The first steps...

[Andy Perrin]

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.

HAH. Yes, that is indeed an indication that it was correctly set! Because the channels are so lopsided (nearly all in red and blue), after a correct WB the result is a dimmer image. The reason it's so monochromatic is because that's just how the world is in UV using Bayer dyes that come with the camera which are not intended for this purpose. Certain flowers are the exception. We (Bernard especially) have been experimenting with ways to expand the colorfullness of UV images by imaging through bandpass filters with different center wavelengths and combining the three images.

[ACRosalino]

Yes, that makes sense... but I was not enjoying much that dimmer image, specially when I had to manual focus a lens at F/8 or F/11.

Here is one jpeg test image captured after setting the "in-camera" WB with the teflon:

 

 

To my UV-blind eyes, it looks very much the same as the other image above (Raw + WB in Sony software)… at least, for my purpose of "pretty pictures", only.

 

PS: the idea of using 3 filters with different UV passbands is not different from what is normally done when capturing astro-images... except, perhaps, that in most cases one uses a monochromatic CCD sensor behind the filters, for additional resolution (all pixels are simultaneously exposed, no matter which filter is being used).

[Andy Perrin]

Yes, that makes sense... but I was not enjoying much that dimmer image, specially when I had to manual focus a lens at F/8 or F/11.

Many of us use the UV LED torches (Convoy S2+ is most popular) when focussing for that reason. It is a "must have" piece of equipment and inexpensive.

 

PS: the idea of using 3 filters with different UV passbands is not different from what is normally done when capturing astro-images... except, perhaps, that in most cases one uses a monochromatic CCD sensor behind the filters, for additional resolution (all pixels are simultaneously exposed, no matter which filter is being used).

Yeah, there is a lot of crossover with that community here, so this was known. I believe several of us have astro cameras.

[dabateman]

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:

 

 

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":

 

 

Thanks,

António Rosalino

 

If you own a Sony camera there is still a free version of Capture one you can download. It only works for Sony cameras though. You should test it out, might work better or worse. Not sure.

Here:

https://www.captureone.com/en/products/express/sony

 

My Capture one version is 6. So has been a long time since I updated. Funny that version 7, after I got mine supports my DF. CO ver6 doesn't.

 

I was having more luck with Raw therapee and now the Raw therapee fork called ART, so have stopped buying software.

[ACRosalino]

One other thing: it seems clear that PTFE/Teflon is suitable for WB when shooting UV images...

What about IR imaging, is the Teflon also recommended for WB or is there a better way? Or “anything goes”, when it comes to IR colors?

Just curious...

[Stefano]

Teflon has a flat reflectance curve in a wide range of wavelengths, so it should be perfect for IR too. Note that, unlike for UV, a lot of materials reflect IR evenly in a broad range of wavelengths, and even white paper can be used.

[Andy Perrin]

Yeah, PTFE works fine for IR. It's pretty nifty stuff.

[nfoto]

Many materials work well enough with IR to get a good first-approximation "white" balance. Asphalt for example is generally OK. Or brick walls. Or nice clouds if they are sufficiently large in the frame. And so on.

 

White paper or snow will do in a pinch, but if you use such materials to adjust exposure, you'll likely end up with a dark image. Snow is rarely genuinely white in IR unless it's fresh and sun is shining directly on it.