This is my primary imaging refractor. It is a lovely piece of kit made by Altair Astro, based in Norfolk. With good quality optics, a beautifully over-engineered focuser and good colour correction, it’s a ‘doublet’ (i.e. it has two pieces of glass in it’s primary lens cell), and is described as a ‘semi-apochromatic’ refractor. This is mostly marketing-speak, but means that although it only contains the two pieces of glass for it’s optics (as opposed to the three contained within a ‘triplet’), it is well enough coated and engineered to eliminate a lot of of the colour fringing and other aberrations that are associated with these types of scopes. It produces, in my opinion, results far above what you would expect, with a very flat field and good colour. It has an objective lens diameter of 102mm, and a focal ratio of f/7, putting it decidedly in the ‘medium’ speed range for imaging. I have focal reducer for this scope to bring this down to f5.6, thereby reducing my exposure time by about 30%, and widening the field of view somewhat. However, as I’ve moved onto CCD imaging, spacing issues when using the reducer with and OAG and filter wheel have meant it isn’t as used as I thought it would be. I will revisit this at some point.
Since my previous Revelation 80mm was a similarly-named semi-apo, and I was completely happy with the results I got from that, I had no hesitation in going for this one when it came up for sale.
I used to use a 9×50 Finder Guider to guide this scope (as shown in these images), mounted piggy-back style, (the use of a finder-guider means that the weight was kept to a minimum – something that’s important when imaging), but moved onto guiding via an off-axis guider. The actual finder I use on this is actually a rifle sight, which costs about half the amount as exactly the same piece of hardware bought as an astronomical red dot finder, even though the actual kit is identical. It even has the same mounting mechanism, and drops straight onto the mounting bracket made for this scope.