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UltravioletPhotography

SD14 Halogen vs compact fluorecent lighting test.


dabateman

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dabateman

This is an information post about a recent test I was trying to find a nice cheap continuous light source. The test used my dust filter removed Sigma SD14 in my basement with no other lighting. A desk lamp is used shining light on the subject. Since I first did this at night all my dandelions were closed. So the Subject is Silver Arrows cactus flower (Mammillaria nejapensis). Hopefully the EXIF data is saved when uploading images here but if not, these are ISO 100, f4, Shutter speed is 20 seconds. Camera is on a tripod, using mirror lock up mode. The Jpegs are straight from camera using Sigma photo pro v 4.2.2 as it directly removes the Jpeg from the x3f file. These have not been modified in any way, straight from camera. The white balance is taken from using the SD14 outside one day and doing a custom white balance off an asphalt road. I find this the best white balance selection in the past. But will need to repeat as it looks a little off than what I was expecting here.

 

First image is M42 50mm f2.8 Steinheil Munchen lens ISO 100, f4, 20 sec using Halogen lamp and Venus baader 2 filter. Here you can see the minimum focus distance is far, but you can see my setup with desk lamp. The advantage of this lens is the focus point is the same in visible and in UV.

 

post-188-0-66885300-1525195765.jpg

 

Second image is Sigma EX 50mm f2.8 Macro lens ISO 100, f4, 20 sec using Halogen lamp and venus baader 2 filter. Much closer focus, but not a minimum. Visible light focus point was 40 cm, UV point was less than that adjusted by multiple shots to get correct. possibly 38 cm.

post-188-0-35901700-1525196220.jpg

 

Third image is Sigma EX 50mm F2.8 Macro lens ISO 100, f4, 20 sec using Halogen lamp and 2mm Zwb1 2.2mm BG39 filter stack.

post-188-0-64226900-1525196330.jpg

 

Four image is Sigma EX 50mm F2.8 Macro lens ISO 100, f4, 20 sec using Compact fluorescent bulb and 2mm Zwb1 2.2mm BG39 filter stack.

post-188-0-78305700-1525196416.jpg

 

Fifth image is Sigma EX 50mm F2.8 Macro lens ISO 100, f4, 20 sec using Compact fluorescent bulb and Venus baader 2 filter.

post-188-0-38285900-1525196477.jpg

 

The halogen bulb says GE Crystal clear 72W 1490 lumens with 3000K look.

The compact fluorcent bulb is GE 23W 1300 lumens with 2700K look and the bulb says contains mercury.

I think this is very interesting. But maybe I am alone.

 

David.

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Andy Perrin

Yes, as stated in the other thread, halogen bulbs are nearly pure IR/Vis. I would not trust any photo with a halogen bulb to be a UV photo without additional proof such as an extra blocking filter test. The BG39 seems to show that blocking more IR makes the image go dark here.

 

I'm not sure what the spectrum of the compact fluorescent is, but I would not trust it to contain much UV either (although it has to be better than the halogen - ANYTHING is, almost). Why not use direct sunshine?

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dabateman

Yes I agree. I can not use the Halogen for UV as I had hoped. However it does lead to a pretty image. I will next test a 175 W Hg lamp and you can still buy them here in the US.

David.

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The magenta highlights in the final photo are likely visible/IR leakage. Only the blue channel contains a significant UV signal. Trying to white balance an image under such circumstances is hopeless--I suggest isolating the blue channel and working it up as monochrome.
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