What man made materials reflect UV?

[Doug A]

Would like to build a "light dome" to place small objects in. Camera and flash would shoot thru hole in roof and the UV light would be bounced around inside. Does aluminum foil reflect UV light? Any other reflective material to try?

 

Thanks,

Doug A

[Fandyus]

Aluminum foil should do. If you want to go really fancy, PTFE sheets.

[Kai]

Look at:

Reflectance - Wikipedia

The pure aluminum surface is therefore perfectly suitable from at least 200-400 nm: neutral in color and highly efficient!

Thin coatings (aluminum oxide) could have an impact. I don't have any literature facts.
But for a long time I used anodized aluminum instead of PTFE as my WB standard for UV-A. The difference to PTFE is not significant in the range 330-400 nm. 

[Andrea B.]

Kai: ...anodized aluminum instead of PTFE as my WB standard for UV-A.

 

That is *very* useful to know, Kai. Thanks.

---

 

 

Doug, I'm not sure you want too much light bouncing around in a photo dome because the light could bounce back into your lens and cause some interesting flare artifacts?? But I will be eager to hear how it works out.

[Andy Perrin]

You want diffused light in a photo dome generally. You don't want aluminum foil with a shiny surface, but perhaps the "dull" surface would do. PTFE seems better for this job to me though!

[Doug A]

Thanks for the link @Kai. It is very informative. Also glad to know anodized aluminum works well for UV WB. Board wrapped with Plumber's tape is so fragile. Supposedly even fingerprints ruin it.

 

@Fandyus thanks for validating aluminum foil. Might investigate PTFE sheets.@Andrea B. agree that flare could be a problem. It might work since the lens will be outside the dome. Have to see. 

@Andy Perrin good point about diffused light. Years ago I built John Shaw's ice cream bucket "light dome". It had a hole cut in the bottom and aluminum foil wrapped inside half the dome. An electronic flash shoots thru the white plastic side wall opposite the aluminum and bounces all around. It produces some of the most glowing, soft light. Hoping it works for UV. I'll modify the design by cutting a window in the side wall for the flash head to shoot thru. 

 

Thanks,

Doug A

[Doug A]

Built a test "dome" today and tried it. Instead of my average ~ISO 1600 At F8 this dome allows ISO 400 at F11. A gain of 2-3 full steps. Wow! that's more than adding a second flash. Granted the angle one can shoot at is limited. It works best for small flowers, low to the ground. But, it does protect the flower from wind. Shot this during 10-15mph wind. Not bad for ~2x lifesize. Wish I'd shot this earlier in the day, before the flower started closing. 

 

Pentax FS K-1, Pentax bellows, Olympus OM 80mm F4 macro head with ZWB1 2mm/BG39 2.3mm stack. Flash filtration hasn't arrived yet. Used standard UV sun camera WB and corrected purple tint with Silkypix. 

 

Used the shiny side of the foil facing the subject. Light quality seems decent to me. I'll build the next dome a little bigger so the lens and bellows can fit through the top hole. Let me know what you think.

 

Thanks for looking,

Doug A

[colinbm]

Looks very good Doug

[dabateman]

Can you show a photo of your dome?

I am having a hard time visualizing it.

Is it like this:

http://www.exo-terra.com/en/products/light_dome.php

 

Or more like this:

https://petapixel.com/2021/03/25/photographer-invents-clever-reflection-blocking-box-for-shiny-products/

[Doug A]

Thank you @colinbm. @dabateman here is a quick pic of the "dome" taken with a Pentax Q. Camera shoots thru hole in the top. Dome is completely lined with aluminum foil, except for the flash slot. The dome needs to be a little larger so the lens and bellows can fiy thru the hole. This dome was made years ago and a bellows wasn't used then.

 

Thanks,

Doug A

[dabateman]

Interesting,  so like a coolwip tub with the bottom cut out.

I was thinking very differently. 

I should make something similar with maybe PTFE wrapped around, or Aluminum foil. 

[Kai]

5 hours ago, dabateman said:

Or more like this:

https://petapixel.com/2021/03/25/photographer-invents-clever-reflection-blocking-box-for-shiny-products/

 

Wow - that's really awesome!!!

[Kai]

That looks very promising, Doug!
I'm looking forward to the pictures.
How do you do that with the modeling light? 

[Doug A]

1 hour ago, dabateman said:

Interesting,  so like a coolwip tub with the bottom cut out.

I was thinking very differently. 

I should make something similar with maybe PTFE wrapped around, or Aluminum foil. 

Yes, but CW tub didn't work years ago for his photography. John Shaw's original design shot the flash thru the plastic wall and aluminum foil covered only the opposite half of the tub. So  CW tub was too opaque. One looked for the more translucent plastic to let more light in.

 

UV won't make it thru any plastic. So a slot has to be cut in the plastic to let thee weak UV in. Now a CW tub would work. But, it may be too small. My next will be a bigger 10-12" across tub to allow lens and bellows in. Instead of cutting a concentric hole in the bottom, I'll try more of a slit like an observatory dome.

@Kai I just set the lip of the dome on the NEMO that was on the ground. Might cut as hole in dome next time to stick torch thru.

Plan was to use all the weak UV and not waste any. 

Thanks,

Doug A (eating ice cream)

[dabateman]

Try searching for clear PMMA boxes. There are also many dome options.  Someone was using that for underwater UV.

There seems to be many options. Some but not all PMMA can transmit UV down to 260nm.

 

Editing above based on Ulf comments.  I have been lucky with UV-t grade PMMA. Many of the ebay suppliers seem to have that. I didn't even know there is UV grade PET. But now searching I see that as another option. 

So there are plastics with excellent UV transmission.  Just make sure you get the correct one. Asking a distributor would be best rather than buying a random dome. 

[ulf]

13 hours ago, dabateman said:

Most but not all PMMA can transmit UV down to 260nm

Do you have a source for this statement?

I thought it was only a few types of PMMA that transmitted UV well.

[dabateman]

Maybe I have been lucky and always gotten a UV-t grade.

I was just reading this again. See figure 5. Some are definitely not good for deeper UV transmission. silo.tips_optical-transmission-characteristics.pdf

 

Look for the word "crystal clear PMMA" that seems to be the high UV transmission grade according to the PMMA propaganda website. 

[colinbm]

What man made materials reflect UV?
Just to get up to speed on this, are we talking about, ' what reflects UV false colour yellow at 350nm lighting ' ?

[Andy Perrin]

Yeah, I think that’s the problem area Colin. A good false yellow pigment is hard to find. It actually is very similar to the issue we have on the short end of the visible spectrum — vis blue pigments are also notorious for being hard to source. There are really only like 4 or 5 good ones. 

[Guest]

Can you just set out a bunch of stuff in the garden and see if the bees flock to it? 

[Andy Perrin]

Hah, BlazerOne. 

[colinbm]

Do we know which pixel, RGB, or combinations gives us the false colour UV yellow around 350nm ?
 

[Stefano]

I think it is raw red. That’s usually the raw color around 350-360 nm, and it becomes orange around 340 nm.

[colinbm]

16 minutes ago, Stefano said:

I think it is raw red. That’s usually the raw color around 350-360 nm, and it becomes orange around 340 nm.

Thanks Stafano

[colinbm]

This is the best I can find at the moment

https://www.visionsystech.com/blog/creating-color-bayer-cfa-color-filter-array