The End of Our Street

[xpatUSA]

Shot in Summer with the Sigma SD1 Merrill + 18-200mm zoom. The UV/IR blocking filter was removed from the camera, making this a so-called 'full spectrum' shot:



These types of shot can be a bit soft because the lens is not designed for focusing IR or UV. APO lenses are better in that regard but tend to be long, heavy and seriously expensive.

Which means that, for most shots, post-processing is quite important. This is not an "IR" shot (no filter on the lens) and I did not swap any channels or use an RGB mixer. I color-balanced on the gray transformer body. WB was in-camera custom off a Kodak R27 card (white side).

The lens shows some softness at top right and some might find the image too garish for their taste.

[Wavelength]

It is beautiful; yet a bit too hot for eyes

[rpcrowe]

In the "old days " of manually focusing cameras and lenses, the lens would often have a IR correction focusing point.



In the case of this lens, the "normal" focusing point is the yellow line. After you were focused normally, you would turn the focus scale so that the red dot coincided with where the yellow line originally was located. This would, pretty well keep the image in focus for infra red work.

Now, with AF lenses, I try to keep my aperture at f/11 or smaller with the expectation or hope that the DOF will cover the difference between focus points of visual light and IR....

[xpatUSA]

In the "old days " of manually focusing cameras and lenses, the lens would often have a IR correction focusing point.



In the case of this lens, the "normal" focusing point is the yellow line. After you were focused normally, you would turn the focus scale so that the red dot coincided with where the yellow line originally was located. This would, pretty well keep the image in focus for infra red work.

Thanks for the reminder, Richard.

Indeed, I suppose that worked well enough with the infra-red film back then although I never tried it myself. The Sigma camera sensors are sensitive up to the limit of silicon (about 1100nm) but, with the UV/IR blocker removed, they also go down below violet into the near UV region. So, in many ways, shooting the camera with no filtration at all presents an image almost impossible to focus unless (as you said) a pretty small aperture is used.

Now, with AF lenses, I try to keep my aperture at f/11 or smaller with the expectation or hope that the DOF will cover the difference between focus points of visual light and IR....

Sounds like a plan - and modern de-convolution techniques can restore a bit of sharpness too.

[xpatUSA]

It is beautiful; yet a bit too hot for eyes

Thanks Nandakumar.

It is difficult to avoid the "heat" with full-spectrum photography, I find. Easy enough to reduce saturation but then image becomes quickly too flat. Same effect when contrast is not applied. The infra-red tends to reduce contrast in the captured image, similar to veiling glare.

[Shadowman]

Nice shot.

[xpatUSA]

Nice shot.

Thank you!

[JBW]

it's a good day I have learned something new

[IzzieK]

I still do not understand why everything seems to be red...even the clouds have a red colour cast. I guess the explanation went above my head...can you educate me further...even just a little bit???? But I like red, lucky colour.

[xpatUSA]

I still do not understand why everything seems to be red...even the clouds have a red colour cast. I guess the explanation went above my head...can you educate me further...even just a little bit???? But I like red, lucky colour.

Yes, Izzie, it's not too hard:

Our eyes can only see light with wavelengths between 380nm (violet) and 730nm (just-visible red). But green vegetation also reflects higher wavelengths (infra-red), mainly from chlorophyll in the leaves. Our eyes can not see these higher wavelengths but bare silicon photo-diodes (of which camera sensors are made) can see much higher, up to 1100nm. These invisible wavelengths would tend to "fog" captured images - so all color cameras come with built-in blocking filters to prevent the sensor from reacting to invisible wavelengths.

On your cameras, this is done by a Color Filter Array (CFA) glued to the surface of the sensor. Therefore, the CFA has two functions 1) separating the visible RGB wavelengths and 2) blocking invisible UV and IR from reaching the bare silicon.

On My Sigma DSLRs there is an easily-removable UV/IR blocking filter, just inside the lens mount. When removed, the red-sensitive part of the Foveon sensor gets lots more radiation on it which is why the raw conversion makes the leaves red.

P.S. The red cast in the clouds could be my Custom White Balance in-camera being off (it was done on a different day) or it could my post-color-balance where I clicked on the gray transformer which itself may not be perfectly neutral gray.

Brian, there's a post here written in Ted-speak about how I obtained that particular image. Probably won't mean much to non-Sigma owners, though.

https://www.dpreview.com/forums/post/59650218

Trivia: the prefixes "infra" and "ultra" (lower and higher, respectively) seem back-asswards, from a wavelength POV. But they actually refer to light energy, which is lower for red and higher for violet.

[IzzieK]

Thanks Ted...I will copy and paste this in my word processor to sort it out in my thinking again.