Filter Transmission Charts #1

[Andrea B.]

Schott IR-Blockers: 2.0 mm thickness

 

[lukaszgryglicki]

I think we can think about adding CuRB and CopperU filters transmission charts - the 1st one seems to be the only good IR blocker if you also want to pass UV-B and even some UV-C.

[lukaszgryglicki]

On 8/31/2018 at 9:49 PM, Cadmium said:

Yep, the square glass filter seen here, part of the original UV-Nikkor kit.

I could not find any photos of the filter box showing a part name/#, so I don't know what it is technically called. And I don't know if that is what Bjorn meant by "FF filter".

This is how it looks like - I can also see throught it with my eyes - everything looks quite similar to that photo from the phone:

 

[dr_narval]

I read a few times, that under certain circumstances one would do best adding an IR cut filter to their Baader U.
Can someone explain when this would be the case?
Sorry if there is a better topic to ask this question.

[ulf]

On 12/3/2022 at 10:08 PM, dr_narval said:

I read a few times, that under certain circumstances one would do best adding an IR cut filter to their Baader U.
Can someone explain when this would be the case?

You wold have to do that when the UV/IR intensity ratio reaching the sensor becomes bad enough to let the IR leakage of the BaaderU become significant.

 

Typical situations are when the UV content in the illumination is low.

It is especially important if the motif has high IR-reflectance and low UV-reflectance, typically that is true for foliage with chlorophyll.

 

A lens with marginal UV-transmission also makes the situation worse, while a lens with good UV-transmission are better as both types normally have reasonably good IR-transmission.

 

All/most UV-pass filters including that BaaderU are based on some kind of filter glass that transmit UV, but also have a transmission peak around 700nm in the beginning of the NIR range.

That gives a filter with some kind of IR-blocking that often is good enough with OD4 (UV/IR) > 10 000, like the later versions of BaaderU.

 

Typical situations needing a higher OD from an added BG-glass would be during sunrise or sunset, or with artificial illumination with a very bright halogen lamp. 

Even if those lamps can produce some marginal UV, the IR-content is vastly dominant.

The same goes for flashes with low UV-output due to coating of filtering effects from their fresnel lenses.

 

A typical indication of IR leakage is if an UV image of foliage gets a less dark/black colour.

That should not be confused with specular reflections of UV at the surface of the leafs. 

 

I hope I have answered you question an an understandable way.

As the situation is complex, it is difficult to explain simplified and still being valid.

 

If needed please ask for clarifications

[Andy Perrin]

17 hours ago, ulf said:

You wold have to do that when the UV/IR intensity ratio reaching the sensor becomes bad enough to let the IR leakage of the BaaderU become significant.

 

Typical situations are when the UV content in the illumination is low.

It is especially important if the motif has high IR-reflectance and low IR-reflectance, typically that is true for foliage with chlorophyll.

...

[*] typo above - should read "high IR-reflectance and low UV-reflectance, typically that is true for foliage with chlorophyl"

[ulf]

Thanks Andy! Corrected.