Crokus

[IxnaX]

 

Full spring sun

 

Sony A6000 full spectrum

 

Tamron 17-50mm- goes to 365nm then hits an immediate dropoff wall

 

Custom in camera white balance

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Image#1-

Crokus Flavus

-Hoya U-330 filter on the lens

-S8612-2mm infrared suppression on the lens
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Image#2-

Crokus Flavus

-Hoya U-330 filter on the lens

-BG38 infrared suppression on the lens - allows some upper level reds

 

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Image#3-

Crokus vernus & Crokus flavus

 

-Hoya U-330 uv filter on the lens

-BG38 infrared suppression on the lens- allows some upper level reds

 

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Image#4-

Crokus vernus & Crokus flavus

 

-Hoya U-330 uv filter on the lens

-S8612-2mm infrared suppression on the lens

[colinbm]

They look impressive.

 

[IxnaX]

7 minutes ago, colinbm said:

They look impressive.

 

Thank you. I got the BG38 for the sole purpose of modifying the "bee vision" stack.

 It lets in those upper level reds and a hint of IR that the S8612 would cut away.

 

Guess this could be called.....

 

"Platypus vision stack"

[Andy Perrin]

Image 2 is especially pretty 

[ulf]

On 1/28/2023 at 9:08 PM, IxnaX said:

Tamron 17-50mm- goes to 365nm then hits an immediate dropoff wall

 

Despite what you said in another thread

"Well just as a "preemptive strike" before i do post my UV data and research and results...all my lenses reach 360nm and one at least 340 and one 330s and possibly lower."

 

This is a statement that I must challenge.

 

I wonder how you define "goes to 365nm" and if you have any real measurement proof of that.

If not, please do not make  such definite statements.

 

A simple diffraction film test like the ones you call spectrascope are far from accurate enough for that.

---

I have measured several modern complex lenses the proper way with a real spectrometer and none of them had a meaningful UV-reach anywhere close to 365nm. Even so, some of those lenses can sometimes be usable for some types of upper UV-A photography.

 

I must confess that I have not measured any of the possible 17-50mm lenses that you might refer to here, but I still do not think what you state is true. At least I suspect there will not be substantial amounts of light passing at 365nm.

 

Modern zooms like this lens have many lens elements made with glass types that often do not pass UV well. The XR-glass in these lenses might be among them. Long passage through many types of modern optical glass limits or blocks UV.

 

They are also AR-coated with complex coatings optimised for the visual range. Outside the designed range of a coating, the coating loses its efficiency and starts blocking, a kind of dichroic filter effect.

 

Here are an image of the structure of two Tamron 17-50mm lenses.

I can count to 22 lens surfaces that have AR-coating.

 

I assume that you have been able to use the lens getting reasonably usable UV-images.

That might be an indication that the lens for some reason is less marginal for UV than other modern lenses, but that is not a proof either of an UV-reach to 365nm.

 

You might even have tried your diffraction spectrascope on that lens and seen some light around 356nm, but as such tests are at most indicative and with almost no accuracy of the light intensity passed they are not at all reliable.

 

[IxnaX]

Ill make this spanking quick....

 

First off...its a nice aluminum scope i bought...not a diffraction film.

It has a prisim and grating.

So yes, i will call it a spectrascope because thats what it is.

 

Measure the proper way? Why..because you say its the proper way? You do realize that utraviolet was discovered and measured in the 1800s right? No fancy pants machines...hell, what im using is more advanced than what they used.

 

You wanna challenge me because you think im guessing ...but at the same time, your challenge contains guesses about what im using...cute.

 

 Not to mention you didnt even know you can do false color IR with an unmodified camera, something ive done for 20 years....

 And ill mention that you just said youve never touched this lens, never measured it, never seen it, never heard of it...but somehow, youre the ultimate expert on this lens....a lens IVE been using the past 20 years...

So youre hardly in a position to be "the word above all".

 

As for the lens reaching 365...ill let the images speak for themselves...

 

Light source- exoterra UVB bulb/365nm flashlight 

 

Teflon tape target

 

Lens- Tamron 17-50mm f2.8

 

Second order to the right

 

Spectrum of the exo terra uvb bulb

No filters

1/6 seconds @ 250iso

Oh...look at that... 360-365 is already showing ....lets turn up the heat right away.

 

 

Hoya U-340 on the lens

S8612-2mm on the lens 

 

1 second@1600iso

 

Image#2 has 365nm line enhanced with 365nm flashlight..for the sole purpose of showing you i know where the 365 line is.

 

 

Hoya U-360 on the lens

S8612-2mm on the lens

 

1 second@1600iso

 

Image#2 has 365nm line enhanced with 365nm flashlight..for the sole purpose of showing you i know where the 365 line is.

 

Hoya U-330 on the lens

S8612-2mm on the lens

 

1 second@1600iso

 

Image#2 has 365nm line enhanced with 365nm flashlight..for the sole purpose of showing you i know where the 365 line is.

 

 

Bottom line is....doesnt take a rocket scientist to figure out a few photons.

  Luckly, i have insomnia at the moment, so i have time to state the facts over someones fiction.

 

 

[nfoto]

It's OK to explain, but please remove the personal emotions in the response. This is not what a UVP discussion should be about.

[colinbm]

Can you overlay these spectra with published mercury vapour lines ?

[ulf]

At this forum it is quite normal to challenge statements to clarify and discuss details, especially if they seem incorrect.

See it as a review of stated facts.

We normally do that in a civilised way without being blunt or rude.

Then openness for new ideas and facts are essential.

By finding potential errors and discussing them we all learn and improve our understanding

 

My post above is not a personal attack.

 

It is understandable and acceptable to be un-knowledgeable about measurement methods if it is not within your specialist competence. It is my specialist competence and I will try to share here if you are willing to listen.

 

The details in how to measure transmission correctly, especially for lenses, are in reality quite complex even if it does not look so at the first glance. If not done correctly the results cannot be used for bold strict statements about absolute cutoff wavelengths. 

 

Unfortunately the information from your prism gadget is far from good enough to give a real information of the actual transmission of your lenses.  To do that you need more advanced equipment. What you can see there is that it transmits some photons around 365nm too, but nothing about the attenuation. That is what transmission measurements are all about.

 

Maybe the problem here beside from the unfortunate emotional reaction is semantic. For me information about transmission is defined like this:

The relative difference between how much light is passed by an optical component or optical system like a filter-stack or camera-lens, compared to the light passed without the optical component.

The result is expressed in percent.

 

Maybe I should tell you more about myself, my knowledge and my equipment?

I want to help you understand that in the optical measurement field I know what I am talking about, just as you seam to be "The Master of IR-Photography with Unmodified Cameras".

 

Let me start with my background.

I am a measurement specialist that have been working for more than forty years with optical measurements and electronics design of measurement equipment. I have been involved in the design of several types of industrial measurement equipment using laser optics. During that time we got four different patents approved about measurement methods where I was the inventor.

 

The last four or five years I have been measuring lenses and filters with my own spectrometric equipment and posted some results here on this forum. During that time I have gradually improved my setup and equipment and optimised the procedures.

 

My equipment:

My private spectrometer is a specially configured model of this type:

https://www.oceaninsight.com/products/spectrometers/general-purpose-spectrometer/flame-series/flame-t-uv-vis/?qty=1

 

For proper spectral measurements you also need a good light source.

For proper measurement an Exoterra UVB bulb is not good enough as the emission varies too much over time and for different wavelengths.

I have an Exoterra UVB bulb somewhere that I got a long time ago just for examining it. 

I know quite well what that is.

Unfortunately you need something more expensive for real measurements. 

 

For  measurements of lenses I mainly use a high power Short arc low noise xenon light source with a special configuration lamp with an emission that reach down below 290nm.

For measuring filters and even deeper UV-transmission of lenses i use this light source that reaches down to 210nm:

https://www.oceaninsight.com/products/light-sources/uv-vis-nir-light-sources/dh-2000-bal/?qty=1

 

The main measurements of lenses are done with a custom-made integrating sphere with a special internal coating suitable for UV-measurement.

This is a requirement of a measurement setup for lenses in ISO standards.

 

Many of the transmission measurements on this forum's section here are done with that equipment:

https://www.ultravioletphotography.com/content/index.php?/forum/645-uv-lens-technical-data/

 

Please have a look there.

 

 

 

[photoni]

@IxnaX  (Mike T on Flikr)

 

@ulf is a correct clarification but you have to consider that an empirical / practical method (even if not constant and perfect)

shows the real sum of the sensitivity of the camera + lens + filters.

 

I don't have the means to measure filters and lenses, but with a simple diffraction grating you can see the difference between a single ZWB1 filter and how much the ZWB1 + TSN575 group cuts (~ UG11+BG39).
The TSN575 cuts all infrared but also cuts the deepest (green) part of ultraviolet.

Green is 330 340 nm ???

Sony A7 f.s. with Soligor KA 35mm

flash light, white balance on a teflon ball

[ulf]

On 1/30/2023 at 12:04 AM, photoni said:

 

shows the real sum of the sensitivity of the camera + lens + filters.

That is correct, and the core of the problem.

 

You cannot separate those components to say anything about the lens UV reach. The result is a combination of all above.

Neither can you tell anything about the real signal drop, especially if you use jpg as that is a compressed manipulated signal.

 

It is good as an indication of the potential ability of the full system. Nothing more.

 

It would be OK to state that the lens in some illumination situations could pass some unknown amount of light down to the region of 365nm but nothing more.

 

I just want to avoid a spread of incorrect theories that later will be interpreted as hard facts.

 

We had that problem here before I made the huge effort of measuring and publishing all UV-Lens data.

Fortunately that was cleaned up as it was based on a wide spread of assumptions just as the one we see above.

[photoni]

29 minutes ago, ulf said:

We had that problem here before I made the huge effort of measuring and publishing all UV-Lens data.

thanks !

Link

[Stefano Rosoni]

Looking at the beautiful photographs of the crocuses posted by IxnaX, of which I appreciate the most (artistically) those with the orange colors due to the contribution of the near infrared, and also seeing the subsequent spectra, and finally as revealers of the "mystery" above all the spectra posted by photoni, I conclude that I have discovered a new fact for me: bayer cameras represent with various colors the narrow spectral ranges of UV only and IR only, as cut by the filters generally used and posted by you in the description.

It seemed obvious to me that the entire UV band was strictly monochromatic because it was managed by the blue channel only, and that the entire IR band was also strictly monochromatic because it was managed by the red channel only. I see that this is not the case, and I think this is due to the influences of the other channels which, in the bands outside their competence, have small returns in sensitivity, which until now I thought were completely negligible. I would like your opinion on this aspect, which seems artistically interesting to me, and thank you for your attention.