Infra Red

[glenafton]

Another brainpicking question. I was fascinated by some photographs taken with an infra red filter fitted to the camera so like the man who tried to run before he could walk I bought an infra red filter ( a Hoya [R72] ) and thought that I could be another Lord Litchfield. When I take a photograph I can get part of the subject in focus but the rest is a blurred image. If I just screw the filter onto the camera ( a Panasonic Lumix DMC-LZ50) the images came out with a red tinge so now I switch to the black and white mode before fitting the filter. I have enclosed a photograph to show what results I get.
The details of the photograph are:
Horizontal Resolution 72 dpi.
Vertical resolution 72 dpi
Bit depth 24
Resolution unit 2
Colour Representation sRGB
F-stop f/4
Exposure time 2.5 secs
ISO ISO-100
Focal length 8mm
Maximum aperature 3
Exposure programme Aperture priority
White balance Auto.
Glenafton

[SmartWombat]

The wavelength of IR is different, so the focal point is different. Images formed by infra-red rays focus slightly further behind the focal plane formed by visible light.

Also f/4 isn't stopped down enough to get large depth of field, even with the small sensor.

It's an interesting experiment though, and if you can stop down the aperture more and use longer exposure time, I think you might get good results.

[freygr]

Most digital camera also have a IR blocking filter in front of the sensor as the sensors are very sensitive to IR. So I'm surprised at how good the photo looks and how short of an exposure to get the photo as with film the exposures I saw listed was in minutes. Yes the IR does focus at a different location than visible light, like SmartWombat said. In fact the most old film lenses had the IR focusing correction marked on lens barrel.

[glenafton]

SmartWombat and Freygr,
Thanks for your help. I will have to keep on trying for that perfect picture.
Glenafton