are these UV pictures?

[Ming]

I took them at the Arnold Arboretum in Boston.  I used a full-spectrum Canon R5, EF 40mm f/2.8 STM, LifePixel's visible bandpass filter for visible light, and Tangsinuo's ZWB2 and BG39 filters for UV and white balance with PTFE.  I used Canon's digital photo professional (DPP) for RAW processing.  The only DPP option that was turned on was the lens profile correction -- otherwise, it's "faithful" output, no sharpening, no noise reduction.  The first five pictures are single frames, but the last image is a composite of 12 frames shot with in-camera focus-stacking and merged by DPP.

My basic questions are the following.  Why is there only purple?  What do I do to get yellow?

Thank you.

Common trumpet creeper, f/11, 1/60 sec, ISO 100

 

f/5.6, 1/5 sec, ISO 3200

 

Clematis cultivar 'Emilia Plater', f/8, 1/125 sec, ISO 100

 

f/11, 0.3 sec, ISO 12800

 

Clematis hexapetala, f/8, 1/500 sec, ISO 100

 

composite of 12 frames, f/5.6, 1/10 sec, ISO 12800

[Fandyus]

Yes, these look solid.

 

If you want yellow, you should try other flowers. Dandelions and rudbeckias are UV yellow for example.

[dabateman]

Yes these look good.

However,  you didn't post this in the correct section.  Postings like this might be better in the techniques,  tests and gear section of the site.

 

As for why only purple, your lens cannot see too deep into the UV,  your filter stack is also more of the upper UV wavelengths and your subjects are just more of the purple flowers than say a dandelion. 

[Andy Perrin]

As people said, the biggest factor was not photographing a UV-yellow flower. For reasons known only to the Gods (should they turn out to exist after all), flowers that are visible yellow are often UV-yellow also. This is not a hard rule, many exceptions exist. But as a way to hunt for things to photograph, it is a reasonable approximation. 

[colinbm]

These are all very good, lovely to see.

[Ming]

Thanks to everyone for the insights.

 

[Andrea B.]

Those are good UV photos. 

 

Sunflowers are usually available in grocery store florist sections. A Sunflower will have a dark central bull's-eye with false-yellow on the outer portions of the rays (petals). The false-yellow may be pale yellow or a more saturated yellow depending on the variety. The Sunflower is a good "test" flower for proof that gear and filters are working as they should. 

Look also for wild dandelions. I usually see those more in the spring, but in some places they are found throughout the summer. Dandelions will have a false-yellow on the outer half of the rays.

[photoni]

10 hours ago, Ming said:

Canon R5, EF 40mm f/2.8 STM, LifePixel's visible bandpass filter for visible light, and Tangsinuo's ZWB2 and BG39 filters for UV and white balance with PTFE

 

They seem to me "right" images in UV.

I ask you which BG39 = QB39 did you use? Tangsinuo is only 1.5mm thick, and it's not enough to stop infrared.

thanks

Antonio

 

P.S. I saw the @nfoto Bladderwort flower

are there any easy-to-find flowers that have a strong yellow-green signature ???

.

[Andrea B.]

The false colours are usually blue-violet, yellow and sometimes a dark green or dark blue-green. I don't recall seeing yellow-green.

[Ming]

12 hours ago, photoni said:

 

They seem to me "right" images in UV.

I ask you which BG39 = QB39 did you use? Tangsinuo is only 1.5mm thick, and it's not enough to stop infrared.

thanks

Antonio

 

P.S. I saw the @nfoto Bladderwort flower

are there any easy-to-find flowers that have a strong yellow-green signature ???

.

The BG39 used for these pictures are 2.3mm thick.

Thank you.

[photoni]

3 hours ago, Andrea B. said:

The false colours are usually blue-violet, yellow and sometimes a dark green or dark blue-green. I don't recall seeing yellow-green.

 

thanks @Andrea B., I would like to discover a common flower that goes a little further than a dandelion, in the 350-340 nm area

thanks

Antonio

2 hours ago, Ming said:

14 hours ago, photoni said:

The BG39 used for these pictures are 2.3mm thick.

well ! I use TSN575 or two QB39 1.5 thickness

thanks

Antonio

 

[Andrea B.]

I would like to discover a common flower that goes a little further than a dandelion, in the 350-340 nm area

 

If you look at the charts for the basic flower pigments,

you can see that any peaks in the UV range tend to be around 350-360 nm. 

LINK

I am not saying there isn't a flower peaking lower though. There might be?

[ulf]

11 hours ago, photoni said:

I would like to discover a common flower that goes a little further than a dandelion, in the 350-340 nm area

To capture that you will need a filter that cut away the upper part of UV-A to avoid those wavelengths dominating the image.

This is because sensors are much more sensitive around 380-400nm than at 340-350nm.

A very thick U-340, 7-8mm or a ZWB2. ZWB1, 8mm will do that, while at the same time reject the IR-leakage peak. No BG-glass needed

[photoni]

3 hours ago, ulf said:

or a ZWB2, 8mm

zwb2 or zwb1 8mm ???

 

perhaps what I would like to know is a flower that appears black with green undertones

 

the A7 with the Meritar 50mm and the Soligor 35mm

has been shown to see green with the diffraction grating.

Thanks

A

.

[ulf]

That was a typo of mine. Should be ZWB1!!.

Corrected above

[ulf]

27 minutes ago, photoni said:

zwb2 or zwb1 8mm ???

 

perhaps what I would like to know is a flower that appears black with green undertones

 

the A7 with the Meritar 50mm and the Soligor 35mm

has been shown to see green with the diffraction grating.

Thanks

A

.

Light from a diffraction grating or an UV-LED is a different thing.

Then there is no light competition from upper UV-A in the same area in the picture

[photoni]

6 hours ago, ulf said:

Light from a diffraction grating or an UV-LED is a different thing.

Then there is no light competition from upper UV-A in the same area in the picture

@ulf I do not understand

 

see ... coherent colors between sparticle and diffraction grating tested by cadmium - LINK

 

I was referring to my test, with flash light - LINK

I asked @Andrea B. to correct the image of the post  but he didn't reply

 

Thanks for the LINK @Andrea B. I see carotenoids, malvidins and pelargonidins with some interesting peaks
but difficult to track down

 

 

[Ming]

15 hours ago, Andrea B. said:

I would like to discover a common flower that goes a little further than a dandelion, in the 350-340 nm area

 

If you look at the charts for the basic flower pigments,

you can see that any peaks in the UV range tend to be around 350-360 nm. 

LINK

I am not saying there isn't a flower peaking lower though. There might be?

Thanks for the link to flower pigments and pollinators.

[Andy Perrin]

Photoni, the diffraction grating or the sparticle both distribute different wavelengths to different locations in the image, so they are not on top of each other and you can see the green. But if you have a very little sensitivity to 340nm and a high sensitivity to 380nm and light at both wavelengths hits the same pixel, that pixel will show only the 380nm because the 340nm barely contributes. 

[ulf]

Thank you Andy for a much better description of the problem than what I wrote.

It was spot on!

 

The only case that still might show a flower with false UV-green colours is if the flower was really UV-dark above 340nm.

Then a second problem arises. you must have a really good IR suppression of the 700nm peak.

As the sensitivity for 340nm is much lower than for 360nm this setup demand more suppression.

It might not be enough with the OD4 I measured  for my ZWB1, 8mm

[photoni]

@Ming sorry for the invasion of your post

@Andy Perrin @ulf  thanks, in fact I asked about a unicorn and how to photograph it with a filter that I don't have. I will wait for your research

[Doug A]

They look like great UV photos to me. I'd be happy to get images this nice. Well done. 

Thanks for sharing,

Doug A

[Ming]

9 hours ago, Doug A said:

They look like great UV photos to me. I'd be happy to get images this nice. Well done. 

Thanks for sharing,

Doug A

@Doug AThanks a lot.

 

18 hours ago, photoni said:

@Ming sorry for the invasion of your post

@Andy Perrin @ulf  thanks, in fact I asked about a unicorn and how to photograph it with a filter that I don't have. I will wait for your research

@photoniNo problem at all.  It's fascinating and I am learning a lot.

[Kai]

Good pictures Ming!

From my point of view everything is fine as far as the color is concerned.
If the IR attenuation is too weak, objects containing chlorophyll could lead to pale green IR overexposure. But I can't see that in your pictures.

I'll give one thing to consider: What is the right brightness?
If you put a PTFE or a matt aluminum plate in the picture and adjust the brightness of the VIS image and the UV image (i.e. same brightness of the PTFE/aluminium plate), your UV pictures with vegetation will appear much darker. This has to be the case, since the green parts of the plants use the light for photosynthesis, i.e. absorb it. Many photos then appear extremely "low key". Since then of course you can no longer distinguish many details and therefore some forum members brighten their pictures. The images then look similar to the familiar world of VIS images.
I then only find the comparison with VIS images pointless...

[Andy Perrin]

Kai, I don’t know why you find comparing to visible images pointless just because the brightness doesn’t match? Even the visible image has had its brightness stretched nonlinearly with a gamma curve usually. Also our perception is exponential. 
 

It is usually the UV pattern on the flower that we care about and most brightness adjustments leave that unchanged.