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Three UVA Dichroic Filters in Sunlight with a Sunflower

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#1 colinbm

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Posted 12 May 2021 - 03:38

Three UVA Dichroic Filters in Sunlight with a Sunflower.
All with the 50mm O D Industries enlarger lens & each CWB

First, Badder U.

Second, SEU Gen 1.

Third, SEU Gen 3.


Attached Image: 2021 05 12 Sunflower UVA Baader U web.jpg


Attached Image: 2021 05 12 Sunflower UVA SEU Gen1 web.jpg


Attached Image: 2021 05 12 Sunflower UVA SEU Gen3 web.jpg

#2 dabateman

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Posted 12 May 2021 - 04:30

Are the exposure settings the same?
There are subtle color differences between Gen 1 and Gen3. I would have expected more of a blue shift. But I am just looking from my phone which isn't the best.

Edited by dabateman, 12 May 2021 - 04:31.


#3 Andy Perrin

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Posted 12 May 2021 - 04:44

Colin, how does it look with a PTFE white balance?

#4 colinbm

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Posted 12 May 2021 - 04:55

Dave, the exposures were all f5.6 at 0.8 seconds.
The ISO did change though as I had it on auto, first & second were ISO 400 & the third was ISO 100.
The colour temperature changes too, first was 4150K & the second & third were 15000K.

Andy, The CWB was on a grey card that I find works for me.
I haven't seen differences in the past with my PTFE block, but now I have a different camera etc I should try this again when sunlight permits & I get a fresh sunflower....
The recent sunflower shots were with the grey card as a backdrop, as this flower was on its last legs I had to place it face up on a table & the background was some of that white spongy close cell foam.

Edited by colinbm, 12 May 2021 - 04:59.


#5 dabateman

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Posted 12 May 2021 - 07:08

Interesting, so you gained 2 stops with the SEU gen3, but loose that green look. Also some of the damage isn't as strong.
Have you looked at the filters with your spectrometer yet?

#6 colinbm

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Posted 12 May 2021 - 07:34

View Postdabateman, on 12 May 2021 - 07:08, said:

Interesting, so you gained 2 stops with the SEU gen3, but loose that green look. Also some of the damage isn't as strong.
Have you looked at the filters with your spectrometer yet?

Baader U

Attached Image: 20210511BaaderU-Ref.png


SEU Gen1

Attached Image: 20210511UVGen1-Ref.png


SEU Gen3

Attached Image: 20210511UVGen3-Ref.png

#7 UlfW

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Posted 12 May 2021 - 10:20

View PostAndrea B., on 07 May 2021 - 05:18, said:

I'm pretty sure everyone knows (or certainly should know) that wide lenses are prone to vignetting when filtered.

I agree we should add something about dichroic filters. Would please suggest the proper terminology for that suggestion? I've never been sure what the dichroic discoloration is called.

The images are not properly white balanced
After a quick round in Photoshop's Auto Colour the jpeg images look like this:

Baader U.
Attached Image: post-31-0-64702800-1620790598.jpg

SEU Gen 1
Attached Image: 2021 05 12 Sunflower UVA SEU Gen1 web.jpg

SEU Gen 3.
Attached Image: post-31-0-62833600-1620790670.jpg

The Baader U show slightly wider colour palette.
I am used to see a more pale blue tone in the bluish areas with my SEU3, but the difference might be caused by differences in camera response or between different filters.

The rather big bump in the spectra in Colin's SEU3 spectrogram do not show up in the images. Such levels would normally be well visible.
I suspect something fishy with the spectrograms, especially as they likely are made with the sun as light-source. That distorts the real transmission of the filter quite a lot.

Grey-cards are not that good for white balance of UV images as they do not have a well defined reflectance in UV.

Edited by UlfW, 12 May 2021 - 10:46.

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#8 colinbm

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Posted 12 May 2021 - 11:00

Thanks ULF, I'll do the CWB again with PTFE tomorrow, when I get another sunflower & in sunlight when it arrives again.
Perhaps the white spongy close cell foam is good for UVA CWB...?
The lens was a 50mm O D Industries enlarger lens.
Yes the spectrographs were in sunlight, which is the same as I photographed in as well.

Full frame of the SEU3 before cropping & with a click WB on the white foam.

Attached Image: 20210512 Sunflower UVA SEU3.jpg

#9 dabateman

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Posted 12 May 2021 - 12:12

Yes your SEU3 or is it mark4 now as I know there is a formulation difference, doesn't look like Ug5 or a thick ZWB3. So I agree with Ulf, that 450nm bump might be an artifact.

I think sunflowers and dandelions give away their UV signatures too easily. I will have to test a dandelion with my 405nm filters to prove that though. A flower with tighter UV signatures would be best, but it might be impossible to standardize that accross the world.

#10 Andy Perrin

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Posted 12 May 2021 - 12:36

Ooh, yes, I like the colors a lot better with the click-WB on the foam. I think the green cast was also obscuring differences in the filters.

#11 colinbm

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Posted 13 May 2021 - 05:42

Another day....another dollar spent & a new Sunflower & a better setup....
The pictures are now full frame, 24mm x 36mm sensor size.
Included in the pictures is the PTFE block.

Same order as before....

First, Baader U CWB.

Second, SEU Gen 1 CWB.

Third, SEU Gen 3 CWB.

Attached Image: 20210513 Sunflower UVA Sunlight BaaderU CWB web.jpg


Attached Image: 20210513 Sunflower UVA Sunlight SEU Gen1 CWB web.jpg


Attached Image: 20210513 Sunflower UVA Sunlight SEU Gen3 CWB web.jpg

#12 JMC

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Posted 13 May 2021 - 08:06

Thank you for sharing Colin, interesting test.

Personally, I think there is merit to your spectra for the filters. Obviously sunlight intensity varies with wavelength so if you're using a filter to take a photo in sunlight it makes sense to know about how and where that filter blocks and lets through that particular light source and how much. There is of course the issue of varying intensity of light when comparing the filters.
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#13 dabateman

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Posted 13 May 2021 - 08:16

Colin this might sound odd. But test your S8612 on top of the SEUgen3. I see a slight bit of a muted brown in the UV dark area and I wonder if there is a hair of IR leakage.

#14 colinbm

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Posted 13 May 2021 - 08:22

View PostJMC, on 13 May 2021 - 08:06, said:

Thank you for sharing Colin, interesting test.

Personally, I think there is merit to your spectra for the filters. Obviously sunlight intensity varies with wavelength so if you're using a filter to take a photo in sunlight it makes sense to know about how and where that filter blocks and lets through that particular light source and how much. There is of course the issue of varying intensity of light when comparing the filters.

Thanks Jonathan, I am no scientist, but that is my feelings....I want to know what is happening in the light that I am using, not in a laboratory.

Edited by colinbm, 13 May 2021 - 08:22.


#15 colinbm

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Posted 13 May 2021 - 08:24

View Postdabateman, on 13 May 2021 - 08:16, said:

Colin this might sound odd. But test your S8612 on top of the SEUgen3. I see a slight bit of a muted brown in the UV dark area and I wonder if there is a hair of IR leakage.

Thanks Dave, good idea, I'll try again tomorrow with the SEU Gen3 & S8612 stack

#16 UlfW

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Posted 13 May 2021 - 11:19

View Postcolinbm, on 13 May 2021 - 08:22, said:

Thanks Jonathan, I am no scientist, but that is my feelings....I want to know what is happening in the light that I am using, not in a laboratory.
I fully agree with Jonathan that there is a merit with your measurements, no offence intended, but in the final end the resulting images are created by a combination of very many things that interact.
Due to the reduced sensitivity of the sensors and intensity in the sunlight, in UV, it will be impossible to determine some things, without more proper laboratory tests too. :smile:

My comment was just intended to clarify that what you were showing was not the transmission of the filters, but the intensity of the sunlight when passing the filters.
I am sure that you know and understand this very well, but for some less initiated readers it could be confusing.

Maybe it is a good idea to be a bit more formal about what we are showing when publishing diagrams?

Edited by UlfW, 13 May 2021 - 11:20.

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#17 colinbm

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Posted 13 May 2021 - 11:45

Ulf said, " Maybe it is a good idea to be a bit more formal about what we are showing when publishing diagrams? "
Do you mean, for me, to make it clear that the measurements are taken in sunlight or the light I am using to take the measurement in, so not to be confused with 'proper scientific' practice, for gathering filter transmittance spectrums ?


#18 dabateman

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Posted 13 May 2021 - 12:20

View Postcolinbm, on 13 May 2021 - 11:45, said:

Ulf said, " Maybe it is a good idea to be a bit more formal about what we are showing when publishing diagrams? "
Do you mean, for me, to make it clear that the measurements are taken in sunlight or the light I am using to take the measurement in, so not to be confused with 'proper scientific' practice, for gathering filter transmittance spectrums ?


What Ulf maybe indicating is that you are not using a spectrometer for your measurements. But rather a light meter or Illuminance Spectrometer. These act and are calibrated differently than a spectrometer or spectrophotometer. A spectrophotometer would give you accurate color information. You device gives you accurate lighting information, which is different than a spectrometer.
I too don't have the best device. A photon multiplier tube and a double adjustable grating with an integration sphere, would be much better than the linear Sony sensor behind a grating that I have. Errors can occur and noise can be bad.
But I didn't buy mine to measure lenses, filters or even lights. So I am doing ok. The original purpose didn't pan out and will still need considerable thought. Also I don't have the money to buy a correct system, and knowing where something cuts off is more useful for me than which lens transmits more at exactly 385nm. Or this lens has a yellow cast, because the 600s are truncated.

Did that make sense?

#19 colinbm

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Posted 13 May 2021 - 12:38

Thanks Dave, yeah sorta, I do know I don't have a big lab in my hands, but it can tell me something about light & wavelengths & is good for measuring the out put of lights.
When I went to school we never did anything about about light & wavelengths & spectroscopes. It was only about 10 years ago I learnt about diffraction gratings & I was amazed & wanted to photograph in UV & IR.

#20 UlfW

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Posted 13 May 2021 - 14:45

View Postcolinbm, on 13 May 2021 - 11:45, said:

Ulf said, " Maybe it is a good idea to be a bit more formal about what we are showing when publishing diagrams? "
Do you mean, for me, to make it clear that the measurements are taken in sunlight or the light I am using to take the measurement in, so not to be confused with 'proper scientific' practice, for gathering filter transmittance spectrums ?

Yes, that is exactly what I meant.

The 'proper scientific* way of measuring transmission involves normalising against any weird light source used.
Do you remember what we did in Excel with your exported raw data from your excellent optical power meter?
Transmission calculations are done by dividing one test spectra with a reference spectra (taken from the light source alone).

For high quality measurements the light source must be stable between reference measurement and test measurement.
The light must also contain enough energy for the spectrum range of interest. Then the sunlight is not very good for what we are searching.
There are several other aspects that are important for a successful measurement, depending on what you want to measure.

All that David is saying is correct and my spectrometer is not ideal either, but by knowing the systems weak spots and understanding what causes them, I have found work arounds that are reasonably good.
A ideal system for measuring lenses in a wide spectrum range would be very expensive and also difficult to run correctly.
Ulf Wilhelmson
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