Why Don't UV / Protection Filters Cut UV ?

[Cadmium]

I am simply not buying that UV eye glasses test photo. And why do you need to use a tri-band filter set up for such a test?

There is something wrong there.

Here is a pic I took outside (again high ISO for hand held), PTFE background sheet, Uvex Amber, sunshine. Baader U, also with U-340 8mm, same, totally blocked.

This was shot under an shed roof that has a skylight, that is the blueish reflection, and other reflections, disregard those reflections.

Look at the top or bottom parts of the glasses, the black part, that has sun illuminated PTFE behind it, but it is black.

However, never look at the sun through such UV protection glasses. For that, only use #12 or #15 welders filter, or ND5 astro sun filter such as the one made by Baader.

 

[Stefano]

Are they dark blue? It seems to me that they are casting a blue shadow.

[bvf]

OK, hands up - I've got leakage. Hadn't been able to detect it before, but it's there. Here are my test shots today through the UVEX glasses:

 

 

All the filters leak IR (as shown by sandwiching them with an R72), and in addition the 380BP20 leaks in the visible. The material here makes the leakage seem huge, but in reality the leakage has not been noticeable in images (e.g. no bright vegetation, no colouring from visible light), and if you look at the sky through the 380BP20 you can see the sky, but only very faintly.

 

I guess the way to purify the 380BP20 and 345BP25 images is to combine them with the Baader U. This won't work for the 315BP25, but I could use an S8612 - although this will aggravate the already very low sensitivity. And I'm not sure there's much benefit. Here's a couple of shots I took outside the back door just now - one through the 380BP20 and one through 380BP30 + Baader U: not much difference.

 

 

[Stefano]

Do you have Hoya U-340 in 4 mm thickness? It transmits well even below 300 nm, but blocks all visible light and strongly attenuates infrared light.

[bvf]

Good point.

 

I do have a U340, but I think it's only 2 or 2.5mm. But wpuld probably be a good filter to use with the 315BP25 and perhaps the 345BP25.

[dabateman]

Depending on the amount of leakage a U340 filter can be the best cure.

I use a 2mm U340 with my 303bp10 filter to block the IR and visible leakage, fortunately outside its leakage points.

I also have used it with others.

 

Testing is best to know.

 

I think I will still spec my amber and orange glasses when I get a chance. This thread has made me interested again in their blocking potentials.

[Stefano]

Hoya U-340 is a very versatile glass. One of my favourite.

[Cadmium]

Are they dark blue? It seems to me that they are casting a blue shadow.

 

No, they are black. Any blue is from the reflection of the the skylight. They are black. Go read the many previous links and topics talking about these Uvex glasses.

Get some if you ever can, they are the best. Ask Bernard where he got his.

https://www.ultravioletphotography.com/content/index.php/topic/2614-uv-eyewear-protection-upgrade/page__view__findpost__p__19704

[Cadmium]

Bernard, Are all those tests shot with the exposure time, same aperture, ISO, all settings exactly the same?

[Cadmium]

Bernard, the top left shot, should not show anything except black if exposed at any realistic exposure time/settings.

I would like to see a shot of any scene, optimal settings and exposure, then the same shot through Uvex, with same settings, lighting, scene.

Such a test should show black only.

 

Also, if you are getting any image like you show with the Baader U + R72 then that is an unrealistic shot, that is a pushed exposure, no normal exposure would ever show any leak through the Baader U,

only extended unusual exposure times would show anything except black.

It is best to start out with realistic exposure times.

[Cadmium]

Do you have Hoya U-340 in 4 mm thickness? It transmits well even below 300 nm, but blocks all visible light and strongly attenuates infrared light.

 

I think he would need more than 4mm for that, and it would loose most of the 380BP20.

 

[Stefano]

Yes, not ideal for the 380BP20 filter, but if his filters are, say, OD 3 or 4 it should fix his leakages (unless they leak UV in the rejected band).

[bvf]

Cadmium - yes, these were unrealistically high exposures. The ISO ratings are on the comparison image. Otherwise, the exposure were all the same. Illumination was 2 flashguns (GN 50) at about 15 cms from a white PTFE sheet. I wasn't trying to simulate normal exposure conditions, but rather to push the limits to see what happened.

 

Re, the U340, the idea is to use it to supplement the IR blockage of the existing 315BP25, which already has a high level of blockage, rather than doing all of the IR blockage itself. At 720nm, a 2.5mm U340 will reduce the already weak IR leakage by a further factor of 40 or so.

 

I'm happy to accept that the Uvex glasses so their job, so I probably won't do any more work in that area. I'm more interested to see what the effect of all this is on tri-colour UV - hopefully it will turn out to be not too significant.

[bvf]

I've now done a couple of comaprison shots for tri-colour UV between using just the base tri-colur filters and adding additional vis/IR blocking filters to them.

 

It looks like the outdoor shots show no difference. However, the shot of the orchid is noticeably more contrasty when the blocking filters are used: this is counter-intuitive to me as I would expect more glass to lower contrast through reflections off the surfaces, but I guess the additional IR blocking is defeating the tendency of IR to show all vegetation (inc. flowers) as white.

 

 

[Andy Perrin]

Wow, the orchid improved dramatically.

[dabateman]

Colin back to the original subject of this thread, this article is interesting:

https://kolarivision.com/uv-filter-effectiveness-article/

[colinbm]

Interesting thanks Dave, Sigma cameras are narrower still.