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Bold claim - Hitech ND filters and UV capability

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#21 dabateman

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Posted 07 January 2019 - 06:13

View PostAndy Perrin, on 07 January 2019 - 05:51, said:

It can't bounce off at some wavelengths and not at others.


However, I want to highlight that this statement is wrong. Yes absolutely you can have light bouncing off at some wavelengths and not at others.
This is how a dichroic mirror works and is fundamental for microscopy. You pass light through and only longer wavelengths are allowed to return.

#22 Andy Perrin

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Posted 07 January 2019 - 06:13

Yeah, I'm betting either made up data or someone has done some processing that they aren't describing in the blurb. Those slanted axes are really odd. But the graphs look like they were made in Excel. Goodness knows!

#23 Andy Perrin

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Posted 07 January 2019 - 06:15

View Postdabateman, on 07 January 2019 - 06:13, said:

However, I want to highlight that this statement is wrong. Yes absolutely you can have light bouncing off at some wavelengths and not at others.
This is how a dichroic mirror works and is fundamental for microscopy. You pass light through and only longer wavelengths are allowed to return.
No, that's not what I meant to say. You can't have some wavelengths bounce off and be registered as negative and others as positive. There aren't any detectors that give negative magnitudes.

Edited by Andy Perrin, 07 January 2019 - 06:16.


#24 dabateman

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Posted 07 January 2019 - 06:24

I think we are in agreement.
Just think how much time we would have to take photos if we only used Excel and Photoshop in "Science".
But then our Dogmas would get out of control.

#25 UlfW

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Posted 07 January 2019 - 06:26

View PostCadmium, on 07 January 2019 - 02:34, said:

Still... "The Academy of Motion Picture Arts and Sciences (AMPAS).... The test measured the spectral power distribution of tungsten light reflected off a spectralon target made of barium sulfate using a Photo Research SpectraScan Model 705 spectroradiometer..."
Sounds pretty impressive, definitely a mouthful.

This is something written by their marketing department just to show off as technically superior.
The perspective graphs are a sign of decorative usage, mabe to try to conceal their ignorance about the measurements.

They have even invented a new spectralon material "made barium sulfate".
https://en.wikipedia...wiki/Spectralon

The method of using a thin metal layer instead of absorbing glass materials might be a good idea if they have a cost efficient production process.
Then they must "prove" that their filters are better than their competitors. As the improvement is in wavelength ranges that almost no camera can see it is rather meaningless.
I do not think that their main target market is our little group with modified cameras. :)

The principle is well known from optical media.
The dual layer DVDs used it in a very controlled way making the outermost information layer semi-transparent, to allow reading of the inner layer.
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#26 Cadmium

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Posted 07 January 2019 - 08:31

I have been reading you talk back and forth, and still my understanding of this hasn't clicked for me here yet.
The "spectralon target made of barium sulfate" is a Labsphere coating called Spectraflect.

1.1 Spectraflect Reflectance Coating
Spectraflect is a specially formulated barium sulfate coating which produces a nearly perfect diffuse reflectance surface.
Spectraflect is generally used as a reflectance coating in the UV-VIS-NIR region and is most effective over the wavelength range
from 300 to 2400 nm.

Page 5 of this pdf:
https://www.labspher...nd-coatings.pdf

#27 Pedro J. Aphalo

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Posted 07 January 2019 - 09:13

I agree the plots at the Formatt-Hitech website are hopeless. This is why I intend to measure the filters myself. On the other hand we need to remember the context. These filters are being sold for normal photography use, not specialized technical use. The claims relate to this use, in relation to these ND filters not affecting the white balance even the -16 EV ones. For digital cameras that are not converted, a range of 375 nm to 800 nm is what is more relevant. There is no excuse for the rubbishy plots... but the filters might be o.k. or even very good, as some others they sell are.

#28 Cadmium

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Posted 07 January 2019 - 09:24

I will just say this again, that I don't see any way of comparing the Schott ND (NG) filter transmission graph with the graphs or info presented by Hitech.
http://www.ultraviol...dpost__p__25403

I don't see any information showing me an actual transmission of their ND filters.
I understand their claims, and that may all well be true, but graphs help me understand things, and frankly their graphs don't help me understand anything, so far anyway.

#29 UlfW

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Posted 07 January 2019 - 11:22

View PostCadmium, on 07 January 2019 - 08:31, said:

I have been reading you talk back and forth, and still my understanding of this hasn't clicked for me here yet.
The "spectralon target made of barium sulfate" is a Labsphere coating called Spectraflect.

1.1 Spectraflect Reflectance Coating
Spectraflect is a specially formulated barium sulfate coating which produces a nearly perfect diffuse reflectance surface.
Spectraflect is generally used as a reflectance coating in the UV-VIS-NIR region and is most effective over the wavelength range
from 300 to 2400 nm.

Page 5 of this pdf:
https://www.labspher...nd-coatings.pdf

I guess it was only a typo, but spectraflect is not spectralon that is a PTFE-based ssintered material.
Ulf Wilhelmson
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#30 dabateman

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Posted 07 January 2019 - 11:34

I now think those graphs worked perfectly.

I never herd of this filter brand berfore this thread. Now I have clicked through both the UK and USA sites and seen most of their products and prices.
And looks like we have started talking about them for two pages now and at least 5 people are looking deeply at their products.

So seems like meaningless plots work that tell you nothing. Remember these are ND filters not even polarized, so no wonder the reflective measurements are so tiny to be pointless.

Cadmium, if you want to compare them hold your favorite brand up to the sun and see how long it takes to go blind. Now hold up there products and you will see they are totally black. Works like a charm.

#31 Andy Perrin

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Posted 07 January 2019 - 15:08

Pedro, I hope you get those filters soon, I would like to see the results. Until then I think I’m staying out of this thread.

#32 Shane

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Posted 11 January 2019 - 01:41

I actually bought a Firecrest (not the Ultra) several years back and ran a transmission spectrum and later compared it to the Breakthrough ND filter. I have to admit I wasn't too interested in it's supposed UV performance so the setup wasn't ideal at that end of the spectrum. However, I can say that Breakthrough performed a little better at both ends, I just don't remember how far into the UV it went. I currently use the Breakthrough for IR 830nm. Would love to share my spectra but they ended up on an external drive which has yet to emerge since my move.

#33 Alaun

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Posted 11 January 2019 - 11:30

Now come on, have a closer look, nothing below 0, these simply are 3D-plots

Attached Images

  • Attached Image: a_3D-graph.jpg

Werner

#34 Pedro J. Aphalo

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Posted 12 January 2019 - 18:06

Here is my attempt at measuring the transmittance of a Firecrest ND 1.2 filter (round 52 mm). The increase in transmittance in from 400 nm to 350 nm is at least in part caused by stray light. I will repeat the measurements next week to investigate this. For the time being I am limited to the range 350 nm to 1000 nm. So this filter has a flatter curve than the ND filters from Schott in their NG series. In addition to the plot from my own measurement, I did find proper spectra in the Formatt-Hitech website. The plots are at the end of a rather long blog post that also shows spectra for cheaper/older types of ND filters for photography from the same company. See https://www.formatt-...density-filters The plots provided by the manufacturer cover the range 300 nm to 1100 nm and are in absorbance units. The plot below shows transmittance as a fraction of one.


Posted Image

Edited by Pedro J. Aphalo, 12 January 2019 - 18:10.


#35 dabateman

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Posted 13 January 2019 - 06:36

Well your spectrum does seem to match theirs, which is a good sign. So if I only want 3% transmission in UV, and through away a ton of light, these do look like good ND filters for that.
However I can't say I have ever wanted to do that. Now can they make a polarizer that keeps 50% of the light through all wavelengths?
That would be more interesting.

Edited by dabateman, 13 January 2019 - 06:37.


#36 UlfW

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Posted 13 January 2019 - 07:24

View Postdabateman, on 13 January 2019 - 06:36, said:

Well your spectrum does seem to match theirs, which is a good sign. So if I only want 3% transmission in UV, and through away a ton of light, these do look like good ND filters for that.
However I can't say I have ever wanted to do that. Now can they make a polarizer that keeps 50% of the light through all wavelengths?
That would be more interesting.
The main strength of this filter-technology is likely that the transmission is more constant over the wavelengths for the higher attenuation-variants compared to what is possible with ionic filter glass.
Can be interesting for some VIS-photography, but too much light that cannot be handled with shorter exposure times is rare in UV-photography.
Ulf Wilhelmson
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#37 Cadmium

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Posted 13 January 2019 - 07:35

Only idea I have come up with for UV, is let's say you had a landscape, where the sky was bright, and the landscape is dark, as it usually is in UV, then you could possibly use the half/half style to darken the sky...
Am I thinking right about that?
However, seems like a regular half/half ND would make the sky even darker, right? But who knows... and the scenario seems little obscure in a few ways.

Edited by Cadmium, 13 January 2019 - 07:38.


#38 Pedro J. Aphalo

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Posted 14 January 2019 - 00:03

Firecrest CPL circular polariser absorbs strongly in the UV... just in case somebody has started wondering...


#39 Cadmium

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Posted 14 January 2019 - 04:43

I thought the bid deal here was that the "Firecrest Filters are neutral across all spectrums, including UV, visible, and infrared."

#40 Andy Perrin

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Posted 14 January 2019 - 05:08

View PostCadmium, on 14 January 2019 - 04:43, said:

I thought the bid deal here was that the "Firecrest Filters are neutral across all spectrums, including UV, visible, and infrared."
Apparently they are (at least compared to the competition) for the ND filters. But if you mean post 38, Pedro is talking about the circular polarizer, not the ND filters.