AR coating and UV?

[Doug A]

Will AR coating on Schott S8612 reduce UV?

 

Thanks,

Doug A

[dabateman]

No it actually improved the transmission, if you are buying from uviroptics (Cadmium).

I have an uncoated and coated 52mm size filters and Its maybe a 3rd to half stop faster.

The coating Cadmium went with reduces reflectance in uv.

[Doug A]

5 hours ago, dabateman said:

No it actually improved the transmission, if you are buying from uviroptics (Cadmium).

I have an uncoated and coated 52mm size filters and Its maybe a 3rd to half stop faster.

The coating Cadmium went with reduces reflectance in uv.

I like the speed gain. 

 

Thanks,

Doug A

[Cadmium]

Hmm, well I don't see much difference either way. I used the AR for surface protection against corrosion.
I have tried meter tests between non-coated and AR, and seen only very minor improved differences.
Here is the test I did:
https://www.ultravioletphotography.com/content/index.php?/topic/4212-schott-s8612-coated-vs-uncoated-test/#comment-40202

On the other hand people with spectrometers have reported the opposite, but still minor.

I don't think it is that important for exposure either way. Get it to protect the glass is the point.

 

[ulf]

I think that the difference Dave sees is mainly caused by batch to batch variations of the glass material and then it is helped a little further by the AR-coating.

The main advantage is as Cadmium sais surface protection and then for the same glass batch there is some further transmission improvement.

 

The half stop improvement David is reported is physically impossible to come from AR only, as AR is just decreasing surface losses. 

The total surface loss is around 9% and the AR coating can not eliminate the losses completely.

 

A perfect (non existent) AR would improve the exposure with around 1/6 stop.

A real world wideband AR coating into UV, but including VIS gives less improvement.

That little improvement is very difficult to notice during a real photo session.

[dabateman]

Its likely I am remembering wrong or I didn't properly check my original S8612 before I quickly tested it.

My original has a tendency to fog up now due to humidity. 

I should test them immediately after each other and ensure both are correctly cleaned. 

 

[ulf]

You could try to treat it with Rain-X for glass and see if it still fogs up over time.

When I did my tests with simple "UV"-filter glass it showed a tiny improvement in UV-transmission and no other bad effects.

With some luck the thin layer helps, at least a bit against corrosion.

[Andrea B.]

Yes, coatings give good protection against oxidation caused by the adsorption of water onto the glass. With care and routine cleaning to remove dust/grit/pollen/whatever, the coatings will last a good long time. Scratches in the coating could eventually let oxidation happen again, I suppose. But these days the coatings seem quite robust and non-scratchable. (Not that I have deliberately tried to scratch an expensive coated filter!)

 

I have some old filters from film days that I don't even remember where they came from. Maybe arrived with on some lens I bought. Anyway, a couple of those old filters have rather coatings showing some thinning (where cleaned too hard maybe?). One has a bit of peeling/flaking.

[Andy Perrin]

Nothing lasts forever I guess, but even without the coatings my S8612 is holding up well after four years now. I have cleaned it in hydrogen peroxide a bit. I’m sure with the coating it wouldn’t even need that. 

[ulf]

After Colins positive report with his wet test I went ahead and coated all my BG-glass filters with Rain-X.

Not that I have had much signs of corrosion, on any of my normal filters but I think the filters also will be easier to clean in general with that coating.

Better to be safe than sorry.

[Doug A]

Update. Just ordered the last Schott S 8612 AR 52mm 2mm thick filter from UVIR Optics. Never saw the S 8612 listed on the ebay store, but a search found it on Etsy. I don't own a Hoya U 340 or 360 yet to complete the stack. UVIR Optics has a 52mm U 340 in stock. Most people here recommend the U 360. Guess I'll use the Igoriginal ZWB1 with the

S 8612 for now. Interested to see how much difference this makes vs the Igoriginal BG39 2.3mm thick filter.

 

Thanks for all the advice,

Doug A