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UltravioletPhotography

The first steps...


ACRosalino

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ACRosalino

Hi everyone

having patiently put together the hardware required to image the "invisible"; it is time to start taking some photos... all from my balcony, as we are not supposed to venture outside, these days.

 

Some first experiments in IR (Hoya R720, Sony 70-300G)

 

post-228-0-76746000-1588446467.jpg

 

post-228-0-81090700-1588449404.jpg

 

and some first experiments in UV (Baader U-Venus 2" filter, EL-Nikkor 80/105)

 

post-228-0-04176300-1588448139.jpg

 

post-228-0-18823200-1588448160.jpg

 

At this stage, I did not worry much about color balances... considering that we cannot see those IR/UV colors, I suppose some "freedom" to process the images can be tolerated?

Now, having said that... is there a guide - here at UVP or elsewhere - about how one can achieve a better, more "standardized" UV white balance ?

 

Thanks for looking and regards from Portugal!

António Rosalino

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Whilst you are absolutely right regarding the "freedom" of setting colour balance in UV/IR, there are sound reasons for using a known target to make the actual balance. For example include a piece of virgin PTFE or a ColorChecker card (its lower right black patch is pretty UV-neutral) in a photo to allow later "UV white" balanicng.
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ACRosalino
Well, I do have a 10x10x1cm piece of PTFE; however, WB tool in PS does not seem to like it much, Temperature and Tint sliders just move all the way to the left...
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dabateman

See if you can snap a custom WB using either the ptfe or an asphalt driveway. Keep that setting. My first favorite custom WB was just off a brightly lite raload using the BaaderU filter.

Adobe seems to have trouble in UV. I have better luck with free RawTherapee.

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RawTherapee collapses entirely on UV NEFs from various Nikons and cannot obtain any useful UV w/b at all. More or less the same behaviour with UV RAF files from my Fuji S5Pro.

 

Photo Ninja has no problem with any raw file so would be my preferred choice. The caveat is PN fails on uncompressed NEFs from the Z cameras, however. Use compressed lossless 12- or 14-bit and all is well.

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With PS, you have either to create your own camera profile for UV or you can do a quick and dirty trick: just proceed as you have done and then aftert ACR in PS use the camera raw filter in PS once again on the same spot. This is not 100% but comes pritty close.
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eye4invisible
That last image, DSC1025 is interesting. The foliage is very dark, but the filter seems to be letting a lot of colour through, especially the reds.
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Andy Perrin

That last image, DSC1025 is interesting. The foliage is very dark, but the filter seems to be letting a lot of colour through, especially the reds.

I was thinking that too! But it's a Baader? So unless it's the original one with the problem, it shouldn't be IR-contaminated. Perhaps it's BGR in addition to weird white balance?

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eye4invisible

I was thinking that too! But it's a Baader? So unless it's the original one with the problem, it shouldn't be IR-contaminated. Perhaps it's BGR in addition to weird white balance?

I don't think there's any IR leakage, due to the very dark foliage. I don't have a Baader U-Venus filter, so not seen it in my own photos. Perhaps it's a pecularity of that particular camera sensor?

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Andy Perrin

I don't think there's any IR leakage, due to the very dark foliage. I don't have a Baader U-Venus filter, so not seen it in my own photos. Perhaps it's a pecularity of that particular camera sensor?

I doubt it. Except for the Foveon, so far all the camera sensors behave nearly the same way with regard to false colors. I'm thinking there is probably some processing step we don't know about, like channel swap.

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ACRosalino

Thanks for all the feedback: even with the teflon square, I still cannot obtain an adequate WB on PS... I always end up with Temperature and Tint sliders in PS set all the way to the left, not sure what I can do to change that.

 

Btw, there is nothing wrong with the Venus filter (2" version) or the Sony sensor.

Here are two examples of the same raw image, just with different processing: one displaying the usual violet tones... the other displaying warmer, more pleasant tones (at least to my eyes):

 

post-228-0-13697600-1588516133.jpg

post-228-0-27298300-1588516163.jpg

 

Which colors do you like more (or hate less)?

 

At this very early stage, I feel that processing UV or IR images is similar to processing deep-sky narrow band images: how to attribute color to very faint objects, of which one never saw and never will see their true colors?

This is the Helix planetary nebula, in Aquarius, aprox. 700 light years away: I captured this image using Ha and OIII filters... certainly not what I would call "true colors", just my personal interpretation of the "Eye of God":

 

post-228-0-81747600-1588518000.jpg

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Tried your plants & pots photo in PN, but colour-balancing a noisy jpg is far from optimal. One reason it is difficult is that the PTFE is totally blown exposure-wise.

 

post-228-0-13697600-1588516133_v1.jpg

 

One really needs a "known" target to ascertain your "UV white" balance. If you have a ColorChecker Passort, try that. At least we have a good idea of its appearance in UV. Or even better, a Sunflower Helianthus.

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ACRosalino

Hmmm.... looks like I may have to invest in one of those ColorChecker Passports, apparently the teflon will always have a tendency to overexpose - that photo above was taken in the shade, no direct sunlight. Here it is, in "normal" colors:

 

post-228-0-48309200-1588525287.jpg

 

PS: I am not sure if there are any sunflowers around, this early May? Hard to tell, being in corona-confinement...

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I use Photo Ninja most of the time for WB these days, still sometimes I use CNX2 or NX-D depending on which Nikon I am using.

By the way, they Baader U is not showing a leak in those pics, ACRosalino is swapping the red/blue (like Clark likes to do).

Yes, the PTFE is overexposed, I usually shoot a separate pic of only the PTFE filling the frame in the same lighting situation, then copy/paste that WB to the others of the same lighting.

I like your second shot. At first I thought it was two shots, then I noticed the crane going up into the 'sky', and then I noticed that was water, not sky... :-)

I like the visual pic also.

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Andy Perrin

Thanks for all the feedback: even with the teflon square, I still cannot obtain an adequate WB on PS... I always end up with Temperature and Tint sliders in PS set all the way to the left, not sure what I can do to change that.

 

Btw, there is nothing wrong with the Venus filter (2" version) or the Sony sensor.

Another option would be to simply set the white balance in-camera. Both my Sonys (NEX-7 and A7S) can do an in-camera white balance without a difficulty. PS will never work for UV white balancing, it's better to use something else IMO. I do actually prefer the standard UV white balance (off Teflon or similar) to color-swaps and others, but that's just my two cents.

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ACRosalino

Still struggling with all this WB stuff: I had the impression that if one shoots Raw images, in-camera WB is not important, being used only to display the jpegs on the camera display?

 

I took a few more images of the teflon (properly exposed), but the PS WB tool always behaves the same way - both Temp./Tint move to the left end of the scale:

 

post-228-0-03000500-1588714535.jpg

 

If afterwards I invoke ACR again and repeat the WB tool process, then I get some intermediate readings:

 

post-228-0-81474300-1588714592.jpg

 

Is this "double-pass" white balance calibration a valid procedure?

If yes, then I suppose I could use the same Temp./Tint parameters for all other images taken under the same light conditions?

 

Questions, questions...

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Forget PS etc. these will never work well on such off-balance images.

 

Having a good V w/b in camera means it's easier to get a good exposure. Or if you shoot video, results are OK straight off camera. My Panasonic GH-2 does this so main reason I kept it.

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I agree, unless you have done a custom camera profile for your camera for ACR, then white balance for UV or IR will not be good in PS compared to Photo Ninja, or the like.

Like Birna says, an in camera white balance, works well with a lot of cameras now, not for most Nikon cameras though.

Regardless, having some program that will permit you to play around easily with WB from a RAW file is quite powerful and handy.

Photoshop/ACR is not a good choice unless you know how to mess around and make a custom camera profile.

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Andrea B.

A brief summary.

 

Color Checker Passport is used for creating camera color profiles and for setting Visible white balance. The CC Passport cannot be used for setting UV or IR white balance because its bright areas do not stay fully reflective in UV or in IR.

 

PTFE can be successfully used for setting UV or IR white balance both in-camera (except Nikons) and in a converter (except ACR). But you must be careful not to overexpose the PTFE photo because PTFE does not have a diffuse reflectivity in UV/IR as does other material such as the more expensive Spectralon. Almost every member here uses PTFE, so we know it is useable.

 

A good reason for setting an in-camera WB under a UV or IR filter is because this reduces the oversaturation of false red colours which obscures detail and makes getting a proper exposure more difficult.

 

An alternate method for shooting in UV/IR is to use the camera's Monochrome setting. Later you can choose your desired color look when converting. When shooting Monochrome, I usually try to move the histogram hump to the middle. (Yes, I know the histogram is for JPGs, but using it for a UV Monochrome has proven to produce a raw file which is easily converted.)

 

To set or to refine a UV or IR white balance during post-processing, use your camera's conversion software. Once you have set the WB, save the file as a TIFF which can then be further processed in PS.

 

If you want to read about creation of a camera profile for UV, see this tutorial: Photo Ninja: How to Make a Custom Light Profile

That tutorial is applicable to Photo Ninja only, but it gives you the general idea of how this is done.

 

Lazy Girl Method: In a converter which has a good click-white tool (not ACR), you can click on any false magenta area to begin setting a UV white balance.

 

 

 

AC, I think you are off to a very good start. I hope that we have answered some of your questions and pointed you in the right direction. If not, keep asking!! :grin:

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I generally agree with the above, but one point needs a slight clarification. The ColorChecker Passport as such cannot give a reliable "UV white" balance, however the lower black patch comes tolerably close and can be used for a first approximation.

 

The main reason the PTFE mustn't be overexposed is the reflection pattern is not Lambertian, ie. equal in all directions or phrased differently, independent of viewing angle. Thus place the PTFE in centre of the frame, or make it fill the entire frame, then use the centre for w/b setting.

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Andrea B.

Yes, thanks Birna.

I had not forgotten about the CC black patch, but thought I written already too much! :lol:

 

There is a certain "art" to white balance in UV that is born of experience and does not require expensive WB tools. After converting gazillions of UV raw files, I can usually white-click them into WB submission by picking just the right magenta area. But for anything documentary, I use color profiles and saved WB measurements made per camera + lens + illumination.

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ACRosalino

Thank you for all the patience and advice, I am still trying to digest all the "guidance".

 

Actually, I already tried in-camera WB with the teflon: the result was almost monochromatic and much dimmer images in the viewfinder, compared to the usual (magenta) Auto WB.

Most likely I am not seeing the full picture, here... but if I always capture raw images, I suppose no data is lost by dealing with WB only later, using an appropriate editing software, other than PS?

 

On that topic, I just realized that Sony indeed has its own Editing software ("Imaging Edge"), which I am exploring now to set WB on my raw images...

It also has one of those easy to use tools which I can point at the teflon, I just tried it on one of my images and the result is as follows:

 

post-228-0-20964500-1588807681.jpg

 

No other processing, just Raw image + WB area selection tool on the teflon - would these colors look more like a "natural" UV image (it there is such a thing)?

At least compared to the same WB in PS ACR, it sure looks less "violet":

 

post-228-0-99425600-1588808385.jpg

 

Thanks,

António Rosalino

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