Here's a question for you

[Andy Perrin]

'll be starting a project later in September (when the filters have arrived) which will prove whether my kit really can make images round 320-325nm. I'm going to try making 3 colour-separation images in the 320-400nm range so that I can create full-colour UV images. At the short wavelength end I'll be using a 315BP25 filter. Long exposure times are expected! Hopefully the OD 6 blocking factor will be good enough to prevent any longer-wavelength leakage.

I saw those filters on Omega Bob's ebay site. I thought about getting them, but at the moment I want to do the same project but on the OTHER end of the spectrum, in shortwave infrared. Because of the water absorption lines there, I think that will provide some very colorful results. I'm having trouble finding overlapping filters, though. If you don't overlap the filters, then you will get colors, but they won't necessarily have the same meanings as the visible light images, where (for example) yellow is in between red and green.

[bvf]

Have you checked out the Maxmax filters that Andrea mentioned? They've the best spectral curves I've seen, but may not have enough overlap for what you need. (And they're quite pricey for my taste.)

 

I had a look round Omega Bob's site for an IR tri-colour set, but all the IR filters have narrow passbands. Might be worth contacting Bob and explaining what you're after - he may be able to come up with something as he did for the UV end.

 

I'm also keen to try this in the IR - shouldn't have the problem with low sensitivity that I'm anticipating at 320nm.

[Andy Perrin]

Have you checked out the Maxmax filters that Andrea mentioned? They've the best spectral curves I've seen, but may not have enough overlap for what you need. (And they're quite pricey for my taste.)

Those are for near infrared (720-1000nm, depending who you ask). I am wanting to do shortwave infrared (1000-3000nm, also depending who you ask). I have a shortwave infrared camera, which is non-silicon (it is actually germanium on top of silicon) that I use. Check out our new SWIR tag! And our new SWIR sticky, written by moi!

[bvf]

Ahhh - my ignorance creeping out there. I'll have a look at the SWIR stuff - I'll probably be frustrated at seeing something else I'm not going to be able to do.

[dabateman]

Bernard, my ignorance also crept in. I assume you to only photograph indoors using controlled lights based on your amazing 3D image stacks that you have shared.

The Exo terra bulb is E26/E27 base. So I don't know of any battery powered unit that can hold one. I have only used them in desk lamps, directed at my subject inside. I have know idea what it would look like outside. I do have a corded lamp for hanging in a car or for utility work, where you can screw in a light bulb. I might try that one day.

 

Like this one:

https://www.ebay.co.uk/itm/Exo-Terra-Reptile-UVB200-Compact-lamp-25w/153463640873?hash=item23bb255329:g:odwAAOSwDPdcwWax

 

But you also said you have a housing for 8 black lights. Is this for straight long tubes? If so then you can see if you can fit in with other wavelengths. What I have learned about fluorescent lights is the first letter is the type, F for fluorescent, G for germicidal. The next number is the wattage and important for you ballast. You can place any same wattage bulb in you fixture. The next group like T5 or T8 is the pin configuration at the end of the bulb. This is the type of bulb your fixture will accept. Then there will be letter codes.

 

So a G4T5 bulb is clear 6 inch long bulb (you don't know length by code, I am just saying) that uses a 4W ballast and has a T5 pin out. So you can put it in a F4T5 fixture. The clear one will mostly output 254nm light and little visible, very dangerous and should be avoided.

Now G8T5e and G15T8e are phosphorus coated bulbs that output 302nm light and are 12 inch and 18 inches respectfully.

F8T5BL is coated, looks white and outputs a range of light from 365nm and up. Little 313nm Mercury line will also be available.

F8T5BLB is black coated. Filtered for just 365nm light. Typically used and sold as black light.

 

I haven't figured out the exact code for a 313nm light yet. One manufacturer uses different end color for the bulbs for each wavelength. But I don't trust that as a copy or counterfeit bulb may have it wrong.

 

For my camera 313bp25 is very green.

335bp10 and 340bp10 are green.

370bp15 is yellow

390bp25 is blue going to violet.

 

Your 315 and 345 may look the same. And if you can get a 313nm Mercury line bulb, may have less exposure time than your 345 filter as the closest mercury line is 335nm, but that line is very weak.

I again don't know what they will look like outside. The sunlight below 350nm is very low. So outside your 345 may look better.

I look forward to seeing your images.

 

[bvf]

Thanks for that, David - that's really valuable input.

 

My plan is to try daylight first for outdoor shots. I hope I can form an image at 320-325 nm, and if I can I recognise it's going to need a long exposure time. So I won't be doing any action shots!

 

For indoor work, I'll try flashguns first (with plastic lens removed). I use cheap-from-China (but powerful) flashguns, and it looks like the tubes are uncoated. Their output spectrum should be fairly even down to 320nm. I may have to use multiple flashes per exposure per shot to get enough light - when I was doing my analysis of UV capability of lenses using prisms I was using 40 flashes per exposure, but that was getting exopensive in terms of burnt-out flash guns!

 

If using flash is impracticable, I'll try continuous light sources - and that's where your info. becomes invaluable.

 

Hopefully I'll have my first result - or at least a good understanding of the (im)possibilities - by the end of September. I'm off on holiday for a while from tomorrow, and I hope the filters arrive and get through customs while I'm away.

[dabateman]

I was using the Canon 199A and didn't see much below 370nm that was better than a continuous light. A compact fluorescent black light was better. I just got 2 more 199A, but only one works. What is the Chinese flash you are using?

 

Also do you have a quartz lens? That will also be your main limit if not. I could see noisey junk through the igoriginal 35mm f3.5 and the Nikkor 80mm EL f5.6, but nothing usable. But that was using UVB ExoTerra bulbs. The 302nm G15T8e bulbs I have are more powerful, but I haven't tried a non-quartz lens with them.

 

[bvf]

I was basing my comment on this generic chart of Xenon flash tube output - haven't recorded where I got it from:

 

 

The following is specifically for a Nikon SB140 - still showing good output down to 300nm:

 

The flash guns I'm using are WanSen WS560. GN 50 (metres, ISO 100). Around $30 (which is good, as I have burnt about 5 of them out through too-frequent flashing).Very easy to remove the lens.

 

Alas, no nice quartz lens. I'm limited to the Kuri (clone), Cassar S, and El-Nik 105. So it is going to be a challenge.

[dabateman]

Ok I see now why you went with the 315 over the 313. You will be pushing just the 320nm to 330nm plus IR through that filter. You will need to get a 330WB80 improved filter, to stack with these filters for added IR suppression. I need to stack it with my 313bp25 filter on a quartz lens as it lets through just too much IR.

Your 345 will thus also be pushing mostly at 360nm so you should see a difference.

I will be interested in your 380 filter results. If its well blocked you maybe able to use that alone. My 390bp25, I can use alone and is my fastest UV only filter. It doesn't pass 405nm through, as I don't see that mercury line.

Only my 390bp25 and 405bp10 don't need to be stacked to prevent leak. My 302bp10, 313bp25 I stack with 330WB80 improved. My 335bp10, 340bp10, 370bp15, I stack with Baader venus filter to avoid IR leak.

 

[bvf]

Yes, my ubnsubtle approach is to blast as much white light as I can at the subject and hope there's enough UV in there to form an image. That's what you have to do outdoors in daylight anyway.

 

So as you say, vis and IR blocking will be key. The filters I'll be using offer OD 6 blocking, which hopefully will be enough. But I may need supplmentary blocking as I resort to long exposures to try and get an image at around 325 nm. The Baader U won't be any good, as that cuts off at 330nm. So I'd have to try S8612 (only 33% transmission at 320nm, but up to about 45% at 325nm) or U340 (about 80% transmission at 325nm - and enough IR blocking to boost the combined OD to over 9).

[Andy Perrin]

Bernard - sounds like the U340 is the better choice there because the S8612 will be changing very quickly in that region?

[bvf]

Yes, you're probably right, esp. with 80% transmission on the U340. But anyway it won't cost anything to try both!

 

I'm off on holiday now - hopefully I'll have something to report by the end of the month.