Rosemary (Salvia rosmarinus)

[Unscenerie]

Hello,

This topic is a comparison between a stack of ZWB1 (3mm) + TSN575 versus ZWB1 (3mm) + NIR blocker (3mm).

Lens used: Soligor 35/3.5

Link to NIR blocker from UVR Optics (https://www.uvroptics.com/index.php?NIRBlocking)

 

The NIR blocker is my second IR blocking filter, and I was surprised when my photos came out with a greenish cast. There's definitely more light coming in through the NIR blocker versus TSN575, but I got so used to the look of black foliage, I want to ask the community why am I getting greenish foliage with the NIR blocker.

 

Both photos were white-balanced in Darktable, I drew a rectangle along the lower edge. I used the standard color matrix.

I don't have a way to measure my filters' wavelength yet.

 

ZWB1 (3mm) + TSN575

 

ZWB1 (3mm) + NIR blocker (3mm)

[colinbm]

Not knowing your camera's UV capability, my guess is you are seeing a deeper reach into UVA with the ZWB1 (3mm) + NIR blocker (3mm) in the last photo.
Some cameras see some yellow / green at lower UVA

[Unscenerie]

1 hour ago, colinbm said:

Not knowing your camera's UV capability, my guess is you are seeing a deeper reach into UVA with the ZWB1 (3mm) + NIR blocker (3mm) in the last photo.
Some cameras see some yellow / green at lower UVA

That's got to be it, Colinbm :) I used Sony A7 (mark 1) FS.

 

Recently, I removed the hot mirror from my Sony NEX5N, and with the same lens and filters, the resulting photo does differ in color from the Sony A7.

 

Actually, I see the same kind of greens/yellows with Sony NEX5N and ZWB1 (3mm) + TSN575 as I'm seeing with Sony A7 and ZWB1 (3mm) + NIR blocker (3mm).

[Andy Perrin]

Hmmm. Ulf says that NIR blocker lets quite a bit of IR through in sunlight at the usual thickness it is sold at. You may also have some IR contamination. 

[Stefano]

I think this is IR contamination. Try to stack something like a Hoya R72 to see if there's a leak.

[ulf]

20 minutes ago, Stefano said:

I think this is IR contamination. Try to stack something like a Hoya R72 to see if there's a leak.

We are lacking two important facts here, The light source and if the sun, time, weather conditions  and also what lens that is used.

Also against what are the images white-balanced?

 

Seeing actual false green UV in a sun-illuminated image is highly unlikely as all camera sensors lose the sensitivity rapidly in lower UV-A.

 

It is true that some cameras see some green at lower UVA, but only with artificial illumination. 

AFAIK all correctly FS-converted cameras with intact Bayer matrix can see yellow with sunlight and motifs like some flowers.

 

Unscenerie say that his ZWB1 is 3mm thick.

That lowers the transmitted IR from that filter, but I do not know if it is enough.

 

Both images above have a more or less greenish tint to the leaves.

I think this mainly is due to the WB and for the 3mm IR-Blocker maybe also some IR leakage.

 

I saw the same tendency, but more so, of paler foliage when, on a UV-marginal lens, I was trying both UG11 and U-360, 2mm (≈ZWB1) together with a BG40, 2mm (for IR that is ≈ like the 3mm IR blocker).  For both types of 2mm UV-pass glass stacked with the BG40 I got substantial IR-leakage.

 

UG11 (≈ZWB1) have it's IR peak closer to VIS (compared to U-360 and ZWB2), making it more sensitive to how good the IR-blocker is.

Very often the BG40 is not good enough to block IR for any of the UV-pass materials mentioned above, when 2mm thick.

That is true especially if the lens is not transmitting that well around 365-370nm.

[Nate]

I get a little ir leakage with the NIR Block using a zwb1 2mm/NIR Block combo. The NIR block works best for me using my antilia uv filter or my Baader U as both those leak a bit of ir on their own. I've stacked a 590nm or an R72 on the front of my combos, If I can see IR using .5 or 1 sec, I think that's not going to work. You might be seeing leakage, or not.

 

EDIT: I forgot to add, that If I do see the ir leakage in foliage I know should be black using my better uv combos, the black will look greenish like that. I use darktable too for WB as well as in camera. Darktable does the best WB out of all my raw editors.

[Unscenerie]

That's a bit disappointing. NIR Blocker was marketed as a better alternative to S8612, hence the name, "NIR blocker".

 

I used Soligor 35/3.5.

Shot last weekend in Slovakia, just before noon.

Sunlight is the only light source, high up above me, with a thin layer of clouds over it.

 

This can't be false green because I'm seeing the greens (and oranges) on everything I point the camera at.

 

I'll test the stack with Hoya R72 on top.

[ulf]

@Unscenerie are you sure that the ZWB1 was 3mm thick?

 

Both the Soligor 35/3.5 I have have a good UV reach.

You can see them here: https://www.ultravioletphotography.com/content/index.php?/forum/643-uv-lenses-normal/

Soligor have had many versions of 35/3.5 so if your model is different a good UV reach is not verified.

 

When I tried Darktable long ago WB was done manually adjusting sliders. That is quite difficult to get right.

It is also very important that WB is done against a surface with constant reflectance  into the UV-A range.

A grey-card do not work properly for that.

 

There are different alternatives that can be used, most based on PTFE materials:

• Expensive: Calibrated Spectralon calibration targets
• Realistic: A piece of virgin PTFE sheet wet sanded with a 250-400 grit wet-sand paper, in random directions, to make it well matted. That is what I use.
• Cheap quick-fix: Several layers of white teflon plumbing seal tape wound around something stiff, or a pice of nature anodised aluminium that is matted enough in the process.

Cadmium was selling a target based on s a special filter material for filtering liquids.

That special type was OK-ish as a WB target. He sent me one for measuring.

I also tried different brands of such filter rounds and their reflectance varied wildly when I measured them with my spectrometer-setup configured for reflectance, compared to PTFE.

 

It is essential that the WB is done on the RAW-file as a file converted to jpg is not linear!

 

Many plants have a surface cell structure called conical cells that can pick up and reflect the sky.

That sometimes lead to that that foliage is not black.

 

If the WB is not good enough those surfaces might look greenish, but I do not think that is quite right as the false UV band looking green has very low sensitivity in most cameras.

As we also see the greenish tone in the first image, with the TSN575, that is a strong indicator that this cannot be false UV-green as that filter is not transmitting those wavelengths.

IMHO that tone would be more proper if having a more yellow tone.

That would be realistic with the UV-reach of the TSN575.

 

 

 

[Unscenerie]

@ulf I was told by the seller my ZWB1 is 3mm thick.

I'll want to measure the actual thickness.

 

My Soli looks exactly like the regular version in your test.

 

(https://www.ultravioletphotography.com/content/index.php?/topic/4468-soligor-35mm-f35/)

 

Using a ZWB2 instead, the possible IR leakage could be lessened.

 

I just remembered I should mention that I'm seeing some ghosting with the NIR blocker; 

Its filter retaining ring is thick, leaving more space between NIR blocker and ZWB1.

 

NIR blocker+ZWB1 below:

 

 

TSN575+ZWB1 below:

 

 

These were crops of the images below.

 

I white-balanced image below to own liking, in Photoshop:

 

 

I copied settings from image above and pasted into image below: 

 

 

 

[Unscenerie]

 

This was an edit made from the NIR blocker+ZWB1

[rfcurry]

Unscenerie,

 

If you are dissatisfied with the NIRBlock, please return it for a refund. BTW, what is the result when you used an R72 over your combination?

 

Thanks,

Reed

[photoni]

On 4/23/2023 at 1:57 PM, Unscenerie said:

ZWB1 (3mm) + TSN575

last year I did a test with the same setup. Sony A7 fs + Soligor 35 mm, ZWB1 /2 (2mm) with diffraction grating.

white balance is done on a roll of teflon tape
I didn't use sunlight but flash light to have a constant, repeatable light in the same position.
This "real" configuration of the camera + lens + filter shows that the TSN575 cuts the deepest part of the ultraviolet (the green part)

I don't have UV Nikkor 105 or Baader U2 or S8612 or BG39 (2mm) or the @rfcurry filter to make a comparison

but I'd like a S8612 or something similar that doesn't cost much to see some green :)

 

P.S. I have two 1.5mm thick QB39 (similar to BG39) together they are equal to TSN575

 

.

[ulf]

@photoni You will only see some false UV-green with these types of of grating generated images or with motifs that are illuminated with UV-LEDs in the needed wavelength range.

AFAIK there are no materials with a strong reflectance below 340nm while being dark closer to VIS.

This means that the upper UV-A band will always dominate the image drowning the false UV-green if you are not starting to take pictures of UV-green 340nm LEDs and subjects illuminated by them.

 

To have any chance of getting a picture with several false UV-colours including the green at the same time, except for grating images you would need a very special filter that attenuates the light in a proper way from 340nm and upwards to equalise the false yellow an blue and also reject VIS and IR very much. AFAIK such a filter do not exist. 

[Unscenerie]

I measured my advertised 3mm-thick ZWB1 (Tangsinuo) at between 2.8mm and 2.85mm.

 

@rfcurrythank you for giving me the option to return the NIR blocker (I've had it since last August). I'm still trying to make it work for me, and more so, I live in Europe, so the shipping costs would make the return unlikely.

 

Lens used in photos below: Soligor 35/3.5 (non-KA version);

Sony A7;

 

Attached below is a photo with a stack of NIR Blocker (3mm) + ZWB1 (2.8mm) + Hoya R72 (I just held it in place in front of the UV stack coz my R72 is 58mm in diameter)

Setting: 10AM, cloudy

Exposure time: 25 seconds

ISO 320, f4

 

 

Attached below is a photo with the same stack as above but now I added a BG39 (advertised as 1.5mm by Tangsinuo)

Exposure time: 25 seconds

ISO 320, f4

 

 

Below is a stack of NIR Blocker (3mm) + ZWB1 (2.8mm) 

at 4 seconds exposure

ISO 100, f4

 

 

And below is a stack NIR Blocker (3mm) + ZWB1 (2.8mm) + BG39 (1.5mm or so)

4 sec exposure 

ISO 100, f4

 

 

I think that in order to use the NIR Blocker for pure UV, I need to pair it with the right ZWB glass... ZWB2 maybe as was mentioned above. 

I've been thinking of ordering some.

 

Stacking the NIR blocker with BG glass would defeat the purpose I think.

[rfcurry]

Unscenerie,

 

That is a nasty NIR leak. You are right, the return would be expensive. Otoh, if I send you the equivalent of a 4mm thick ZWB1, it should deal with that leak, at no charge to you. Theoretically, a 2.8mm ZWB1 should work, but each melt from each Chinese foundry seems to be different.

 

The glass - ZWB1 eq 4mm thick (as measured by me on a Beckman-Coulter spectrophotometer) - paired with the NIRBlock (from Ulf's data) should produce the result below.
If you want the ZWB1 eq, I can send it via USPS First Class mail (to keep my costs down) if you message me your shipping address.

Thanks.

Regards,

Reed

[Andrea B.]

For your consideration......

 

That color in the 2nd posted photo is not green. It is mostly yellow. Remember what happens when yellow becomes unsaturated and darker? It starts to look like an olive-green.

I ran two samples for you. Beside each sample I put a circle of the sampled color at full saturation and full brightness. 

 

 

Because white balance is never "perfect" there very well may be some bits of green somewhere in this photo. But the basic false colors are the usual blue and yellow.

[Andrea B.]

REFERENCE:  Abney Effect? 

I never can remember the name of this color phenomenon. I think it is the Abney Effect. I'll try to find out for sure.

 

for yellow

 

 

for blue

[photoni]

On 4/30/2023 at 7:05 PM, ulf said:

@photoni You will only see some false UV-green with these types of of grating generated images or with motifs that are illuminated with UV-LEDs in the needed wavelength range.

AFAIK there are no materials with a strong reflectance below 340nm while being dark closer to VIS.

This means that the upper UV-A band will always dominate the image drowning the false UV-green if you are not starting to take pictures of UV-green 340nm LEDs and subjects illuminated by them.

 

To have any chance of getting a picture with several false UV-colours including the green at the same time, except for grating images you would need a very special filter that attenuates the light in a proper way from 340nm and upwards to equalise the false yellow an blue and also reject VIS and IR very much. AFAIK such a filter do not exist. 

-

Yes, thanks, @ulf  I understood that the "brightest" part 360-380 nm turns off the other colors

link

but I would like a ZWB2 + an IR cut that doesn't cut the lower (green) part of the UV too

-

All this out of curiosity, for me it is not a job and I have no budget for these things,

I would rather invest my money in another field of photography, the ancient photographic techniques of the wet plate etc.

-

the rosemary images of this test do not have an object to make a standard white balance, therefore they can be "developed" in a thousand different ways.
I thought the second photo with more green meant a wider view of 340nm.

-

like this ?

link

[ulf]

1 hour ago, photoni said:

I thought the second photo with more green meant a wider view of 340nm.

-

like this ?

link

I think in both cases the green is from IR leakage. The Baader U in some versions have more IR-leakage.

I have seen that effect myself with a reasonably OK Baader-U.

 

I bet that the big bright green leaf in the link you refer to did reflect IR very strongly, making it possible to penetrate the Baader U filter.