Possible better UV filter stack?

[Cadmium]

Anyway, @Cadmium, how thin can you grind filters? I know you can reach 1 mm, but can you go below that?

 

I have made 0.75mm thick S8612 before, but I will not go below 1mm now, too hard to do without loss.

[Stefano]

I see now, sorry I missed that part. What is your formula for the conversion?

 

I wouldn't use LED's, they will often time penetrate beyond normal. Use some kind of normal light. I have seen 365nm LED's penetrate through 830nm...

Weird, but true. Testing things with LED's can often times give weird results.

 

You still have not convinced me to buy or stack a UV stack with a BG3 or B-410 filter.

I think a good UV stack is all you need.

Basically, you get a tiny bit more Uv at the same iR suppression.

 

Typical stack: Hoya U-340 (2 mm) + S8612 (1.75 mm). OD 4.9706 at 690 nm, 59.1 % peak at 350 nm, 3.75 mm total thickness.

Improved stack: Hoya U-340 (2 mm) + S8612 (1.25 mm) + Hoya B-410 (1.25 mm). OD 4.9788 at 720 nm, 62.8% peak at 350 nm, 4.5 mm total thickness.

 

The main question is: is it worth it to have 3.7% more UV transmission (even more if I make the U-340 thinner and the S8612 thicker), but at a price (literally), with 0.75 mm of increased total thickness?

[Cadmium]

With your above example, you are gaining 3.7% UV peak amplitude?

I don't think it is worth it. You would need to glue it to get any benefit. I have not done the math, but just stacking it will probably loose as much as it gains.

[Stefano]

Yes, you would probably need to glue it to get that little advantage. You can get to 65-66% with BG3 (to eliminate green leaks) and 1 mm thick Hoya U-340 (+ S8612 + probably B-410). I did an extreme example where I reached 69%.

[Cadmium]

I just now tried it again, just to make sure I didn't dream it...

I stacked these two stacks:

Stack #1 Schott UG11 1mm + Schott S8612 2m (compact fluorescent bulb visually black, no light)

Stack #2 Hoya U-340 1mm + Schott S8612 2mm (compact fluorescent bulb looks visually green)

 

Stack #2 Isolation leak tests:

Hoya U-340 1mm + Schott S8612 2mm + Schott OG530 2mm (compact fluorescent bulb looks visually green)

Hoya U-340 1mm + Schott S8612 2mm + Schott RG630 2mm (compact fluorescent bulb visually black, no light)

 

So there is some visual leak with the U-340 1mm in the 500nm range, and not with the the UG11 1mm.

I was not dreaming this.

[Stefano]

Did you invert stack #1 and stack #2? It seems that UG11 leaks.

[Cadmium]

Further test:

Stack #2 stacked with:

OG550 (compact fluorescent bulb looks visually green)

OG570 (almost entirely black, extremely hard to a faint bit of light, basically black)

OG590 (same, basically black)

RG610 (black)

 

Stack #2 stacked with:

Schott BG3 2mm (compact fluorescent bulb visually black, no light)

 

So it seems to be that the U-340 1mm has a visual leak between 500nm and 560nm, or if you want to include the very faint almost undetectable upper part, then 500nm to 610nm.

Sometimes dreams come true...

[Cadmium]

Did you invert stack #1 and stack #2? It seems that UG11 leaks.

 

My UG11 1mm is black when stacked with S8612 2mm? Using the compact fluorescent bulb I am using (white).

 

Invert? You mean put the S8612 behind and in front? That will not make any difference.

 

Keep in mind, some Chinese glass is marketed and sold as Schott and Hoya glass.

So, for example, UG11 (and or U-340) might not be real UG11 (or U-340)...

Or, UG11 might actually be U-340... etc....

 

I am working with the real stuff here...

[Cadmium]

Oops! I see what you mean about stack #1 and stack #2 being inverted, yes I inverted those in my post, I will go fix that. Sorry... thanks for pointing that out.

I fixed it. I do that stuff all the time, so keep an eye on me, and let me know. There is probably a lot of my posts out there that were never corrected...

[dabateman]

I just now tried it again, just to make sure I didn't dream it...

I stacked these two stacks:

Stack #1 Hoya UG11 1mm + Schott S8612 2m (compact fluorescent bulb visually black, no light)

Stack #2 Schott U-340 1mm + Schott S8612 2mm (compact fluorescent bulb looks visually green)

 

Stack #2 Isolation leak tests:

Schott U-340 1mm + Schott S8612 2mm + Schott OG530 2mm (compact fluorescent bulb looks visually green)

Schott U-340 1mm + Schott S8612 2mm + Schott RG630 2mm (compact fluorescent bulb visually black, no light)

 

So there is some visual leak with the U-340 1mm in the 500nm range, and not with the the UG11 1mm.

I was not dreaming this.

 

Looks like you still have it mixed.

So Hoya U340 has a leak when 1mm thick between 500nm and 600nm.

 

Schott Ug11 when 1mm thick does not have that leak.

 

Stefano, if the difference is not more than a third of a stop, you would not see the gain. So not worth it. From 60%, you would need it to be at least 80% (a 20% gain) or you will not notice the change. That is why those numbers are special.

 

If however you only had 10% transmission and you improved it by just an additional 10%. Then you would have a full stop difference (total 20%) and would be happy.

[Cadmium]

I still have it mixed? Oh, I see, I called Hoya Schott and Schott Hoya, forgot to edit that, will fix that, thanks.

Yep, I think it is all corrected now.

 

https://www.ultravioletphotography.com/content/index.php/topic/3709-possible-better-uv-filter-stack/page__view__findpost__p__33003

[Cadmium]

Stefano, 5 pages, 900 views...

Regardless of my advice, I still think your ideas are interesting.

[Stefano]

Stefano, 5 pages, 900 views...

Regardless of my advice, I still think your ideas are interesting.

They will remain here for people to try them.

[Cadmium]

Stefano, I will point out that the U-340 8mm stack transmits from 280nm to 380nm at 70% Ti with only one type of glass, and fairly sharply I would say.

https://www.ultravio...dpost__p__32745

 

Of course, if you want up to 400nm, which IS preferred and advised with/for the usual UV friendly lenses, then you would want to use some other filter, because the 8mm filter is not 380nm - 400nm friendly.

To all of those reading this, unless you have a very special UV specific lens, I don't recommend a filter that cuts off at 380nm. Get a filter that goes to 400nm or even 405nm if your lens is not all that good for UV.

[Stefano]

Stefano, I will point out that the U-340 8mm stack transmits from 280nm to 380nm at 70% Ti with only one type of glass, and fairly sharply I would say.

https://www.ultravio...dpost__p__32745

 

Of course, if you want up to 400nm, which IS preferred and advised with/for the usual UV friendly lenses, then you would want to use some other filter, because the 8mm filter is not 380nm - 400nm friendly.

To all of those reading this, unless you have a very special UV specific lens, I don't recommend a filter that cuts off at 380nm. Get a filter that goes to 400nm or even 405nm if your lens is not all that good for UV.

Sadly, this stack can not be improved with BG3, B-410, B25, etc. It leaks outside the range where this filters block. Anyway, I think that the Hoya U-340 is an amazing glass, very high, deep UV transmission and very strong IR-blocking capabilities.

 

Today I removed my ZWB1 filter from my UV stack, and the difference is quite evident. Much more sensitivity (probably at least 3-4 stops), and much richer colors. Still, shooting at ISO 1600 makes my images noisy, but I can't avoid this.

 

One of the images I took today. ZWB2 (2 mm) + chinese BG39 (2 mm). White balance in-camera with a paper tissue (I don't have PTFE).

f-stop: f/2.9, ISO 1600, 1/30 s exposure.

 

Since my camera can go up to 1/8 s in normal mode (up to 60 s in starry sky mode), I could have lowered the ISO. The yellow circle is a 30 mm x 3 mm thick ZWB1, the blue goggles are normal polycarbonate goggles.

[dabateman]

I think you are having amazing luck with that compact camera.

Enjoy taking images.

[Stefano]

Do you think that my lens goes deep into UV? Can I hope to get to 330-340 nm in the future?

[dabateman]

My guess would be no. It might be limited to just 360nm. But I have no idea.

If its common bk7 glass then your limit is 350nm. Because you have so few elements, is why I think you are getting great UV images.

For glass see:

https://www.edmundoptics.com/knowledge-center/application-notes/optics/optical-glass/

[Stefano]

I ordered a 340 nm LED a few days ago, it will take a while for it to arrive. I can put the link if you want. If my camera can see it (and it would be better to remove the chinese BG39 from my filter, maybe my 3 mm thick ZWB1 will be enough), it would mean that I can force it to at least 340-345 nm. I will never see the green 340 nm component of sunlight in normal photos (It should be green, right? Another thing to test), but with long exposures and 340 nm-only light I could get some images. We will see if this is possible.

[Andy Perrin]

Yeah, definitely you won’t see it in sunshine but you might force some through with an LED.

[Cadmium]

I warn against using LED's for testing filter transmission.

LED's can have extremely intense emission peaks that will basically drill through just about anything way out of range.

A much better way to test is with common light that you will be photographing. Not the sun directly, but the sky, or some other light bulb that is not an LED.

You can use a small bandpass filter against the sky or flash, just like you are doing and showing above.

Not that the 340nm LED won't be interesting to have and use, but I think it will result in some inaccurate and confusing conclusions.

[Andy Perrin]

I didn’t think he was trying to test the filter, just see if he could view anything at all at 340nm?

[Cadmium]

Sounds interesting, just keep this example in mind of a Convoy S2+ Nichia 365nm (no U-340 filter) shot with a full spectrum camera through 850nm IR longpass filter.

We might not expect to see the narrow band of the Nichia 365nm LED through an 850nm longpass filter.

There are many such examples using narrow band or other LED's that would not be expected to be seen through various filters that should block the emission of the LEDs in questions.

A lens is no different, and is even less of a blocking filter, but if what is being tested is the blocking or transmission of a lens, then I strongly advise against using an LED to test it with,

because you will get misleading results.

 

This is a 2 second exposure, f/8, ISO 200, but one might not expect this transmission given the narrow band of the Nichia LED.

[Stefano]

Sounds interesting, just keep this example in mind of a Convoy S2+ Nichia 365nm (no U-340 filter) shot with a full spectrum camera through 850nm IR longpass filter.

We might not expect to see the narrow band of the Nichia 365nm LED through an 850nm longpass filter.

There are many such examples using narrow band or other LED's that would not be expected to be seen through various filters that should block the emission of the LEDs in questions.

A lens is no different, and is even less of a blocking filter, but if what is being tested is the blocking or transmission of a lens, then I strongly advise against using an LED to test it with,

because you will get misleading results.

 

This is a 2 second exposure, f/8, ISO 200, but one might not expect this transmission given the narrow band of the Nichia LED.

I think that you are actually seeing 850 nm light (maybe 800 nm+) coming from the LED. Try putting another layer of RG850 and repeat the experiment. If it is UV, then the intensity of this leak should drop to almost zero, if it is IR it should stay almost the same. LEDs, especially short wavelength ones, fluoresce exited by the same light they produce. Nichia LEDs are very high quality LEDs, no doubt there, but I saw, for example, red light coming from blue LEDs with a diffraction grating. Your 2 mm U-340 filter that you sell for Convoys should block all IR beyond 800 nm, see if this does make a difference. Keep in mind that probably a RG850 (2 mm, or any normal thickness) will have at least OD 10 or more in UV, these filters block OOB light very well.

[dabateman]

Cadmium,

You may have a dead convoy on your hands. I have one like that. The other is good. But one transmit IR like that. I use it for the UV hot spot as its also weaker than the good one.