Baader U and Invisible Vision 308nm filter comparison for skin imaging

[colinbm]

Just a mention, a year of so back we had access to liquid copper sulphate fiters that are for blocking IR.

Water will block IR too.

 

Col

[Andy Perrin]

Water won't block IR until you get pretty deep into the IR (Cadmium found that it started to get darkish around 1050nm, and I found that it was inky in 1480-1600nm). Or unless you use a really large thickness.

[lukaszgryglicki]

 

• Blocking IR in a 308: Whewie! This is a tough one. Either S8612 or any BG glass is just going to kill the 308 transmission and move the peak. No good.

How about using CuRB UVR filter to block IR with 308 filter? https://www.uvroptics.com/index.php?CuRB

 

[colinbm]

@rfcurry Now that the IR can be blocked from UVC pass filters, what is needed is a better ZWB2 or Hoya 325C that passes below 250nm, both these filters are used for fluorescent photography with 254nm UVC tube lights, but they attenuate approximately 50% of the mercury spike at 254nm. I know the graphs say otherwise, but they are not short enough.

[lukaszgryglicki]

I'll be buying this 308nm filter - this is the exact measured data for actual filter that I'm buying: https://docs.google.com/spreadsheets/d/1y2XAs5Y12vt_tVL7wj4EZregpfbQ8yrxny7_OY7qyrY/edit?usp=sharing

 

[dabateman]

1 hour ago, lukaszgryglicki said:

I'll be buying this 308nm filter - this is the exact measured data for actual filter that I'm buying: https://docs.google.com/spreadsheets/d/1y2XAs5Y12vt_tVL7wj4EZregpfbQ8yrxny7_OY7qyrY/edit?usp=sharing

 

The blocking doesn't seem so good. But you should be able to stack it with 2mm U340/Ug11/zwb1 to get a nice UVB peak at 308nm.

[lukaszgryglicki]

Asked them if they can provide few samples transmission data - if they do, I'll pick up best & buy, if not I'll buy this one, this is anyway the 1st filter that should allow UV-B for me without much more complications.

 

The blocking doesn't seem so good. But you should be able to stack it with 2mm U340/Ug11/zwb1 to get a nice UVB peak at 308nm

Won't this kill UV-B transmission below 310nm? I hope CuRB will eventually help, but seems like CuRB doesn't transmit down to 200nm as @rfcurry initially given hope. He will recheck transmissions of CuRB because there is a hope that he used some 270+nm passing glass instead of quartz passing from 190nm. Will see.

 

Hope that Invisible 308nm will be very good even alone :/

 

 

 

[JMC]

1 hour ago, lukaszgryglicki said:

I'll be buying this 308nm filter - this is the exact measured data for actual filter that I'm buying: https://docs.google.com/spreadsheets/d/1y2XAs5Y12vt_tVL7wj4EZregpfbQ8yrxny7_OY7qyrY/edit?usp=sharing

 

Looks a little different to mine. Mine had a slight bump at around 790nm (about 0.02%) and then it started to rise again above 1000nm (which is like the one you have shared). I guess he is tweaking the coatings. As I've mentioned before, this will most likely need additional filtering to use in sunlight (that's not what it was designed for). Something like 2mm U-340 would be good as David mentioned. 2mm of U-340 will have around 70-80% transmission at 308nm.

[lukaszgryglicki]

I only have 4mm U-340 - will tha work in your opinion?

Otherwise I can use CuRB?

Or even CopperU?

[JMC]

40 minutes ago, lukaszgryglicki said:

I only have 4mm U-340 - will tha work in your opinion?

Otherwise I can use CuRB?

Or even CopperU?

Yes, it'll work, but obviously will reduce the 308nm as well as blocking the other wavelengths. So your exposure time will increase. What feels like a long time ago now I did some transmission work on U-340, including 4mm - https://www.ultravioletphotography.com/content/index.php?/topic/2383-good-practice-and-setup-for-spectrometer-measurements/&do=findComment&comment=19186

 

At 4mm thick you should still letting abut 50% of the 308nm through, and blocking pretty much everything in the visible and IR (especially when combined with the blocking of the IV308 filter). Definitely try it with and without the U-340 though, be interesting to see your experience with it.

 

[lukaszgryglicki]

Makes sense, will try once I havethat IV308 filter.