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UltravioletPhotography

Kolari Vision UV redness


Nemo Andrea

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Nemo Andrea

I decided to go take some pictures of flowers with the Kolari vision UV bandpass filter (previously discussed here). One thing I noticed with one particular flower that the resulting images had a very noticable Red / Browness to them. You have previously informed me this might be the result insufficient supression of IR.

 

The image is below. White balance was set at a different location in the sun earlier during the session. White balance in post doesn't fix the problem for me. (I have an underexposed image with a teflon strip as WB reference if you would like to try yourself)

 

(out of camera jpeg) [ ISO 6400 ] [ f/2.8 ] [ 1/40s ] [ Sigma 30mm F2.8 DN Art ] [ Panasonic G7 ]

post-261-0-95649000-1589109182.jpg

 

For comparison, other images did not exhibit this problem; it seemed to be specifc to this flower type. (which was white in the visible)

 

(out of camera jpeg) [ ISO 1600 ] [ f/2.8 ] [ 1/6s ] [ Sigma 30mm F2.8 DN Art ] [ Panasonic G7 ]

post-261-0-84776100-1589109545.jpg

 

If you have any thoughts on this I would certainly appreciate hearing about it.

 

p.s. I still haven't sent over the filter to @UlfW for measurement; This would be the best way to figure things out and I hope to do so eventually.

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Hard to tell without further supporting data and images.I'm not even sure which flower species this is. Do you have other photos, for example taken in visible, and/or photos of its foliage?

 

The second flower seems to be Allium ursinum which has white flowers and being rendered blueish in UV is not unexpected.

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Nemo Andrea

Good point, I went back to have a quick look at the flower and it was labeled as ''Vanhouttei spirea" (''Spiraea x vanhouttei" on the sign). Related to this forum entry I guess?

 

Some images of this particular species below.

post-261-0-91715700-1589119134.jpg

post-261-0-70088600-1589119140.jpg

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A number of allies of Spiraea have quite UV dark flowers so your specimen show, more or less, an expected pattern. The false colours might be a different issue of course as Andrea's species was different from yours.

 

What is worth keeping in mind that "UV white" balancing needs the subject to show some variation across the recorded response. Meaning the balancing sometimes can be quite unstable and veer off into different directions. Could you provide me with a RAW file, then I'll have a go at it?

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Nemo kindly sent me some RAW files and my conclusion is this is a problem caused mainly by the lens being not very suitable for UV imaging, plus the still not resolved question of an IR leakage through the Kolari filter.
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eye4invisible

I, too, have my doubts about the IR blocking ability of the Kolari Vision 365nm UV filter. This is a cropped SOOC image of dandelions, taken with the Sony 28-70mm kit lens on a full spectrum A7. The centres are nowhere near as dark as they should be, to my mind:

 

post-116-0-58844700-1589142897.jpg

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I, too, have my doubts about the IR blocking ability of the Kolari Vision 365nm UV filter. This is a cropped SOOC image of dandelions, taken with the Sony 28-70mm kit lens on a full spectrum A7. The centres are nowhere near as dark as they should be, to my mind:

 

post-116-0-58844700-1589142897.jpg

 

Wow that some really strong IR leakage. Looks like just 4 mm of ZWB2 glass.

 

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eye4invisible

Wow that some really strong IR leakage. Looks like just 4 mm of ZWB2 glass.

I have no idea what glass KV uses. Going to wait for another sunny day and stack it with an S8612 to see what happens.

 

I got this filter about 2 years ago, when I used my Nikon D3200, and the centres used to be darker, even with the Nikkor 18-55mm kit lens. I'm wondering if there's been some oxidation that has caused this.

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It may be camera difference.

For example, with some cameras you can get away with using UG1 2mm or U-360 2mm stacked with BG40 2mm, it works pretty well with my cameras, but some cameras will show a warmer center on flowers such as rudbeckias, dandelions, etc..

Change that stack to using S8612 1.5mm to 2mm, and that Red/IR will be suppressed.

The photo I saw on the link you posted at the top shows some definite Red/IR leak with the rudbeckia example you posted there:

https://www.ultravio...dpost__p__30732

The brown center of that rudbeckia should be black.

The same goes for the dandelions Andy shows above.

So there is some kind of red/IR leak. You will see that brown turn to black if you stack that filter with S8612 1.5mm to 2mm (assuming the U glass is UG1 2mm, which I have a hunch it is, but it might be thinner).

You could also use BG39, which has the same Red/IR suppression as S8612, just a more limited UV.

Even BG40 2mm might work, hard to know.

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I'm somewhat surprised by comments about the Kolari UV-pass filter leaking IR. My testing of the KUV showed it to be a very robust IR blocker. Now it is entirely possible that the manufacture of the KUV has changed. I don't think so, but I could try to find out.

 

For me to help with this analysis, it would be good to have a raw file (or 2 or 3) from anyone experiencing

a white balance problem with the KUV. Upload raw files to some app like Dropbox and provide me or Birna with the url.

  • First I would run the raw file through Raw Digger and determine its histogram profile and compare that to other examples.
  • Then I would white balance the file in an app known to have a good white-click (NOT photoshop or ACR).
  • If possible, I would also compare your photo to others of the same subject to see what "should" be happening.

Andy, your example seems to show low UV transmission. The Kolari UV has only 60% 50% max UV transmission. If you combine it with a kit lens, then you are likely to get results such as shown. Don't use kit lenses for reflected UV photography !!!

 

Nemo, that Sigma Art lens is likely to have lots of coatings. Like Birna said, I would not expect it to work well for UV.

 


This has the makings of a good experiment for all of us to try. Make UV photos with a recent kit lens and with a really good UV-capable lens and compare. I'll give this a try. (Gotta think what is a good kit lens choice. I don't have too many of those.)

 

I don't have any dandelions right now. Darn!

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Forgot to add: If you set white balance in-camera, please remember that under filtration in-camera WB measurements might not always be "accurate". I've seen this with both Sony and Panasonic conversions in-camera white balance. Added: and also with my converted Pentax K.

 

I have an example posted here:

https://www.ultravio...s-with-my-gh-1/

 

Here is what I mean by "accurate".

In my linked example above, I set a white balance in-camera in my Panasonic Lumix GH1 conversion against a Spectralon white standard under what we'll label for now Filter X under the BaaderU. After I subsequently white-clicked the Spectralon area during conversion, I got big color shift. If the in-camera white balance is "accurate", then there should only be a very minor color shift, if any at all, when re-setting WB via the white-click on the Spectralon.

 

White balance of false colours is a bit of an art, not quite a full science. It would be nice if there were some robust standard for white balancing false colours, but there is not. Everything affects white balance: the camera and its color profiles, the lens and its color casts (if any), filters, illumination and finally what converter you use. Not all WB algorithms are the same across gear and software platforms.

 

You can get a fairly good standardization by creating a new color and WB profile against color & WB standards for every shoot which takes into account camera, lens, filter, illumination.

 

===>>> My point here is that the above red/brown-toned straight-out-of-camera JPG made with Nemo's Panasonic 7 might not have had an accurate in-camera white balance.

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I did receive the RAW files including one taken off a PTFE slab. False-colour w/b was very unstable with these files. They in fact presented themselves best as b/w.
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Do you think it's the lens? Sigma Art lens has lots of coatings.

 

Also, that particular spirea flower may not have a false color in UV?? Hence your black and white comment. I have some BaaderU photos like that. See Lomatium, for example: http://www.ultravioletphotography.com/content/index.php/topic/321-lomatium-triternatum-nineleaf-biscuitroot/

See also https://www.ultravioletphotography.com/content/index.php/topic/2432-aegopodium-podagraria-bishops-weed/

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All flowers have "false colours" in UV. Sometimes so dark they are near indistinguishable from true black.

 

My experience with many lenses is they might apparently record in UV yet the output is nearly deprived of chromaticity and making a stable, reproducible w/b can be almost impossible.

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Do you think it's the lens? Sigma Art lens has lots of coatings.

 

Also, that particular spirea flower may not have a false color in UV?? Hence your black and white comment. I have some BaaderU photos like that. See Lomatium, for example: http://www.ultravioletphotography.com/content/index.php/topic/321-lomatium-triternatum-nineleaf-biscuitroot/

See also https://www.ultravioletphotography.com/content/index.php/topic/2432-aegopodium-podagraria-bishops-weed/

 

Just recently tested my micro four thirds Sigma Art 30mm f2.8 lens and it cuts off at 355nm (no transmission below there). The 50% transmission point is around 375nm give or take a couple wavelengths.

 

Is the G7 full spectrum converted? All your previous stuff was with a Canon 1000D. Panasonic have much stronger UV blocking than Olympus cameras.

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Easy to test for a leak.

I know I have said this before, but I will say it again, just in case someone has never heard this method before.

Shoot a optimal UV exposure with the UV-pass filter in question.

Using the exact same settings as the first photo, shoot another shot with some longpass filter (450nm to 650nm, say) in front of the UV-pass filter. Same exposure, same aperture, same ISO, etc...

If the second photo shot through the UV-pass filter + the longpass filter stacked shows any faint image, then you have a leak.

Symptoms of a leak is warm or colored center where it should be black, but regardless if you agree with that symptom or not, try the stacked longpass test, and see if the image is black or some faint image.

The test can be forced by using longer exposure time for the stacked longpass image, but don't do that, use the same exact settings in order to see what might be mixing with the UV-pass shot.

Any longer stack exposure will only give you a false ratio.

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Well, my goodness! If Sigma Art lenses can transmit that much UV, then why are we bothering at all with old creaky 35/3.5s off Ebay? Price probably. "-) But it's really hard to understand how the UV gets thru all that multi-layered coating on the Sigmas. Like, I believe you, but wow.

 

 

 

All flowers have "false colours" in UV. Sometimes so dark they are near indistinguishable from true black.

 

Birna, somehow we are talking past one another. :lol:

Do you mean that all flowers have false colours in UV after white balancing the raw file? If so, then do black/grey/white count as false colour? When I linked the Biscuitroot above as lacking false colour, I was referring to the blue/yellow false colours which that flower does not show after WB. The white-balanced Biscuitroot has almost no saturation, just looks grey. You have to beat the Biscuitroot file with a really big stick to get any colour cast out of it. But I don't do that. When I convert raw UV files, I set saturation to what you could call "normal" or "standard". I try not to pump it.

 

It's false colour, so everyone can decide for themselves what saturation means for false colour. :lol:

 

****

 

Another point to consider amongst the other possibilities which have been raised. At ISO-6400 on a Panasonic you're going to get a lot more noise than you would from a Sony A or Nikon at ISO-6400. Noise and/or noise reduction can sometimes mess up either raw or white balanced colours. Not sure that's going on in Nemo's photo, but wanted to add this reminder.

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Well, my goodness! If Sigma Art lenses can transmit that much UV, then why are we bothering at all with old creaky 35/3.5s off Ebay? Price probably. "-) But it's really hard to understand how the UV gets thru all that multi-layered coating on the Sigmas. Like, I believe you, but wow.

 

 

Pedro discovered the Sigma 30mm f2.8 m43rds art lens and told ne about it here. Last I heard it was his UV lens of choice.

But I haven't seen him around here in about a year.

 

I asked him a microscopy objective question about a year ago and never got a response. His website also seems to be down.

 

I now hope he is ok.

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The false-colors after "UV white" balance rarely if ever are truly without *any* chromaticity.
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I think that the grey in some dark UV-signatures is the result of specular reflection in tiny structures of cell surfaces, too small to resolve.

Then the chromacity might have been inherited from other sources than the flower itself.

 

Jonathan's experiment with polarisers hint in that direction:

https://www.ultravio...dpost__p__35578

 

At least pure black lacks of all colours, even if you push the saturation very much like some members here like to do.

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Iridescence from conical cell structures is often associated with otherwise UV-dark flowers.
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Iridescence from conical cell structures is often associated with otherwise UV-dark flowers.

That is logical as the cell structures sometimes are very small.

Are there any examples of flowers showing real Iridescence with a distinct colour the way some butterflies do?

 

Iridescence is working best if on a dark background.

Same as the fancy chamelion pigment paints. The primer used is black.

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Not like a butterfly. More like a minutely varied mosaic of colour. Angle of incidence makes the entire flower structure "glimmer". I noticed this phenomenon very clearly on a small Papaver in the SW deserts on the trip Andrea and I did back in 2012. The flower itself came out almost jet black, but already in the finder of my camera I saw the shimmering lights.
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