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UltravioletPhotography

[Filter Test SEU Gen2 #3] Filter Speed & A Windy Bull's-eye


Andrea B.

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Last Update [2018.07.19 10:45 EDT Introduction beefed up.]

 

[Filter Test SEU Gen2 #1] Introduction to the SEU Gen2

[Filter Test SEU Gen2 #2] White Balance, Raw Histogram & Andrea's "White Signature"

[Filter Test SEU Gen2 #3] Filter Speed & A Windy Bull's-eye

[Filter Test SEU Gen2 #4] Dealing with the Usual Dichroic Effects

[Filter Test SEU Gen2 #5] Landscape Interlude

[Filter Test SEU Gen2 #6] Monochrome Museum Comparison

[Filter Test SEU Gen2 #7] Measured Filter Transmission

[Filter Test SEU Gen2 #8] Dichroic Reflection Detour

[Filter Test SEU Gen2 #9A] Longpass Stack Wandering Discussion. See #9B for results.

[Filter Test SEU Gen2 #9B] Longpass Stack Results

[Filter Test SEU Gen2 #10] What good is a filter test without a Rudbeckia?

[Filter Test SEU Gen2 #11] A Fascinating New Rudbeckian View

[Filter Test SEU Gen2 #12] Summary


 

Filter Speed

 

"Filter speed" is not a real definition. :D I'm simply using this as a shorthand term for a informal comparison of exposure times for a set of filters used with the same gear under the same light at the same time. I ran this informal test to determine the "speed" of the new SEU Gen2. Results naturally do not provide any kind of absolute measurement, but rather a relative comparison of exposure lengths for a scene photographed with the different filters in the test set. Of course, such an exposure length measurement depends on so many variables that I'm not going to even attempt to list them all. I'll just remind anyone new to UV photography that exposure times in our interesting genre are dependent on gear, lighting and location. At the end of such a test, the conclusion would always be informally stated that filter A tends to have shorter exposure times than Filter B or Filter C for the given gear, lighting and location.

 

Here is one sample of the photos that were made to use in the comparison. For each filter at each stop the exposures times were increased in 1/3-stop increments until the histogram of the outlined area over the Spectralon was as far to the right as possible. To run this kind of informal test do be sure that the sky is cloudless and that sunlight is steady. Or try it indoors under more stable lighting conditions.

 

d610_uvNikkor_uvSeuGen2_sun_f5.6_20180713swhME_1163702histoArea.jpg

 

 

FILTER SPEED TEST: For each UV-pass filter, photograph the subject at f/4.5, f/5.6, f/8 and f/11.

 

Question: Which of the 3 UV-pass filters has the shortest exposure time at each stop?

 

Answer: The SEU Gen2 has the shortest exposure times for this scene, lighting and location. The results are summarized in the chart below which shows the maximum brightness histograms of the outlined area on the Spectralon for each filter at each stop. I would certainly expect the SEU Gen2 to show the shortest exposure times in similar tests.

 

Subject: Edmund 5" Spectralon Square & Color Checker Passport (2014)

The Spectralon was recently sanded.

 

Gear: D610 + UV-Nikkor 105/4.5 + UV-Pass Filter + Sun

 

UV-Pass Filters: For my initial tests with the SEU Gen2 I chose two other commercially manufactured UV-pass filters for comparison, the classic BaaderU and the recent KolariU.

  • BaaderU :: 350fwhm60 :: approx 80% at peak :: OD > 3.5??
  • KolariU :: 365fwhm40 :: approx 50% at peak :: OD > 3.5
  • SEU Gen2 :: 392fwhm50 :: approx 74% at peak :: OD > 4.5

Exposure: f/4.5, f/5.6, f/8.0 and f/11.0 for various speeds @ ISO-400

 

Processing: Screen shots were taken of the brightness histogram of the selected white area on the Spectralon. Labeling was added in PS Elements #11.

 

Comment_1: It is clear from this informal test that the SEU Gen2 is a faster filter than the BaaderU or the KolariU as used here on the UV-Nikkor and the full spectrum D610. And I can confirm this observation from the other scenes which I have been shooting with these three filters over the last few days with other lenses. Given that the SEU Gen2 captures so much of the band between 370-400 nm as well as some violet light past 400 nm, this result makes sense because that's where most of the UVA in sunlight lies.

 

Please don't be tempted to overanalyze informal results like this. If you need to make a more detailed quantative judgement about "filter speeds", then your best tool is Raw Digger where you can look at the actual count of the light gathered at each stop. I wanted to show something here that anyone else could reproduce with no special apps.

 

I also note that increasing exposure times in 1/3-stop increments does not always bump the exposure up quite like one would expect as you can see from the brightness histograms in this composite chart. Sometimes the exposure goes a little bit further than expected or not quite as far as expected. (So many variables at play!)

 

Comment_2: There is a natural bias in this test due to the three different filter peaks. There will naturally be more UV light available in sunlight as we move from the BaaderU's 350 nm to the KolariU's 365 nm and then to the SEU Gen2's large UV-light gathering in the 380-392 nm band. The KolariU pays a price for its lower transmission rate. It would be interesting to try to repeat such a test using a broadband UV-flash in a controlled environment.

 

Comment_3: As a side note, for the BaaderU and KolariU, the red channel reached full saturation first. For the SEU Gen2 the red and blue channels reached full saturation almost simultaneously with the red channel leading by a very tiny margin. Histograms for this result are not shown.

 

 

Results at a Glance

Those denominators increase from top to bottom and from left to right. Those are monochrome (brightness) histograms you are looking at. The white light is naturally piled up on the right-hand side, but did not hit the wall.

d610_uvNikkor_sun_composite_20180713swhME_1157601chart.jpg

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[Last Update: 2018.07 19:08 EDT]

 

A Windy Bull's-eye

 

What is the classic test which proves a filter's UV-worthiness? Photographing a known UV floral signature. I found a nice Hawkweed (Hieracium kalmii), a ligulate member of the Asteraceae family, which has a diffuse UV-dark central bull's-eye typical of that kind of Dandelion-like flower. The sunshine was strong. I've been getting 5+ UVA-B readings with my Solarmeter, but it was windy. The motion blur in these photos does not get in the way of the convincing performance of the SEU Gen2 of capturing a floral UV-signature.

 

I will revisit the UV floral signature in a subsequent topic because flowers are also good subjects for showing the sharpness of any filter. So let's have a bit of fun here with my wind-flawed Hawkweed photos.

 

 

FLORAL UV-SIGNATURE TEST: Photograph a flower with a known UV-signature.

 

Question_1: Does the filter capture the UV-signature?

 

Answer: Yes, but I'm going to tease you with this one.

 

Question_2: Which filter made which UV-signature? :lol:

 

Answer: ??? Your choices are from the set {BaaderU, KolariU, SEU Gen2}.

 

Subject: Heiracium kalmii

 

Gear: D610 + UV-Nikkor 105/4.5 + UV-Pass Filter + Sun + Wind

 

UV-Pass Filters: Not sayin'.

 

Exposure: f/11 at various speeds @ ISO-400

 

 

Hawkweed #1

hieracium_2.jpg

 

Hawkweed #2

hieracium_1.jpg

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This topic is now open for comments. Although I do have some formatting details to add to the second post.
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[Last Update: 2018.07.19.08.31.EDT] Second post now complete.

Last Update [2018.07.19 10:45 EDT Introduction beefed up.]

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Your white balance on the Hawkweed is fantastic. My guess is #1 is the Baader u, do to slightly stronger yellow and #2 is SEUmk2. However, for my vary own reasoning I may have it backwards as I typically like more blue in my images, and your excellent WB is throwing me off. But I will stick to that guess.
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I also think the image #2 is from SEUmk2, but my guess is based on my measurements of that filter.

 

Image #1 is more difficult, but I do not think it is from a Baader U.

At least with my camera the UV-black areas are not that brownish with Baader U.

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We have to be careful with false colors !! Saturation is a choice not a reality.

Photo Ninja is a very colorful converter. :lol: :lol: :lol:

 

I took the two raw photos through an NX2 conversion.

Does your guess change? :rolleyes:

 

Hawkweed #1

hieracium_2b.jpg

 

Hawkweed #2

hieracium_1b.jpg

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Yes it does change everything.

I am probably wrong this time too. :(

This exercise is about how difficult it is to tell the difference between filters because there are many other factors in the post process that can change the final result beside the filter.

 

It is really fun to try to logically analyse the difference and match it against earlier experiences.

With some luck it might be slightly better than flipping a coin to decide. :D :D

A dice would probably be a better tool to use to randomly select one of three alternatives. :) :) :)

 

In this new image set the tone difference of the (false)-yellow petals remind me of the differences I'm used to see when comparing lenses with different deep UV-reach.

#1 has a slightly more pale, cold nuance than #2.

To me that equals #2 having the peak transmission at shorter wavelengths than #1.

 

#2 also have a greenish tint in the dark central areas.

The same effect sometimes occur for me with the BaaderU, but never with the S8612 U-360 stack.

Images with BaaderU, I think get this tint due to the filters weak IR-leakage, not present with U-360 + S8612.

 

Based on the new image set my guess is:

#1 = SEU2 with an UV-peak close to VIS.

(Also this series is all about SEU2 and if my #2-guess is correct too, by elimination #1 is most likely the SEU2)

 

#2 = BaaderU with a deeper UV-peak and familiar trace of IR leakage.

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Ulf: This exercise is about how difficult it is to tell the difference between filters because there are many other factors in the post process that can change the final result beside the filter.

 

Indeed, that is so true. Each different converter has its own way of profiling a camera and measuring white balance, to name just two things. In a UV file small differences in profiles or tools lead to different appearances in finished photographs, especially because we are white balancing and processing false colours. Sometimes it seems that nudging a slider just a tiny little bit too far can produce an unexpected outcome in a UV file but that same nudge would make little difference in a Visible file. :lol:

 

And I was just thinking about how companies like Adobe have spent literally millions of dollars and millions of man-hours to ensure that their software produces a Visible photograph which looks like a Visible photograph should look. (Don't take me to task for that "should" statement, please!) But nobody has ever spent any money or time at all to ensure that a UV photograph emerges from a converter with any kind of standardized look or normalized appearance.

 

One sure fire way of determining which filter made which photo is to show the raw composite of each photo made before white balance and other edits are applied. I will post those raw composites for the Hawkweed photos after I finish my last two test series.

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Ulf: This exercise is about how difficult it is to tell the difference between filters because there are many other factors in the post process that can change the final result beside the filter.

 

One sure fire way of determining which filter made which photo is to show the raw composite of each photo made before white balance and other edits are applied.

 

That is exactly how I tell the difference between filters and lately lenses with similar focal length but different UV-range.

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:D :D :D

 

That Raw Digger app has been a very useful tool to have, hasn't it? I should write to Iliah and tell him of our use of RD for seeing the "white signature" or false color signature of a UV-pass filter or filter/lens combination.

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