Am I getting an image at 303nm?

[Stefano]

Thanks Bernard. I like your Lily at 303 nm, really shows the strong absorption at these low wavelengths. These single element lenses are quite good if used properly, they will never be comparable to an actual UV lens of course, but if you don't want to spend thousands they do the job well.

[bvf]

I've tried again to get a daylight image using the 303BP10 filter, this time using a second U340 filter to add more IR blocking. This time did get an image - of sorts! Results are below. I'm confident this is a UV image - adding an R72 to the filter stack or simply closing the window killed the image.

 

Lighting was UK mid-winter sunlight at about 10.30 a.m.

 

So you can get an image at 303nm with a modified A6000 camera and a UVFS lens - but image quality is like Fox Talbot's images in Lacock Abbey. A high sun in the summer would of course reduce the exposure time, and the reduced UV scattering might might provide some more detail in the image. But it probably won't allow for prize-winning landscapes.

 

First, here's a comparison image through a 315BP20 filter + single U340. ISO 400, 30 secs, ISO 400:

 

 

Here's the best I could get through the 303BP10, with 2 x U340 (2mm I think) and a ZWB1 (again 2mm I think). Focus and framing are out as there was no liveview image to work with. Image straight out of the camera. f/11, 30 secs., ISO 3200:

 

 

And here's the image with some post-processing:

 

[colinbm]

I do like this one Bernard..."First, here's a comparison image through a 315BP20 filter + single U340. ISO 400, 30 secs, ISO 400 "

[Stefano]

Bernard, I think you can't get much more than this. 302 nm under sunlight is really the limit.

[bvf]

Bernard, I think you can't get much more than this. 302 nm under sunlight is really the limit.

 

I'm sure you're right. Of course, with a 303BP10 filter there is still a reasonable amount of transmission up to about 308nm, so this will have been contributing to the image.

 

But with flash I could get good images with the 303BP10, so this answered the original question, triggered by a comment from Cadmium: can the sensor on an off-the-shelf consumer camera, adapted to full spectrum, reach down to 300nm, with the limiting factor normally being the lens?.

[JMC]

Bernard, if you've not seen it here's some of my work on looking at sensitivity that far down - https://www.ultravioletphotography.com/content/index.php/topic/3150-enhanced-uvb-sensitivity-in-monochrome-converted-eos-5dsr/page__hl__%20sensor%20%20uvb%20%20monochrome

 

On my Canon the sensor coverglass itself was blocking all the short wavelength UVB even when the filter stack was removed. Removing that resulted in it being bale to see down to 308nm with my filter setup (and I suspect even lower if I had suitable filters and light sources).

[bvf]

Jonathan - if I understand that link correctly, with your multispectral 5D SR (which I assume means a standard camera with the internal UV/IR cut filter removed) you're effectively getting nothing at 308 nm.

 

Then you say you could get lower (at least to 308nm, perhaps deeper) by removing the cover glass. Not sure what you mean by the "cover glass" - a clear glass to replace the UV/IR cut filter, or the sensor's factory-sealed coverglass?

 

Alan Burch, who did my full-spectrum conversion, does not replace the UV/IR cut filter with anything. So if by "cover glass" you mean a UV/IR cut replacement, the full-spectrum Sony A6000 would be equivalent to your Canon with the cover glass removed and we're getting compatible results.

 

On the other hand, if by "Cover Glass" you mean the factory-sealed coverglass, then we're getting different results. The Canon needs to have this coverglass removed to get down to the low 300's whereas the Sony A6000 is getting down to 303-ish with that coverglass still in place.

[JMC]

Bernard, the cover glass I'm referring to is the one that's directly attached to the front of the sensor.

 

On some cameras this seems to be glass, on others something else. On my Eos 5dsr it started blocking UV just below 400nm, and by 300nm was essentially opaque. It was only when I had this replaced with a different cover glass (Schott WG280, and I've also had quartz on a couple of cameras) that I was able to see anything down that far.