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UltravioletPhotography

Asahi 253.7 UAT Filter - Very Leaky


Andrea B.

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The little paper which comes with this interesting filter says:

  • λ max = 252.5
  • Tmax = 17%
  • Δλ1/2 = 12mμ

So that seems to list the peak, the maximum transmission at that peak and the half-bandwidth.

 

The filter is one of the 5 UV and IR filters which came with my Ultra-Achromatic-Takumar boxed kit which I'm going to try to start testing now that we are beginning to see some occasional sunlight.

 

These two photos here are rather glumpy, but I had everything set up for other tests and couldn't resist trying a shot or two. I have no idea at this point what kind of leaks this filter has. It is duly noted that 253.7nm is the "germicical" wavelength.

 

GH1-broadband + Asahi 85/4.5 UAT + Asahi 253.7 UV-Pass Filter

f/4.5 for 1/1.3" @ISO-800

White balance was made against the snow.

GH1_asahi257_outdoors_UAT_20150311wf_165208pn.jpg

 

 

GH1-broadband + Asahi 85/4.5 UAT + Asahi 253.7 UV-Pass Filter + BG39

f/4.5 for 1.3" @ISO-800

White balance was made against the snow.

Now, that BG39 filter cuts in around 300nm, so what is getting thru here if the half-bandwidth is around 240 - 264 nm ? This is going to be interesting.

GH1_asahi257_andBG39_outdoors_UAT_20150311wf_165217pn.jpg

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The 2nd foto had IR blocker BG39.

 

Today I have some actual sunlight :( so I can try to test more using the IR pass filters.

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BG 39 isn't that efficient for blocking IR. In particular, when the primary spectral transmission band might be more or less unrecordable by the camera, secondary lobes take on a prominent role for the final result.
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Gotcha!! Thx.

 

Any suggestions as what to test with? I have BG 38/39/40 and B+W 092/093 IR and S8612. I also have this BG 470 thing which I need to look up. And I have 3 Baader color bandpass filters for dark blue, light blue and green.

I could also stack it with the BaadU.

 

Maybe I'll just try them all and we'll go from there.

 

Gotta go buy some sunflowers.

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Do you have the original technical manual for this system? It might provide details of the illumination source intended to be paired with this filter. Filters for isolating specific Hg lines were probably used. I betcha the CWL of your other 4 UV filters correspond to Hg lines.
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There are two bandpass interference-type UV filters for the mercury lines:

  • 253.7nm [252.5nm, 17%, 12nm]
  • 365nm [364nm, 23%, 24nm]

 

And there are five IR filters.

  • One bandpass interference-type filter at 862nm [865nm, 85%, 51%].
  • Four absorption-type longpass filters at R62A, R68A, R62B, R68B.

The difference between types A and B filters is the mounting. The manual states that Type A was used for such IR films as Sakura Sekigai and Type B for Kodak Infrared.

Strictly speaking, the four longpass filters are IR+Red pass filters.

 

We don't know which filters were originally included in the kits. There are 6 filter slots in the box. All 7 filters are mentioned in the UAT85 manual.

 

The manual exists on line. I'll look and see if it says anything about light.

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I misread "5 UV and IR filters" but your 2 UV filters correspond with the 2 most prominent UV Hg lines.

I am sure already knew that. Sorry, call me Captain Obvious :(

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The manual mentions that the Types A and B differ only in the way they are mounted. But later on it states that Type A was used for such IR films as Sakura Sekigai and Type B for Kodak Infrared.

 

The R62/68 are absorption filters. The calibrated filters are interference filters. Added this above.

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It is safe to say that this filter leaks everything !!! I just made some test shots with IR and Vis bandpass filters to post later this evening.

 

I'm sure when used with film, there were no problems. Unforch, we have digital so I probably will not be putting this filter to actual use.

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Ok here's some results of stack tests. Just for fun. This Asahi 253.7 sieveFilter isn't going to get used as it is incredibly leaky in Uv and Visible and IR. That about covers everything I think.

 

Exposure details are on each foto. All were at ISO-400 except for the Baader Uvir Cut foto #2.

 

1. The 253.7 sieveFilter acts just like a BaaderU when stacked with a BaaderU.

Demosaic + brightening curve and white balance. No other edits.

GH1_UAT85_253.7Sun_BaadU_wbManual_20150312wf_123412pn_demGamWBProf.jpg

 

2. Might be useable for visible work with a Baader Uvir Blocker and some profiling.

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_UvirBlock_wbCloudy_20150312wf_122438pn_demGam.jpg

 

3. Or it can be a pretty good B+W 093 IR-pass filter if you like. Just stack it with an 093.

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_IR093_wbManual_20150312wf_123721pn_demGam.jpg

 

 

 

I got curious about what visible colours the filter might be passing. Apparently all of them! The colour filters were all stacked with the Baader Uvir Cut to try to stay as Visible as possible.

 

4. Baader Blue 435nm Bandpass + Baader Uvir Cut

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_Baad435+UvirCut_wbAuto_20150312wf_132507pn_demGam.jpg

 

5. Baader Bright Blue 470nm Bandpass + Baader Uvir Cut

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_Baad470+UvirCut_wbAuto_20150312wf_132256pn_demGam.jpg

 

6. Baader Green 500nm Bandpass + Baader Uvir Cut

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_Baad500+UvirCut_wbAuto_20150312wf_132757pn_demGam.jpg

 

7. Baader Yellow 495nm Longpass + Baader Uvir Cut

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_Baad495Long+UvirCut_wbAuto_20150312wf_131801pn_demGam.jpg

 

8. Baader Orange 570nm Longpass + Baader Uvir Cut

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_Baad570Long+UvirCut_wbAuto_20150312wf_131801pn_demGam.jpg

 

9. Baader Red 610nm Longpass + Baader Uvir Cut

Demosaic + brightening curve. No other edits.

GH1_UAT85_253.7Sun_Baad610Long+UvirCut_wbAuto_20150312wf_131929pn_demGam.jpg

 

**********

 

Here is a bonus foto. I took the Visible #2 above, white-balanced it and applied a GH1 colour profile. Looks pretty good for a visible UV foto. :(

GH1_UAT85_253.7Sun_UvirBlock_wbCloudy_20150312wf_122438pn_demGamWBProf.jpg

 

 

**********

 

OK, I had my fun with that. I don't think we can actually record anything down there at 253.7nm anyway even if we should find some source of germicidal illumination. AND had a non-leaky filter.

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Andrea,

 

Great set of blocking filters!

 

Interposing the correct blocking filter is quantitatively definitive and often required in quality photochemistry & photobiology research.

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