UV, VIS & IR Comparisons on a Clear Day

[lonesome_dave]

Just had a storm pass through recently that cleared the air and left some snow on the mountains so I thought I'd do a UV-VIS-IR comparison series today. The hills are about 12 miles away and the mountains are about 40 miles out.

 

All shots were taken with a Sony A6000 FS-converted with Sirchie 60mm quartz lens.

 

UV Filter- Baader-U

 

VIS Filter- Kolari UV-IR Block

 

IR Filter- Zomei 950nm

 

The lack of edge sharpness is really obvious in the VIS shot because of the much wider spectrum captured. I should have maybe used a green filter to limit the spectrum enough for this all-quartz lens to get a sharper image. The Sirchie lens was designed for narrowband forensic work and not for this kind of photography.

 

These are reasonably lined up well enough to do a blink comparison if you download them. The reduction of haze in each step due to declining Rayleigh scattering of the longer wavelengths is easy to see here.

[Stefano]

Very nice comparison. I could try to stack them in a false-color image, if you want.

[lonesome_dave]

Thanks Stefano, that would be nice. Not sure they will line up well enough for that. There was so much focus shift between the spectrums that the image size changed as well. I tried to crop them to fix the framing before resizing but only got it close.

[Andy Perrin]

Knowing the peculiarities of that lens very well, you did an excellent job here!

[Stefano]

I downloaded the images, converted them to black-and-white (the UV and IR ones had a slight color cast), colored the images and stacked them.

Red channel: IR;

Green channel: VIS;

Blue channel: UV.

 

I had to increase the height of the visible image, since it was 10 pixels shorter than the other two. I didn't stretch it, I added 5 rows of black pixels on the top and bottom. Then I lowered the IR image by 3 pixels. They are still not properly aligned, and the weird thing is that if I align the top the bottom gets more disaligned.

 

Anyway, here it is:

 

It looks nice, I like it.

[Andrea B.]

Which mountains are we looking at in the background? The tall ones in the background. Are those the "Four Peaks"?? Very interesting in IR!

 

They are still not properly aligned, and the weird thing is that if I align the top the bottom gets more disaligned.

One of the photos probably needs a vertical alignment to correct for a little bit of camera tilt?

Will Zerene Stacker (or other similar app) align them?

[lonesome_dave]

Great job Stefano! I was worried the UV one would put a blue haze over everything. 

I'll do another one and try a smaller aperture to minimize the focus shifting. I kept the aperture almost wide open to eliminate the artifacts this lens gets in VIS & IR. I'll also try to not bump the tripod while changing filters!

 

Yes Andrea, those are 'the' Four Peaks, 38 miles in the distance. Snow has melted away today.

[Andrea B.]

I've done that so many times! Bumped the tripod, that is.

It's never easy to change filters without some small shift in rotation or tilt. 

 

It took me a minute or two to recognize Four Peaks. It has been a loooong time since I lived in Arizona.

[lukaszgryglicki]

It's never easy to change filters without some small shift in rotation or tilt

This is why I asked once about "filter wheel" - I cannot find any that I can just buy - say wheel with 3 filter threads on two circles that allows mounting 3 52mm filters and then just rotate them by hand without remounting. 3 filters would be ideal to ANY possible RGB (output) mapping from whatever 3 mono images you want.

 

[dabateman]

3 hours ago, lukaszgryglicki said:

 

 

This is why I asked once about "filter wheel" - I cannot find any that I can just buy - say wheel with 3 filter threads on two circles that allows mounting 3 52mm filters and then just rotate them by hand without remounting. 3 filters would be ideal to ANY possible RGB (output) mapping from whatever 3 mono images you want.

 

I am sure I have seen at least one 52mm filter wheel. Just check Astrophotography sites.

There is also this one:

https://www.thingiverse.com/thing:2962128

[lukaszgryglicki]

OK, nice to see, but it is big and has 6 filters not 3, but I'll check this when I'm back from Hawaii PTO.

 

[Foxfire]

The stacked image, was wondering how similar it would be with a picture made with just a camera without UV/IR cut and no filters. 
But thanks for the demonstration of what Sirchie lens can do.

[photoni]

I also did a test, the different magnification and rotation of the 3 files is a big problem.
This photo of mine is similar to Stefano's, but I increased the contrast and sharpness

.

 

[lonesome_dave]

Superb job Toni! You should send me the bill for that work.  :-)

 

Well, I have to say the image size shift between infinity focus at 350nm and infinity focus at 950nm is more trouble than I can deal with. Not sure if a better lens with more correcting elements like fused silica or one of the flourites would be better but that size change creates problems with post editing that I don't have the right software for (not to mention editing skills) to get perfect alignment. So I will leave the project of well-merged tricolors of super-wide spectrum UV-VIS-IR images to those who are better equipped. I will stick to making multi-spectrum sets that are aligned well enough for blink-sequence comparisons.

 

The purpose of my post was to elaborate on the observation I made 50 years ago and posted a few weeks back about the effect of wavelength on landscape haze. Here I wanted add IR to the sequence and use current images. The effects of Rayleigh scattering vs wavelength are well known. I just wanted to illustrate it with a few images that made it very obvious. Strangely the tricolor versions seem to lose all that haze, but they are beautiful. Thanks guys.