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 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 most of the colour 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 ration of f/7, putting it decidedly in the ‘medium’ speed range for imaging. I will be investing in a focal reducer at some point to bring this down to f5.6, thereby reducing my exposure time by about 30%. In the meantime, I’m going to be experimenting with my C8 focal reducer, as I’ve read good things about this combination in the past.
Since my previous Revelation 80mm was a 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 use a 9×50 Finder Guider to guide this scope, mounted piggy-back style, which makes the whole setup easier to balance. The use of a finder-guider means that the weight is kept to a minimum – something that’s important when imaging. 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.