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Black background for full spectrum imaging

Newbie here.

I am looking for buying advice in order to get a completely black background in both UV, visual and IR light.

To be clear, I want advice on materials (or possibly paint) that reflect practically no light, including no ultraviolet and no infrared light.
Is black felt for instance a good material for such a totally black background? Or will I get some UV or IR radiation from felt?

Hopefully the ultra-black material won't cost me (another) fortune...
 

Jerome Marot

Well-known member
I have no idea about a material, but you can always get a dark background by constructing an enclosure protected from light behind the subject. That works at all wavelengths, obviously.

Black fabrics usually reflect quite a bit of IR, so black felt is probably not going to work.
 

Dr Klaus Schmitt

Well-known member
Newbie here.

I am looking for buying advice in order to get a completely black background in both UV, visual and IR light.

To be clear, I want advice on materials (or possibly paint) that reflect practically no light, including no ultraviolet and no infrared light.
Is black felt for instance a good material for such a totally black background? Or will I get some UV or IR radiation from felt?

Hopefully the ultra-black material won't cost me (another) fortune...
Hey Lars,

this is a tricky one, as most materials change their behaviour outside the visible spectrum, as I had the same problem for my multispectral photography.
There are ultra black materials based on nano-fibers (Vantablack) but extremely expensive and also very difficult to handle as it cannot be touched, since
the vertical nono-tubes easily break. There is a special black color which was invented by a british artist, but he only sells it directly and only to people he
trusts, so not that easy to get. It is made by UK artist Stuart Semple as "Black V3.0" but also his V2.0 black is pretty darn good! Here is a source.

I don't have both, but I use a special felt like black flocked material called PROTOSTAR which is being used in astronomy to absorb internal reflections in mirror
lenses for astronomy, rather easy to use and pretty good, yet not completely black (so has a tiny bit of residue color). If I was you, I would start with that and
see how it performs, as it is no big investment. Be careyful not to get fingerprints on it, as it immediately shows, wear gloves to attach it!



Velvet is another option (see HERE) if you need to hang it, but I'm not sure about UV and IR, never tested that.

As an example, look at these works of mine, done against that black PROTOSTAR background and see what you think about it:

Visible Light:



Ultraviolet Light:




Infrared Light:
 
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Thanks again.

I saw the graph in the other link you posted with the graph which made me jump on it. Even though it's not as black in the IR region as the visible, I think and hope it will be enough. For my purpose and lighting conditions, I expect IR level to be moderate as worst.

The reason I want such a black background is that I want to be sure that any light in the UV and IR range that the subject emits will be visible on the (full spectrum converted) camera and not covered up by or mixed with light from the background.
 
Lars,

What are you photographing. Also please describe your camera and optics!

Asher
Hmmm. I thought I could get away with not saying exactly what it is... Since it's a kind of test where I don't know if I will get anything at all on the camera, I will only say what it is, when and if there is a result at all. Sorry, I know this sounds mysterious, but I won't embarrass myself with first saying what the goal is and then later find out that it was impossible.

Regarding camera and optics, I have just received my (Jenoptik) Coastal Optical 60mm f/4 UV-VIS-IR Apo Macro lens. That's going to be my main lens. Before that I have bought a few UV-capable lenses based on advice from Klaus Schmitt's blog (and other sites I think): an old EL-Nikkor 80mm f/5.6 and a Kuribayashi 35mm f/3.5 clone plus I have a 28mm f/3.5 lens on the way too.

The camera for this project is on the way, so not much fun yet. I went for a full spectrum converted Sony a7 (first gen) camera since it's full frame and doesn't have issues with internal IR light at high ISO and long exposures that the later versions allegedly has. (I don't know yet if that precaution was necessary though.) In addition, I have ordered a bunch of filters - both UV pass, dual band (UV + IR) and IR pass. I only have two of them: one UV pass and one hot mirror type. The rest is on their way (hopefully).
 

Asher Kelman

OPF Owner/Editor-in-Chief
You are committed to this! That’s awesome. This is a thrilling adventure and we are rooting for your success!

I do things that I am hardly qualified to do all the time, but I get the best advice and plan very carefully and mostly succeed!

So this project of your resonates!

Asher
 
You are committed to this! That’s awesome. This is a thrilling adventure and we are rooting for your success!

I do things that I am hardly qualified to do all the time, but I get the best advice and plan very carefully and mostly succeed!

So this project of your resonates!

Asher
Thanks for the encouragement. I should perhaps add that I bought the CoastalOpt lens used locally at a reasonable price. At first, I didn't even consider it for the second hand price, but in the end I convinced myself that I could just sell the lens after the project is completed and probably not lose much (if anything).
 

Asher Kelman

OPF Owner/Editor-in-Chief
Thanks for the encouragement. I should perhaps add that I bought the CoastalOpt lens used locally at a reasonable price. At first, I didn't even consider it for the second hand price, but in the end I convinced myself that I could just sell the lens after the project is completed and probably not lose much (if anything).
Lars,

Considering the value of doing something you dearly wish to accomplish, the cost of a high end respected tool is often not only wise, but also relatively painless.

As, by it’s already recognized name and value it is likely to be sight by others in the future!

Asher
 

Dr Klaus Schmitt

Well-known member
Thanks for the encouragement. I should perhaps add that I bought the CoastalOpt lens used locally at a reasonable price. At first, I didn't even consider it for the second hand price, but in the end I convinced myself that I could just sell the lens after the project is completed and probably not lose much (if anything).

Wow, I'm impressed. I was lookig for one for many years...but that hotspot issue and dwindling performance at deeper wavelengths made me rather invest into several UV-Nikkors 105mm...
 
Wow, I'm impressed. I was lookig for one for many years...but that hotspot issue and dwindling performance at deeper wavelengths made me rather invest into several UV-Nikkors 105mm...
It was pure coincidence and luck that a photographer here in Norway had his Jenoptik / Coastal Optical lens in mint condition up for sale. Regarding the hotspot issue, fortunately it's only at short focus distances and that is solved when using a (long and narrow) hood. The decrease at longer(?) wavelengths that you mentin is not something I have read, but for my purpose, this lens is probably the best available.

And by the way: The flower in UV, visual and IR you posted above, is beautifully photographed.
 

Dr Klaus Schmitt

Well-known member
It was pure coincidence and luck that a photographer here in Norway had his Jenoptik / Coastal Optical lens in mint condition up for sale. Regarding the hotspot issue, fortunately it's only at short focus distances and that is solved when using a (long and narrow) hood. The decrease at longer(?) wavelengths that you mentin is not something I have read, but for my purpose, this lens is probably the best available.

And by the way: The flower in UV, visual and IR you posted above, is beautifully photographed.
Thank you! Sounds like Birna / Bjorn Roerslett actually.... ;-) And indeed, that problem could be mitigated, we talked about that a few years ago when this came up. Jenoptik saw no need to work on this.
 
Thank you! Sounds like Birna / Bjorn Roerslett actually.... ;-) And indeed, that problem could be mitigated, we talked about that a few years ago when this came up. Jenoptik saw no need to work on this.
You are welcome. And I would also like to thank you for all the testing etc. you have done and shared at your blog.

Regarding the seller of the CoastalOpt lens, I agree that a good bet would be Birna & Bjørn Rørslett, but for the record, it wasn't.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Lars,

You have all your lenses then?

I hope you will get some pictures with your optics outside of your special undisclosed goal!

Since you are privileged to both live in Norway and have the capability, can you share with us with more mundane subjects?

Asher
 
Lars,

You have all your lenses then?

I hope you will get some pictures with your optics outside of your special undisclosed goal!

Since you are privileged to both live in Norway and have the capability, can you share with us with more mundane subjects?

Asher
I don't have all my UV-capable lenses yet. A 28mm is still in the mail and a rear lens element to the 35mm is also in the mail (since the rear element was in really bad shape). And the EL-Nikkor I have bought unfortunately has haze which I so far haven't removed completely. I am going to soak the lens elements in lighter fluid for a couple of days and see how it goes, but if that doesn't help, I will have to buy another.

Regarding sharing images, I would then post outside this sub-forum since I still haven't received my full spectrum converted camera. However, I have uploaded images I did in a short test with the CoastalOpt 60mm f/4 lens on my Nikon Z6 versus three other lenses in the same focal range that I have: Nikon Z Nikkor 50mm f/1.8S, AF Micro-Nikkor 55mm f/2.8 and Voigtländer Nokton 50mm f/1.2 Asph VM. All shot at optimum f-stop. As I said, it's just a short test, nothing more. Here's the link:

 
Hey Lars,

this is a tricky one, as most materials change their behaviour outside the visible spectrum, as I had the same problem for my multispectral photography.
There are ultra black materials based on nano-fibers (Vantablack) but extremely expensive and also very difficult to handle as it cannot be touched, since
the vertical nono-tubes easily break. There is a special black color which was invented by a british artist, but he only sells it directly and only to people he
trusts, so not that easy to get. It is made by UK artist Stuart Semple as "Black V3.0" but also his V2.0 black is pretty darn good! Here is a source.

I don't have both, but I use a special felt like black flocked material called PROTOSTAR which is being used in astronomy to absorb internal reflections in mirror
lenses for astronomy, rather easy to use and pretty good, yet not completely black (so has a tiny bit of residue color). If I was you, I would start with that and
see how it performs, as it is no big investment. Be careyful not to get fingerprints on it, as it immediately shows, wear gloves to attach it!


Velvet is another option (see HERE) if you need to hang it, but I'm not sure about UV and IR, never tested that.

(...)
For reference and possibly of value to others reading this thread, I want to report my initial findings now that I have received the black velour with self-adhesive back from First Light Optics. Immediately when I saw it indoor under halogen lamps, it didn't appear as dead black as I had hoped, but after looking at it in cloudy daylight, it looked not too bad, but still less black than I hoped.

It is also important to note that the black velour flocking material First Light Optics sell is actually and unfortunately not as black as Protostar. The material I bought from FLO is D-C-Fix velour foil/film. A test shows that the D-C-Fix velour is not nearly as black as Protostar. See here:



I will use the D-C-Fix velour now I have bought it and see how it does. It may be black enough in practice.
 
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Asher Kelman

OPF Owner/Editor-in-Chief
You have done a great job.

Watch out for birefringence of some synthetics. Some synthetic blacks are a very very dark purple.

Can you get mesh of the darkest material.

That over a deep box lined with the darkest velvet would be very, very black!
 
Update:
My initial impression regarding the D-C-Fix velour was right. It reflects quite a lot of IR compared to ordinary black paint. See attached photo.

(Short version of my original post that I can't get posted even though I have been trying countless times the last days.)

Black velour versus regular black paint.jpg
 
What surface do you need to blacken?
I think a smooth surface will be best as long as I have the two halves angled toward each other, so they reflect each other so to speak: black against black.

I might try to go to a shop selling (clothing) fabrics with my full spectrum converted camera and the above black velour and paint to see if they have anything blacker in UV-VIS-IR.
 

Asher Kelman

OPF Owner/Editor-in-Chief
If you have a piece of aluminum, wipe it down with blackening solution from a Good hardware store. It’s actually dilute phosphoric acid and turns the metal black. Or you can use matte anodized aluminum.

Asher
 

Asher Kelman

OPF Owner/Editor-in-Chief
You need the Vantablack and likely you will be allowed to receive it as you are doing research. You can enquire here. But it’s best if you have an academic appointment in a university or from a business as they absolutely don’t sell to private individuals.

you have to check that it works in the UV spectrum too!

Asher
 
Thanks for your suggestions, Asher. I will have to pass on the Vantablack for more than one reason (price is going to be stratospheric is one of them), but I will consider using (diluted) phosphoric acid on aluminium. Another option is to use the super black paint that Klaus referred to in an earlier post.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Thanks for your suggestions, Asher. I will have to pass on the Vantablack for more than one reason (price is going to be stratospheric is one of them), but I will consider using (diluted) phosphoric acid on aluminium. Another option is to use the super black paint that Klaus referred to in an earlier post.
There are now alternatives to Vantablack that are even less reflective. BTW, one can get a sample on Aluminum foil for $50. What size do you need?

Asher
 
I have decided to go the less troublesome route and ordered the super black paint. Since ordinary black paint was black in IR too, I hope "Black 3.0" will be as good and hopefully even better than that. In the above UV shot, exposure is 10 and a 1/3rd stops higher than in the IR shot and 11 stops higher than the unfiltered full spectrum shot, so UV response is low. Shipping from the UK and getting it through the customs here in Norway means I will expect to receive it in about one or two weeks.
 
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