• Ultraviolet Photography

Out of the Fire

4 replies to this topic

#1 dabateman

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Posted 18 April 2020 - 07:58

Fun series with my favorite image first.
Collected using my homemade 39mm focal length single lens and a rear mounted 1.25" SvBony 0.5x focal reducer in a C-mount adapter at the mount of the lens. The focal reducer punches up the light, still gives a sharp center and helps to smooth out the background.

All images used 2 ExoTerra UVB lights directed at the very tinny flower, was only a couple mm wide.

Favorite image UVB 313bp25 with U330WB80 improved filter 13 seconds exposure at ISO 800, unknown but mostly open aperture:
Attached Image: UVB_313_330WB80_39mm_SvBony_B.jpg

Other fun images from the series:

UVA 330WB80 improved filter only:
Attached Image: UVA_330WB80_39mm_SvBony.jpg

8mm ZWB1 filter:
Attached Image: 8mm_ZWB1_39mm_SvBony.jpg

4.32mm ZWB2 with 2mm ZWB1:
Attached Image: ZWB2_ZWB1_39mm_SvBony.jpg

4.5mm ZWB3 with 2mm S8612:
Attached Image: 45mm_ZWB3_2mmS8612_39mm_SvBony.jpg

Visible image of the flower:
Attached Image: Visible_39mm_SvBony.jpg

Alternative UVB image, but I like the first one better I think.
Attached Image: UVB_313_330WB80_39mm_SvBony_A.jpg

Edited by dabateman, 18 April 2020 - 08:01.

#2 colinbm


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Posted 18 April 2020 - 08:47

fantastic DIY UV lens

#3 Bernard Foot

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Posted 18 April 2020 - 13:33

Any idea what wavelength you can get down to with this lens, David?
Bernard Foot

#4 Andy Perrin


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Posted 18 April 2020 - 14:58

What range does the focal reducer pass? That seems like it might be a bigger limitation than the lens.

#5 dabateman

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Posted 19 April 2020 - 05:15

I tested the focal reducer here:

Its passing 300nm, but looses the 2 stop increase advantage. Just equal exposure at 300nm with much wider field of view. I didn't test it at 254nm.
The lens may have been rated as UV grade, which would be real fused silica. So thats 190nm. But some of the fused silica elements I got are just quartz. All of them are great at 254nm. I still don't have a good deep UV light source. I am hoping I can get a 207nm light as they become more popular with the current state of the world.

I may need to test the focal reducer at 254nm now. A 200mm focal length concave element works ok with this element. But its not as central sharp as with the reducer. But the concave element allows for much wider field of view as it increases the back focus distance of the lens, while holding the same apearent field of view. The focal reducer decreases the back focal distance and thus pushes the element into mostly close up photography. As with my set up of 6mm mount adapter + 13mm aperture control ring + 19.25mm (m43rds flange) I already run into the back focus distance for infinity of just the 39mm focal length element.
But I do have a 12-19 helicoid on between the mount adapter and the aperture ring for these images. So I could have gotten much further back. It just wouldn't have been as interesting an image. The focal reducer fits in the dual M43rds to c-mount/M42 adapter. So do my c-mount modified concave elements. So I can play around.
I should test my concave elements immediately behind the 39mm element before the aperture ring to see if that works. That is a typical lens setup that I haven't tested yet.

Edited by dabateman, 19 April 2020 - 05:17.