Schott S8612 coated vs uncoated test

[Cadmium]

A test of the slight difference in transmission between S8612 uncoated and coated filter.

These are identical filters, same thickness same glass, one has an AR coating optimized for 360nm (common AR coatings are optimized in the 500nm range).

The main reason I made the AR coated S8612 filter version is to reduce surface corrosion over time, but AR coatings also improved transmission, but ever so slightly as is demonstrated below.

 

Photo of filters used in these tests:

 

BLAK-RAY (model J221) meter, comparing S8612 uncoated (left) and AR coated (right) using Convoy S2+ 365nm UV Nichia LED torch/flashlight with Hoya U-340 2mm filter on torch/flashlight.

 

Actual UV pass photo using Hoya U-360 2mm + S8612 2mm (uncoated left, AR coated right).

These shots are set up using Aperture Priority mode, the camera didn't detect enough difference to change the exposure time, and you can't see the difference unless you were to flash back and forth between the two shots, the AR coated version (right) is slightly brighter. I shot these multiple times with the same result differences.

 

And too those of you in my neck of the woods, Happy Thanksgiving!

[Stefano]

Nice test. Yes, the difference is little, and a camera is usually the least sensitive "machine" to these things. A spectrometer or your meter are more sensitive.

 

You also took nice, colorful UV images. Which lens did you use?

[Cadmium]

I used my Kuribayashi 35mm f/3.5 lens (@f/5.6). ISO 200. Exposure 0.77s. Nikon D7000 UV/IR.

 

Here is an animated GIF file, not sure if it will work on here, in every browser, or any, for anyone or all, or at what speed.

This animation flips back and forth between the two shots

Darker = S8612 uncoated, lighter = S8612 AR coated.

Both shots have identical exposure and camera settings.

These are 100%, 'actual pixels' resolution. However, click on the image to view 'actual pixels' size. Full pixel resolution.

 

[Stefano]

Thanks Steve. Works for me (Google).

[eye4invisible]

Nice comparison, Steve!

 

The Kolari Vision AR coatings are claimed to also reduce hotspots on their IR filters. Maybe a UV hotspot test is next?

[dabateman]

But the AR coating clearly moved the deer to better grass. Doesn't that help. Or is that a lama?

 

Thank you for this test. I was hoping for a stop more light. But clearly at best is about a 1/6 stop.

[Andy Perrin]

Hotspots in UV aren't usually a problem. Dichroic filters produce color variations, but that's not the same as the hotspot problem.

 

What I would like to see is a test of lens/filter flaring, with light coming toward the lens. I have had problems when the sun is in the path of the photo.

[Cadmium]

Andy Broomé, Since there is no hot spot with this lens or filter. or with these photos... then... ?

I have not encountered UV hot spots. Maybe with some bad lenses? Reducing a hot spot with a filter? Never heard of that.

 

A spectrometer test comparison may be on the horizon, and would add broader info.

These actual photos using this stack is probably the most likely use of this filter for UV.

As I said, the primary reason for coating the filter was to protect the surface, these tests are more to establish any difference with photographic results, plus or minus from the uncoated version.

The longevity of the surface protection remains to be seen, but given the high quality of the AR coating invested in here it should stay protected for a very long time.

[JMC]

Nice one Steve.

 

If you have any spare of the coated S8612, it would be good to clean a piece of the coated and uncoated the same way, and then leave them together in the same pot (not touching though) and monitor them over time for signs of degradation.

[ori333]

@Cadmium,

 

Where can I find your filters?

[dabateman]

@Cadmium,

 

Where can I find your filters?

 

 

It might be against forum rules for Cadmium to post a response. But I, having no financial gain fully recommend his filters and they can be found here:

 

https://www.ebay.com/str/uviroptics

 

Or here only, anywhere else is a scam that I fell into.

 

https://www.etsy.com/shop/UVIROPTICS

 

[dabateman]

Cadmium,

On the same line as this original thread. I was wondering what the cost comparison or even availability of using 0.5mm WG280 glass glued to either side of the U340 and S8612 filters.

This would also allow for thinner filters to be supported and stronger. Is wg280 or even fused silica more durable and less oxidation prone than Ug11, ug5 and S8612?

I might have to look into that.

[Cadmium]

Ori333, Sorry, I didn't see your message earlier.

 

I have some WG280, but it is rather expensive to use as cladding. Also. I will not go thinner than 1mm.

I don't think you will need to support thinner filters, most UV filters are thick enough to support them selves.

Other than the -300nm 50% transmission point of the the WG280, there are other options available, such as D263, which comes in various thicknesses.

I have some D263 in 0.15mm thick, yes, that is very thin, less than 1/6 of a mm, like paper, you can even gently bend it, and it can be glued on as a cladding, but gluing is time consuming.

D263 doesn't quite have the UVB reach that WG280 has, but it doesn't cost near as much, and for UVA it does the job.

It is available, but no less expensive after gluing twice for one filter, three times for a glued stack.

AR coating is the way to go if you want to protect a surface from corosion, and it actually makes transmission slightly better rather than losing transmission from the cladding glass or glue.

A bottle of hydrogen peroxide costs $1.95? Just clean your filters often, check them, if you find spots that will not rub off with a microfiber cloth then it is time to clean your filter.

Best to remove the glass from the ring, and soak them in HP for a few days, then scrub with the same, or use cerium oxide polish, or both.

If you ask me, cladding is for the birds, but it is available if desired.

[dabateman]

Ok makes sense. I was just thinking that AR coatings can come off and can be scratched.

So its either hydrogen peroxide or AR coatings.

My 313bp25 and 330WB80 improved filters have oxidation on the back UG11 glass. That will be much harder to clean as I can't soak it and risk scratching up the front coated side. So started thinking about my others. These two seems to be my only ones half coated. Others are double coated or not at all.

The 313bp25 has start to get little circles so can't put cleaning it somehow off forever.

[Cadmium]

Some of the the little 12.5mm diameter BP filters I got from OMEGA evidently aren't coated on the back either, and are starting to show some corrosion.

I think you can soak them, I would not be concerned with that. I think the front coating will not fail from soaking and the ring will probably be fine, only concern might be the label/markings, but that is probably OK also.

Try one...

[Cadmium]

Example of a 330WB80 20mm size, front is dichroic, back is raw U glass, Back is corroded.

I tried some hydrogen peroxide applied and scrubbed with a Q-tip, worked pretty good just like that actually, but I am now soaking it for a day or two.

It will be fine. The real problem with letting the glass go this long without cleaning it is that it can result in uneven glass surface, a glass texture can result.

So it is best to clean the glass earlier and often, that way the glass remains more pristine and cleaning is much faster and easier.

Here is what it looked like before any cleaning. I believe this is a filter from OMEGA on eBay, rather old, maybe from about 2012.