Comments please about Image-Laboratory camera conversion ad on Ebay

[Andrea B.]

To clarify:

 

A dual-bandpass UV+IR filter such as the U330/340/360 or UG1/5/11 will transmit both UV and IR.

 

However, using such a dual UV+IR filter on a converted digicam will only record an IR photograph in sunlight

because there is about 3% UV and about 53% IR in sunlight (at sea level on a good sunny summer day).

 

So, I repeat, we cannot make a legitimately dual UV+IR photograph.

 

Do you agree or disagree with this observation?

 

Please let me hear your comments!

I'm not going to "argue" with you if you disagree or agree or whatever. :D

I am simply attempting to make a clear, correct observation and would like to ensure proper wording.

[nfoto]

One might in principle get a UV + IR record if the filter had 20 times more attenuation of IR than UV ....

 

However, that would not solve the problem of the camera recording UV and IR largely to the very same colour channel.

[Andrea B.]

Suppose you had a filter and lens which transmitted UV and IR at 100%. Then the 3%::53% UV/IR in sunlight hits the sensor in a 1::17or 1::18 ratio. Does anyone have any doubt that we are recording an IR photo?

 

ADDED: That comment is incorrect because I should have written "hits the lens".

After the 1::17 UV/IR light hits the lens, then the dual pass filter changes the ratio further by having a higher UV transmission than IR transmission.

Even so, it is mostly IR light eventually hitting the sensor. I think we are recording IR photos with these filters.

[Andy Perrin]

Why not make a UV record, then an IR record separately, and then combine the images in the appropriate channels? You would have to align the images very carefully but I think it could be done for a static scene?

[colinbm]

My observation, is that a dual band UV + IR filter just makes a greyer image (less contrast) in landscape, as the properties of a UV image & the properties of an IR image are mostly opposites.

Col

[Cadmium]

"Dual Band" filters:

There are many filters that can be placed in that category, but it is not a label that Schott uses for any of their classifications (for example).

The term can refer to any filter that has separate bands of transmission, often with one foot in the UV range, and another in the IR range, but these can be shifted.

There are a lot of 'dual band' filters not mentioned here (above).

There is a big difference between an IR shot with an IR filter and a Dual Band shot with a UG1 or U-360 filter (as an example).

The IR only shot will be black and white (if using some IR longpass filter above about 780nm/800nm).

The Schott UG1 or Hoya U-360 will have white foliage and blue/lavender skies (when appropriately white balanced on the foliage), and this is the result of the 'dual' mix.

 

My favorite dual band look is the one I have mentioned, there are others also, like the BG3 look that some like, and many others.

These kinds of 'dual band' filters are often used on full spectrum cameras as alternatives to any number of IR longpass filters, either 'false color' IR or full black and white IR, as a way of adding color, and having blue skies with out needing to swap channels (in the case of 'false color' IR, 590nm for example). Taking separate UV only and IR only shots and combining them in post would be a whole other thing of course.

UG5 and U-330 are of course very special dual band examples, because it they have a higher transmission in UV and an attenuated transmission in visible range. This works well for UV+Blue+Green+ mixes, but only when stacked with IR suppression to remove the IR band from that dual transmission.

 

...and I know that all of you already know everything I have just said, I am only stating it for the sake of the 'balcony'.

 

Some other dual band filters compared, any of which can be stacked with various BG type glass to block Red/IR and restrict the transmission into UV+... mixes (or UV-only in the case of the U-360).

[Andrea B.]

Bjørn: However, that would not solve the problem of the camera recording UV and IR largely to the very same colour channel.

 

In the linked post below I analyze the channels for a Visible, Infrared and Ultraviolet backyard landscape shot.

In both the IR and UV shot, all three channels are recorded in.

I also show some samples from the larger photos which illustrate the the opposite light/dark tones in IR and UV for the sky and for shrub leaves.

UV: sky bright, leaves dark

IR: sky dark, leaves bright

 

http://www.ultraviol...ing-comparison/

[Andrea B.]

Andy: Why not make a UV record, then an IR record separately, and then combine the images in the appropriate channels? You would have to align the images very carefully but I think it could be done for a static scene?

 

Yes, this would be multispectral channel stacking. We have many examples posted here & there.

I'm not sure what the "appropriate" channels would be however.

[Andy Perrin]

"Appropriate" being different channels, Andrea, so that they aren't on top of each other, as you alluded to. Which order, I have no idea. If you wanted bluish skies, putting the UV in the blue channel sounds like a good plan, though?

[Andrea B.]

Andy, here is one example of a channel stack: http://www.ultravioletphotography.com/content/index.php/topic/699-cucurbita-cf-pepo-ornamental-gourd/

We have others, but not everyone is applying the tags when they post an example.

 

UV in the blue channel does not always produce blue skies. It depends on what is in the R and in the G channels. :D