What tests can I do to determine the UV limit of my camera ?

[Stefano]

With a quick search I found this: https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.accuteoptical.com/optical-filter/bandpass-filter/nbf-254w13r&ved=2ahUKEwiSzbiOx4ODAxVvR_EDHVftBaEQFnoECBEQAQ&usg=AOvVaw19rFBKKZy5iDjTpb2l6geP

 

It doesn't have OD 6 blocking above 320 nm, it's less than OD 4 there. You could take one image with the filter, an identical image (same settings) with a longpass filter in front that blocks UVC, and subtract them. Anyway, it was just a quick search, maybe you can find better filters.

[colinbm]

@lukaszgryglicki My best suggestion is to use narrower band LED lights.

[lukaszgryglicki]

Can you give me an exact example of narrow band 254nm filter that don't leak above 300nm?

I have one such filter and I can see through it with my own eyes which is rather unexpected...

I mean - it can pass even only 20% of 254nm band but then I want it to BLOCK everything above until at least 1500nm with OD6 or even OD8.

 

 

[Stefano]

About seeing leaks, I have a solar filter for telescopes, those which look like tinfoil. I think they are OD 5, basically an OD 5 ND filter. Through it, I can see the Sun (it's intended for that), halogen lamp filaments, high power LEDs, and if I look outside a window in a bright sunny day I can barely see something. So if a filter has OD 5 blocking, you can force a leak visibile with your eyes.

 

You probably need more, I would say at least OD 6. OD 5 wasn't enough for my UVB sunlight photos, for that maybe at least OD 7-8 is needed, but since you want to use artificial lighting maybe you need less extreme blocking.

[Stefano]

There's this one: https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.avr-optics.com/catalog/optical_filters/individual_filters/ff01_254_8&ved=2ahUKEwjBy5GRh4eDAxXg1QIHHW42CMYQFnoECA8QAQ&usg=AOvVaw3KSJZlqZwbQyv_qqjWZPlA

 

It has >50% transmission (let's say 50% to stay a bit conservative), and it has about OD 3 blocking in visibile and near-infrared, with higher blocking in UVA. Two of them stacked would have OD 6 blocking almost everywhere, and would transmit about 25%. Some ZWB3 glass can attenuate leaks in the visibile spectrum.

[ulf]

23 minutes ago, Stefano said:

There's this one: https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.avr-optics.com/catalog/optical_filters/individual_filters/ff01_254_8&ved=2ahUKEwjBy5GRh4eDAxXg1QIHHW42CMYQFnoECA8QAQ&usg=AOvVaw3KSJZlqZwbQyv_qqjWZPlA

 

It has >50% transmission (let's say 50% to stay a bit conservative), and it has about OD 3 blocking in visibile and near-infrared, with higher blocking in UVA. Two of them stacked would have OD 6 blocking almost everywhere, and would transmit about 25%. Some ZWB3 glass can attenuate leaks in the visibile spectrum.

Can it be bought? When I search for that filter on their website further up in the structure it is not found.

[Stefano]

Here they say it is obsolete. As a replacement, they offer this.

 

Is isn't as narrowband (15.2 nm FWHM), but has slightly higher transmission (about 65%). They claim average ODs of:

> 6 between 200-236 nm;

> 4 between 263-450 nm;

> 2 between 450-600 nm.

 

I don't know if you can find raw transmission data, and we don't know how much it blocks IR.

 

Stacking two of them will double the OD, and reduce transmission to about 40%, being conservative. The 450-600 nm range (blue to orange) would stay weak at only OD 4, but a ZWB3 filter would help.

[colinbm]

ZWB3 cuts the 254nm down to 40% alone.

[Stefano]

It depends on the thickness. It is a trade-off between maximising transmission at 254 nm and minimising leaks.

[ulf]

2 hours ago, Stefano said:

Here they say it is obsolete. As a replacement, they offer this.

 

Is isn't as narrowband (15.2 nm FWHM), but has slightly higher transmission (about 65%). They claim average ODs of:

> 6 between 200-236 nm;

> 4 between 263-450 nm;

> 2 between 450-600 nm.

 

I don't know if you can find raw transmission data, and we don't know how much it blocks IR.

 

Stacking two of them will double the OD, and reduce transmission to about 40%, being conservative. The 450-600 nm range (blue to orange) would stay weak at only OD 4, but a ZWB3 filter would help.

 

From the filter spec: Angle of Incidence0 ± 7 degrees  (±15°)

Clear aperture 22mm

 

For a 105mm lens like the UV Nikkor the FOV values are
Horizontal 19.46°  Vertical  13.04°. Diagonal 23.28°

 

That means that the blocking spec is not true for all the image surface.

 

The front lens element of an UV Nikkor is also bigger than 25mm.

 

A custom 50mm costs only $2,213.00 each and you'll need two of them.