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UltravioletPhotography

Filter Transmission Charts #2


Andrea B.

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Then by all means write a better program using better math that uses your better calculation. :)

I am just pointing out the new feature which is better than not having that feature, as all the previous version didn't have,

and on occasion some have complained about combi Ti graphs that I have posted because they don't represent true transmission.

So... what should we do, post Ti graphs and have people complain, or post T graphs and have people say those arn't correct either?

All I am doing is pointing out a new feature that was not there before, not in the version Andrea is using, and a great added improbvement.

If you don't think the math is correct in the Schott program, then make something else.

 

Steve, what you have written, was a very valuable input about the Schott program I hadn't observed before!

That made me think and I just wrote my conclusions and tips.

 

I didn't mean to complain at all.

Sorry if it sounded like I did.

 

I have no programming skills at all and have to stick to the Schott program.

It works quite well for an Excel document.

There is no problem for me that the Schott program don't do all the advanced math for a completely correct simulation.

 

Now after your input I'm simply trying to help everyone to use the Schott program better. That is easy to do.

The T output plots are valuable and I like to use them too, but input data must be chosen correctly, just as you chose the correct filter type you are interested in.

 

That is done by setting the value of Peff to another value than the default 0.91

The 0.91 is an acceptable general value, but only valid for a single filter or a cemented stack.

 

For an air spaced filter stack of two filters the value would be 0.912 = 0.83

If you for some reason stack three filters 0.913 = 0.75 could be used.

 

Even better Peff values, can be calculated from the filters material properties that then is multiplied together.

Peff is (1-Reflectivity)2 for a single filter.

For a stack you multiply the individual Peff values for each filter-type together to get a combined Peff .

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One thing that should be mentioned from a photography point of view, is that going from 80% transmission to 70% will not really be noticed. But going from 10% to 20% would. Also if you have a filter with only 10% transmission, you may need a better filter.

However from a uv photography point of view 5% IR will kill the shot.

 

I fully agree with this.

 

About IR leakage I can see faint traces of that even in my BaaderU images. (new version) .

I have measured the leakage levels around 730nm to 0.01% (OD4)

If low IR leakage is a goal a S8612 + U-360 stack would perform better.

 

There are also other cemented UV-stacks on the market with very good IR performance.

Andrea made an interesting comparison test here:

http://www.ultraviol...rcing-shootout/

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Andrea is using the 2017 Schott Excel calculation program and making only Transmittance charts.

 

Just so it's clear what I'm doing. B) B) B) Or trying to do!!

 

The charts are only meant to be some kind of general guidance to the types of UV-pass available.

We cannot let perfection get in the way of "good enough for general guidance".

 

You do know, I hope, that if any of you would like to contribute charts having a higher level of accuracy (such as considering reflections, available UV-light, lens type, sensor type, altitude, latitude, weather(!) and the entire host of factors affecting how we record reflected UV light), then you will always have a place to publish them here on UVP. They would always be welcome!

 

Now, I have to get busy........

 

I love you guys!! This place is so cool and so much fun!!!!

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Andy Perrin
I am willing to do a full calculation for a simple stack (at just one wavelength, as an illustration of the method), but I'm a little reluctant to, because I don't know how much interest there is? It would be a LOT of math, and probably half a day's work to write it up, and I really don't want to do it unless there's interest. When I wrote up my Independent Component stuff, the only response was from Andrea. And I avoided equations entirely for that post.
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Andy -

I think it would be a waste of your valuable time to go that deep, as the deviation in results compared to results from the simplified methods are too small to affect any normal use of ta stack.

 

Do you see any flaws in my reasoning above so far?

Sometimes my thinking takes incorrect shortcuts I cannot see myself. :)

 

My reason for searching a intermediate improvement is to use results from the Schott program to verify that my spectrometer measurement methods are reasonably correct.

I am trying to improve my confidence of the methods to detect and find workarounds in the process limited by me array spectrometer.

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When I wrote up my Independent Component stuff, the only response was from Andrea. And I avoided equations entirely for that post.

When I searched for that topic I could not find anything. I looked though all the topics the forum say you started without success.

Please help me find it.

I think I have read all your topics lately, but try to avoid commenting images even if they are very nice and yours often are.

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Andy, it would be interesting. But I don't think you should take the time unless you simply want to satisfy your own curiosity or unless you had some other outlets for the work. We are a specialized site, but the interest in deep methods might not be there. You can always add something later.
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Oh please don't avoid commenting images! This is a photo site. Comments are always welcome even if just one sentence or just a couple of words.
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Andy Perrin

Andy -

I think it would be a waste of your valuable time to go that deep, as the deviation in results compared to results from the simplified methods are too small to affect any normal use of ta stack.

 

Do you see any flaws in my reasoning above so far?

Sometimes my thinking takes incorrect shortcuts I cannot see myself. :)

 

My reason for searching a intermediate improvement is to use results from the Schott program to verify that my spectrometer measurement methods are reasonably correct.

I am trying to improve my confidence of the methods to detect and find workarounds in the process limited by me array spectrometer.

No, I agreed with you! Your reasoning is fine. The purpose would not be to obtain numerical results but to explain the details of physics involved so that people can understand where the approximations are being made here. For photographic purposes, only rough calculations are really needed. Spectroscopy might benefit from more detailed calculations, but only if people are curious.

 

Independent Component post was here:

http://www.ultravioletphotography.com/content/index.php/topic/2849-revealing-the-faded-text-on-an-old-building-ad-with-ica/page__view__findpost__p__22270

Purpose of the post was to explain the method and what it can do, not for image quality, really. The idea was to gain information from the image, not beauty in this instance.

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OK, that article was interesting.

 

I read it twice, but could not find any meaningful comment to make.

I feel like too much empty commenting is like spamming.

 

Details of physics are always interesting, even when the math goes above your math level.

If you should go all the way with the reflection details I suggest you go one step further and do it for non normal incidence with all the complex math involving polarisation effects.

Together with multiple internal reflections that would be a beast problem to solve analytical. :D

Just joking. Too much work!

 

It is way above my math competence.

I saw some of it, enough to understand its presence, when working on a birefringence measuring system, for optical storage media, where I designed the electronics and precision mechanics.

It was more than 25 years ago, so the details are a bit blurred in my memory.

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@Andy,

I read that with great interest. I was surprised that the details were mostly revealed by the IR and not uv image.

 

I have been very busy with home recovery efforts, after recent purchase. That I haven't been around on anything lately.

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