Doubts about UVIF

[Andy Perrin]

Thanks Cadmium!

 

According to that scan, the "E" designation means they are unstable, so I guess buying an old --E filter is a bad idea if you want the given spectrum and not some time-altered version. I just bought a new 2E from B&H.

[Cadmium]

Bernard, No, don't use Tiffen 2A unless you have a accurate transmission graph for it.

You want something that cuts off ABOVE 400, 415/420/435 is ideal. 400 is too close for comfort.

I think the 2E is best. Or KV-418.

[ulf]

I think the Tiffen 2A can be a good filter to use for UVIF to avoid filtering out any blue and VIS-purple fluorescence just above 400nm.

That will give the full true VIS-spectra.

 

A 2E-filter is more yellowish and can be used if less blue tones is the goal, making the rendering the picture in warmer tones.

However these filters are cutting very steep and might eliminate sometimes valuable information from the image.

 

These are accurate transmission measurement graphs for Tiffen Haze 2A:

 

The full spectrum graph in green show that the filter has no AR-coating and a transmission just above 80% in VIS.

The slight bend near 400nm is due to measurement limitations with a full spectrum light source

 

With only the deuterium UV light source activated I can show that the transmission at 400nm is less than 0.5%. (purple graph)

Green graph is kept to show the crosstalk artefacts from VIS+IR into the UV-range

No box-car filtering applied.

[Stefano]

I think cutting at 400 nm is OK. Both the Baader U and the ZWB2 filter on the torch cut about there. If you use U-340/UG11/ZWB1 on the torch, you will cut lower, thus you can be even more sure there is no UV entering the camera.

 

It is enough to re-try the torch test in post #17 to see how well you are cutting. Or if Bernard has a Convoy S2+ he can use it. If it has the U-340 nm filter on it, it will cut at ~390 nm, and there shouldn't be any UV contamination.

[ulf]

I think cutting at 400 nm is OK. Both the Baader U and the ZWB2 filter on the torch cut about there. If you use U-340/UG11/ZWB1 on the torch, you will cut lower, thus you can be even more sure there is no UV entering the camera.

 

It is enough to re-try the torch test in post #17 to see how well you are cutting. Or if Bernard has a Convoy S2+ he can use it. If it has the U-340 nm filter on it, it will cut at ~390 nm, and there shouldn't be any UV contamination.

 

I completely agree. Either filter is enough in combination with these torches.

The LEDs used has a rather low remaining stray emission intensity above 400nm.

 

Filtering is a must, but even after 2mm ZWB2 or U-360 the attenuation is sufficient.

[Andrea B.]

In response to Bernards original question, a small observation from my own experiences: the UV-induced, visible fluorescence from a subject can and very often does illuminate other non-fluorescing parts of the scene if the fluorescence is strong enough. So, it is good practice to note what is actually fluorescing as you view your subject before making the UVIVF photograph. During post-processing it is fair game, IMHO only, to slightly suppress the reflected fluorescence if you wish to call attention to the actual fluorescence.

 

[i would like to show you an example of this, but as usual my day already seems to be filled up with committments and chores. I'm writing a note to myself to look for this example this evening.]

[Cadmium]

I think U-340 2mm (torch) and 2E (camera lens) is the perfect combination.

That being said, if you want glass in stead of gel filter, then that's something else.

And if you want to cut off higher, like 335nm, then again, you will need to work that out, stacking or whatever.