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Taking one shot through the same lens in visible and ultraviolet light

Asher Kelman

OPF Owner/Editor-in-Chief
Klaus,

I would love to see the UV blue bg removed so the UV-reflected flower will stand out as that is a winner in vibrancy!

Asher
 

Dr Klaus Schmitt

Well-known member
Klaus,

I would love to see the UV ble beg removed so the UV reflected flower will stand out as that is a winner in vibrancy!

Asher
That flower was in located in front of a crackled glass which gets that vibrant color when shot in UV unfortunately as it transmits UV only to about 380nm...
 

Dr Klaus Schmitt

Well-known member
Klaus,

I would love to see the UV ble beg removed so the UCLA reflected flower will stand out as that is a winner in vibrancy!

Asher
Tat flower was in located in front of a crackled glass which gets that vibrant color when shot in UV unfortunately as it transmits UV only to about 38...
 
I'm about to get started shooting UV and IR and would love to know how you get both UV and VIS image in one shot. Or is that involving a secret filter / technique somehow? I saw the other post where you showed images saying you worked for BBC where they asked for colorful UV images instead of more or less monochrome images.

Regards,
Lars
 

Asher Kelman

OPF Owner/Editor-in-Chief
Lars,

You arrived at the right place. Welcome to OPF.

And yes, Klaus will likely have all the answers you need!

Asher
 

Dr Klaus Schmitt

Well-known member
I'm about to get started shooting UV and IR and would love to know how you get both UV and VIS image in one shot. Or is that involving a secret filter / technique somehow? I saw the other post where you showed images saying you worked for BBC where they asked for colorful UV images instead of more or less monochrome images.

Regards,
Lars
Welcome here Lars!

Well, I used a beamsplitter for that, but I keep a few things for me, what's on my site http://uvir.eu is made public ;-)
 

Asher Kelman

OPF Owner/Editor-in-Chief
I'm about to get started shooting UV and IR and would love to know how you get both UV and VIS image in one shot. Or is that involving a secret filter / technique somehow? I saw the other post where you showed images saying you worked for BBC where they asked for colorful UV images instead of more or less monochrome images.

Regards,
Lars
Did you get a sufficient reply?

Asher
 
Welcome here Lars!
Well, I used a beamsplitter for that, but I keep a few things for me, what's on my site http://uvir.eu is made public ;-)
OK. Thanks for your reply.

If I understand it correctly, a beam splitter is composed of two prisms put together where some of the light goes right through and some is going out in a 90-degree angle. In other words, you must have two identical cameras and lenses to do the job - and most likely also different filters on each lens in order to capture visual and UV separately.

Anyway, this is obviously much more advanced than I want to go into. Interesting to know, but beyond me!
You are obviously doing some photographic wizardry (y):D
 
Klaus is an academic! Likely as not he expects you are knowledgeable.

However explain what you understand and where you are lost!

He is smart enough to steer you in the right direction if you make it clear where you are in your decision making.

Asher
I think I understand the general idea (if what I concluded above is correct) of the basic setup, but I won't follow that (advanced) path. I will stick to one camera and lens at a time.
 
It is quite some effort admittedy, changing filters at otherwise unchanged setup is much easier actually, and as long as the subject / object does not move, very good results can be obtained easily!
Thanks again. Slightly off-topic, but still related:
Since I haven't received my converted camera yet, I am wondering where the UV and IR wavelengths "land" in the Bayer filter of the sensor. At first, I assumed that UV will be found in the blue channel and IR in the red channel, but then I thought that UV is beyond violet and when talking RGB signal, violet is a mix of blue and red...

In short, I am wondering if - for instance - it would be possible to "filter out" infrared by lowering or even turning off the red channel in Photoshop. Or will I then also turn off / lower parts of the UV signal then?

Will UV light "land" in all RGB channels? Or just blue and red?
 

Asher Kelman

OPF Owner/Editor-in-Chief
Lars,

Read this.

When one is using an RGB color space, the various light energies are mapped as best as possible into a scheme of a matrix of additive colors perceived as all the colors shown in a limited 2D triangle.

Light energies outside of the wavelengths of visible light will be either cut off and not represented or remapped to the triangle edges.

You are asking is infrared or UV that is not cut off by filters would be mapped at all and contribute to the adjacent red or blue of the RGB perceptual triangle.

I think that those leaked wavelengths beyond the visible spectrum would be either lost or else remapped to the edges and falsely enrich “colors” there.

I think the right question is “what color space does one set the camera to in a camera where cut off filters have been removed?”

Asher
 

Jerome Marot

Well-known member
At first, I assumed that UV will be found in the blue channel and IR in the red channel, but then I thought that UV is beyond violet and when talking RGB signal, violet is a mix of blue and red...
The idea that a camera will extends its sensitivity to nearby bands by still working in the same manner is generally wrong (it is only true for Foveon sensors, because of the way they work).

The filter matrix on your camera is not designed for IR and, usually, the pigments used are transparent to IR. That means that IR is present in all channels.

As to UV, I seem to recall that it usually is only present in the blue channel. Here again, because of the pigments used. But silicium is not very sensitive to UV anyway, so you will only be able to detect its signal when using, in front of your lens, a filter which cuts everything but UV.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Jérôme,

Good point about IR contaminating all 3 channels! One can easily forget that!

Do you know what “color space” one sets the camera to when one removes the factory IR UV filter and replaces it with optical glass?

Would you choose ProphotoRGB or it makes no difference, when photographing nebulae?

Asher
 

Dr Klaus Schmitt

Well-known member
Thanks again. Slightly off-topic, but still related:
Since I haven't received my converted camera yet, I am wondering where the UV and IR wavelengths "land" in the Bayer filter of the sensor. At first, I assumed that UV will be found in the blue channel and IR in the red channel, but then I thought that UV is beyond violet and when talking RGB signal, violet is a mix of blue and red...

In short, I am wondering if - for instance - it would be possible to "filter out" infrared by lowering or even turning off the red channel in Photoshop. Or will I then also turn off / lower parts of the UV signal then?

Will UV light "land" in all RGB channels? Or just blue and red?
Depends on Sensor: Nikon sensors react to UV mostly on the RED channel after blue whih ends around 380nm! And forget that idea to separate channels, any bit of IR any sensor is SO MUCH MOR sensitive too that it ruins any UV image!

Here have a look:

 

Dr Klaus Schmitt

Well-known member
Oh and btw. even if you COULD split the channels for UV and IR, how would you make sure the plane of sharpness for UV and iR would be the same??
Only very few and very expensive lenses allow that..
 
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