I'm looking for a translation

[photoni]

A tip from you who you have a lot of "eye" and experience

Is arrived new bg25 and a bg18 (he didn't have the gb39 - ø75mm)

I did some tests for my wet collodion search

I used the A7 F.S. with various old Nikon lenses, which I don't put because the results with the same stack of filters is the same.

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All RAW files developed with Capture One, All filters 2 mm thickness

Eninchrom flash light with "light" tube without anti UV yellow

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Then I compared the standard Nikon Z7 with the old Nikkor-H 50 F2 (born in 1967) with and without the BG25.

The answer with the filter is logical, cut all IR and yellow, the Blu area has no details, does not see UV, the sunflower is all dark.

The photos with A7 F.S. And the various filters have confused me.

Can you help me interpret photos?

The graphics of the filters is easy to understand, but the diversity of the results of color i dont understand it; Depends on the pile, the lens or sensor?

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Thanks

Toni

[Andrea B.]

The colors depend on the filter and then on the white balance you apply to the file during conversion. To a certain extent, the color can depend on whether the lens lets in more or less UV light. I am assuming here that we all agree that all or most Bayer-filtered cameras capture color the same way.

 

Here is a chart for your BG39 and BG25.

 

The BG39 (blue line) passes both ultraviolet and visible light up to and including red. The BG39 passes so much visible light, that this filter can be used to produce a visible photo if the photo is made in good sunlight or if a normal visible flash is used. There is much more visible light from the sun than there is UV light. The visible color may be slightly "off" from a BG39 unless you add a color correction profile, but that's not something to discuss here.

 

The BG 25 (green line) passes UV and visible light in the violet, blue, green range (mostly) and a lot of Infrared light too. It seems to suppress only visible orange/red. The combined Visible and Infrared light will overwhelm any UV light, so you probably will not see strong UV-absorbing (dark) or UV-reflecting (bright) patterns from the subject you are photographing. It is possible that if you use a UV-flash, you would get slightly more UV effects from a BG25.

 

When the two filters are combined as BG39 + BG25, shown by the black line in the chart, you get mostly the characteristics of the BG25 because it is the more restricted filter. However, in the combination, the BG39 is cutting the Infrared light. So when these two filters are used together you can capture some of the UV patterns of your subject. Again, using a UV-flash would help this combo if that is what you want. (UV patterns, I'm referring to.)

 

As for the colors of the BG39 + BG25 combination which you show in the posted photo, those depend on the white balance you have applied to the raw files.

 

 

Peak: 70% transmittance at 405 nm

1% at 308 nm and 510 nm

OD3 302 nm and 522 nm

Transmits the most UV of the three combinations.

[colinbm]

Interesting examples Toni.

[photoni]

I edited the text of the photo

 

Thanks Andrea ! My question was different.

 

I don't understand why photo 6 is different from photo 4 (I put two BG25).

(it has the same colors but a different contrast and detachment in the petals)

 

I don't understand why photo 5 has different colors from 4 (BG 18 and 39 should have very similar graphics)

 

Keep in mind that the white balance was done in the same place for all 6 photos

 

do you think there is a contamination of IR in some photos?

 

I would also like to see the graph of photo 6 with BG39 (2mm) + two BG25 (2mm)

and that of photo 5

I don't have Exel :(

[Andrea B.]

I don't see any IR contamination in either photos #4 or #6.

And the charts do not show in IR contamination with the stacks of BG39 + BG25.

 

Look at the first chart showing the stack BG39 x 2.0mm + BG25 x 2.0mm. You can see that the visible light at 1% transmittance hits about 510 nm and does not reach OD3 until 520 nm.

 

In the second chart the visible light at 1% crosses at 490 nm and reaches OD3 at 500nm. So there is more visible light being passed in the thinner 4.0 mm stack used in photo #4. That might change the appearance of UV-absorbing (dark) areas.

 

Peak: 63% transmittance at 400 nm.

1% at 330 nm and 490 nm.

OD3 at 322 nm and 500 nm.

[Andrea B.]

Here's the BG18 + BG25 chart.

 

Peak: 50% transmittance at 415 nm.

1% at 330 nm and 510 nm.

OD3 at 322 nm and 522 nm.

Transmits the least amount of UV of the three combinations.

[Andrea B.]

I think that it is not the colors which should be considered. Perhaps look instead at the tonality (lightness/darkness) of the results?

 

Comment: It is really difficult to analyze a mix of visible and ultraviolet light.

 

Maybe the following will help understand?

First I selected (separately) the petal tips, center disc and petal bases to determine the average color for each.

 

 

 

Then I desaturated the colors and looked at the brightness of the tips, center and bases.

 

Observation 1: The flower tips and bases are brightest in the two bottom photos using stacks

which transmit less UV.

Observation 2: The flower disc is darkest in the top right photo using the stack which transmits the most UV. Then the thought occurred that perhaps this photo was slightly underexposed resulting in the darker outcome?

Observation 3: I'm "giving up" now!! Any other comments or suggestions are welcome in order to help both Toni and me understand this interesting mixed light result.

Observation 4: It is best to look at the raw files in Raw Digger in order to better understand the exposure values in each channel.

[photoni]

Comment: It is really difficult to analyze a mix of visible and ultraviolet light.

 

Andrea ... I have to reread what you wrote ten times :)

in the meantime I joined your three curves with Photoshop.

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Yesterday I took some shots with the Hasselblad and the 120 macro + Fomapan 100 panchromatic film, with the BG39 + 25 + 25 stack, I still have to develop the 120 roll.

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Today I picked up some old wet collodion iodizer

after 5 attempts I have a result. I have to varnish it and scan it

.

another moment

: -S

[Andrea B.]

Toni -- I should ask this question: what is it that you want to capture with these particular filter stacks? Is it a combination of both Visible and UV light?

 

That is rather unusual. You might be the first person seriously working in mixed Vis + UV.

 

I hope that something I wrote might have helped to answer your questions!!

 

I find it very interesting that the luminance/brightness/lightness of the false colors can interfere with our understanding of what wavelengths we have captured in the photos. For example, I did not realize that flower #4 was the least bright one (using the HSB) when I first looked at them.

 

There are other ways to analyze those flowers. You can look at the monochrome luminance or lightness as well as the desaturated brightness. Which is the best way to analyze them? I do not know.

 

The "bottom line" is whether you are getting what you want from these filters -- or not.

[photoni]

The "bottom line" is whether you are getting what you want from these filters -- or not.

 

Thanks Andrea

My research for the purpose of pure research of UV light (inducing and reflected) is less spectacular.

I'm trying to figure out how to approach the wet collodion (and bees) vision

 

I think this stack of filters (part of the visible + UV) is the right way.

 

I attach the photo of the flower (almost withered) wet plate, as an example.

4x5 inch taken with a lithium formula. Darlot Petzval lens (4 lenses in 3 groups) from 1870, 11inch f4,5 - direct light 3000W

 

Tomorrow I'll put the photos on film.

 

There remain 2 points that are difficult to quantify

- the transparency of the lenses used

- the sensitivity of the sensor with Bayer filter

these are two things that should overlap the "theoretical" transmission graphs of Schott filters

[Andy Perrin]

The one thing I have learned from this board about bees is that we will never be able to reproduce their vision because they don’t use images the way a human does. They sense UV, but they use it to find the horizon. They see flowers but they are very nearsighted and don’t see details from far away. It’s not as simple as finding the right filter spectrum when both the eye structure and the brain that interprets the images are wildly different from a camera or a human brain.

 

I think you will have more luck with collodion!

[OlDoinyo]

Have you checked the UV transmission of the Darlot lens? I assume you do not have a spectrometer or a Sparticle array, but what about a simple pinhole test?

[Andrea B.]

The link below is an example of some flowers which have been colored to represent the way a bee might detect the reflecting and absorbing areas. This representation is *not* how a bee actually "sees". As Andy has mentioned bees do not form brain images. They use their detection of UV, blue or green wavelengths for processing contrasts (against background), edges (of flowers, for example) and direction (UV from the sun is "up").

 

https://www.ultravioletphotography.com/content/index.php/topic/1988-bee-vision-bouquet-you-saw-it-here-first-jk/

[photoni]

I apologize for using "bee vision"

is the least of my questions / problem !!!!!!!!!!!!!!!!!!

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roller 120 is developed, but is still wet.

The first impression is that with the 39 + 25 + 25 stack it works poorly,

the lens and the film do not emulate the wet plate.

[Andrea B.]

No need to apologize!! I only want to make sure a few relevant facts are available to all.

Making artistic choices is entirely another matter.

 

Bummer, that the stack did not work well for the emulation.

[photoni]

Have you checked the UV transmission of the Darlot lens? I assume you do not have a spectrometer or a Sparticle array, but what about a simple pinhole test?

 

in this post I asked which is the simplest test to verify the UV transparency of the lenses.

https://www.ultravio...dpost__p__49436

 

I tried the Petzval with the A7 f.s.

I don't understand how far it sees ... but it works well,

it is similar to the two old nikkor-H 50 and 24mm

 

I don't know about the pinhole test .

[dabateman]

Artistically,

I like 2mm Bg18 + 2mm BG25 and the 4mm BG25 with BG39.

The colors look great.

[Andy Perrin]

The pinhole test is when you take a pinhole picture of the lens (pinhole pictures allow all wavelengths through) and see how much the lens is blocking. You put PTFE behind the lens.

[dabateman]

To set up a pinhole test, you will need a strong UV light source and a completely visible blocking UV filter.

 

You could try it outside on a bright sunny day. Have a sheet of PTFE or piece of cardboard wrapped in plumbing tape. Place the subject lens in front of that on a table outside. Make sure sunlight is visibly passing through the lens on to the sheet. No dark shadows. Then setup your full spectrum converted camera with a pinhole lens, and place your strong UV filter stack on the pinhole lens. Like a 2mm U340 with 2mm S8612 filter. This will block all visible and IR light that is reflected from the PTFE sheet. Now photography the sheet and the lens. In your photo, you need to capture both the sheet and the sheet seen through the subject lens.

Then as Andrea does, look at the differences in intensity of light between the sheet seen through the lens and with out the lens.

If the sheet is black through the lens, then its blocking all the reflecting UV light. If its slightly off grey than not too bad.

I hope that makes sense.

[photoni]

these are two shots on Fomapan 100 film

developed 9 minutes in Rodinal-R09 - 20 ° 9 '

standard and with BG18 + BG25 stack

 

not bad

[photoni]

Have you checked the UV transmission of the Darlot lens? I assume you do not have a spectrometer or a Sparticle array, but what about a simple pinhole test?

 

 

I have to carefully read your post and others.

 

https://www.ultravioletphotography.com/content/index.php/topic/1670-pinholes-and-uv-photography/

 

I have a lot of experience, ten years ago I bought with a group of Italian Flickr enthusiasts some very perfect microscope holes (abrasion method, not laser) with a diameter of 0.15 - 0.20 - 0.30mm

I tested the various diameters with Leica, Mamija 6x7, and large format 4x5 and 8x10.

the best result is obtained with the large format, I decided to use only 8x10 on film and print in contact with ancient bluprint and Vand Dick techniques.

 

thanks Andy and dabateman

 

I have to find the time to understand and do

[ulf]

You do like this:

Place a PTFE sheet so that it is illuminated by sunlight.

Place the lens to be tested in a position so that the camera can see light through the lens and also the PTFE surface beside the lens.

Take a picture, in RAW, with a multispectral converted camera with the pinhole lens plus a suitable UV-pass filter stack.

This gives very long exposure times.

 

White balance the image against the PTFE and compare that with the light seen through the lens.

 

A lens with bad UV range will show darker blue light only passing.

A good lens for UV will almost not change the light at all.

 

A vast speed improvement could be had if the pinhole is replaced with a plano convex (PCX), fused silica (FS) lens-build.

That lens-build can be made very primitive without any helicoid, as there is no need for very good focus, just a reasonably long extension related to the focal length of the PCX FS lens element.

A UV-pass filter is still needed.

[Andy Perrin]

Photini, look at this thread, it has a good photo of the setup for a pinhole test:

 

https://www.ultravioletphotography.com/content/index.php/topic/2197-test-carl-zeiss-jena-tessar-50mm-f28-vs-el-nikkor-80mm-f56/page__p__15820#entry15820

[photoni]

Photini, look at this thread, it has a good photo of the setup for a pinhole test: https://www.ultravio...5820#entry15820

 

Thank you ! now everything is much clearer

 

below I put a shot with Darlot Petzval 11 "f: 4.5

Sony A7 f.s. mounted on the back of the large format

(in front of Sony BG38 2mm + BG25 4mm)

 

there are many chromatic aberrations even if I put a waterhouse (diaphragm) f.11

[photoni]

On 9/10/2021 at 12:57 AM, Andrea B. said:

Toni -- I should ask this question: what is it that you want to capture with these particular filter stacks? Is it a combination of both Visible and UV light?

 

That is rather unusual. You might be the first person seriously working in mixed Vis + UV.

 

I hope that something I wrote might have helped to answer your questions!!

 

I find it very interesting that the luminance/brightness/lightness of the false colors can interfere with our understanding of what wavelengths we have captured in the photos. For example, I did not realize that flower #4 was the least bright one (using the HSB) when I first looked at them.

 

There are other ways to analyze those flowers. You can look at the monochrome luminance or lightness as well as the desaturated brightness. Which is the best way to analyze them? I do not know.

 

The "bottom line" is whether you are getting what you want from these filters -- or not.

 

Thanks Andrrea , I was re-reading all this ...

{I see that I cannot edit the previous post .... there is an error, the stack is BG39 2mm (not BG38) + BG25 4mm}

While reviewing the site, I studied Schott filter charts

For the research I am doing it seems to me that it is better to use BG3 (ZB2) instead of BG25 (QB29) because it sees less yellow and more UV.

... BUT ... if collodion is sensitive between 325 and 510 nm .... what do my old "normal" lenses see ... where should I cut the graphs ???

P.S. I plan to order a BG38 2mm (QB-21) and a ZWB-1 8mm (UG11) from Tangsinuo
I looked for a filter equivalent to the S8612, is there something cheap or is there only the BG39 (QB-39) to cut the reds / IR?

 

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