Sigma fp full spectrum output with Mercury Lamp.

[colinbm]

Sigma fp full spectrum output with Mercury Lamp emission lines.
I have made a scale of wavelengths for the rear screen of the Sigma fp, showing the emission lines of a mercury lamp.
To get the emission lines I have used a quartz diffraction grating in front of a UV Nikkor 105mm lens.
I have mounted a polished aluminium 0.9mm wire at minimum focus in front of the lens.

In a dark room, shining the mercury lamp at the polished aluminium wire gives its reflected light that is diffracted by the quartz grating in front of the UV Nikkor 105mm lens.
I then using geometry to create a wavelength scale to stick on the rear screen of the full spectrum Sigma fp.
This is in preparation for when I receive back another Sigma fp that is being converted to UVC mono, in a couple of weeks. Hopefully I will see a few more emission lines to the left side 

 

 
 

[dabateman]

Colin is 0 the light source? 

Do you think that redish UV line is the 365nm line?

If you blow the exposure way out can you see deeper lines in UV?

I am surprised thats all you see.

Maybe try a baader venus u filter or great UV stack on the camera to see if you see deeper into UV.

[colinbm]

@dabateman Thanks Dave
Yes 0 is the aluminium wire that the light is reflected off.
I have used a 340nm LED light & I only get the right hand side of the bell slope, not the peak bright line.
I just tried a 30sec exposure, but no difference at the UV end, but the very faint lines at the IR end are a bit clearer.
 

[colinbm]

I have another with the deuterium lamp.
It is showing a slight more to the left, maybe 350nm ?
 

 

[Lou Jost]

I hope your monochrome mod captures UV-C. I suppose a monochrome conversion is easier on these Foveon sensors than on a sensor with a Bayer matrix??

[colinbm]

@Lou Jost The Sigma fp is a Bayer CFA camera, with a Sony sensor.
I have a few of the Sigma Foveon cameras, they are not as good for UV but are better for IR photography,

[Lou Jost]

9 hours ago, colinbm said:

@Lou Jost The Sigma fp is a Bayer CFA camera, with a Sony sensor.
I have a few of the Sigma Foveon cameras, they are not as good for UV but are better for IR photography,

Oops, thanks for the correction. I had thought all Sigma cameras used Foveon sensors.

[JMC]

I would guess that the lack of visible lines below 365nm with the normal full spectrum is a combination Bayer filter strongly absorbing the light, along with the original sensor coverglass also absorbing the UV - these new coverglasses seem to start absorbing at around 400nm and then gradually get more and more opaque down to about 300nm where they block pretty much everything. The monochrome conversion will remove the Bayer obviously, but will also replace the coverglass (I am assuming with fused silica if you plan on seeing UVC). This will certainly improve sensitivity between 300 and 365nm. As for UVC if that is the goal, sensitivity will still be low compared with >300nm, so don't expect to suddenly see UVC as if it were 365nm for example. I've seen down to 254nm with one of mine (converted d850), but not below that as I don't have lights of shorter wavelength.

[colinbm]

@JMC Thanks Jonathan
I have asked for JGS1 or equivalent to be used in the mono conversion, I am wanting the furthest into UVC that this camera can give.
I have the UV Nikkor 105mm lens & lights from 200nm & up. The Deuterium lamp & the quartz grating will tell me what this camera see.
In a couple of weeks I will know.

[JMC]

8 minutes ago, colinbm said:

@JMC Thanks Jonathan
I have asked for JGS1 or equivalent to be used in the mono conversion, I am wanting the furthest into UVC that this camera can give.
I have the UV Nikkor 105mm lens & lights from 200nm & up. The Deuterium lamp & the quartz grating will tell me what this camera see.
In a couple of weeks I will know.

Ok Col. Good luck.

[colinbm]

@JMC Thanks Jonathan
I am sitting on the edge of my seat.

[Akira]

Which color mode do you use?  As you would know, SIGMA fp allows the color mode to be turned off, which should be suitable for assessing the response of the sensor.

[colinbm]

@Akira STD, standard colour mode & AWB, auto white balance. I shoot raw DNG & convert to jpg. No processing has been done.
I have also taken a spectra with a 296nm LED with the mercury vapour lamp. Sigma fp full spectrum converted camera.