21 replies to this topic

[microbat52]

I never put photos of myself on the internet but guess I dont even recognise myself so should be fine.

In IR, I think I was using the 760nm filter. I have no idea who this blue eyed fairy is. So freaky but I love it.


Then I tried UV. It was hard. The sun is low and super soft. I didnt manage to figure acceptable settings before getting hungry and heading back home. Its noisy and the contrast is rubish.
She looks like a witch kinda and I like that.
This was using the ZWB1 and BG39, 2.5" f4.5 and iso 1600 ( this camera cant really handle iso above 800, I need more sun)



(Ugh any help with this one appreciated, im a bit confused with the violets in the sky and the lack of contrast everywhere else)

[Andy Perrin]

Did you flip the channels in the UV photo? (Most of us don't do that, except for Clark, so it's good to write "presented as BGR" somewhere so people can interpret your image properly). Typically un-channel-flipped UV photos have yellow skies if you white balance off something UV-neutral like PTFE/Teflon.

Aside from that, it looks fine. In UV there is very little diffuse reflectance from the surroundings, unlike in the IR, so you need direct light on your subject. It looks like the light may be coming from behind here, and that's part of the exposure problem.
--

I love the IR one, you make a nice fairy.

Edited by Andy Perrin, 17 January 2021 - 20:29.

[microbat52]

Thanks Andy

No I didnt swap anything, and Im not sure what to white balance it against since I dont think I have any PTFE... I just let darktable balance it out for me..
Any alternatives to white balance on? Items easy to get hold of?

Ill try see if i can get yellow skies.

The sun was in my face but it was low winter light with high clouds so very very soft. I need spring to arrive already!!!

[Andy Perrin]

PTFE is cheap and easily available on eBay. You can in-camera white balance off any asphalt street and it will get you in the ballpark though, assuming you have one of the cameras that can set a UV white balance in-camera in the first place (I believe Nikons can't, Sony definitely can since that's what I have, and I don't know about the rest). If you have the RAW in PhotoNinja, you can click white balance off anything magenta and it will also work. I don't know if darktable allows a UV white balance to be set. Some programs can (PhotoNinja, for example) but some can't (Adobe Photoshop, notoriously).

The truth is just that in UV, objects like to absorb, and that makes for dim scenes. It's a dark world in UVA, and it only gets darker as you head towards UVB and UVC (no sun!).

Old selfie with half-sunscreened face (in direct sunshine, no clouds, in summer):


I look way too smug, but in my defense I was thinking "I finally got an in-focus UV selfie!"

Edited by Andy Perrin, 17 January 2021 - 22:37.

[Stefano]

I would also add that the sky is relatively bright in UV, and a significant amount of UV light comes from it. That’s why shadows aren’t very dark in UV, while they are very dark in IR. You should face the brightest sky region to have more illumination.

[Cadmium]

I like your hat

[dabateman]

Stunning!

The UV looks correct to me. Depends really on the lens. I used to create a custom white balance off black asphalt. That would work most of the time. If not some plumbing tape wrapped around a business card or a block of PTFE (same thing) will work.
If your not afraid of the command line. Trying dcraw might actually white balance it off average. Its not too far off into the blue/purple.

[microbat52]

Ill try the asfalt, although i think unless i get enough sun my camera will struggle to white balance it.

If not ill try to get some PTFE tape.

I think ill leave this one as B&W and try more hopefully with more sun!

Thanks for all the tips!!

[Cadmium]

How are the photos white balanced?

[microbat52]

It was spot white balance on darktable, I think I used a big square (spot) to cover most of the image.

[Cadmium]

Exposure?

[nfoto]

Stefano, on 17 January 2021 - 22:23, said:

I would also add that the sky is relatively bright in UV, and a significant amount of UV light comes from it. That’s why shadows aren’t very dark in UV, while they are very dark in IR. You should face the brightest sky region to have more illumination.

That statement would be correct for the old time using Kodak HIE film, not for digital infrared. IR shadows are usually pretty "open" in digital.

[microbat52]

Cadmium, on 18 January 2021 - 09:18, said:

Exposure?

1/1.7" sensor, 2.5s f4.5 and iso 1600. I got much better results with the sky at 4-6s and iso 400-800 but I cant stay still.
I need to give it another try in better conditions where i dont need to go above iso 800.

[nfoto]

Orientate the subject (yourself) and camera 180 degrees, try again. As stated elsewhere in the thread, the UV world is a dark place. You need fill-in light.

[microbat52]

nfoto, on 18 January 2021 - 15:18, said:

Orientate the subject (yourself) and camera 180 degrees, try again. As stated elsewhere in the thread, the UV world is a dark place. You need fill-in light.

Thanks! Will try different orientations next time ( once the sun decides to come back....ugh British weather.....)

[nfoto]

No problem -- currently doing UV under winter conditions with frost fog blanketing everything. Still possible, but maximum sharpness is tricky if one is using a hand-held camera. I try to aim for shutter speeds 1/10 sec or faster.

[Andy Perrin]

I always find selfies really hard even in visible light. The difficulties compound when you have to imagine how the landscape looks to a camera operating where human eyes don't see. (Eventually you get used to how the world "looks" in UV and IR and can make some adjustments before shooting, but that is hard in the beginning.)

[Cadmium]

microbat52, on 18 January 2021 - 12:40, said:

1/1.7" sensor, 2.5s f4.5 and iso 1600. I got much better results with the sky at 4-6s and iso 400-800 but I cant stay still.
I need to give it another try in better conditions where i dont need to go above iso 800.

So manual exposure, not aperture priority, spot/center weighted/matrix? That is often how I do mine, AP/CW.
For white balance, when using a WB target (PTFE), I like to take a separate photo, try to fill the frame with the target, use AP/spot or CW, optimize the exposure for the WB target.shot,
then I white balance that WB target center in Photo Ninja, and copy that WB to the shot I want to WB.
For the sky shot, set AP to spot for the dark area, perhaps, and then apply the WB shot to that shot.

[microbat52]

Thanks everyone for all the tips!!!

[Andrea B.]

A nice experiment!

There isn't as much UV in sunshine in the winter so long exposures at high ISOs are the norm. And ditto Birna's suggestion.

Reflected UV photography has typically a very wide dynamic range which many cameras cannot handle. Because of that you have sky blowouts and blocked shadows in the UV photo. In some converters the raw file can be tweaked a bit to mitigate those problems.

May I have your permission to download your UV photo and show you what can be done?