[Theme] Pictorial UV

[Andrea B.]

Lovely, Akira.
I always enjoy how well UV brings out texture in petals.

[Akira]

Lovely, Akira.
I always enjoy how well UV brings out texture in petals.

Thanks, Andrea.  I realized the mysterious beauty of Oenothera came from its exquisite UV pattern in addition to the fact that it blooms at night.

[Bjørn Rørslett]

Akira: not all species in the Evening Primrose genus (or close allies) exhibit the classic bull's-eye UV pattern. Thus, that your capture didn't show this, is no hard evidence the photo failed.

[Akira]

Bjørn, if I understand correctly, the central dark area is the bull's-eye pattern which looks almost as yellow as the outer part under VIS.

[Andrea B.]

There is a UV-dark central area that I see. It is not very large.

[Bjørn Rørslett]

IR contamination of the UV signature is of course the ever present danger.

[Akira]

I have to agree that the IR contamination cannot be removed completely in this combo (D2H, U-360 and BG-40).

The last one was shot without BG-40 deliberately to add IR portion for more flexible color control.

[Andrea B.]

With a 2mm thick BG40, the IR leak lessens to somewhere between OD3 and OD4. So a lot depends on the form of illumination as to how much of that potential IR leak will actually show up in the photo.

In a recent experiment, I stacked an IR092 filter on top of the U360+BG40(2mm) to test for red and/or IR leakage. I also tested the alternate IR-blocker S8612 in a 2mm thickness. The results are found in this topic: http://www.ultravioletphotography.com/content/index.php/topic/1709-u360bg40-u360s8612-baaderu-ir-leak-test/


The dark red against the paler pink is an elegant contrast.

[Akira]

Andrea, thanks for the link.  A convincing reminder.

My BG40 is 1mm thick and shows 2.3% transmittance at 750nm, and the 2.5mm U-360 has an IR bump that peaks at 750nm with the 10% transmittance.

Considering that the UV modified (meaning, with the protection window removed) flash I used emitted a fair amount of IR, its contamination should be present in my last images.  Considering that he shape and the size of the central dark area of both images with and without BG40 looks pretty much identical, it could be safe to say that the IR contamination doesn't really affect the bull's eye pattern.  Maybe.

[BW]

I dont no what I`m doing, I dont know where I go. The first stumbling steps in UV, thanks to Bjørn

[Bjørn Rørslett]

Not bad for a UV newbie, Børge ... The D40X at your service I presume.

 As you should be well aware of by now, the false colours in UV captures are truly false, meaning it's up to you how they show be rendered and perceived. That gives a very wide artistic license and nobody can shoot you down for not obeying the 'rules'.

Out of curiosity, which filter(s) did you use? That is a recurrent theme amongst UV shooters.

[BW]

The D40x behaves like a well trained dog, as long as I get the focus shift right. I think I do now. The colors are a real treat. One never know where it ends. Suits me just fine

[Bjørn Rørslett]

I'm pleased to hear. That specimen of D40X has secured a surprising number of my better UV captures up to to 2013/2014.

[BW]

I know some of the things you have achieved with the camera, so right now the limiting factor is behind it

[Andrea B.]

... it could be safe to say that the IR contamination doesn't really affect the bull's eye pattern.  Maybe.

Akira, I was thinking about this. How important we consider the IR washout that occurs with "leaky" UV-pass filters probably depends on the nature of the UV photography in progress. If the goal is artistic and the IR contamination is minor, then perhaps it doesn't matter too much. If the goal is documentary, then we must add on more IR-blocking and crank up the artificial UV illumination to ensure we are achieving a good representation of the UV-signature for the given scene. Of course, we are never capturing an actual UV-signature because the raw data must be tweaked in order for human eyes to see a photograph instead of a flat, dark mess. 

Having said all that though, it is surprising how many people do not realize that all UV-pass glass leaks IR and that it is necessary to block as much as possible in order to claim that the photograph is UV. For example, the U-330 - if used without any IR blocking at all - passes so much IR, that it can be used as a kind of funky IR filter outdoors in sunlight where the ratio of UV/Visible/IR is about 5/45/50 (depending on location, altitude, time of day).

Well, I am rambling on here.......this is what happens when one attempts to think.