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Infrared Filters
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#1 dabateman

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Posted 09 April 2020 - 06:52

It was warm this evening and I felt like testing a new lens that I made with a couple of odd filter combinations.
These were photographed using a single fused silica biconvex lens that is 50mm in diameter and has a 39mm focal length. The maximum F stop out of this element is 0.78!, but with my 25mm to 1.5mm opening aperture control ring it changes from F1.56 to F26. This lens was mounted on my full spectrum Olympus EM1 camera in the later evening with some sun as light.

Experimental filter was 3 x 1.45mm thick ZWB2 air gap spaced with one 2mm thick ZWB1 into a frame. This still seem to leak IR though, so these look mostly to be infrared images:

Handheld, WB for UVa, ISO 800, 1/8 second, unknown f-stop:
Attached Image: Zwb2_43_ZWB1_2_A.jpg

Handheld, WB for UVa, ISO 800, 1/8 second, unknown f-stop:
Attached Image: Zwb2_43_ZWB1_2_B.jpg

Experimental filter with 3 x 1.5mm thick ZWB3 air gap spaced into a frame. Much more IR in this image:
Handheld, WB for UVa, ISO 200, 1/1250 second, unknown f-stop:
Attached Image: ZWB3_45.jpg

Experimental filter 700nm band pass with SvBony UV/IR cut filter stacked with 1.5mm thick ZWB2:
Handheld, WB for IR, ISO 200, 1/50 second, unknown f-stop:
Attached Image: UV_IRCUT_ZZWB2_15.jpg

All the above were taken at unknown aperture, that just seemed fun.
The maximum aperture I can get out of this lens is F1.0, mounted directly with my M42 to M52 step rings as the outer diameter is 39mm. Its very dreamy.

Edited by dabateman, 09 April 2020 - 17:35.


#2 Andy Perrin

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Posted 09 April 2020 - 15:31

Yeah, kind of a pretty bokeh on there. I would like to see some UVA pics taken with some non-Chinese filters. I wasn’t sure why you chose those anyhow.

Edited by Andy Perrin, 09 April 2020 - 15:32.


#3 dabateman

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Posted 09 April 2020 - 17:28

Just testing some filters, when the bumblebees started working again.
Was curious if this combination of ZWB2 with ZWB1 still would leak IR. There is obviously enough in the 700's to kick out the little amount of UV available from the sun after 6pm, with it lower in the sky.

This lens works well for UVC on the imager. Keeping the registration distance clear in my mind is fun.

The last photo above in my series is my favorite. Just checked and its WB was different, used my IR preset to make it more golden. It was originally more IR blue.

Edited by dabateman, 09 April 2020 - 17:33.


#4 Andrea B.

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Posted 09 April 2020 - 17:42

David, if you have time, I'm interested in also seeing a photo of the lens you constructed, maybe mounted on the camera?

BTW, there is a tradition of "dreamy", super-fast lens photography. When the Nikongear website was first started many years ago, there were a lot of photographs posted which were made with old Rodenstock fixed-aperture TV or X-ray lenses retrofitted to work on digital cameras. We called it Rodenstockography. Birna started it, but I'm not sure what year. Beautiful photos can be made with such lenses by carefully managing the very, very thin plane of focus and placing it for maximum effect. Those lenses did not prove to be useful for UV/IR work however.

Those are definitely IR photographs. Looks like an Andromeda shrub which should be flowering about this time of year on the East Coast?
Andrea G. Blum
Often found hanging out with flowers & bees.