Jump to content
UltravioletPhotography

opuntia ficus indica - opuntia schumannii


Recommended Posts

the opuntia ficus indica (prickly pear) photographed in the sun

it is an altarpiece collected in Naples many years ago.

I also have a variety with orange flowers that hasn't bloomed yet.

photographed with Sony A7 full spectrum

with BG39 (very similar to a standard view), without filters, BG25 and BG39 + 25.

the black and white files are Jpeg directly from the camera with 2000 ° K balance

the RAW color files have been processed with camera raw (Photoshop CS6)

.

what do you think of the white balance?

.

Thanks

Toni

post-141-0-34612700-1625308748.jpg

Link to comment

I think the colours are interesting for what you can get with PS.

Unfortunately CameraRaw is not capable of handling the extreme WB these images really needs.

 

To see how a more powerful WB can turn out, I recommend you to try the FastRawViwer:

https://www.fastrawviewer.com/

That is the program I use for overviewing and culling my RAW-files, before conversion.

 

I think you will be surprised about the colours of the flower by BG39 + BG25

 

That program is unfortunately not a Raw converter, just a RAW-viewer, but it is very usable for previewing RAW-files.

If you like the capabilities there are several programs that can handle extreme raw files better than CameraRaw.

Link to comment

Interesting series Toni.

I can't comment on the WB, but I think some are over exposed to get a good WB, but I can't be sure ?

Link to comment
I think the colours are interesting for what you can get with PS. Unfortunately CameraRaw is not capable of handling the extreme WB these images really needs. To see how a more powerful WB can turn out, I recommend you to try the FastRawViwer: https://www.fastrawviewer.com/ That is the program I use for overviewing and culling my RAW-files, before conversion. I think you will be surprised about the colours of the flower by BG39 + BG25 That program is unfortunately not a Raw converter, just a RAW-viewer, but it is very usable for previewing RAW-files. If you like the capabilities there are several programs that can handle extreme raw files better than CameraRaw.

 

I downloaded FastRawViweri is very fast as a display, but it is very limited in the color temperature range (up to 15,000 ° K, ACR up to 50K) then it has no curve correction function.

I know how to use ACR much better, I immediately deleted this from my small SSD :)

I also tried Capture One but this too is limited to 15,000 ° K.

Unfortunately the Nikon soft does not open Sony ACR, it should be the best soft for raw management.

This is the same photo 100% reworked

post-141-0-02022300-1625326206.jpg

Link to comment

Interesting series Toni.

I can't comment on the WB, but I think some are over exposed to get a good WB, but I can't be sure ?

 

I quickly used the Sony in Auto ISO mode at f: 11, (lens Nikkor-H 50 f:2) some are clear

you must keep in mind that the flower is yellow illuminated by a blade of the sun with the bottom in shadow.

the light parts are reflections of the sun on the surface of the petal

Link to comment

That looks much more like I expected from a proper WB.

It is well known that ACR is NOT able to handle these extreme RAW files.

 

This is a quick first result I get from FastRawViwer without any effort of optimisation, just a one click WB on the background:

No fiddling with adjusting any colour temperature. That will not work well as there is also avery strong tint in these type of images.

I FRW you can manually set the channel gain from a reference image with a good WB-reference if needed.

post-150-0-55255500-1625375540.png post-150-0-32822700-1625375740.png

 

I suggest that you do not dismiss this program that fast as it actually is a really valuable tool for examining the raw files.

It is well worth the effort learning how to use it.

To WB an image in the program is just the first step to properly examining many different aspects of an image

Link to comment

Ulf W

Cadmium

Thanks.

.

 

the post title could be:

"the colors of the UV world that we do not see are debatable ... disputable ... questionable"

it is true that Adobe camera raw can not do a white balance automatically!

I started from your images and came to this with ACR.

As I said at the beginning, it is a personal evaluation, my brain thinks that a blue tone is closer to reality than a green one :-)))

.

If we then consider a standard conversion in BW the results are similar

.

post-141-0-60911500-1625382698.jpg

Link to comment

You have full freedom of using any colour-result for these images as they are false colour images.

If the goal is to create BW images, it matters even less.

 

However normally we have been using WB against something reasonably neutral for UV-based images.

Then my and Cadmium's images are showing colours more normally seen.

For me that purple background indicate a not properly made WB.

 

A very strict WB against PTFE seldom give the most pleasing result for BUG stack images.

Often an auto-WB selecting the entire image or a well selected part of it gives a better result.

 

The BG39 + BG25 stack you used is similar to one of the BUG stacks that is based on S8612 and BG3.

I usually call that a BUG3 stack.

Link to comment

You have full freedom of using any colour-result for these images as they are false colour images.

If the goal is to create BW images, it matters even less.

 

However normally we have been using WB against something reasonably neutral for UV-based images.

Then my and Cadmium's images are showing colours more normally seen.

For me that purple background indicate a not properly made WB.

 

A very strict WB against PTFE seldom give the most pleasing result for BUG stack images.

Often an auto-WB selecting the entire image or a well selected part of it gives a better result.

 

The BG39 + BG25 stack you used is similar to one of the BUG stacks that is based on S8612 and BG3.

I usually call that a BUG3 stack.

 

it's a long story...

after 25 years of digital photography I returned to primitive black and white photography, not only with film (panchromatic) but also with the wet plate technique (Collodion - TinType - Ambrotype)

This emulsion made at the moment is sensitive only to blue and uv light (orthochromatic) ...

so I looked on this site for help to emulate this "vision" with the Sony A7 full spectrum

You can see my old posts.

Now I use the A7 with pleasure to see a preview.

this below is a tintype on black anodized aluminum 18x24 cm of "Van Gogh sunflowers"

I also really like using the A7 with a normal A25 / R25 red filter around 580nm for landscape photos

Thanks

Toni

 

P.S. in this post

https://www.ultravioletphotography.com/content/index.php/topic/306-cymbalaria-muralis-ivy-leaved-toadflax-another-example/page__hl__%2Bcymbalaria+%2Bmuralis__fromsearch__1

Nico Chalwatzis Writes: “simulated bee-colours”: composite image of the UV image (-> blue) (greescale conversion) and the blue (-> green) and green (-> red) channel of the visible light image. The goal of this is to mimic the spectrum that bees and other insect-pollinators can see.

can you explain me better ?!

post-141-0-89073200-1625389288.jpg

Link to comment

 

it is true that Adobe camera raw can not do a white balance automatically!

I started from your images and came to this with ACR.

As I said at the beginning, it is a personal evaluation, my brain thinks that a blue tone is closer to reality than a green one :-)))

 

 

Toni you can ultimately use any color you want. The problem is its mostly all false as we can't see it. The second problem is the way our cameras see it with their color filter array.

We have settled for BGGR arrays. The blue sensitive plummets after 400nm and is gone below 380nm. So our cameras tell us that deeper UV is yellow in the 370s and green below 340nm. With blue making a little comeback in around 254nm.

So a white balance image generally from various users with a typical camera may not look how you would expect and be green in the purple part of the spectrum.

 

Now if we settled for CYMG sensors the colors are even more crazy. I have a sensor like that and need to play around more with it.

Link to comment

We have settled for BGGR arrays.

The blue sensitive plummets after 400nm and is gone below 380nm.

So our cameras tell us that deeper UV is yellow in the 370s and green below 340nm.

With blue making a little comeback in around 254nm.

 

I'm confused.

I found and then worked out this diagram.

the UV part has a logic.

the IR part is inverse ... in fact the exchange of the R>B B>R channels is used

post-141-0-67208600-1625408760.jpg

Link to comment

The curve for the Z5 at that link is for the total sensor response. Its not broken down into the separate RGB dye channels. Those individual channels and their spectra response is how we white balance in the flase color for UV photography.

With a UG5 or U330 or ZWB3 filter that UV response looks green when white balanced.

Deep UV is also green, due to the sensitivity of those green and red channels that you can see in that spectrum I have above.

 

CMYG sensors are rare. Mostly used in old fixed lens compact cameras. One of the old Sony 728 cameras used something similar. Mine is the Lodestar x2 color guiding camera. It has a C-mount and can take lenses, but its very low resolution.

Link to comment

I have lost track of the question here.

Don't be confused by the Nico link, that shows composites, mixing channels from more than one photo (UV and Visual), that is a whole other thing.

Link to comment
The curve for the Z5 at that link is for the total sensor response. Its not broken down into the separate RGB dye channels.
I agree Cadmium, the topic has changed from what it started with.

 

David, No I can not agree about that!

Its not broken down into the separate RGB dye channels because the RGB dye transmission is not at all included in the transmission displayed here.

Maybe the link for the Z5 you refer to led us to different pages and graphs.

 

https://www.primaluc...?___store=world

What I see is just a transmission graph of the cameras UV-IR rejecting filter stacks in front of the camera's sensor.

These stacks come before the light reach Beyer matrix and do not include any sensor sensitivity at all.

The graph show the transmission of the original filter and the one PrimaLuce use to replace it with.

 

For showing a camera sensor you need the combination of the transmission in this graph and the transmission of the individual RGB dyes, including the microlenses and the sensitivity of the silicon sensor.

I know you know this David I am just

Link to comment

Ulf,

I am completely confused by your response.

To summarize what changed. You and Cadmium provided images that where better white balance corrected, but where green.

Toni said hold on they shouldn't be green but blue. As we are looking at UV and blue/purple part of the spectrum.

 

I said you can make the images how you want, but we humans can't see UV so its all false color and the dye sensitivity of our cameras causes a correctly white balance image with UG5/U330/ zwb3 filter to be green for UV.

Toni than provided a hand drawn artist view for what the RGB dyes in our cameras should see and again was confused.

 

I provided measure, from a research paper curves for the actual spectral response of the dyes in a BGGR sensor (what we all have) and special case CMYG sensor, I have one , to make the point thats its all false color.

 

So now you're back up to speed and hopefully less confused.

I didn't provide that Z5 link Toni did.

 

As you can see green and red dyes on our sensors are not perfect to only respond to light in their respective parts of their spectrum. Actually this is by design, Red looks better to us if it is sensitive in the blue part of the spectrum in general photography. The side effect of that is that it is responsible for most of the UV detection as well below 380nm as the blue dye is not sensitive to wavelengths less than 380nm. So for Toni its not all blue in UV.

 

If you only want blue though you can use a Foveon sensor, where only the top blue layer is sensitive to UV from 335nm and up. Or use Fuji color instax film, similarity all the UV response is in the top layer and comes out blue.

Link to comment

David, Sorry if I interpreted things incorrectly.

 

I thought you commented on the Z5 link Toni posted before and I commented on your comment.

 

Your graph and previous comments are quite OK while the Z5 link from Toni is not about sensor sensitivity and misplaced as a comparison item.

Link to comment

Thanks guys

let's start with my problem

I bought these two cheap filters (not Schott) BG25 and BG39 to emulate the wet collodion (theoretical sensitivity from 325 to 510nm)

With Sony A7 and these two filters I see the previw on camera of the BN photo quite well.

the problem arises when with curiosity (not necessity) I want to see the colors.

In this photo I am lucky to have a neutral gray concrete background.

my brain says no white balance of the three is fine!

 

P.S. i used Capture One which works better than ACR

post-141-0-02865500-1625469688.jpg

Link to comment

Toni,

 

All this looks good and I think it was I that argumented for using the BG25-stack earlier this year too, based on the different sensitivities of UV and VIS by a converted camera.

As you say for B&W none of the colours matter and I think you have a good starting point for digital emulation of the wet processes.

 

All our discussions here are because we normally see the coloured pictures as important and your's did not look the way we are used to see them. Please ignore that for your emulation purpose.

 

If you in the future want to experiment more with this kind of filtering with BG25 you can try to get that type of filter in other thicknesses than 2mm.

A thinner filter will increase the VIS part of the light and a thicker will decrease the VIS part making the UV more accentuated as the balance between the two parts of the spectra will change.

A thicker filter will naturally also increase the exposure time as it absorbs more light.

 

The cheap Chinese alternative for BG25 is called QB29.

Tangsinuo on eBay can sometimes do custom variants if asked, but just now they do not show any QB29 in their store.

Link to comment

Chinese ZB1 is also equivalent to BG25. Mine gave a more orangeish than red for foliage when used with out an IR blocking filter. Some QB29 might have the IR start too much into the upper 500s than mid 600s so they are more yellowish.

 

Link to comment

I don't think the ZB1 has the plateu in blue and green that BG25 has. It looks like QB29 have that.

Still the ZB1 might be interesting, especially without stacking with any BG-glass.

post-150-0-09248800-1625487278.png

post-150-0-94081600-1625487343.png

 

I do not trust these graphs very much though.

Link to comment

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
×
×
  • Create New...