UV TriColour and UVB photography with a Soligor 35 mm f/3.5 lens

[Stefano]

 

Of course not through a window. And not under clouds, etc.

 

But the point is exactly "10-15mW UVB 310 nm Led can easy beat sunlight 310nm if distance be some first cms."

 

Stefano said it's not much, but it certainly is, if we are comparing the LED to the sun in his photos above.

 

 

Usually LEDs aren't that monochromatic. There's usually 20nm spread or so, isn't there?

I too think that the amount of UVB in sunlight should be really low, but the LED is not very powerful. I think the Sun appeared brighter in live view than the LED (when I took a photo of the Sun).

 

LEDs aren't monochromatic, but they tend to be more so as the wavelength decreases. The transmission of my lens is much higher at 315 nm then at 310 nm, and so is the intensity of sunlight (not that much higher, but still higher). My LED is not very useful for photography with my current setup.

[Stefano]

Nope,

The SvBony 0.5x focal reducer is a single positive meniscus element lens about 21mm diameter mounted in a 1.25 inch holder.

You can easily remove that single coated element from the holder and mount it into a 25mm filter ring.

Its K9 glass equivalent to Schott B270 glass. Its very high transmission at 310nm, atleast 80%. But I can't properly do absolute transmission curves, so best not show one.

David, if the transmission is 80% that would be awesome. As I suggested, if you take a photo of the lens at 313 nm you can more or less see how transparent it is. If it looks mostly transparent, then we can say it is usable there.

[Andrea B.]

I don't want to interrupt your discussion, but I want to post a test for Andrea.

Thank you for trying!!

I need to get in gear and order myself a 310 and 320 nm, preferably narrow.

[colinbm]

What are the Chinese filters you are using ?

[Stefano]

I bought them from here: https://m.it.aliexpress.com/item/1005001777401409.html?browser_id=4dc5b6e7ae19418f8626b54c0740de76&aff_trace_key=66832033ccbb4d7a98fc4f0ee8f3dba9-1625764745313-00163-UneMJZVf&aff_platform=msite&m_page_id=17a872cf4e32107964cd1c798028ba00c295723936&gclid=&_imgsrc_=ae01.alicdn.com%2Fkf%2FH04dc8b595170452d99ae8beefd2674dbf.jpg_640x640Q90.jpg_.webp

 

He (or they) also sell other filters at other wavelengths, and they sell those 310 nm filters too. I suggest contacting the seller if you want one.

 

I have no affiliation with the seller.

[colinbm]

Thanks for that link Stefano, looks good...

I tried the quartz single lens with a 310nm filter in sunlight & I could see no-thing.

 

Pointed at the Sun at 8000/sec I got a tiny dot of bright light, here below is a 100% crop....

 

[Andy Perrin]

colin, 1/8000th? Even with that filter not passing much, it can't be good for your sensor if it exposed that quickly, it's like shining a magnifying glass on it.

[colinbm]

Yes I have always wondered, but with such a dark filter ?

[colinbm]

I took the lens off the camera & went outside in full sunlight & focused the lens on my hand, after 10 seconds I only noticed a small increase in temperature ?

[Andy Perrin]

How dark can it be if it exposed in 1/8000th? My solar filter (which is intended for the purpose) exposes in more like 1/15th.

 

The hand test is more convincing if aperture was the same. Not sure if photobleaching is an issue though

[colinbm]

Probably way out of focus too.

I wasn't going to cook my face while trying to get focus on such a tiny spot ?

[Stefano]

Colin, do you have a 310 nm filter?

Try to see what you see with a diffracton grating and the Sun. I did an experiment some time ago where I imaged a halogen bulb with the 310 nm filter (single) with a diffraction grating, and I saw an orange bump (I get orange at around 340 nm) and a green bump (310-315 nm). By putting a magnifying glass on top of the halogen bulb, the green bump disappeared and the orange one stayed. I can post the images later if someone is interested.

[colinbm]

Yes I have a 310nm filter. That is what I took the Sun with above.

I could see an orange flare in the lens, but no green.

I haven't seen a diffraction grating showing below about 360nm ?

I don't know how you could see 310nm with a diffraction grating & a halogen bulb ?

[Stefano]

In this forum there is a transmission spectrum of the grating I used somewhere, I think Ulf posted it. It does reach the low 300's, but it's not very transparent there.

 

Halogen bulbs (especially the older uncoated ones) do emit some UVB.

 

Also, Jonathan saw green too at 308 nm: https://www.ultravioletphotography.com/content/index.php/topic/3150-enhanced-uvb-sensitivity-in-monochrome-converted-eos-5dsr/page__view__findpost__p__25927

[Stefano]

Here it is: https://www.ultravioletphotography.com/content/index.php/topic/2643-first-attempt-with-linear-filter-grating/page__view__findpost__p__19967

 

Well, it doesn't seem to reach 310 nm, so now I wonder if I saw something else.

[ulf]

Halogen bulbs (especially the older uncoated ones) do emit some UVB.

 

Are you sure about that it is a meaningful amount of UV-B?

What is your source for that statement?

 

Normally all incandescent lamps act reasonably similar to black body emitters if the glass / quartz bulb allows.

 

The bright ones with high colour temperature often has quartz bulbs to handle the heat and need forced cooling.

They have often a lifetime rating of 50 hours or so.

I have experimented a bit with such lamps for calibrating my spectrometer for a relative output power linearisation.

 

The old dentist curing lamps also used such lamps, but only for curing UV-A sensitive filling materials.

[Stefano]

Halogen bulbs are sometimes used for reptiles to provide some UVB light.

 

Here you can calculate blackbody curves and you can see that at 3000 K the intensity at 300 nm is about an order of magnitude less than the intensity at 400 nm.

[ulf]

Halogen bulbs are sometimes used for reptiles to provide some UVB light.

 

Here you can calculate blackbody curves and you can see that at 3000 K the intensity at 300 nm is about an order of magnitude less than the intensity at 400 nm.

I was not saying that there were no UV-B just very little compared to all the other output.

The special halogen reptile lamps for UV-B might be mercury-doped to get some extra deeper UV.

[Stefano]

I am not at home now, but I will post my images as soon as possible.

 

I agree that the UVB output is almost zero compared to UVA + VIS + IR, but it seems that my filter is good at blocking that. Also I think I was using 4 or 7 mm of ZWB1 stacked on the filter to block IR.

 

I tried to point a 365 nm flashlight at the camera with a single 310 nm filter, and my camera saw nothing. This indicated very good blocking, at least at 365 nm.

[dabateman]

Stefano,

The practical cut off for that grating is 320nm. Your not really going to see anything below that.

The bulb Jonathan was using in that test was a special HgXe bulb for a spectrometer. The Hg part stands for Mercury, so he was using the weak Mercury lines.

Yes I too have a couple reptile heat lamps, but they are Mercury bulbs as well.

 

An uncoated halogen bulb, like I also have, there is nothing below 350nm. And that 350nm is very weak compared to the IR. Its a very good bulb to see the IR leakage through the Baader venus u filter.

[Stefano]

I'm back with some tests.

 

Halogen bulb test

 

.CR2 images rendered as .jpg in Photo Ninja removing all ticks (raw colors).

 

f/3.5(?), ISO 1600, 120.5 s exposure. Single 310 nm bandpass filter + ZWB1 glass (7 mm ?) + diffraction grating on the lens:

 

f/3.5(?), ISO 1600, 120.3 s exposure. Single 310 nm bandpass filter + ZWB1 glass (7 mm ?) + diffraction grating on the lens, magnifying glass on top of the halogen bulb:

 

You can see how the green band disappears.

 

 

Sun grating test

 

.CR2 image rendered as .jpg in Photo Ninja removing all ticks (raw colors).

 

f/3.5, ISO 25600, 1/15 s exposure. Double 310 nm bandpass filter + diffraction grating:

 

Notice how the diffracted image (on the left) is almost a perfect circle, this means that it is very monochromatic. The multiple Suns are due to the alignment of the filters, as rotating them rotates the pattern.

 

Sun leak test

 

.CR2 images rendered as .jpg in Photo Ninja removing all ticks (raw colors).

 

f/3.5, ISO 25600, 1/4000 s exposure for all images.

 

Double 310 nm bandpass filter:

 

Double 310 nm bandpass filter + diffraction grating:

 

Double 310 nm bandpass filter: + BrightLine 340/26 filter:

 

With more exposure, I can push a leak through the 340/26 filter. This filter has 1% transmission at ~323.3 nm: https://www.avr-opti...ers/ff01_340_26

 

Other photos

 

The Sun at around 3 PM was bright enough to take some (noisy) images, still better than usual.

 

.CR2 images rendered as .jpg in IrfanView keeping the green channel only. All with double 310 nm bandpass filters.

 

f/3.5, ISO 25600, 60.4 s exposure.

 

f/3.5, ISO 25600, 60.1 s exposure.

 

f/3.5, ISO 25600, 60.1 s exposure.

 

Edit: the first halogen tests were done stacking the 310 nm filter with 7 mm of ZWB1 glass (if I remember correctly). This was done to remove IR leaks, but shouldn't change the UV spectrum much.

[ulf]

An uncoated halogen bulb, like I also have, there is nothing below 350nm. And that 350nm is very weak compared to the IR. Its a very good bulb to see the IR leakage through the Baader venus u filter.

That is exactly what I have experienced.

There are also some expensive calibration lamps for spectrometers that are halogen lamp based. They to only reach around 350nm.

 

I expect anything else going deeper is helped by mercury.

[Andy Perrin]

Ordinary undoped halogen is rotten for UV imaging. It is lovely for near infrared and SWIR. My halogen can blast IR through most UV filters and stacks I own, except the thickest S8612 stacks. It is a bad choice for UVA imaging much less UVB.

[Stefano]

Yes, in fact I needed a long exposure just to photograph the filament. My LED, which is still useless, looks perhaps 10-100 times brighter.