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Hoya U-340 "gets the blue out"

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#1 Cadmium

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Posted 31 December 2018 - 02:19

This is for those who may wonder if U-340 really cuts 'blue/visual-violet' leakage from MTE and Convoy 365nm Nichia LED torches.
I am filtering the camera lens with Baader UV/IR-Cut filter (in the front) + three other 415nm to 420nm longpass filter versions added behind the UV/IR-Cut to cut a little more.
Here I show two rows, one where the MTE 303 Nichia 365nm UV LED is filtered with the Hoya U-340 2mm filter, and another row showing how much blue/visual-violet is emitted when the torch/LED is unfiltered.
So if you have your MTE 301/303 or Convoy S2+ 365nm Nichia filtered with Hoya U-340, then what you see is not blue/visual-violet emitted by the torch/LED, but only fluorescence from the target materials.

Also NOTE: There is no GG420 glass fluorescence when the GG420 filter is added behind the Baader UV/IR-Cut filter,
in fact all of the longpass filters perform exactly the same way when added behind the UV/IR-Cut filter.

All of these longpass filters cut blue/visual-violet at approximately the same point, 415nm to 420nm range, which cuts off a little more of the Baader UV/IR-Cut filter transmission.
The Baader UV/IR-Cut filter transmission unfortunately reaches down slightly below 400nm. The difference only shows slightly in these tests.

Longpass filters tested:
Schott GG420 2mm
Schott KV418
Wratten 2E gel filter

The main point I am trying to illustrate here is just that there is a definite difference between a filtered torch and a non filtered torch with the amount of blue/visual-violet emission.
Attached Image: Cut_Blue_Torch_Basic_1280.jpg

#2 Andy Perrin

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Posted 31 December 2018 - 03:27

All photos are with the same exposure, right?

#3 Cadmium

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Posted 31 December 2018 - 03:46

Nope. Kind of, but not all. It was using Aperture Priority center weighted.
All = ISO-800, F/8, all share the same white balance.
Top row (filtered torch): 1/100s, 4s, 4s, 4s, 4s.
Bottom row (unfiltered torch): 1/30s, 1s, 1s, 1s, 1s.

The unfiltered versions are much brighter in visual than the filtered versions. Very consistent other than that.

Edited by Cadmium, 31 December 2018 - 04:40.


#4 Andy Perrin

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Posted 31 December 2018 - 05:41

You should really standardize the exposure, at least between the two unfiltered camera lens pics. Like, the top one might be dimmer just because you exposed for 1/100th vs 1/30th? (I don't really believe that's the main reason, I'm just pointing out that you have to standardize the exposure here to make the pictures informative.)

Edited by Andy Perrin, 31 December 2018 - 05:42.


#5 Cadmium

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Posted 31 December 2018 - 05:49

I simplified the comparison for you Andy.
I removed the two left hand shots from the comparisons in my first post. Those two shots didn't have much relevance to the what is being illustrated, they only made things confusing.
Now we can concentrate on the basic point, which is how the U-340 filter on the 365nm torch cuts off the blue/violet visual light leak.

Furthermore, I fixed the exposure on the bottom row to match the top row.
Here is the updated version, which makes the whole point even clearer.

Attached Image: Cut_Blue_Torch_Basic_Same_Exposure_1280.jpg

Edited by Cadmium, 31 December 2018 - 07:07.


#6 dabateman

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Posted 31 December 2018 - 12:17

Cadmium,
Don't you have a convoy S2+ to test with?
I think that would be more relavent as it is pushed hard and may have more of a red spectrum shift than the MTE.

#7 dabateman

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Posted 31 December 2018 - 15:05

It may be good to indicate how long the Convoy has been on, if you test it. Since I remember UlfW had slight blue shift with the led after being on for 15 minutes.

Also may be good to indicate if fresh batteries, although I think you always said you use freshly charged one.

#8 Andy Perrin

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Posted 31 December 2018 - 15:59

Yes, this is much better. We can see that filtering the torch is essential and also that the Baader works fine without any extra protection.
-

dabateman- I doubt the Convoy would make much difference. I think Ulf's test just showed a few nm drift in the peak? With the filtering as Cadmium has shown, it's hard to see how that would make a significant change in the results.

Edited by Andy Perrin, 31 December 2018 - 17:51.


#9 Cadmium

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Posted 31 December 2018 - 18:57

Have to point out once again, this was a simple test to SHOW how the torch filter removes visual violet/blue.
This has to do with the torch filtration, nothing else.
This was and is simple.
It is not about filtering the camera lens, those filters are there in this test to block UV so we can see how much visual violet/blue light is present from the unfiltered and filtered torch.
Simple.
I am not monitoring the temperature, the color shift over time, all of that is for some other test, and someone else to perform which is not part of the point of this simple test.
If you want temperature/time tests, go here, been there, done that already, this topic is not about that, this topic has only one simple point.
http://www.ultraviol...5458#entry15458

However, I always use fresh batteries when I do torch tests, yes of course.
I don't have any Convoys at the moment, or I might probably have used one of those instead, but they are probably the same for this simple test.
If you want to test the convoy this way, do so. I rather doubt I will be doing this test again, the U-340 2mm filter should work the same, the 303 is the most powerful of the three torches I have.

The inspiration for this test was that many people say, "I still see 'blue' with a filtered torch". The point is here that the U-340 2mm filter blocks 'blue' light emitted from the torch,
and what people are seeing is fluorescence.
Simple.

#10 dabateman

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Posted 31 December 2018 - 19:33

Yes,
I think I was being overly picky.
Just looking back at the spectrum of the Convoy filtered using a Zwb1. Looks good and the U340 filters are better. I also have all this to test if I really care. But from a recent test the conviys seem better.

#11 JCDowdy

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Posted 01 January 2019 - 00:10

The UG11 does a pretty good job of attenuating >400nm, as my spectral analysis showed.

Given that U340 is considered generally equivalent to UG11 your demonstration confirms this.

I need to run a spectrum on the ZWB1 filtered Convoy S2+. Given the scant LED emission >650nm I think ZWB1 might trim the >400nm nicely as well.

#12 dabateman

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Posted 01 January 2019 - 06:54

View PostJCDowdy, on 01 January 2019 - 00:10, said:


I need to run a spectrum on the ZWB1 filtered Convoy S2+. Given the scant LED emission >650nm I think ZWB1 might trim the >400nm nicely as well.

Well it has been done before here:
http://www.ultraviol...h__1#entry19543


#13 JCDowdy

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Posted 01 January 2019 - 17:11

View Postdabateman, on 01 January 2019 - 06:54, said:

Well it has been done before...

Yes, I saw that. I meant to compare on my system.

#14 UlfW

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Posted 01 January 2019 - 18:02

View Postdabateman, on 01 January 2019 - 06:54, said:

Well it has been done before here:
http://www.ultraviol...h__1#entry19543
When looking back at those measurements now, I must confess that I think I made a mistake when guessing the ZWB-type. :(
It is more likely a ZWB2 filter I have measured and miss-labeled.
I do now think that I have never had a ZWB1.
Not sure what I originally ordered from China.

My conclusions still holds that due to the rather low VIS-emission from the Convoy S2 UV-lamp the resulting spectrum would be clean enough for most UVIVF-photography, even if it was filtered by ZWB2.
A ZWB1 or preferrably UG11 would be even better.

Will go back and edit my test referred to above.
Done.

Edited by UlfW, 01 January 2019 - 18:15.

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#15 JCDowdy

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Posted 02 January 2019 - 17:41

View PostUlfW, on 01 January 2019 - 18:02, said:

When looking back at those measurements now, I must confess that I think I made a mistake when guessing the ZWB-type. :(
It is more likely a ZWB2 filter I have measured and miss-labeled.
I do now think that I have never had a ZWB1.
Not sure what I originally ordered from China.

My conclusions still holds that due to the rather low VIS-emission from the Convoy S2 UV-lamp the resulting spectrum would be clean enough for most UVIVF-photography, even if it was filtered by ZWB2.
A ZWB1 or preferrably UG11 would be even better.

Will go back and edit my test referred to above.
Done.


Funny you say that because I have come to the same realization.

The filter I ordered from the Convoy webstore was not a ZWB1 but rather a 20.5mm diameter ZWB2 that fits the Convoy S2+ and so that is what I will test.

The ZWB1 in that diameter does not seem to be as common an item.

#16 Cadmium

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Posted 02 January 2019 - 22:07

I don't see much reason to use Schott UG11, U-340 works the same at 2mm thick, and it is half the price. The reason people are using 365nm peak U glass (UG1, U-360, ZWB2) is because they think it works better for the LED's 365nm UV peak,
but it doesn't cut below 400nm, and that is the point, to cut below 400nm. So I would not use those personally.

#17 UlfW

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Posted 03 January 2019 - 06:45

View PostCadmium, on 02 January 2019 - 22:07, said:

I don't see much reason to use Schott UG11, U-340 works the same at 2mm thick, and it is half the price. The reason people are using 365nm peak U glass (UG1, U-360, ZWB2) is because they think it works better for the LED's 365nm UV peak,
but it doesn't cut below 400nm, and that is the point, to cut below 400nm. So I would not use those personally.
You are right about UG11/U-340. I wrote UG11 above as I know the Schott names better.

I agree that the U-340, 2mm is the optimal filter for this if the need for attenuation at 400nm is high.
That is the safest choice, especially if a few things are fulfilled:

If the light from the LEDs contain enough light at 400nm to need more attenuation than 1/100 to avoid problems.
If the camera has UV-Cut filters, internal or external that pass enough light to the sensor at 400nm.
If the intensity of the fluorescence is very weak.

The LEDs used in the Convoy UV-torches has a rather weak VIS-emission that do not need very much attenuation.
Most modern cameras has internal UV-Cut filters cutting at 410-420nm.
If the used camera has that kind of cut-off, the need filtering of the light must not be fulfilled at 400nm, but at 410-420nm instead
UG1, U-360 and possibly ZWB2 has a much better attenuation at those wavelengths. UG1 has OD5 at 415nm!

There is a slight transmission-advantage (10%) for UG1 over UG11 at 370nm for equal thickness. At 365nm the transmission is almost identical.

If I should design an ideal filter for a Convoy UV-lamp to be used with a camera-system with an UV-Cut at 415-420nm I would go for an UG11 or U-340, 0.8-1mm .
Such filter would give 15-20% more light than the UG1 or U-360, 2mm with a slightly better VIS-cutoff.
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#18 Cadmium

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Posted 03 January 2019 - 09:33

And you can always use a Baader U, if you can stick it on the Convoy somehow... you can screw it on a MTE with a step up ring.

#19 UlfW

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Posted 03 January 2019 - 09:47

View PostCadmium, on 03 January 2019 - 09:33, said:

And you can always use a Baader U, if you can stick it on the Convoy somehow... you can screw it on a MTE with a step up ring.

A 2" Baader U could handle two or possibly three Convoys mounted closely together.
A 3D-printed gadget in a good shape mounted around the torches and with a suitable step-ring might work.
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#20 Cadmium

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Posted 03 January 2019 - 09:54

Gaffers tape... great stuff, doesn't leave a residue.

Edited by Cadmium, 03 January 2019 - 09:54.