[Filter Test] U-340 x 1.0 mm and ZWB1 x 1.5 mm: Visible Light Leaks

[Andrea B.]

A few years ago I ran an unfair test on the ZWB1 for visible light leaks. In the test I compared the ZWB1 to the wrong UV-pass filters. I have since retired that topic.

 

The equivalent filters to ZWB1 are Hoya U-340 and Schott UG11. These should be used in any comparative tests of the ZWB1.

 

Anyway, today I was cleaning filters and decided to look at visible light leaks in my Hoya U-340 x 1.0 mm and ZWB1 x 1.5 mm by making some long exposures. Each dual bandpass filter was stacked with a Baader UV/IR-Cut filter to cut UV and with an S8612 x 2.0 mm to cut IR. I focused on a brightly colored bunch of Coreopsis flowers and ran 5", 10", 15" and 30" exposures. They are attached below.

 

For both filters, a lot of visible light was captured. That is not unexpected given the thinness of the two filters. When this kind of glass is used as a substrate for either a dichroic or an absorptive UV-pass filter, the manufacturer would ensure that this visible light leak would be blocked along with all the passed IR. However, we cannot so easily block visible light leaks in our Do-It-Yourself UV-pass filter stacks.

 

We've had some discussion on the forum about the validity of such forcing tests. I can support the view that we should only check for visible light leaks in our UV-pass filtration by using normal exposure times. But I wanted to make a forcing test anyway to ensure I captured a lot of the visible leak so that I could look at in Raw Digger.

 

 

Nikon D610-full-spectrum + UV-Nikkor 105/4.5 + Sunlight (lots of it)

All photos f/8 @ ISO-400.

All photos as shot, no edits.

Resized and labeled in Photo Mechanic.

 

The Nikon was set to a custom visible white balance.

 

It was windy!!

 

U-340 x 1.0 mm + S8612 x 2.0 mm + Baader UV/IR-Cut

5 seconds

10 seconds

15 seconds

 

 

ZWB1 x 1.5 mm + S8612 x 2.0 mm + Baader UV/IR-Cut

5 seconds

10 seconds

15 seconds

 

---

Here are 30" second exposures for making Raw Composites.

 

U-340 stack as above for 30"

It's like we almost have an actual visible photo here from all this leaked visible light. But the colors are a bit "off". The coreopsis is yellow with a dark red center. So there isn't enough yellow here.

 

 

U-340 stack for 30" Raw Composite,

No white balance, no color profiles.

But I suppose I thought there was going to be more green leak?

 

 

ZWB1 stack as above for 30"

Same remarks about color....not enough yellow.

 

 

ZWB1 stack for 30" Raw Composite

Again, not as green as expected.

 

 

Conclusion:

I don't have anything from this that we didn't already know except that I had thought the visible light which would get through would have more green. Mostly I just wanted to see what happened when I tried these long exposure stacks.

[Andy Perrin]

Well, they definitely do not look like IR or UV, so the blocking filters are working as intended I think. The color seems red-orange in the raw composites? Given our previous thread, I'm surprised you didn't go with BG38 2mm + Baader UV/IR cut.

[dabateman]

Andy is that a joke?

The BG38 lets in too much IR, and the red would be much stronger through the U340/Zwb1.

But if you just want a visible image than yes Only using BG38 and UV/IR cut filter should result in slightly faster exposure times. Might even be able to capture that slug without motion blur.

 

So looks like you do have a decent copy of a Zwb1 filter. As it gets thin, it lets in more on the Red IR side.

 

[Cadmium]

I would not use ZWB1 or anything Chinese. For this I would use Hoya U-340.

Of course, thickness is important. Keep all thicknesses the same.

Generally 2mm is best used for U glass, but if you use thinner then that requires thicker BG glass.

[Andy Perrin]

Andy is that a joke?

The BG38 lets in too much IR, and the red would be much stronger through the U340/Zwb1.

But if you just want a visible image than yes Only using BG38 and UV/IR cut filter should result in slightly faster exposure times. Might even be able to capture that slug without motion blur.

 

So looks like you do have a decent copy of a Zwb1 filter. As it gets thin, it lets in more on the Red IR side.

No, it's not a joke, why is it "too much" IR? If we know that stack produces correct colors with a white balance + profiling and you want to know what color a visible light leak is, shouldn't you use the stack that produces correct colors to deduce the leak color? Although it seems like it will just get even more red. I mean, the Baader is already suppressing the IR a lot, the BG filter is just to correct the colors in visible.

[Andrea B.]

I can easily repeat this using the BG38.

I just grabbed the S8612 by rote as being the best IR-blocker.

[Andy Perrin]

Only if you want to. I think we can predict it will get more red. I was just trying to explain my reasoning to David.

[Andrea B.]

By the way, the U340 and ZWB1 are leaking around 550 nm as per a comment earlier by Cadmium and from transmission data.

That would be green, yeah.

[ulf]

I don't think Cadmium has tested ZWB1, only U-340.

I made transmission measurements of my ZWB1, 1mm that show a good OD at 550nm in another thread that show an OD > 4:

https://www.ultravio...dpost__p__48438

 

The U-340 perform better than ZWB1 in UV and UV/IR-peak ratio.

The decreased OD in the VIS range for U-340 might be a telltale of Hoyas way to improve performance in other parts of the spectrum.

It can also be that there are yet again a big spread of performance for different Chinese filter glass batches with the same name.

[diant]

The decreased OD in the VIS range for U-340 might be a telltale of Hoyas way to improve performance in other parts of the spectrum.

I think so too, because Hoya cook his U340 without Potassium and put in it not too many Nickel.

All phosphate glasses like U340 (I mean UG-11, UVG1/2/5 etc.) are stained by Ni and Co. Co has a perfidious small green secondary window (after UV-blue and IR primaries) which must be suppressed by Ni firstly and Potassium secondly. (Role of K is not obviously, but it prolongs main abs. band of Ni from violet-blue to the red end of spectrum and so covers the secondary Co green window).

Hoya don't use a Potassium at all and put in mix not too many Nickel as compared to Schott. Why? I may only guess - they obtain a height of U340's main UV window a bit higher than Schott and have not a far-IR leakage. May be here is the clue?