8612 photo in the first post above as a reminder that this ZWB1-1.5 stacked with a good IR-blocker seems to be actually useable as a UV-Pass Filter for an exposure time under 2". Futher experiments can probably determine whether the Visible leak plays a role in longer ZWB1-1.5 stacked exposures. Also, a thicker ZWB1 might be somewhat more robust against Visible light leaks.
Attached Image: buvirCut+uvZbw1-15+s8612-2_15sec_sun_20170817wf_5325.jpg



Reference: Baader UV/IR-Cut Filter over BaaderU UV-Pass Filter
Composite: f/8 for 15", 20", 25", 30" @ ISO-400 in Sunlight
No adjustments were applied to these frames before constructing the composite in PSE 11.
The BaaderU is very robust against visible light leakage. The visible areas which begin to show up between 25-30" are light leak from the D610's upper LCD which should be covered during long exposures. (The LCD light leak may not be easily visible depending on your monitor and the photo resizing needed to display here. But it is there in the larger raw version.)
If you did give this file a very, very extreme exposure or illumination push in the converter, then you could force out some evidence of visible leakage in the longer exposures, but that's not how we work on our UV photos. Converter forcing should not be used to prove anything.
Attached Image: buvirCut+BaaderU_composite.jpg


Reference: Baader UV/IR-Cut Filter over U360-2 + S8612-2 as UV-Pass Filter Stack
Composite: f/8 for 15", 20", 25" @ ISO-400 in Sunlight
No adjustments were applied to these frames before constructing the composite in PSE 11.
This 4mm U-360 stack is very robust against visible light leakage. The visible areas which just begin to show up at about 25" are light leak from the D610's upper LCD which should be covered during long exposures. I did not make a 30" exposure. (The LCD light leak may not be easily visible depending on your monitor and the photo resizing needed to display here. But it is there in the larger raw version.)
If you did give these files a very, very extreme exposure or illumination push in the converter, then you could force out some evidence of visible leakage in the longer exposures, but that's not how we work on our UV photos. Converter forcing should not be used to prove anything.
Attached Image: buvirCut+U360Stack_composite.jpg
Andrea G. Blum
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#3 Andrea B.

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Posted 18 August 2017 - 06:23

Testing for Infrared Leak in the ZWB1 (1.5mm) - Part 1

The ZWB1 was stacked with a 2mm thick Schott RG9 IR-bandpass filter to test for IR leakage. The RG9 transmits aproximately 3.5% at 700 nm quickly reaching 50% at 720 nm. Transmission then runs at about 95% between 780-800nm before tapering back down to 50% by 1025 nm.


Schott RG9 (2.0mm) over ZWB1 (1.5mm) Solo in Dual Bandpass Mode
f/8 for 1/4" @ ISO-400
Like any other dual bandpass glass used in UV-pass filtration, the ZWB1 (1.5mm) filter is going produce an IR photo when stacked with an IR-bandpass filter. There should be no surprises here, OK? The hint is in the name of the glass type. This test is just for the record!
Attached Image: zbw1-15+rg9-2_1-4sec_sun_20170817wf_5380pnShad50Ill1002.jpg

Here is the raw composite of the preceding frame.
Attached Image: zbw1-15+rg9-2_1-4sec_sun_20170817wf_5380rawComp02.jpg
Andrea G. Blum
Often found hanging out with flowers & bees.

#4 Andrea B.

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Posted 19 August 2017 - 18:54

Testing for Infrared Leak in the ZWB1 (1.5mm) - Part 2

When shooting the preceding examples my last IR leakage test was going to use a stack consisting of the Schott RG9-2 over a proper ZWB1+S8612 UV-pass filter stack.
Then, I ran out of sunlight!
So, my dear members, be patient. I'll get there soon as I can.

Got it done! Of course, the scene is going to look a bit different.



Schott RG9 (2.0mm) over ZWB1 (1.5mm) + S8612 (2.0mm) as UV-Pass Filter Stack
f/8 for 30" @ ISO-400
No adjustments were applied to this file.
It should be no surprise that a properly IR-blocked ZWB1-1.5 dual bandpass filter does not leak IR. Here is a 30" result. A companion UV photo is shown next to indicate the nice sunny shooting conditions.
If you did give this file a very, very extreme exposure or illumination push in the converter, then you could force out some evidence of leakage (especially around my D610's stupid upper LCD), but that's not how we work on our UV photos. Converter forcing should not be used to prove anything.
Attached Image: zbw1-15+s8612-2+rg9-2_30sec_sun_20170819wf_542501.jpg


ZWB1 (1.5mm) + S8612 (2.0mm) as UV-Pass Filter Stack
f/8 for 1.3" @ ISO-400 in Sunlight with S8612 IR-Blocker
Reflected UV photograph.
Attached Image: uvZbw1-15+s8612-2_1.3sec_sun_20170819wf_5407pnShad50Ill1001.jpg
Andrea G. Blum
Often found hanging out with flowers & bees.

#5 Andrea B.

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Posted 19 August 2017 - 19:19

Please notify me of any errors, typos, misleading statements or other garbles!
I will cheerily make necessary corrections. "-)

Note: My UVA/UVB sunlight was measuring between 3.5-4.0 mW/cm2 as recorded by my Solartech UV meter during the tests. The altitude is only a couple of hundred feet here.

CONCLUSIONS
  • The camera and lens play a role in the results achieved with any UV-pass filter.
  • Results in this Test apply only to one particular type and thickness of ZWB glass: ZWB1 (1.5mm)
  • Remember that our reports of the lower quality of ZWB glass are informal. Do be on the lookout for striations, waves, surface pits or mars in ZWB glass or any of its companion optical glasses. Bubbles are always ok in filter glass. Return bad ZWB glass for a refund if you get any.
  • In good afternoon summer sunlight an UV/IR-blocked ZWB1/1.5 + S8612/2.0 UV-pass filter stack shows Visible leakage in a 3" long f/8 exposure @ ISO-400. With longer exposure times, that visible leakage increased. However, the ZWB1/1.5 + S8612/2.0 UV-pass filter stack itself produced a good reflected UV photograph in a 2" long f/8 exposure @ ISO-400 which seemed comparable to those frames made with the BaaderU dichroic filter and a U-360/2.0+S8612/2.0 filter stack. Further tests would be needed to determine whether the Visible light leakage would contaminate a UV photograph to a significant degree under different illumination or when the ZWB1 filter is used in another thickness.The possibility of Visible light contamination is certainly there for any longer exposures when using an IR-blocked ZWB1/1.5 stack.
  • Due to its visible light leakage, a ZBW1/1.5 filter should NOT be used over a UV-Led torch to cut visible light leakage in the violet or blue region for UV induced Visible fluorescence photography (UVIVF).
  • It should be no surprise that a properly IR-blocked ZWB1/1.5 + S8612/2.0 dual bandpass filter does not leak IR. I ran a 30" exposure at f/8, ISO-400 with an S8612/2.0 over the ZWB1-1.5 and had no evidence of IR leakage.
  • General IR-blocking reminder: Stacking any dual bandpass glass such as the ZWB1/1.5 with a proper IR-blocker such as Schott S8612 reduces UV transmission, usually reduces bandwidth and may shift transmission peak. The main consideration for IR-blocking is the choice of a reasonable thickness in the IR-blocking glass. Thinner IR-blocking requires shorter exposures so as not to induce any IR-leakage. But don't overkill the IR-blocking either or you will lose too much UV transmission. An IR-blocker between 1.5 - 2.0mm in thickness is usually sufficient. (Comments welcome on this!)
  • Schott BG39 is not recommended as an IR-blocker over dual bandpass glass because it just cuts too much of the UV bandwidth and transmission. BG39 is a good IR-blocker though.

Andrea G. Blum
Often found hanging out with flowers & bees.

#6 Andrea B.

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Posted 19 August 2017 - 21:15

Cadmium:
ZWB1 1.5mm can only really be compared directly with UG11 and U-340 (not really with U-360). Also, 1.5mm thick should really only be directly compared with the same thickness of another type of glass. But, theoretically, ZWB1 is suppose to be the equivalent of UG11 and U-340, so if you were to compare UG11 1mm, and U-340 1mm with ZWB1 1.5mm, then it would stand to 'reason' that the ZWB1 1.5mm stack 'should' have better visual and IR blocking, so that would be a logical and relatively valid test i think. Comparing the ZWB1 to 2mm thick U glass may not be quite a fair presentation, especially when using U-360 which is another type of U glass.

Andrea:
My original comparison was simply to provide a typical reflected UV photograph to test that the ZWB1-1.5 also can make a typical reflected UV photograph. This indeed was the case.
But I certainly do take your point!! The primary problem for my setting up an additional test is that I do not have any other 1.5mm thick U glass. For UG11 I have only .75mm and for U-340 I have only 1mm and 4mm. I am rather awash in UV-pass filters and U glass currently, but never in the correct thicknesses!!! :rolleyes:
Andrea G. Blum
Often found hanging out with flowers & bees.