UV-Green object

[Cadmium]

Just a thought....1000nm leak is double the wave length of green, ie half of 1000nm = 500nm or green ?

 

I don't know what that means. Can you elaborate on that idea, how does it apply here?

[OlDoinyo]

For what it is worth, I have obtained the following test images.

 

Camera: Sony A900

Lens:Steinheil Cassar-S 50/2.8

Exposure for all frames: 3.2 seconds@f/2.8 and ISO 800

White balance: 2700G9

Additional image workup: none (display intent RGB)

Light Source: Audi Q7 right taillight (incandescent type)

Conditions: nighttime (some outdoor lighting but minimal ambient UV)

 

 

 

Remarks:

 

1) The Kolari filter had to be held manually in front of the lens in frame 3 due to the lack of a proper adaptor. it consists of a BG-type glass.

 

2) The image in frame 2 has no real chromaticity because the absorption bands of the reseau dyes do not overlap the transmission window of the 093. The tint is purely an artifact of the white balance.

 

3) BGR intent makes the lights appear chartreuse-yellow rather than the hues seen here.

[Cadmium]

Clark, Thanks.

It would be nice to see the Baader U shot white balanced as you would normally white balance a Baader U shot, and then use that same white balance for the Baader U + 093 stack.

It would be nice to see these shots in the daytime do that other UV can be seen/compared as with Hornblende's outdoor daytime images.

Are you using the same exposure time for each of those?

I want to try this also.

Your test here kind of leads me tto think that the 'green' is coming from the 900nm Baader U leak range, somehow, but it should be white/gray, not green, I would think.

[OlDoinyo]

It would be nice to see the Baader U shot white balanced as you would normally white balance a Baader U shot, and then use that same white balance for the Baader U + 093 stack.

 

That is what you see above. The WB setting used is typical for a landscape shot with this gear.

Are you using the same exposure time for each of those?

 

Yes, as far as I know.

 

but it should be white/gray, not green, I would think.

 

It would be that if you ran the white balance with reference to a hard black-IR filter. But that is not what was done here.

 

To illuminate something with UV so that it will appear greenish, shine the broadband source of your choice through a 340BP10 onto a neutral target of your choice, and photograph that. Or use a 320-340-nm laser.

[Cadmium]

OK, I will go try it.

[Hornblende]

I finaly found a UV green "object" wich is not caused by infrared leak of white balance shenanigans.

The object is in fact a synthetic ruby from my gemstone collection, here with a synthetic emerald and a synthetic sapphire for comparison.

 

Visible light - Canon 6D full spectrum - El Nikkor 80mm f/5.6 - Lifepixel UV/IR cut filter - WB on PTFE - Sunlight



 

Ultraviolet - Canon 6D full spectrum - El Nikkor 80mm f/5.6 - Baader U - WB on PTFE - Sunlight



 

Here is a transmission spectrum of a synthetic ruby.

http://image.noelshack.com/fichiers/2017/14/1491668201-flamefusrubyint.jpg

[Andy Perrin]

I tried expanding the UV portion of that spectrum using the highly-useful, but defunk, program GraphClick, which lets you extract data from graphs by clicking on the curve.

[Andrea B.]

What illumination was used to make the photograph of the synthetic gemstones?

That can affect the false colour.

[Hornblende]

Zut I completely forgot to mention the illumination.. It was bright sunlight.

[Andrea B.]

Thanks.

 

I'm also a little concerned about the cyan colour cast?

[Hornblende]

I alway have a cyan cast in my UV pictures when something is overexposed, like the sky.

[Andy Perrin]

What are you white balancing against if the PTFE is cyan?

[Hornblende]

On the PTFE. But since the PTFE is not quite uniforme, some of it can take a cyan cast.

The place where I do the WB appears white though, but it is not very noticeable.

[Andrea B.]

In some converters, that cyan cast can be removed.

[colinbm]

It is funny that the shadows have a white halo ?

Col

[enricosavazzi]

Just a thought....1000nm leak is double the wave length of green, ie half of 1000nm = 500nm or green ?

Are you thinking about even harmonics? The phenomenon of interference as exploited in interference filters is of course related to harmonics. See e.g. https://www.semrock.com/Data/Sites/1/semrockpdfs/constructionofopticalfilters.pdf .

 

I am unable to say whether it might explain the present case, though. Multiple coatings of different thickness behave differently than a stack of layers all with the same thickness.

[colinbm]

Thanks Enrico, I am not a scientist of this, but I was thinking along the lines of harmonics or octaves.

Col