In August 2005 I visited Zane Hammond's Magellan Observatory in Australia. It is located near Lake Bathurst, New South Wales. Eh? You can't find tiny Lake Bathurst on your map? OK, it is about a half hour's drive from the nearest town, Goulburn (population 24,000), and about an hour from Canberra. Elevation is about 750m; and it is indeed a very dark site, augmented by that extra-special transparency they seem to have down-under. On my second night at his "Farm Stay" I spent a few hours piggy-backing on Zane's Newtonian + Losmandy G11 to check out a recently acquired Hutech-modified Canon 20D and a Canon EF 200mm/2.8L lens. Other nights were a bit hazy, cloudy or rainy (or poor me too exhausted from sightseeing in Canberra) and I did not get around to use his observatory again. I also present below some example Infra Red landscapes taken with the modded 20D. Read on; text under the photos. Click on "original" to see the images at a reasonable size. No worry (as the Aussies would say); I have not posted the full size multi-megabyte versions. Yeah.
Some details on the modded 20D: Hutech removed the Canon IR Blocker/Antialiaising filter over the sensor and replaced it with clear glass that has anti-reflection coatings. The clear glass is required so as to retain autofocusing capability. The camera now acquires very high sensitivity at wavelengths between the deep red, >600nm, all the way up to nearly 950nm in the Infra Red. The deep red H-alpha line, at 656.3nm, is astronomically very important for emission nebulae and is responsible for much of the nice red coloring in astronomical photos. In reality, the eye is very insensitive to such a deep red and most cameras designed to reproduce colours faithfully, i.e. non astro-dedicated cameras, would also be equally insensitive to this deep red. The Hutech modification is specifically meant to allow the capture of this deep red. But it brings with it the bonus of the Near Infra Red.
My modded 20D may now be used in at least 3 different configurations:
1. No filters at all, capturing all wavelengths from Near UV at 350nm up to Near IR at 950nm. Useful for heightened sensitivity, about 3x higher than the stock 20D, using mirror telescopes, including SCTs, that can satisfactorily focus all these wavelengths, on subjects where colour balance is not too important; e.g. globular clusters and remote galaxies.
2. A pop-in UV/IR Blocking filter is inserted right infront of the mirror box but behind the lens. A Hutech Type 1 cuts off light longer than 700nm, thus allowing H-alpha to pass through. This configuration enables the camera to be used for normal photography (portraits, landscapes, etc) and produces decent colour balance by using "Custom White Balance", calibrated against a white sheet of paper in the relevant lighting. It is also useful for taking astrophotos of nebulae, etc using refractive optics, i.e. camera lenses or APOs.
3. No pop-in filter, but a Hoya R72 is used over the lens. The R72 looks black but passes through the Near IR longer than 720nm and the 20D records it up to about 950nm. This is quite a wide band and, surprisingly, the camera is more sensitive than the stock version is to visible wavelengths. It also autofocuses quite happily right through that black filter. This configuration is useful for IR landscape or portrait photography (makes pimply brides end up with smooth-looking skin). Unfortunately if the R72 is forward of the reflex mirror then the viewfinder goes black. If Hutech places the R72 next to the sensor, the camera becomes dedicated to Near IR. I use it with the blacked out viewfinder. It is also very easy to make your own IR-pass pop-in filter from a Kodak Wratten 89B gel. This turns out to be cheaper and superior to an R72 infront of the lens, since you can use the same 89B pop-in for all your lenses and telescopes.