Relatively cheap UV bandpass filters

[Stefano]

Second-hand UV bandpass filter wheel on eBay: https://www.ebay.com/itm/265176710496

[nfoto]

Should be ideal for our experimentally inclined UVP members ...

[dabateman]

Looks like someone bought it. They look better than the wheel I bought from him years ago. That is how I got my 300bp10 filter. The blocking wasn't great on my set.

[colinbm]

I got it to add to my UV sparticle :-)

[Stefano]

I bought a 340 nm bandpass filter from him, perfect together with 340 nm LEDs. Another 2 filters and I can do UV TriColour like Bernard (provided they have good blocking and I find a way to attach them).

[colinbm]

I bought a 340 nm bandpass filter from him, perfect together with 340 nm LEDs. Another 2 filters and I can do UV TriColour like Bernard (provided they have good blocking and I find a way to attach them).

 

They would be best behind the lens.

Perhaps a Low cost solution, make a 25mm, quartz, fused silica or BK7 lens & place the filter in the tube ?

[Stefano]

That would work too. The advantage is the increased sensitivity at shorter wavelengths. The Soligor goes down to about 310 nm, even a bit lower if one pushes it: https://www.ultravioletphotography.com/content/index.php/topic/4468-soligor-35mm-f35

 

Bernard experienced issues using the Soligor because it is a wide angle lens, and got better images with the 50 mm Focotar-2: https://www.ultravioletphotography.com/content/index.php/topic/3967-full-colourtri-colour-uv-and-ir (I can't make a direct link, but if you search in the first post you will find a discussion of the issue).

[colinbm]

But what is your sensors 'realistic' limit ?

[Stefano]

Good question. I only have the coverglass above the sensor, and I don't know how deep it passes UV. The sensor itself should reach 300 nm I think, this topic was discussed here: https://www.ultravioletphotography.com/content/index.php/topic/4201-am-i-getting-an-image-at-303nm

 

I don't want to generalize, but it seems the lens is usually the limiting factor. My camera is not the same as Bernard's, even the brand is different, so I can't compare them that easily, but I assume the sensors are more or less similar.

 

With my current lens 310 nm is the limit, and sunlight ends at about 300 nm (there was a graph somewhere, can't find it now), so even with a better sensor I can't hope for more. But honestly, the answer to your question is "I don't know".

 

Edit: found some graphs: https://www.ultravioletphotography.com/content/index.php/topic/2323-sol-solar-radiation-spectrum

 

There is some variability, but the end seems to be a bit below 300 nm.

[Stefano]

BTW, the seller has another filter wheel if anyone is interested: https://www.ebay.com/itm/265176692879

[ulf]

Looks like someone bought it. They look better than the wheel I bought from him years ago. That is how I got my 300bp10 filter. The blocking wasn't great on my set.

High blocking is not always that important.

 

I bought some 600 µm optical fiber-cables for UV from him to maximise the input from the integrating sphere to the spectrometer.

They worked fine.

[Stefano]

High blocking may be needed for uses like TriColour. I don't even know how I will mount mine, but I don't think it blocks UVA (out of band), visible and IR well-enough alone. For applications like Jonathan's fluorescence excitation (https://www.ultravioletphotography.com/content/index.php/topic/4628-thorlabs-fluorescence-standards-uv-wavelength-dependence) high blocking isn't needed. Thinking about that, I don't even know why I asked him if his filters had good blocking. OD 2 is probably enough.

[dabateman]

Ulf on a spectrometer used to filter light as designed, these are perfect.

But on a camera used optically, then you need to stack it to avoid the IR leakage.

 

I bought a set and a 300bp10 filter from him years ago. The individual 300bp10 filter ended up actually being a 310bp10 filter. This was actually excellent for me as it gave me 260, 280, 300, 310, 340, 350, 380, 400 bp10 filters in 12.5mm size. For light filtering they are perfect. For camera imaging, not so much as there are various IR and UV leakages. But all block out all visible light, which is good. Also all were about 20% transmission.

[Stefano]

Does he have a constant supply of them? Also, what brand are they? I guess either Thorlabs or Edmund Optics.

[Andy Perrin]

They look like Omega and are labeled like Omega filters.

[Stefano]

Thanks Andy.

[ulf]

The seller seams to sell broken up machine parts from outdated equipment.

Such parts can indeed be usable for other things.

If the filters in the filter wheels has been used to clean up and filter light from a high power UV-lightsource they can be a bit degraded due to heating, and even less well suited for photography.

Such configurations with filter wheels or quick filter changers are rather common in some measurement equipment.

[Stefano]

Other 340 nm bandpass filters, not as cheap though: https://www.ebay.com/itm/254947790588

 

I don't know this seller, so I can't tell if it is reliable or not. They sell other filters too, but not UV.

[Stefano]

I had a similar experience as David's.

I also bought (couldn't resist) a 300BP10 filter, as the graph indicated some transmission up to about 320 nm and so I could push my Soligor to the limit. He checked it and it actually peaked at 315 nm, which is actually much better as my lens transmits some there.

[JMC]

I bought one of the filter wheels from that guy along with a couple of other filters. The ones I got which were below 350nm had max transmission of 10-15%. The 258nm one had a leak at around 520nm. Not measured them above 800nm. Some of them were pretty corroded (oxidised) on the un-coated side. Not sure what I'll use them for yet, maybe a UVB/C sparticle.

 

The graphs.

 

[Stefano]

Interesting Jonathan, you have a very nice set now.

[colinbm]

Thanks Jonathan for the graphs.

I bought the first filter wheel so my filters are mostly the same.

My wheel hasn't even left America yet, so could be a couple of weeks yet.... :-(

[Stefano]

Others found on eBay:

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ebay.com/itm/NEWPORT-10LF10-325-LASER-LINE-FILTER-25-4-MM-325-2-NM-CENTER-10-2-NM-FWHM-/164724131671&ved=2ahUKEwiv0bzT46zxAhVzDmMBHR86DLoQjjgwAXoECAYQAg&usg=AOvVaw04eb14zkwOQ99G_6f0_Vw4

https://www.ebay.com/itm/124707156634

https://www.ebay.com/itm/274773696739

https://www.ebay.com/itm/254532495662

https://www.ebay.com/itm/333998074280

 

Not all cheap to my standards, but they are there if anyone is interested.

[dabateman]

I purchased previously your third link, the NBP360.

My sample leaks visible and IR so the 0.1% indication there is no lie. But if you use it with other filter you get a tight 360 or 370 peak. Mine is about 95% transmission at 370nm.

 

I still need to test it more to find its best purpose. If you needed a filter for a 365nm light source, it would work well.

[JMC]

Bottom one is slightly worrying - 225nm, 12nm bandpass. Advert says the OD is 1. Hopefully a typo....