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UltravioletPhotography

Sigma sd Quattro. 3rd and final test (for now!)


Adrian

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Another test with the Sigma sd Quattro, for UVR. This time, a Rudbeckia flower shot with the Sigma in monochrome mode, and the full spectrum converted Nikon D300 converted to monochrome in the raw converter.

 

Technical specs:

Visible light: Sigma sd Quattor with internal hot mirror removed, replaced with hot mirror over lens, balanced with Colour Passport checker

UVR Sigma (centre) 105mm El Nikkor with Baader U filter. 2 x full spectrum Metz flash guns, f/8. Monochrome mode set on camera. 200 ISO

UVR Nikon (right) 105mm El Nikkor with Baader U filter. same lighting. f/5.6. I have tried to match the densities of the two UV images by eye. 200 ISO

 

Interestingly the subject required more exposure when camera was set on mono mode. The Nikon is definitely shaper when viewed at high magnification, though fine focusing was difficult with the electronic viewfinder of the Sigma.

The final test for now as I have to send the camera back to Sigma!

post-47-0-31258000-1540389818.jpg

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Adrian, lovely test!

It inspires me to try to get back to my own botanical work which seems to have fallen by the wayside.

And our dear Rudbeckia -- the classic UV test flower. :lol:

 

Looks like the Sigma Quattro has no trouble capturing this floral UV-signature. The contrast is slightly low, but that is easily tweaked.

 

Interestingly the subject required more exposure when camera was set on mono mode.

 

In my experience, the false colour red channel (Bayer) usually saturates quickly and gives a misleading view of what is proper exposure for a UV photo. You think you are overshooting, but almost everyone underexposes UV photos. For UV work I very often switch to Monochrome with the Nikons because the JPG histogram then shows me the brightness (reflectivity, in a sense) and enables a better exposure "to the right" and thus less noise. If the B&W histo hits the right hand wall, then you know that you have truly overexposed and blown all 3 channels.

 

The Nikons have great headroom, meaning that one or two oversaturated channels can usually be pulled back successfully so I don't mind overloading a red channel in UV work. (Other cams may also have headroom, but I only know about Nikkies.) The D810 had 1-3 stops headroom and I could pull back 3 blown channels with that camera. It gets tricky though, sometimes the color can be ruined a bit with a 3-channel satuation. Best to just need pullback on only one channel.

 


P.S. Adrian, if you did send me a dropbox link, then it was lost in my recent AOL email mess. AOL downloaded 6 to 8 of all my emails. We had quite a time cleaning that up. I'm afraid I might have deleted some emails that I wanted to keep. But there were 1604 emails suddenly in the list to deal with.

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