Holy smokes the EM5mk2 can see 254nm

[dabateman]

Warning. Do not try UVC (254nm) photography unless you take the proper precautions. Wear 100% cotton cloths to cover your body, EYE PROTECTION is MANDATORY!!!

 

Ok still excited. With Jonathan's success with Sony sensor I thought I would test out my newly converted Olympus EM5mk2 by Kolari, which has fused silica on the sensor inplace of the UV/IR cut filter.

 

These images are with my custom 39mm single fused silica lens element and 254pb25 filter. I might test the UAT to see how it performs.

 

First to scare you a visible reference of some of the mold I need to image:

 

Then same jar with same 39mm lens, at the same closed down aperture, lens moved forward on rail as I roughly know where the focus shifts to, ISO 6400, 10 seconds, the aperture might be close to F22:

 

These are my UV beads with 39mm lens open, ISO 1600, 1/2 second exposure, F1:

 

These are the same UV beads with 39mm lens slightly closed down ISO 1600 1 second:

 

This lens is a best case as single element and has massive focus shift to select out specific wavelengths. Its good in that its really close for 254nm, and further back for each additional wavelength. But bad in that it would be very hard to use it for UVC, UVB, UVA tri color image. But for IR I need to move it more than a foot back.

These results are much better than my full spectrum EM1 with UAT as I couldn't focus that in live view, even at maximum ISO. The EM5mk2 allows for focusing in live view with this lens at least.

 

So the Sony sensor in the EM5mk2 is more sensitive to UV than the Panasonic sensor in my EM1. I wouldn't have guessed that, actually didn't guess that and thus the test.

 

 

I didn't white balance these, just used the standard WB I have for UVA. The base in the beads shot should be white.

[Andy Perrin]

Do you not like the KSS for this?

[dabateman]

Easiest to test a fast lens that I know will only be looking at UVC.

But yes now I need to test both the KSS 60mm and the UAT, as I like the idea of a UVV, UVB and UVA tricolor image and will need a corrected lens for that. Those are my only corrected options.

 

I would love it if Sigma made an EF mount autofocus macro fused silica 30mm / 35mm macro lens. That would be ideal for me. Useful on many cameras, AF, corrected and wider than available focal length.

[JMC]

Nice one David. Is the deep green a result of white balancing approach then? I see deep green for the 300ish nm region (when whitebalanced for that region), but down at 254nm mine was much more grey and muted, with there being red and blue contributions to the image as well as green.

 

EDIT - the UAT should be fine down there, although may need a bit of refocussing.

[dabateman]

Andy Yes the KSS works and it works with High Resolution shot mode at F4. However your subject needs to be high contrast or be dark in UVC to see something.

 

Liveview works too. I needed to use Liveview boost mode 2 for manual, ISO max 25600, then dropped the shutterspeed to 1/5 seconds. Just to rack focus.

The UAT needs the front element to move slightly more forward from visible to UVC.

The KSS needs the front element to move BACK slightly from the visible reference. I was surprised by that.

 

Here are some images of the UV beads which are UV black and easy to focus on. I have two 15W 254nm lights on them and using my 254bp25 filter for all images but visible.

 

KSS UV beads visible reference shot:

 

KSS UV beads in UVC, lens at f4, ISO 1600 and 5 seconds shutter speed:

 

KSS UV beads in UVC, lens F4, ISO 1600, 5 seconds and camera set to High Resolution shot mode. This is resized in Infranviewer so may not show all its majesty.

 

UAT UV beads visible reference shot:

 

UAT UV beads in UVC, lens F4.5, ISO 800, 5 seconds:

 

UAT visible dandelion seeds reference image (a wisher):

 

UAT UVC dandelion seeds ISO1600, 15seconds shutter speed, F4.5. Since its not absorbing its much harder to see.

 

Here is a 100% crop from the High Resolution shot mode:

[Cadmium]

KSS = ?

UAT = ?

 

Sorry, I don't usually follow your UVB / UVC discussions.

[dabateman]

Sorry Cadmium,

KSS 60mm f3.5 lens is a fake clone of the Resolve optics 60mm f3.5 quartz lens. Its a C-mount lens that is pulled from a Sirchie handheld UV imager used in forensics to look at fingerprints following the superglue trick. See this or not when a bunch of us bought them really cheap:

https://www.ultravioletphotography.com/content/index.php/topic/3402-60mm-f35-c-mount-uv-lenses-on-ebay/

 

The 60mm macro isn't the best lens for sharpness generally. But last night it was very good at close distance and at 254nm. So what its actually designed for might be what it is actually best at. It was much sharper at 254nm than the UAT.

 

So now what is UAT?

The Pentax 85mm f4.5 Ultra-Achromatic Takuma in M42 mount. My most expensive peice of photography equipment and literally almost cause me to get a divorce. It came a lens only, not with fancy case or any filters or correct caps. It was about 3800.

[Stefano]

Your second-last image looks very washed-out for some reason. Do you have any idea why?

 

In general, you can stop down your lenses to improve sharpness. Since 254 nm is a short wavelength, diffraction will kick-in later.

[dabateman]

Yes not much contrast there. I used the UAT, which isn't as sharp as the KSS and the dandelion fluffy seeds (at least when dry from being stored) are white at 254nm not black. The depth of field is also really thin so that stem is not in focus . So its white on glowing background which I tried to control with a hood.

 

Basically not much point in imagining a head of dandelion seeds. But night try again to compare the KSS on the monochrome pi which can shoot movies at 254nm vs the Em5mk2 which can do a high resolution shot mode.

[dabateman]

Jonathan reminded me not to get too excited as I haven't shown any controls here. Which is bad, I usually hit hard on wanting controls on controls. So this post will show what I should have started with.

 

I am confident that the EM5mk2 actually is seeing the 254nm line now after this test.

 

Here is a screen grab from the Schott Excel program to indicate show the filters that I have placed infront and behind the 254bp25 filter. Using this it should help to determine if the images I am seeing with the KSS 60mm Macro imager are in fact UVC.

 

These are crops from my filters that I scanned previously using my spectrometer:

254bp25:

 

303bp10:

 

1mm UG11:

 

2mm U340:

 

I haven't gotten around to scanning my small 2mm S8612 filter that I used here, but shouldn't be too different than this 52mm 2mm S8612 filter I scanned:

 

So with these filters and using the KSS 60 mm F3.5 lens at F4 and two 15W E26/E27 UVC 254nm germicidal mercury bulbs I have imaged a leafy carrot shoot placed inside the UV beads. I still don't have flowers yet from my zombie carrots. Hopefully soon.

 

Visible reference image:

 

254bp25 filter ISO 1600 F4 at 8 seconds exposure time:

 

2mm S8612 placed behind the 254bp filter at the exact same exposure conditions, and its black. So we know what I am seeing is not fluorescence in higher UV from any glow of the filter.

 

Control with 3mm ZWB3 placed in front of the 254bp filter to see the effect of adding glass on the exposure (F4, 8 seconds, ISO 1600):

 

Now some tests to find the wavelengths I might be seeing. The 303bp10 filter placed in front or behind the 254bp25 filter looked the same, so I am just showing the in front images:

303bp10 in front of 254bp25, ISO 1600, F4, 8 seconds:

 

303bp10 in front of 254bp25, ISO 1600, F4, 30 seconds exposure, Still Black.

 

Here is 1mm Ug11 placed behind the 254bp25 filter at F4, 8 seconds, ISO 1600, this is much darker than the control 3mm ZWB3. So its cutting the UVC light.

 

Which looks the same as when in front (1mm Ug11 placed in front the 254bp25 filter at F4, 8 seconds, ISO 1600):

 

This is 1mm UG11 in front (which looked the same as behind, not shown) with 20 Seconds exposure, this is still not as bright as the 3mm ZWB3 control, so cutting off more than a stop of light and its not just do to the addition of the extra 1mm of glass.

 

Here is 2mm U340 placed behind the 254bp25 filter at F4, 8 seconds, ISO 1600

 

Here is 2mm U340 placed behind the 254bp25 filter at F4, 20 seconds, ISO 1600. This image is more green and different indicating that the light through this filter is higher UV wavelength.

 

Here is 2mm U340 placed in front of the 254bp25 filer at F4, 20 seconds, ISO 1600:

 

 

Now I am confident that the images I am seeing from the EM5mk2 are in fact UVC.

 

Interestingly the KSS 60mm Macro needs a very slight movement of the lens further away from the subject at 254nm. This may indicated that the coatings are only optimized for visible and 254nm imaging, which is what the lens is designed for and the imager where the lens comes from allows for visible and UVC imaging only.

 

When testing the 303bp10 filter stacked with a 2mm U340 (to remove that IR leak you can see in the spectra above), the focus shifts, the colors are more green. So it might be hard to use this lens for multiple UV imaging and stacking the images:

[Stefano]

Do you still have the coverglass? Reading your description in the first post I understand they replaced the UV/IR cut filter (which isn't the coverglass) with fused silica. If so this means that the coverglass lets in some UVC, and this is quite surprising.

[dabateman]

Yes this camera has color filter array and original cover glass intact. Only the dust shaker and original UV/IR blocking filter where removed, and replaced with fused silica. As far as I know. A standard conversion. I also sent in my 43rds 9-18mm lens on adapter to insure infinity correction.

I have the original dust shaker and original blocking filter and still need to test them.

[Stefano]

To me, it is impressive that you can see UVC with the coverglass + CFA. Imagine the sensitivity gain you would have with a monochrome camera with the coverglass replaced with fused silica like Jonathan's camera. This may explain why your Raspberry Pi HQ camera is so sensitive to UVC. I think monochrome sensors are inherently quite sensitive to UVC, then adding the CFA and the coverglass lowers their sensitivity to almost zero.

[colinbm]

To me, it is impressive that you can see UVC with the coverglass + CFA. Imagine the sensitivity gain you would have with a monochrome camera with the coverglass replaced with fused silica like Jonathan's camera. This may explain why your Raspberry Pi HQ camera is so sensitive to UVC. I think monochrome sensors are inherently quite sensitive to UVC, then adding the CFA and the coverglass lowers their sensitivity to almost zero.

 

 

Stefano, don't forget the 'Micro Lenses' that are of an unknown transmittance...?

[Stefano]

Yes, we don't know their transmission, but they probably have an impact. How much is difficult to know, we should test a sensor with only them removed but with the CFA still in place.

[Andy Perrin]

Guys, Jonathan did that test already with his half-debayered sensor. We know the micro lenses were actually helping not hurting.

 

I mean conceivably not all cameras have the same material for micro lenses but based on what we have seen so far (eg most companies sharing the same Bayer dyes) probably it’s the same.

[JMC]

Guys, Jonathan did that test already with his half-debayered sensor. We know the micro lenses were actually helping not hurting.

 

I mean conceivably not all cameras have the same material for micro lenses but based on what we have seen so far (eg most companies sharing the same Bayer dyes) probably it’s the same.

 

Andy, my test on the sensor with half the Bayer filter/microlenses removed, only went down to 280nm though. Below that I don't have any empirical evidence either way, on a 'with and without microlenses' sensor. However my images with the A7III with the Bayer filter AND microlenses still in place did still give an image at 254nm, so they are certainly still letting the light through down there.

[dabateman]

Following up I realized I forgot to test the simple long pass filters. Happily the Tiffen 2A in front of the 254bp25 filter is black at 1600ISO. F4 and 60 seconds exposure. So is my longpass 700nm IR filter.

So no UV, no visible and no IR leakage accounting for my signal. Happy that worked out this morning as was silly not to test first.

[Andy Perrin]

Andy, my test on the sensor with half the Bayer filter/microlenses removed, only went down to 280nm though. Below that I don't have any empirical evidence either way, on a 'with and without microlenses' sensor. However my images with the A7III with the Bayer filter AND microlenses still in place did still give an image at 254nm, so they are certainly still letting the light through down there.

 

I'd forgotten that you stopped at 280nm, although maybe you could retest it down to 254 now? But I bet they are not a huge impediment based on what you just pointed out about the A7III+Bayer+microlenses test.

[JMC]

 

I'd forgotten that you stopped at 280nm, although maybe you could retest it down to 254 now? But I bet they are not a huge impediment based on what you just pointed out about the A7III+Bayer+microlenses test.

 

Unfortunately, 280nm was as low as I could get with my spectral sensitivity measurement system. But, yes as you say, less of an issue after the result with the A7III.