Russian Lomo UV filters transmission (3mm and 5mm)

[Andy Perrin]

That info is 5 years old now. Recently there has been evidence that at least one Chinese manufacturer (Tangsinuo) is making filters that are mostly high quality, although I don't know whether the OD of blocking is typically the same as Schott's. But there is no reason to assume the material quantities are exactly the same between ZWB and Schott glasses in the first place, so if there is a systematic difference then it would simply reflect a slightly different recipe.

[diant]

... then it would simply reflect a slightly different recipe.

This idea is first to strike. But strange to think, Andy, that Chinese optical engineers, knowing about poor visible blockage their UV-pass glasses, had not come to idea of adding some more Co and Ni in their mix materials... This is so easy and simple way to fix the problem that I think it almost improbable situation. Ni and Co are so easy treated (exist in melted glass only in bivalent form) that the glass couldn't be spoiled even if you choose reducing conditions instead oxidizing or vice versa.

I gingerly suspect that the point here is different. May be no any real difference in visible blockage of ZWB, Schott and Hoya at all? May be - if we take a similar silicate glasses (ZWB2, UG1 and U-360) at similar thickness - we obtain similar OD in visible region? That may be examined everyone who have spectrophotometer and 1mm ZWB2 sample. (Unfortunately, I have not now).

 

Another one hypotheses (yet hardly probable I think): if the difference is still real and was not fixed by simple adding Ni-Co by their (Chinese) engineers, then it may be that the absence of pure Fe-free sand in all China (!) play the role?..... But I could not even guess about it...

[Andy Perrin]

It very much depends on if the "poor visible blockage" was considered a problem by the engineers, or just an acceptable amount of leakage. Many applications don't require the amount of blocking that our photo setups demand.

 

But I don't have a spectrometer setup. Jonathan or Ulf could possibly test this, or may already know the answer.

[dabateman]

Those comments were based from a spectrum, not from testing an actual filter. Its not clear how that spectrum was obtained, was it calibrated, was the baseline corrected, was there drift. Just as the handrawn curves for ZWB glass can't be trusted, I too wouldn't trust these.

We know many errors can be made trying to record the absolute spectrum.

 

Also early seconds sold cheap on Ebay, may not have been so good. With uneven pouring and striations. But better stuff looks to be available now and its hit more mass production. Especially with ZWB2 glass being so popular in flashlights.

 

[diant]

It very much depends on if the "poor visible blockage" was considered a problem by the engineers, or just an acceptable amount of leakage. Many applications don't require the amount of blocking that our photo setups demand.

Yes, I also thought in that direction. May be, may be...

 

Its not clear how that spectrum was obtained, was it calibrated, was the baseline corrected, was there drift.

...

We know many errors can be made trying to record the absolute spectrum.

Ok. I think that all "puzzles" with ZWB may be solved if we will have a spectrum of thin sample - 1mm or more better 0,5mm ZWB. In last case it is enough to have OD 2,0 data to say about visual blockage of usual 2mm ZWB filters with sufficient accuracy. As I understand almost every device can take 2,0 OD measurements without significant errors of calibration.

[ulf]

It very much depends on if the "poor visible blockage" was considered a problem by the engineers, or just an acceptable amount of leakage. Many applications don't require the amount of blocking that our photo setups demand.

 

But I don't have a spectrometer setup. Jonathan or Ulf could possibly test this, or may already know the answer.

Unfortunately I do not have any ZWB2 1mm to measure and compare with my UG1, 1mm.

 

I do have a ZWB1, 1mm, that I just measured and it indeed do have a strong blocking in the visual range.

If that was the main goal this filter would be an excellent filter.

 

These are my transmission graphs:

ZWB1 1mm from Tangsinuo.

 

 

It is likely that the attenuation is even better in the VIS area.

Here it is limited by system measurement noise and I did not care to improve the measurement further with averaging.

The graph between 400nm and 440nm is also affected by a light source change from a deuterium lamp to a halogen lamp.

This area is likely lower in reality. Please disregard these measurement flaws.

 

However for our needs with UV photography a much more important aspect is the ratio between the UV-peak hight and the IR-peak height.

Normally that ratio is smaller for ZWB1 than for UG11 and U-340.

The UV peak of ZWB1 do not extend that far into UV either.

 

It seams like the Chinese optical glass engineers know how to get a good VIS attenuation, but they might lack knowledge of how to fully copy filter glass made by Schott and Hoya.

 

It might also be that the performance is good enough for the market of ZWB filter glass and that improvements would be too costly.

To filter a LED UV source do not need good IR attenuation.

 

All filter glass has batch variations and the published transmission data from Schott and Hoya are to be considered as typical transmission averages for many batches.

Data from Schott and Hoya has a few guaranteed transmission values for specific wavelengths.

So far I have not seen any such data for Chinese filter glass.

[Andy Perrin]

Thanks Ulf!

[diant]

Ulf, thank you very much! That is all we need, I think.

From your graphs we see that usual 2mm ZWB1 Tangsinuo's glasses should have OD>4 in 400-665nm region (and >6 in around 415-658).

It is enough for many applications.

Here in Russia I use to block IR with our BGG-21 (СЗС-21) glass 5-6mm. It has a steep cut at ~650 nm (4D) and at ~680 nm (6D), but in the same time has good int. transmission in 360-370-380-390-400 region (56-81-90-96-98%). BGG-21 should be a good pair for ZWB1 (2-3-4mm) and the more so for ZWB2.

 

> So far I have not seen any such data for Chinese filter glass.

Yes, I've too.

A week ago I've tried to convinced the managers of SVBony (large Chinese optical company) that some additional information on their filters can rise its prestige and attract attention to their products as a serious one, but they do not hasten to hear my words (unfortunately). Though they says that they will consult "the technical staff of the factory for the requested spectrogram".

 

Your notion that UV peak height improvements may be too costly appears very probable to my mind.