Tuesday 20 August 2013

Michael Nichols lions

I know from the work of Colin Jackson at the BBC Natural History Unit that you get some fascinating shots using infrared cameras with lions at night. You would imagine that National Geographic would also come up with something impressive when covering the same subject.

Michael Nichols spent months photographing lions on the Serengeti and I'll do no more than direct you to a page of his images (some infrared) on the NatGeo web site ... especially a mesmerising shot of a lion called C-Boy. The accompanying piece appeared in the August 2013 edition of the magazine.

I'll be returning to the annals of National Geographic in future posts as they played a significant role in several historic infrared imaging adventures.

Tuesday 13 August 2013

DSLR infrared sensor response

Camera manufacturers tend to be coy about releasing the spectral response of their sensors: they're (logically) more concerned about how the camera as a whole performs than how the sensor might deal with infrared (or UV).

A peek behind that curtain has come courtesy of Christian Mauer of the University of Applied Sciences in Cologne. His thesis Measurement of the spectral response of digital cameras with a set of interference filters (January 2009) is interesting in its own right but if you work your way down to Appendix A page 81 (section A.1.7) you will find the spectral response of a Canon EOS 450D without its IR blocking filter. It shows the usual bump in blue response just beyond 650 nm so that the respective responses of the red, green and blue channels at 800 nm are around 20%, 30% and 40% of the peak green response (at 540 nm) respectively. All channels come together at 20% at 850 nm and the response is monochromatic beyond that.

These figures are actually showing the spectral response of the sensor plus its Beyer filtering, since the underlying sensor is monochromatic and should have a smooth response curve peaking at around 600 nm and slowly dying away to over 1000 nm. However, this explains the strange colours when you take infrared images through a 720 nm filter and why ones through an 850 nm or longer filter are colourless.

Saturday 3 August 2013

60 megapixels of near-infrared

Back in April, I wrote about the Leaf Credo wide spectrum backs which had been set up to shoot near infrared out of the box at resolutions up to 80 megapixels. Yair Shahar (from Leaf) and I spent a couple of hours on Primrose Hill in London trying the 60 megapixel version out with both a Mamiya body and a technical camera.

The image as shot with the 60 mp back is an extraordinary 8984 by 6732 pixels. With a suitable lens the resolution is also impressive, giving scope for huge detailed prints. To give you an idea, here is a 6200 by 4000 crop from a shot through a 950 nm filter looking south from Primrose hill directly towards the Shard.

If I zoom in on this until you're looking at it pixel for pixel, this is what you see just to the left of centre on the horizon, between the two dark buildings to the left of the Shard.

This was with a Mamiya 80m lens (half a second at f9, ISO 50). With a technical camera lens the image was even sharper. I have found that infrared can produce very interesting cloud images even on an overcast day, presumably because of a different balance between the brightness of the ground/trees (which show up bright in infrared due to the Wood Effect) and the cloud base. You can focus using live view with this back, which is pretty well essential for such a shot, as is a tripod. The back has no anti-aliasing filter. In general you don't need one for landscapes although there was one distant building in the scene we shot that exhibited some moiré, which was easily removed/disguised.

Leaf use another of our shots from that test on their guidelines brochure.

I had hoped to be able to do more infrared tests with the Credo during July but, unfortunately, it wasn't possible due to my work load. But the main point is made by the brief trip to the top of Primrose Hill, which is that you can produce dramatic landscapes with this kit. I'd love to see what a real landscape photographer could come up with, given more time and better weather. The Credo WS back is also proving of interest in art conservation and for forensics. There is a lot to be said for the 'shoot first and examine later' ability of very high resolution images.

[My thanks to Leaf and Yair Shahar for their help with this test.]