I wanted to fit my RC telescope with a focal reducer. My Meade 0.33 lens was not really appropriate but I thought it worth trying. The major problem was that I could not fit it close enough to the telescope for it to operate at its designed distance from the focal point of the telescope. So I fitted it as close as I could and then found I could just mount the camera close enough to the lens to achieve focus. The pictures below in light from Hydrogen were taken to try out the system and to estimate what reduction I was getting. This and other measurements indicated I was getting 0.45; as the focal length of the RC is 1600 mm this gave me a nominal 720 mm focal length — not that different from my LX200 with the same focal reducer.
The picture taken by a Starlight Xpress MX716 monochrome camera through an Astronomik Hα-CCD filter. It is a combination of pictures taken with exposures of 8, 16, and 32 seconds. Each picture was a stack of 10 frames aligned manually in RegiStax5, and the pictures combined by RegiStax and enhanced by wavelets 1-2 = 5.
As a comparison, this picture was taken in exactly the same way as that above but using an Hβ filter. The β line of Hydrogen is weaker than the α line and you can see that this is so in the picture. (The pictures are not adjusted to allow for the different sensitivity of the camera to the two wavelengths of light so don't read too much into the apparent difference.) This reduces the brightness of the hydrogen-emitting regions but does not have much effect on the stars (which are largely saturated anyway). So the contrast between the two is enhanced and you may notice that the trapezium stars stand out better in the Hβ picture.
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