4 replies to this topic

[enricosavazzi]

A few pictures from my Yellowstone visit last June. I am still sidetracked with other projects and did not have much time to organize my pictures, but here are some results.


UV with Baader U. There isn't so much to see aside from the contrast between living vegetation (almost black, as usual), water and wet soil (also dark) and dry soil, especially the white (in VIS) dried geyser sinter.


Panoramic view of a geyser basin. UV with Baader U. Same as in preceding image, UV imaging is mostly useful to tell dry ground from wet ground, but not much more.


NIR. A lot more detail is visible in the wet areas with 800 nm low-pass filter.


A thermal pool. UV imaging is good when the angle and illumination provide reflections from the water surface.


NIR with 800 nm filter. Manually color-balanced to intentionally keep some of the original mauve tint.


A fantasy NIR image with low-pass astronomy orange filter. I made an arbitrary RGB balancing, but did not swap channels.

Edited by enricosavazzi, 02 September 2017 - 13:59.

[Andy Perrin]

Interesting! Is the vignetting on purpose, or was that just a function of what lens you had with you? It gives the pictures a kind of old-time feel.

[enricosavazzi]

Andy Perrin, on 02 September 2017 - 14:07, said:

Interesting! Is the vignetting on purpose, or was that just a function of what lens you had with you? It gives the pictures a kind of old-time feel.

The vignetting is caused both by the filter ring (I used 30.5 mm filters on the trip, for portability in the field) and by the mount of the lens shade (when used). Obliquity of light rays through the filter near the edge of the lens may also be a factor. The lens is a Pentax-110 18 mm f/2.8 (the native filter mount is 30.5 mm), and already vignettes a little on Micro 4/3 without filters. This is not surprising since the 110 format is quite a bit smaller than Micro 4/3. I left in the vignetting on purpose, rather than cropping it out or correcting in post-processing. As you say, it gives images an old-time feel.

Edited by enricosavazzi, 03 September 2017 - 06:46.

[Andrea B.]

Quite interesting Enrico! I had been eager to see these.
You got some really nice fotos.

The differences between the #2 (UV) and #3 (IR) images are somewhat subtle.
But in #4 (UV) and #5 (IR) there is a reversal of light/dark in the sky, water, and trees which is dramatic.

Was there any false color in the UV images?

[enricosavazzi]

Andrea B., on 08 September 2017 - 17:09, said:

Was there any false color in the UV images?

The lens I used on the trip (Pentax-110 18 mm f/2.8) passes only about 375-400 nm in the UV, so there is no significant false color.