Another Red Seaweed

[Adrian]

Another red seaweed with UV induced fluorescence, this time a filamentous species possibly Griffithsia sp. Unfortunately the specimen is decaying rapidly, so I will have to wait until I can get to the seaside again to do more!

 

Technical specs. Nikon D800 (not converted) with 105mm micro-Nikkor lens. Fluorescence shot: approx. 20 seconds @ f/16, with Convoy S2+ UV LED torch. No filters used

 

I have also tried the specimen using an IR luminescence technique, and will post this separately.

[Oliver Krohn]

Using a UV bandpass filter on the flashlight may increase the quality of the UV induced image, because there is still a significant amount of blueish, visible light. A cheap filter like this should be sufficient: https://de.aliexpress.com/store/product/ZWB2-filter-for-365nm-light/330416_32649282235.html

 

A UV cut filter on the lens can further increase image quality.

[Cadmium]

My opinion of Chinese filter glass is quite low. First of all, these so called ZWB.. (and the like) are not all made by the same people, they do the same with other brands also,

if you find Schott glass of Hoya glass sold from China, you can be assured that is not what is advertised, and these ZWB... filter melts can be made by any number of different places,

there is no consistency between them, they are not quality controlled by the same people.

Furthermore, I find the graphs they show to be only rough estimates, and dubious, and they don't portray the inefficient results I get from their glass compared to Schott or Hoya glass.

Their graphs are linear, not diabatic, which gives me no way to calculate actual OD suppression when doing stacks.

 

That being said...

My main point I wanted to make here is that although some might think that a 360nm filter peak would be best to use for a 365nm UV LED, it is not.

The reason we use 340nm peak U-340, and UG11 filters for 365nm UV LED torch filters is because those cut clean below 400nm. Thus cutting off ANY possible blue leak.

Generally, 2mm thick 360nm glass has a tiny bit of blue leaking, so it is best to use U-340 or UG11 (instead of U-360 or UG1).

So if you use China glass, then you may want to use ZWB1 (the 340nm peak version), if you trust their graphs, which I don't.

I have tested ZWB1 enough to know that it doesn't transmit UV as efficiently as Hoya and Schott.

Remember, ZWB... can be purchased for pennies and resold as so called Schott and Hoya... you will not know the difference unless you compare them side by side.

Anyway, the point is, use 2mm thick 340nm peak glass, not 360nm peak glass for 365nm torch filtering.

[Andy Perrin]

My own tests have tended to back up what Cadmium said above. I have some of that dubious "Schott" glass (it is an IR blocker clone) given to me with my eBay camera conversion, and it definitely is not real Schott and does a cruddy job.

[Oliver Krohn]

Of course, this all may be right. But those chinese filters are extremely cheap and there are sizes available which fit into a flashlight without any modification. So far I personally haven't made bad experience with things I bought in China (mostly electronic parts). But of course, you can't expect the highest quality. I did not yet bought chinese filters, but I thought they are worth a try, since they are available for almost no money. For use on a torch, even a cheap filter should reduce visible light significantly. But if the transmission level for UV is low, well, that would turn such a filter into total rubbish. :( Thanks for the advice.

[Andrea B.]

For use on a torch, even a cheap filter should reduce visible light significantly.

 

No, not really. The few of us who have run tests know this is not true. The blasted ZBW filters don't transmit UV as well as other filters, and they have visible light leakage.

 

And I DEFINITELY would not use one of these ZBW filters in work for a scientific paper because sooner or later someone is going to question the validity of the results.

 

Here is a summary of links so far: Those ZBW filters again.....

[Oliver Krohn]

For scientific use the price of a high quality filters should not matter much. But for my private equipment it does. That's why I am looking for cheap alternatives. Did not realize that ZWB filters are so bad, since I didn't buy one yet. But if I look at the transmission curve of ZWB1, it should be absolutely okay for non-scientific use with a 365 nm torch in a darkened room, since it reduces visible light significantly, at least better than not using any filter at all. Of course, you can't expect a ten-fold cheaper filter to be as good as the expensive ones, that's absolutely clear.

[Andy Perrin]

But the transmission curve is not reliable.

[ulf]

I would not trust any of the transmission curves for ZWB glass published om the net.

As there are no reliable source for these materials there is no way of telling the quality of the glass.

The "official" transmission list found in Andreas link above in post #6, is questionable too in my opinion.

 

It is correct that you'll get some improvement even with a bad filter.

If you sacrifice a lot of UV-light by placing two filters on top of each other, the attenuation will be even better.

This is not optimal and can cost you double exposure time, but it might be better than nothing.

 

I bought some ZWB1 just to measure how bad they were.

By accident the were not that bad at all.

 

I will soon post about how I measured my filter and the resulting transmission graphs.

 

However those results are only valid for the filters I got!!

There is a high risk that other cheap ZWB1 are not as good!

[Andrea B.]

But if I look at the transmission curve of ZWB1, it should be absolutely okay for non-scientific use with a 365 nm torch in a darkened room, since it reduces visible light significantly, at least better than not using any filter at all.

 

A good 365nm UV-Led torch should not be emitting great quantities of visible light.

 

UV-induced visible fluorescence photos made in the dark (with all ambient light blocked) using a high-quality-bin Nichia-chipped UV-Led torch do not show much difference whether UV-pass filtered or not --- even though we do think there is a small amount of violet light being emitted by such chips.

I do filter my UV-Led torches with a BaaderU or with a U-340+S8612 stack (inexpensive and good).

 

Oliver, in this UV game we all enjoy, there are unfortunately not always good results from the inexpensive filters or UV-led torches (or other gear). We have always tried to help people find the least expensive way to enjoy UV photography. Currently the least expensive good filtration for a UV-led torch is some Schott or Hoya dual-bandpass glass stacked with a blue-green IR blocker. I will send you via our PM system some recommendations for this and for other inexpensive, good UV-pass filters. (Note: See also our Stickies in the Refrence section.)

[Cadmium]

With a Nichia LED you can use no filter if you want, but you may get more reflected blue, blue that is not from fluorescence.

You will not need to stack U-340 and S8612 on a Nichia 365nm torch, there is no green, red, or IR from the Nichia 365nm LED. All you need is the U-340 to cut off the led light below 400nm, and assure there is no possible blue leak.

U-340 is not as cheap as 'Chinese' ZWB1, but U-340 is half the price of UG11, and works to cut blue below 400nm at 2mm thick. That is all you need if you want to cut any possible reflected blue from mixing with actual visual fluorescence.

 

If you use a flash, then that is a whole other situation, then you will need to use a stack, typically U-340 2mm + S86123 2mm, because the flash will have very strong visual and IR content.

It will have a strong UV content also, assuming you are using the right kind of flash that emits UV which often includes modification (removing clear plastic from front).