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UltravioletPhotography

PTFE as Background for Photo


Andrea B.

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EDITOR'S NOTE:

The formal UV-signature post for Brassica juncea has been split so that the technical discussion below does not interfere with the botany.

Start with Post #4 below for a discussion of PTFE as a background in a photograph.

There is also some other tech talk.

 

 

(WIth reference to a photo in the above link...)

The first photo needs to be brightened up a bit. Various ways to do that. First, do they have the sRGB profile?

***

And thank you for providing the Chinese name. :)

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Yes, they are all in sRGB-IEC61966-2.1 (whatever that means:)

On my monitor I thought the UV one here is too bright... I also used levels in Photoshop to see if they were ok (since I do not know how to do it in PN) before uploading.

 

These photos need to be brightened up a bit. Various ways to do that. First, do they have the sRGB profile?

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I like the way this one looks in UV. You must have a nice garden!

 

What are you using as a surface to rest the subject upon, as sheet of PTFE? I have on occasion stood a sheet of PTFE up behind a subject but had not considered using it as a platform.

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John,

 

yes, it is a square block of virgin PTFE. it is working so well, I am thinking of drilling different sized holes to it, so I can sit a flower to it better (flatter). it should not affect my WB since it will be small compared to the whole area?

 

I like the way this one looks in UV. You must have a nice garden!

 

What are you using as a surface to rest the subject upon, as sheet of PTFE? I have on occasion stood a sheet of PTFE up behind a subject but had not considered using it as a platform.

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You planted an idea!

How about a short section of PTFE rod (see eBay item 281713880231) with a hole drilled ~1/2 way through from the end.

Makes a little PTFE flower vase!

 

I would guess that if the PTFE is of reasonably good purity the WB should not suffer. It might limit exposure for UV-dark subjects, I think it would work better if we could source some UV-neutral gray bulk teflon instead. I am sure I have seen it somewhere other than gray Spectralon standards.

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John,

 

Yes, I did find that when the flowers are too dark in UV, I have to +3 EV and then PhotoNinja will complain that the white is too bright to do WB. We need black Teflon for these? :)

I drilled 2 holes last night. perhaps one at the center should be enough.

 

You planted an idea!

How about a short section of PTFE rod (see eBay item 281713880231) with a hole drilled ~1/2 way through from the end.

Makes a little PTFE flower vase!

 

I would guess that if the PTFE is of reasonably good purity the WB should not suffer. It might limit exposure for UV-dark subjects, I think it would work better if we could source some UV-neutral gray bulk teflon instead. I am sure I have seen it somewhere other than gray Spectralon standards.

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.......PhotoNinja will complain that the white is too bright to do WB......

 

Are you trying to WB on a blown highlight?

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Yes, but if you do that PN complains. However, it is not always obvious that an area is blown.
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I can avoid that by using "copy settings" too. I do not have a profile yet.

 

Andrea, does the cheaper color set from ebay (e.g 221797313280, $73) do ok under UV? or is it only good for visible light? Thanks, Zach

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John,

 

Thank you! Would you know if it works under UV? It does not really say.

 

Zach

This looks like a good deal - 151714415792

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Would you know if it works under UV? It does not really say.

 

Yes and no.

As I understand it the preset profile, while only designed to refine or correct the images captured under VIS filtration, also serves to "standardize" the out of band UV false color response.

I am likely over simplifying the concept which is to me still a bit counter intuitive.

Please see: Photo Ninja: How to Make a Custom Light Profile

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I have gone through your profile building before with visible light. I am not certain if one needs to do one for UV or not?

Intuitively, I thought (although I might be wrong!) the colors might needed to be reflecting the same "wavelengths" under UV? perhaps this does not matter? (all colors will be messed up under UV? but since the same yellow flowers in visual, could be either bright or dark under UV, makes think that different dye might behavior differently under UV?)

 

The PN instructions says one can shoot a computer screen for the same purpose...but I doubt that I can do that for UV (I am assuming that that is no UV coming out from the computer screen:)

 

Or, is it only really needed for visual shots?

 

 

Yes and no.

As I understand it the preset profile, while only designed to refine or correct the images captured under VIS filtration, also serves to "standardize" the out of band UV false color response.

I am likely over simplifying the concept which is to me still a bit counter intuitive.

Please see: Photo Ninja: How to Make a Custom Light Profile

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Profiling in Photo Ninja is for visual shots.

The profiling tool does not know how to deal with a CC Passport which has been photographed in UV.

 

However, I typically make a Preset to use as a pseudo-UVprofile in Photo Ninja.

 

Preset as a pseudo-UVprofile for UV fotos:

  • Shoot white standard in UV light and open foto in PN.
  • Color Correction:
    • Drag the color correction dropper over the main "white" area to set Temperature & Tint.
    • Light source: choose an existing visible Custom Light profile for the camera in use.
    • Mode: choose From profile.
    • Click Apply.

    [*]Then save what you just did as a Preset.

    [*]Preset > Save > Subset > All > OK > Enter preset name > OK

Next time you bring up a UV foto made with that camera using similar UV illumination,

then you can choose this pseudo-UVprofile to initialize the foto prior to additional edits.

 

I find it saves time to have this kind of preset.

When creating it, I usually add other frequently used settings before saving.

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EDITOR'S NOTE:

The formal UV-signature post for Brassica juncea has been split so that the technical discussion below does not interfere with the botany.

Start with Post #4 below for a discussion of PTFE as a background in a photograph. There is also some other tech talk.

 

Sorry for getting off topic.

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Apologies not necessary!

These are important questions and discussions.

So when I split them on occasion,

it ensures they do not get lost in the botanical section where folks are less likely to see them.

 

We always encourage any relevant discussion and question. :)

 

I also have a nice slab of Something (PTFE? PTFE-like?) to use as a background. But it got dinged with a ballpoint pen mark. And discoloured in the effort to remove that. Which was more than a tad distressing. Turns out it can be lightly sanded, so I am trying now to repair it.

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There are grey spectralon or other reflective targets.

http://www.pro-lite....use_targets.php

 

If needed, I just use anything that gives a nice smooth-ish background and change the colour later in NX2 with a color point.

 

Added Later:

Didn't we once talk about barium sulfate coatings?

(I don't know what the substrate has to be for that?)

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I have not ever worked with the Zenith material.

Yes, barium sulfate is an alternative, there are ways to prime a surface and get a "paint" to stick.

I think I will go over to the fabric store and see if they will let me photograph some swatches in the sunny parking lot.

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Spectralon is crazy expensive. So I am wondering if the Zenith stuff also costs an arm & a leg with the other two thrown in to make up the difference.
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Yes, I have read this 1993 paper.

 

One thing it is unclear on is which simulated solar spectrum their Xe-arc was calibrated to replicate. Given their interest is in durability for spaceflight I assume it was an extraterrestrial spectrum very much richer in shorter wavelengths naturally attenuated by our atmosphere. Reflectance coatings for deep UV applications are subject to significant degradation.

 

Our uses as reflectance targets will never expose materials to these wavelengths thankfully elsewise the planet would rather more hostile to life as we know it.

 

I would not be surprised if the makers of Spectralon and other equivalent materials have corrected this issue since this study was run, as you seem to imply.

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