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UltravioletPhotography

UV+VIS+IR TriColour/multispectral


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Today we went on lake Como and of course I took a lot of images, in visible and invisible light. I made some TriColours with infrared in the red channel, visible in the green channel and UV in the blue channel. I still have to improve the technique, but the results are not too bad in my opinion.

 

Camera: full-spectrum Canon EOS M

 

Lens: Soligor 35 mm f/3.5

 

Filters:

UV: ZWB2 (2 mm) + Chinese BG39 (2 mm);

VIS: Chinese BG39 (2 mm) (only);

IR: Hoya R72;

 

All images taken at f/8 and ISO 100. The channels were obtained by converting the whole images to B&W. Except for the second image, all images are the "raw" stacks, no WB applied. I did apply it in Photo Ninja in the second image by clicking the base of the column at the right.

 

post-284-0-36620200-1625077807.jpg

 

post-284-0-64337700-1625077814.jpg

 

post-284-0-42629300-1625077819.jpg

 

post-284-0-16607700-1625077856.jpg

 

post-284-0-44704700-1625077865.jpg

 

post-284-0-36425300-1625077873.jpg

 

Normalizing the exposure times for the visible images, these are the exposures required for UV and IR:

 

UV: ~200-250

VIS (+UV*): 1

IR: 2-2.6

 

*The BG39 filter used alone passes visible light as well as UV. The resulting image is almost completely VIS-only, but the sky does have a slight violet tint.

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I love your posts, Stefano.

I would personally, if I were to edit those images, shift the color balance a bit more towards the magenta, some images seem very greenish, particularly the sea.

My ZWB2 arrived today as well. It's quite nice with the BG39, isn't it? I'm just about to put out a comparison post with my ZWB1.

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Thanks Fandyus.

 

Yes, the last one in particular is greenish. This is probably due to the different exposures for the images (I didn't always use the same values). One improvement I should do is to find the exposures needed to expose a white reference (PTFE or a paper tissue) the same way in UV, VIS and IR and apply those exposures when taking the photos. I should do this in various conditions, such as midday sunlight, morning/evening, cloudy day and shade. That should produce more balanced images.

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My ZWB2 arrived today as well. It's quite nice with the BG39, isn't it? I'm just about to put out a comparison post with my ZWB1.

Yes, it is quite nice. 360-type and 340-type U-glass give similar images, but some objects may appear a bit different (what you see as strong/dark lavender with the ZWB2 will appear black/darker with ZWB1).
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No problem

 

Do you own a PTFE sheet? I have one in transit on the way to my place right now

 

Edit: Do you own a ZWB1 as well?

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Andy Perrin
Stefano, why not just put a PTFE reference in one photo to get a white balance from in your favorite program and adjust the exposures afterwards?
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No, I don't have one yet. I really should get one.

 

Just saw your ZWB2 and ZWB1 comparisons, your images are very similar. Probably not unusual, but I would have expected something more.

 

Other comparisons:

https://www.ultravioletphotography.com/content/index.php/topic/2738-ug2a-and-four-other-uv-filter-pass-filter-combinations

 

I remember another one from Steve, I can't find it now.

Not the one I was searching, but this shows the differences too: https://www.ultravioletphotography.com/content/index.php/topic/2265-question-about-kolari-filter-test/page__view__findpost__p__16436

 

Here's a test I did with my old camera, that didn't have a very deep reach because of the lens: https://www.ultravioletphotography.com/content/index.php/topic/3697-differences-between-normal-uv-and-deeper-uv

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Stefano, why not just put a PTFE reference in one photo to get a white balance from in your favorite program and adjust the exposures afterwards?

That would be the best way to do it, but I think I can't always do it. In the landscape images it would have been difficult.
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Andy Perrin
Nah, you just have to take a separate photo with the same settings with the WB target. Then once you work out the necessary exposure changes, you apply them to the landscape image's channels.
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Nah, you just have to take a separate photo with the same settings with the WB target. Then once you work out the necessary exposure changes, you apply them to the landscape image's channels.

You mean doing that every time? I was thinking of doing the same but in some situations only and then generalizing the results, as I wrote above.
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Andy Perrin
You have to do it every time. Unfortunately it’s quite sensitive to the exact light at that particular moment. Even the sun going behind different amounts of haze changes the spectrum.
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Yes, probably this is what I have to do. The UV/IR ratio in particular varies a lot. This can be seen using a U-glass filter in dual band UV/IR mode, the color palette varies a lot from midday to the evening.
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No, I don't have one yet. I really should get one.

 

Just saw your ZWB2 and ZWB1 comparisons, your images are very similar. Probably not unusual, but I would have expected something more.

 

Other comparisons:

https://www.ultravio...er-combinations

 

I remember another one from Steve, I can't find it now.

Not the one I was searching, but this shows the differences too: https://www.ultravio...dpost__p__16436

 

Here's a test I did with my old camera, that didn't have a very deep reach because of the lens: https://www.ultravio...v-and-deeper-uv

Thanks, Stefano. I'll check the posts.

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When I have done wideband images in the past, the vegetation came out more yellow-orange rather than bright red. Perhaps the treatment of the visible band was different.

 

Hexadecagon House Multispectral Series:Wideband

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When I tried here using a white standard (paper tissue) foliage did come out orange. I think that's the right color, as it is black in UV (almost no blue), green in visible light (some green in the final stack) and white in IR (a lot of red), so the final result is red + some green which gives orange.
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Try using the following for the 3rd and 4th photos, which lack enough contrast and micro-contrast.

  • Auto-levels to adjust each channel separately, OR
  • Move the white point of the histogram to the left and the black point of the histogram to the right to adjust the luminance/brightness of the 3 channels combined.

Then hit that result with a USM (10, 50, 0) or USM (5, 100, 0) to bring out some detail.

 

The auto-levels will change colors slightly, so you will probably prefer brightening up the photo with the second adjustment which does not change colors.


 

The clouds are so cool! They are showing a time series or whatever it is that we call that these days.


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P.S. I really want to see the Lake Como area some day. Looks lovely.
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Try using the following for the 3rd and 4th photos, which lack enough contrast and micro-contrast.

  • Auto-levels to adjust each channel separately, OR
  • Move the white point of the histogram to the left and the black point of the histogram to the right to adjust the luminance/brightness of the 3 channels combined.

Then hit that result with a USM (10, 50, 0) or USM (5, 100, 0) to bring out some detail.

 

The auto-levels will change colors slightly, so you will probably prefer brightening up the photo with the second adjustment which does not change colors.

Which software allows this? I have IrfanView, Photo Ninja and RawDigger.

 


Lake Como is very nice. I suggest you visiting it if you can.

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Stefano: Which software allows this? I have IrfanView, Photo Ninja and RawDigger.

 

I do not have Irfan View in order to be able to make any reccies about it. So I'll give you my usage of Photo Ninja with the warning that all edits are global. Sometimes global Sharpening or Detail enhancement can also bring out noise in the wrong places. Then Sharpening/Detail must be applied in some other app.

**********

 

My basic approach to Sharpening/Detail is to initially defuzz the raw file just a bit but then to wait until after resizing to apply final Sharpening/Detail.

 

For initial defuzz Sharpening of a raw, unresized photo, I use PN's recommendation of Radius between 0.5 and 0.7. So set Radius at, say, 0.6 and then move the Strength slider to 50 or more. Look at the photo at a 50-100% magnification while adjusting the Strength slider.

 

For detail enhancement of an already resized photo prior to posting, or for initial defuzzing of a raw, unresized photo, set the Detail slider to between 8-15. It is very easy to go nutso with the PN Detail slider because it gives things an "interesting" look.

Use it with restraint. :grin:

I particularly like using the Detail slider (10-20) on IR photos because PN Sharpening does not work as well on IR. (IMHO, YMMV)

 

If I defuzz the raw photo with Detail, then I usually do not use Sharpening, and vice versa. I then sharpen or detail desired areas, either locally or globally, in another app after resizing.

**********

 

Black and White Point adjustment in Photo Ninja is not as easy as it is in other apps which have moveable histogram endpoints for the luminance/brightness histogram and for each channel separately. I don't really know how to do Levels in PN and I'm not sure it is possible. I only know how to do B&W endpoint tweaks in PN.

 

B&W Point adjustments are not always needed.

**********

 

White Point Adjustment brings more light to the photo.

 

If the photo is somewhat underexposed, then use Exposure slider to bring the edge of the histogram to the right. Don't go so far that you create Highlight blowouts beyond a -0.5 to -1.0 recovery. Then follow that with the Illumination slider if more light is needed. The Illumination slider compresses and so will not blow highlights. It is a really great tool for general brightening of photos.

 

If the photo is properly exposed, then if needed move the Illumination slider to the right to bring more light to the midtones.

 

If the photo is overexposed, then move the Exposure slider to the left as needed. Follow that up with a reset of the Highlights slider. The Highlights slider can quickly dull the highlights you want to keep, so watch out for that.

 

Take, as a general rule, that the Highlights slider might need readjustment after using the Exposure slider.

**********

 

Black Point Adjustment to unblock shadows or to add more dark tones.

If the left side of the histogram is climbing the left wall, move the Black slider to the right -- if the result looks good. If only 1 or 2 channels have hit the left wall in a small way, it's sometimes OK to ignore that. For most of the photos we make and post online, Black Point adjustment isn't needed. When printing, it is much more important to adjust the Black Point to avoid blocked areas (no detail).

 

If the left side of the histogram is too far from the left wall, you can move the left endpoint closer to the wall -- if you need to add darker tones to the photo. This is a judgement call. Sometimes using the Contrast slider is the best way to recover some darker tones.

 

Black Point adjustment in Photo Ninja goes hand-in-hand with the Shadows slider. Simply moving the Black Point will not necessarily bring out all the details in dark areas.

**********

 

Shadows Adjustment

The PN Shadows slider is the best such tool I've ever used. But it needs to be used sparingly in order to avoid wrecked contrasts. It is quite tempting in some landscape photos to overlighten darker areas with the Shadow tool and reveal all those "hidden" details. But the result can look un-natural. No single recommendation works for every photo. You simply have to experiment with Shadows.

 

 

That's all I gots.

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