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UltravioletPhotography

White Balance in ACR vs Photo Ninja


Andrea B.

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Does anyone know why ACR does not "properly" white balance UV files?

 

This photo was made in sunlight with a D600-broadband + Soligor 35/3.5 + BaaderU UV-Pass filter.

 

Converted in ACR. White balance dropper applied.

600_4030_WB_in_ACR.jpg

 

Converted in Photo Ninja. White balance dropper applied.

600_4046pn.jpg

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ACR doesn't do a very good job of white balancing IR either, that is why we used CNX2, and now Ninja.

ACR can be edited to have camera profiles, which supposedly will make it white balance IR and UV shots better, but I have no experience with that.

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Andrea, whereabouts in the image did you apply the white balance dropper?

The YouTube video quoted shows the use of a Colour Checker Passport for creating a custom profile but I thought the grey scale on this system was not good for UV radiation, or have I got that wrong?

What grey targets do people use? I looked at the Spectralon ones, but they are very expensive (unless anyone knows a cheaper source for them). I have bought a roll of grey PTFE tape, and have wrapped several layers of that around a glass block, which seems to do a reasonable job. Any other ideas for a good grey target for balancing UV images please?

Also, can I ask Andrea if your Soligor 35mm lens needs a large focus correction - I have one of them and it is very difficult to focus in UV!

Thank you

Adrian Davies

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Adrian, I tried applying the ACR white-balance dropper at various places in the photograph. My general experience has been that if you white-click a magenta area you get very close to the "usual" UV white balance in a UV-supportive converter. ACR is not a UV-supportive converter.

 

I use calibrated Labsphere Spectralon diffuse reflective standards for setting white balance in UV, Vis or IR. Usually I shoot the two which reflect at 99% and 75% evenly throughout the UV, Visible and Infrared regions.

 

For typical UV photographs, using a white Teflon or PTFE slab as a target is quite acceptable. PTFE is not perfectly diffuse and so may more easily blow out, but that is controllable. I also do have a PTFE round to test with.

 

Usually it is best to work with a more strongly reflective target than grey. I suppose it depends on just how grey the grey is. "-)

 

The Soligor 35/3.5 --- is a fairly bad lens!! Mine is not particularly sharp nor contrasty. It has either vignetting or a rather large hotspot - not quite a hotspot, really - but a large, slightly brighter center. It is prone to flare. But the Soligor 35 serves its purpose for the occasional wide-angle UV experiments I want to make.

 

To focus the Soligor, I focus wide open at 3.5 then stop down to the desired f/8 or f/11. That depth of field covers any minor focus shifts that happen when the aperture is stopped down. I make and check focus in UV while shining a UV-LED torch on the subject to see the subject on Live View. I zoom in on Live View to verify focus. The UV-LED is used only for focusing because I prefer a wider band UV illumination source like sunlight or UV flash.

 

Creation of a custom colour profile using the CC Passport is done for work in Visible light. Such a Visible colour profile may be applied to your UV work, but it only improves the UV false colours and does nothing at all about white balance. The CC Passport cannot be used to create a UV-false colour profile. I have tried to do this in a couple of converters just to see what would happen. What happens is that the profiling software cannot reconcile the UV false-colour patches with the standard Visible colour patches and produces a totally unusable mess.

 

***********

 

Added a Minute or Two Later:

Specifically in the two photographs shown above, I settled on using the gravel path in the lower left-hand corner as an area in which to drag white-click droppers.

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  • 2 weeks later...

The Soligor 35/3.5 --- is a fairly bad lens!! Mine is not particularly sharp nor contrasty. It has either vignetting or a rather large hotspot - not quite a hotspot, really - but a large, slightly brighter center. It is prone to flare. But the Soligor 35 serves its purpose for the occasional wide-angle UV experiments I want to make.

 

Which Soligor 35/3.5 do you have, Andrea. There are countless versions of Soligor 35/3.5, some of which are optically and mechanically identical to Kyoei Acall lenses (and I do not mean the ones that Igor calls "clones"), and come are very different.

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  • 6 months later...

ACR white balance is quite limited (between 2000-50K) and UV photos need less than 2K. Even in PhotoNinja if you use the picker you will get the correct WB, but enter the same data manually (you can't enter lower than 2K) and your WB will be off the charts (literally) :D

 

http://clancode.hu/!uv/wb.jpg

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Which Soligor 35/3.5 do you have, Andrea. There are countless versions of Soligor 35/3.5, some of which are optically and mechanically identical to Kyoei Acall lenses (and I do not mean the ones that Igor calls "clones"), and come are very different.

I have the enlarger Soligor 35/3.5 :) it's good for UV but has just a slightly smaller image circle as APS-C, so a very tiny vignetting occurs.

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  • 3 weeks later...
enricosavazzi

My Soligor here:

That is one of those I found to perform well in UV (with some individual variation).

 

The thing to watch out for is damage at the center of the rear element. It protrudes from the back, and in some mount types if you lay the lens on a table with its rear at the bottom, the glass touches the table surface. About one-third or one-quarter of those I bought on eBay had this problem (out of a sample of about ten).

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Scratched rear elements are common on Noflexar 35 mm lenses as well. The similar 35/3.5 wide-angle constructions from other brands share their fate.

 

As to "UV w/b" by a simple click-white operation, Photo Ninja, Silkypix, and RawTherapee all can do a good job. ACR and AfterShotPro (ASP) fail miserably.

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