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UltravioletPhotography

BG60, BG64, BG40, S8612


Cadmium

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Occasionally someone asks me if BG60, or BG64, and a few other BG##'s are useful for what we do.

Here is a diabatic and linear comparison of BG60, BG64, BG40, and S8612, all 2mm thick.

I will let you decide if you see uses for the BG60 and BG64.

I have looked at these years back, and I don't see much use for them personally, but I am open to persuasion, if you see some need or use yourself, then I would be interested to know.

My feeling is that BG60 and BG64 don't do what we want a BG filter to really do, especially not for UV stacking, and not for visual range use either.

They both cut more UV than BG40 or S8612, and even if we used BG60 at 1mm thick, it doesn't compare favorably to S8612.

Any which way I compare them, any thickness, I don't see any reason why we would want to use either of them.

However, please post if you see something I don't.

 

post-87-0-56420300-1545209108.jpg

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Cadmium,

I thought the 60-64 series were advertised for extreme environments and for medical?

So if your taking Uv images in a dentist office and the patient vomits bile, you would be covered.

Or if you decided to take uv images in a hurricane, you would be ok.

Of course you would need to stack that 60-64 on the outside. If you have it first, then the ug1 or ug11 last, you through away all that blood and bile protection.

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One more thing, the info about BG60, BG61, BG62, BG63, and BG64 having a special coating... I am not exactly sure such a coating comes with the glass, it may mean that IF those glasses are coated...

For example, compare the individual data sheets for BG40 and BG60.

 

BG40

https://www.us.schot...jun-2017-en.pdf

 

BG40 says,

"Long-term changes of the polished

surface are possible under some

circumstances.

 

BG60

https://www.us.schot...jun-2017-en.pdf

BG60 also says,

"Long-term changes of the polished

surface are possible under some

circumstances.

 

BG60 has the added reference about 500 hours,

"no visible surface damage after 500 h

of humidity test 85 °C / 85 % rh"

 

There is this Schott page, saying:

"Equipped with a specified coating, these filters remain completely transparent for more than 1000 hours without any surface corrosion and deliver extraordinary image quality."

https://www.schott.c...il-2015-eng.pdf

 

However, this may not actually mean those glass types come WITH such a coating.

"Equipped with a specified coating, ...", may actually mean, When/If Equipped with a specified coating, THEN...

Their filter glass is sold in 4mm thick sheets that need to be lapped down to a thinner desired thickness, and the 4mm thick surfaces need to be polished, and they are not coated.

 

By the way, the "BG 60/61/62/63/64" links in the Sticky don't work.

http://www.ultraviol...vvisir-filters/

 

Moot point in a way really, because I see little if any use for these.

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I think it's the IF version you mentioned. I think they are meant for smartphones and the like. Not the best filter performance but the tradeoff is greater durability especially if you apply the coating too.

 

I found this link which explains that people are (or were) using the BG60 series to make the smartphone lenses. It’s pretty neat. Link is 2012 so I don’t know how popular that approach became.

http://www.cioe.cn/cioec/luntan/ppt/gx/1/4.斯特芬·莱歇尔-光学滤光玻璃:红外截止滤光片的基础知识和应用.pdf

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  • 3 months later...

Good afternoon (in France...),

 

Interesting post, at first I had the same impression about these filters than Cadmium, and then I found myself in a situation where BG60 glass is useful. Let me explain :

  • Back in the end of 2018, I wanted to have a Canon 5D IV converted to full-spectrum. The conversion was done by Kolari, and I took it for a walk as soon as it was received. Looking at the pictures taken in UV, I found a big issue: the 5D IV is suffering from internal IR leak due to the LED of the shutter. The leak was visible from 800iso, whatever the shutter speed was, so it appears to not being usable, and I was very sad. But at the same time, I wanted to find an alternative solution, and I mailed several specialists from this forum to confirm or not the solutions I had in mind.
  • Here are the solutions:
    • Internal conversion with S8612, for me the best IR blocker. Problem: uncoated filters can oxidize quickly, which is dramatic for an internal conversion. Coated S8612 is also hard to order for small quantity.
    • Internal replacement of the led by a FLIR led. Two problems here: the small place to replace the LED due to the mirror of the reflex, and the coast of such operation.
    • Internal conversion with BG60. This last solution came at the end, and seemed the most appropriate to do both UV and visible photography.

I had my 5D IV converted back by Kolari with a BG60 filter, and I received it yesterday. Here is what I can say regarding my first tests:

  • Visible and UV photography are both possible. UV photography requires an additional UV bandpass filter such as Hoya U360.
  • I did a comparison between my 5D IV BG60 and my 6D full spectrum, both with the same lens, the same light source and the same subject. I did not have time to upload the pictures on my PC yet, but the results in term of exposure are as followed:
    • Canon 6D FS + Kolari UV bandpass filter: F/4 - 2"5 - 100iso
    • Canon 5DIV BG60 + Kolari UV bandpass filter: F/4 - 4" - 100iso
    • Canon 5DIV BG60 + Hoya U360 2mm filter: F/4 - 2" - 100iso

So using only a Hoya U360 filter is enough to perform better than with the Kolari UV bandpass filter, BG60 giving the IR-cut properties. Results are similar in term of colors. Of course the use of S8612 would give better performance, but in this particular situation BG60 allows me to do both UV and visible photography with less layers of glass and with an internal conversion.

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The S8612 and BG60 thicknesses used in these graphs were chosen to keep the Red/IR suppression of the stack equal to each other at OD5, one could use thinner or thicker versions depending,

Normally, I would use S8612 at 1.5mm to 2mm for this stack. The S8612 1.6mm thickness is an odd hypothetical thickness, but it keeps it at the same OD5 as the BG60 1.5mm for this comparison.

Changing suppression thickness will of course change UV peak amplitude, but the comparison stays proportional to each other.

Using BG60 will cut UV peak amplitude, move UV peak to a slightly higher nm, and reduce UV band width.

This should translate into longer exposure time, and a bluer looking shot (using BG60), individual white balance will make them look basically the same.

U-360 2mm + S8612 1.5mm to 2mm delivers the closest SOOC color to Baader U shot using the same white balance.

Using UG1 instead of U-360 will reduce UV peak amplitude even further.

 

post-87-0-13955800-1554921050.jpg

 

post-87-0-44249200-1554921058.jpg

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Also, I should add, from my experience, S8612 looks more blue than BG40 and BG38, and thus BG60 should look more blue also.

BG40 and BG38 look the most natural for visual to me.

This may not be as noticeable once the are individually white balanced, but of the BG type filters, BG40 and BG38 are usually used for visual shots because they are not as blue.

Bluer < S8612 - BG39 (looks the same to me) - BG40 - BG38 - Baader UV/IR-Cut filter > Redder

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