Latest Attempt with the Omega 293BP10

[Andrea B.]

You are going to laugh at this result, for sure!!! :grin:

 

The CO105 has a long grooved nose with lots of distance between the first element and the end of the tube. The 293bp10 filter is about 1.25" wide and can be placed into the tube where it can rest in the grooves well enough to make a photo if you are really really careful not to bump anything.

 

However, let's just say that eventually I lost patience trying to focus. Tried and tried and tried. But with a lens which doesn't internally focus and having a filter resting precariously in its grooves, it was hopeless. So I gave up on that and simply tried to capture some light, any light.

Here's the result.

 

D610 + Coastal Optics 105/4.5 + Omega 293BP10 + Sunlight

f/4.5 for 2.5" @ ISO-6400

That exposure certainly indicates that there was not much light available. Lens was wide open and ISO was cranked.

 

As shot.

That's a Rudbeckia on the left. How it got from center to left I don't know. Did I mention it was windy?

 

As shot.

Flower now behind some stems.

 

 

Raw composite.

Raw Digger does not pump up the outputs of its raw composites (and rightfully so). However, for this raw comp I increased the saturation in Photo Ninja to emphasize the fact that green and yellow was recorded. I also fluffed around with b/w endpoints just to try to bring make the photo look more "normal".

 

Does this raw green and yellow indicate recording around 300 nm? Or does it indicate perhaps something undesireable like a green leak? The Omega filter is dichroic with one very shiny side, so I would be surprised if it had much leak. But I have not tested for leakage, so won't make any claims here.

 

There is a clear UV-signature on the Rudbeckia. Well, "clear" in the sense of "obvious" rather than "in focus".

 

 

Raw Digger auto white balance.

I've set the RD preference to render white balance in the raw colors. This looks pretty much the same as the preceding raw composite (except that I did not increase the saturation in this one).

[Andy Perrin]

Interesting. You definitely captured light! Can you get a ring for that filter and do it properly with focusing?

[Andrea B.]

What are we "supposed" to be getting around 300-310 nm? green? yellow?

I don't know what the shoulders of this filter are. I would think fairly wide unless it is hard coated. So I might have been imaging around 320??

[JMC]

With mine it's green down there. I would guess you're seeing a combined effect of much more light around 360 nm along with strong reflectance and more camera sensitivity around 360, giving the yellow bits.

[Andy Perrin]

Jonathan, how could she be getting 360nm with a 293nm filter, unless you mean it’s leaking?

 

If it’s a leak, maybe stack with a 330WB80?

[dabateman]

I would stack it with a 330WB80 improved if you have one. Yes its green down there for my Olympus camera.

My 302bp10 and 313bp25 are a little leaky even rated over OD5 blocking. At this wavelength the quantum efficiency will be less than 1%. So you need to add photons or you will see anything.

The only filter which has amazed me is my new UVc one that Jonathan, Andy and I got. It really has amazing IR blocking. I tested with Halogen lamp in the Resolve thread Jonathan started.

[JMC]

Andy, as an example. Say the sunlight has 10x more UV around 360nm, and the camera is 10x more sensitive, and we know some flowers are very reflective in that 360nm ish region (also say 10x more reflection for sake of argument). Multiple these all up and the sensitivity to the 360nm light present becomes 1000x that of the 293nm light. How much is a leak? If you have OD3 in that region but the overall sensitivity is 1000x the wavelength of interest the blocking fails.

 

Ive chosen 10x to make the example simpler. There is virtually no 293nm light in sunlight, so 10x difference may well be conservative there.

[Andy Perrin]

Jonathan, I understand, I just wondered if you were saying there WAS a leak in your opinion. I've never seen much of a leak in my Omega filters, but I've never tried doing 293nm either.

[Andrea B.]

Multiple these all up and the sensitivity to the 360nm light present becomes 1000x that of the 293nm light.

 

Knowing the gear is vastly more "sensitive" at 360 nm is one thing. Blocking that area and recording well below it is quite another.

[Andy Perrin]

Andrea, I bet your flash might help? Don’t some of those put out UVB? You could stack the filter and use a flash, I’m thinking.

[Andrea B.]

I will get back to this little filter eventually. And try the flash. And test for leaks.

 

I want to make sure that everyone understands that I'm making *no* claims about what I recorded!! This was just an experiment.

 

This filter definitely has a raw signature different from any filter peaking around 340 or 350 nm. But we cannot say at this point that that signature indicates recording around 300 nm without further testing.

 

I also want to look to see if I got any transmittance chart when I bought it. Omegabob always includes one. So I must have it somewhere.

[dabateman]

Andrea, I bet your flash might help? Don’t some of those put out UVB? You could stack the filter and use a flash, I’m thinking.

 

Not down there, unless Andrea modified a Godox AD200 with quartz bulb. I have now been playing with this. Its still quite black below UVA.

Andrea you could get a 302nm bulb, that would be your best bet. They are cheap, just get a G8T5e. The G part is germicidal, the 8 part means 8W, the T5 is the base, will fit any F8T5 fixture. The most important part is the last e. That means it has phosphor coating on the bulb and is not clear, but will output 302nm light. A G15T8e would also work and F15T8 under counter fixtures are still easily available. You just have a longer dangerous light to deal with. Or you could buy a old or new Gel dock box with a filter. But those are just under $1000, a bit expensive for just a test.

[Cadmium]

When you say as shot and raw composite, these have some white balance from the camera.

Like if I turn on my camera, and shoot a raw file, it has the white balance from whatever the camera was set to when I turned it on.

Please explain.

Why would we laugh at the pics?

 

The only thing I can say is that for such a low nm, the pics you are showing look rather green, more like 330-340nm range.

IF your sensor is able to capture the 293nm, then it would stand to reason that is might look more turquoise/cerulean, and no yellow, especially given the 10nm wide bandwidth.

From my tests, the color tends in that direction when uninhibited by the lens or filter.

[Andrea B.]

The “as shot” has a white balance from the camera (Which was specially created. It’s not quite UniWB but close.)

 

The Raw Composite from Raw Digger has *no* white balance. It is demosaiced raw data with a standard conversion curve but no use of WB multipliers and thus represents the raw color record (after demosaicing). I don’t use white balanced colors to judge reach. I use raw colors. There is too much variation in how white balance is measured/created across gear platforms and software apps. And some cameras which can measure WB through dark UV or IR or other filters don’t measure it accurately.

Anyway, the green/yellow in that raw comp may not be the same green/yellow you get in sparticle work.

[JMC]

Jonathan, I understand, I just wondered if you were saying there WAS a leak in your opinion. I've never seen much of a leak in my Omega filters, but I've never tried doing 293nm either.

Andy, to me it looks like light outside the 293nm region is being captured, hence the yellow in the image. As for it being a leak, I don't like the term 'leak' in this situation, it's just a characteristics of the whole system. I have little doubt, if Andrea were to use an approx 300nm light source with that filter, then the whole image would be green. HOWEVER that is assuming the Nikon is behaving the same way as my Canon in that region.

[Andy Perrin]

As for it being a leak, I don't like the term 'leak' in this situation, it's just a characteristics of the whole system.

Sure, but that's true of every other case too. When people saw IR in Baader U pics, we called it a leak, and same for 330WB80. If the proportions of light are skewed enough, any filter will leak. I guess you can use any word you want, it just seems like we've always used "leak" before, with the understanding that it isn't a property of the filter really.

 

In this case, I hadn't had much of a problem with any other Omega filters (including the 330WB80) so I wanted to confirm that that "out of band light punching through" was what you were arguing was the issue. It does seem like there is just too little 293nm in sunshine to image, even with a normally well-blocked filter, though -- I accept the conclusion.

[JMC]

Andy, I doubt you'll see an effect like this with the other filters. The 'leak' or whatever everyone wants to call it, for me at least, is due to it trying to be used in an area with so little light and so little camera sensitivity.

 

I hadn't realised I was arguing anything, I was just commenting on Andreas green/yellow image.

[Andrea B.]

I don't think Andy meant "arguing" in the sense of arguing but rather in the sense of "debating".

 

And we do use "leak" colloquially a lot on the forum.

 

But anyway, there is no doubt something going on with this 293BP10 filter that further tests will show. Of course the sun has been unavailable since I made the Green Blur Test above. So I haven't been able to get out and try any stacking to test for passage of undesired wavelengths. (There! I didn't use "leak". :lol: Just having some word play. Kindly ignore.)

[Andy Perrin]

I don't think Andy meant "arguing" in the sense of arguing but rather in the sense of "debating".

Exactly. (I am now wondering if we're having some sort of cross-cultural language barrier thing? In my area, "I'm arguing for X" or "you're arguing X and I'm arguing Y" is frequently used without any implication beyond neutral debate, and that was the sense intended.)

[JMC]

No, it's my fault. Words are not my strong point, and I often misinterpret things.

[dabateman]

No, Jonathan's country (UK) saw that our country (USA) had issues so decided to go one better and dissolve itself.

No argument here. the USA uses funny terms. Like "war on drunk driving". Really? We now shoot you if you're drunk?

 

I didn't think either of you were arguing. Some terms have specific meaning to people. Leak can mean many things.

[dabateman]

But to resolve the issue. Andrea, carefully screw your Baader venus filter on the lens. Infront of your 293bp10 filter. If the image turns black then you know what you are seeing is not UVA (320nm to 400nm).

Then remove the Baader and test with LP 400nm filter, any equivalent you have. If image then goes black your not seeing Vis or IR.

Thus you will know if you are seeing UVB. Anything less than 320nm in daylight.

[Cadmium]

Arguing, or whatever you want to call it, may be an essential part of science, and it seems like about half of you are PhD's...

It is to be expected that there will be disagreement, it challenges our thinking, we learn from that, and we come to a better conclusion as a group.

[Andrea B.]

OK, so here is a post about what I learned today.

 

Summary: There is not much 293 nm light available outdoors.

:lol: :lol: :devil: :devil:

 

Now that I have dispensed with the irony of concluding what we already knew,

I'll show you the 293BP10 UV-pass photo attempts for today.

 

The subject was a Color Checker Passport against a slab of Spectralon (5" x 5") which was set up in the grass. The sunlight was behind me. The UVA/B Solarmeter was reading between 4.0-4.5 mW/cm² which has always been quite enough for a typical afternoon reflected UV photo. (Ddded: in the higher UV range, that is, around, say 350 - 360 nm.)

 

I used the CO 105/4.5 because its long grooved nose permits fitting in a small diameter 1.25" filter like the 293bp10. I velcroed around the little filter just to try to make sure nothing was leaking around the grooves. I wrapped the camera and lens with a towel to take care of any little light leaks such as the bit around the top LCD of the D610.

 

As shot

Do you see an image? Me neither. Remember how I was saying above that it was extremely difficult to get a good focus with this filter? Today I could see absolutely nothing in the LCD. I eventually had to focus without the filter, tape the long-nosed front tube into focus-place and then re-place the filter inside it. (Also, sweat rolling into eyes. Pesky gnats. Etc.)

 

 

Raw Composite

Again, no image. Just sort of a noisy pink.

 

Photo Ninja Conversion

First thing I did was click around till I found the Spectralon. Then I averaged the white balance over the Spectralon. In such an extremely low amount of light, the Spectralon had to valiantly struggle to produce a reflection. Thankfully it managed that and I found it and was able to bring out what image there was hidden in this mess. I've only managed again to capture light -- but barely any detail.

[Andrea B.]

So that was very frustrating. Then it occured to me that there might be more available low-UV light if the lens faced the sky where there would be lots of scattering, reflection and/or whatnot. So I aimed at the sky between some trees. Lost focus however. The tape would not hold well in the heat.

 

Side Note: I think the CO 105/4.5 is the wrong lens for this experiment. I want to try again with either the UAT or the UV-Nikkor.

 

As shot

This time I won't have to hunt for the image.

 

Raw Composite

Still mostly pink.

 

Photo Ninja Conversion

I saved the Spectralon White Balance made for the first set (in the preceding post) and applied it to this photo. Then I boosted the saturation a bit because the orangey sky was a kind of surprise. Please don't take this white balance as being accurate. It was borrowed (reasonably, I think), but sometimes a change in direction can slightly alter where WB properly lies. There is also lots of color noise. I didn't want to apply lots of processing so I left the noise.