Why is filter removal needed in
All DSLR cameras have sensors which are sensitive to infra-red light. Camera manufacturers
install IR filters to keep most IR energy from reaching the imaging sensor in order to maintain a correct colour balance similar to what our eyes see.
Unfortunately, these filters also attenuate hydrogen-alpha radiation which is
very important for capturing the red nebulosity in astronomical photographs. A typical IR filter blocks as much as 75% of the light arriving to the chip in the H-alpha wavelength.
By removing the stock IR filter or replacing it with a Baader IR filter that is transparent to hydrogen-alpha, the
camera's sensitivity for astrophotography is greatly increased.
Orion Nebula with a standard DSLR camera
This image has been taken by a Canon 350D with the original IR stock filter installed. With this configuration, the camera has blocked up to 75% of the hydrogen-alpha light emission. Image courtesy of Matt M.at SGL
Orion Nebula with the same camera after filter removal
As you can see, the camera's sensitivity to H-alpha radiation has increased noticeably. Nevertheless, some star bloating and halos are present. This is due to the fact that the Canon 350D model only has one filter in front of the sensor. By removing it, the sensor is exposed to IR and UV light which results in bloated stars as lenses don't bring IR and UV light into focus at the same point as visible light. For this camera model, a Baader filter replacement would have solved this problem. Later camera models such as the Canon 450D or 1000D come with two filters in their optical assembly, making it possible to remove the colour correction filter whilst still retaining the IR UV Cut filter to avoid star bloat
Why am I only selling these models?
The canon 450D, 1000D and 1100D cameras are some of the most affordable models which use a digic III or IV processor. They come with a number of interesting features for astrophotography such as live view for easy focusing with a Bahtinov mask. Also, unlike the older cameras such as the canon 350D, the optical assembly in this model comes with two filters. One of the them is a low pass IR UV cut filter which is retained in the modification. This filter is needed when the camera is used in refractors in order for the telescope to achieve focus at all wavelengths. In the modification, the only part removed is the terrestrial colour correction filter, responsible for blocking much of the hydrogen-alpha radiation typical of emission nebulae.
IR cut filter removal comparison
In this picture you can see how the camera is much more sensitive in the red channel after modification. The original IR filter blocks 75% of the hydrogen alpha radiation present in emission nebulae.
All the cameras have had their sensors checked for scratches or dead
pixels both prior and after modification. Time and weather permitting, I make an effort to test them in
prime focus with my telescopes.
SW200P reflector telescope (1000mm focal length) on a HEQ5Pro. Guiding with PHD through a Stellavue F50 finder and an Orion Starshoot Autoguider.
SW Evostar 80ED DS-pro with 0.85 SW focal reducer on a HEQ5 Pro. Guiding through a SW 9X50 finder scope and a Orion Starshoot Autoguider via an adapter from Modern Astronomy
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back to you as soon as I can to let you know what cameras are available.
Cheap Astrophotography is an 'evening and weekend' enterprise because of the demands of my full-time employment. I'll do my best to fill orders and respond to emails promptly; however, please realise that there may be times when I cannot respond as quickly as I would like to. I appreciate your patience.Thank you for your custom.