Some unusual UG filters. UK supplier, H V Skan

[dabateman]

I have to wonder how they test for Ti, do they glue the light bulb and spectrometer to the glass?

 

Just math. We had a thread with Andy about a couple years ago.

 

Jonathan,

Don't mean to cause you any stress. Just have fun with your filter. My post, oh so many ago, was to just say cut it with atleast 2mm of S8612 and have fun.

 

I used to have a great 1mm thick ug5 filter, that I got from a microscope filter package. But cracked it in half when polishing it 2 days ago. It was 50mm in diameter. Hopefully I can carefully break it some more to fit a smaller ring.

I still have my 1mm UG11 that I polished from a seperated Cheap Omega filter. Thats about 24mm in diameter.

So kinda have 1mm UG11 glass and 1mm Ug5 glass. I could try to post a comparison at that thickness if you want.

I have been quite busy with the current state of the world though.

[Cadmium]

Yeah, Jonathan, don't stress about any of this, not at all.

[JMC]

It's bizarre, isn't it. I look back now to when I originally found these guys and ordered the filter, and a lot of has happened to us all since then. When I originally ordered these, the only one that I needed for a project was the UG5 0.5mm, the others I just got because they were no longer manufactured, and I thought it'd be nice to get some old glass to have a play with. Of the 4, the only one there is an issue with is the one I needed for a project. Unfortunately little things like this tend to gnaw away at me, and keep me awake at night, especially when what seems to me to be a simple issue of a mis-labelled filter does not for some reason seem obvious to the supplier. I want to be clear though, I am not having a go at them, everyone is under immense pressure at the moment, and there are a lot more important things to be focused on than filters.

 

Now though it looks like even if I can get one made up, it'll be months down the line. That project will just have to wait for now.

 

David, don't worry about comparing the UG5 and 11 1mm filters, unless you want to see that yourself.

[ulf]

I have to wonder how they test for Ti, do they glue the light bulb and spectrometer to the glass?

As others said it is a result of calculations after a few measurements.

If you need a very accurate result those calculations can be quite complex, literally.

The surface reflection-losses depend on the materials refractive index and you ac do some simplified calculations from that.

However the refractive index varies with the wavelength.

The reflection factor in the Schott-calculator is fixed, but the difference will not matter much.

 

If I should set up an experiment for this I would use two polished glass sheets/discs, from the same glass-batch, that have a big thickness difference, like 0.5mm and 4mm.

Those thicknesses can be accurately measured.

Then I would make a good transmission measurement of (T), at a suitable wavelength, for the two sheet/discs.

As the the result is affected identically by the surface-losses that part can be insulated from the absorption of the material.

[JMC]

The suns out and I thought I'd get some photos with these lenses (unfortunately the wind is still here as well). Slight problem, my s8612 has all got surface oxidation, so needs a clean. However I have BG39 2.5mm Chinese copy (which, I have reported on here - https://www.ultravio...dpost__p__17097) which will have to make do for the mean time.

 

Images taken with a Canon EOS 5DSR multispectral conversion. Asahi 85mm UAT lens (f16), with the 'fake BG39 2.5mm' on the lens for all the shots. Dandelion subject on the lawn. 10% diffuse reflectance standard for white balance. White balanced in Darktable and output as JPEGs. No further modifications to the image other than resizing. I did a few different exposures a stop apart for each one, and chose the ones which looked similar-ish (mk1 eyeball).

 

UG2, 1mm, 4s exposure

 

UG3, 1mm, 1/25s exposure

 

Mystery filter, 0.5mm, 4s exposure

 

UG12, 3mm, 4s exposure

 

There is a pronounced green tinge to the image for the 'mystery filter' (doesn't appear in the UG2 and UG12 images). This green tinge was expected given the transmission spectra for it, and goes to show how even a small leak in the blocking can have a huge impact on the image. Plus of course that image shows some movement due to the wind - I swear I am cursed with that filter.

 

Shame I couldn't use the S8612 for these, but will give them a clean and hopefully will be able to use them again in the future.

 

 

EDIT - like a numpty I forgot to do a control image with the Baader U when I did the others. So just rushed out and got one. Sun position has changed (it's about 2PM now vs 12PM for the others), and of course the Dandelion has wilted, but it's better than nothing. This was 4s at the same settings as the others.

 

Baader U, 4s exposure

[dabateman]

Interesting, that 0.5mm mystery filter (ug11) kind of looks like 1.5mm ug5.

 

Looks like some fun filters. The UG3 could almost be your new visible.

 

[JMC]

David, yeah I quite like them, especially the UG2. Thankfully I have managed to clean my s8612 filters (thanks to Steve for telling me about using hydrogen peroxide for this), so can redo the experiments with the correct blocking filters when I get chance. I'd expect exposure times to improve a little bit as a result of using the s8612.

[Alaun]

I clean the stuff coming out of the S8612 off just with a bit of shampoo under running water and then put the filter on a radiator to get it dry. It does not look oxidised but more like something (a Cu-salt?) is diffusing out of the glass.

 

Would be nice to get some of the coated S8612

[JMC]

I clean the stuff coming out of the S8612 off just with a bit of shampoo under running water and then put the filter on a radiator to get it dry. It does not look oxidised but more like something (a Cu-salt?) is diffusing out of the glass.

 

Would be nice to get some of the coated S8612

Alaun, yes I used the word 'oxidation' in error, as I couldn't think what else was suitable. It did come off easily with the hydrogen peroxide on a q-tip, and it left a blue/green stain on the q-tip itself. If it is leaching out as a salt, it'd be interesting to know whether this impacts the filter transmission over time. However I get the feeling they'll out live me.

[JMC]

Here's a transmission plot of the filters, when combined with the Chinese fake BG39 (2.5mm thickness) filter I used, as measured on my Ocean Optics FX spectrometer. I have called the mystery filter 'UG11 0.5mm' in this one, as the plot is the same as UG11.

 

 

Just for comparison, here's the same plot, but using Schott s8612 (2mm thickness) from UVIRoptics as the blocking filter.

 

 

This really does emphasize how much more UV you get when using Schott s8612, and at the shorter wavelength end as well. While you can't see on this scale, the IR blocking is essentially the same between the 2 filters (between 700 and 800nm which is as far as I can go).

 

Also I noticed that the fake BG39 varied in transmission as I moved it around on the spectrometer, presumably due to slight variations in thickness. The Schott s8612 did not vary in the same way.