Or indeed cat

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David Arditti

Yes. The idea of carrying an f/11 4-inch refractor on an adequate German equatorial mount up and down stairs doesn’t seem like a realistic option to me.

I don’t recall ever looking through a Mewlon, but everybody says they are superb. However, there are advantages to the closed-tube cats, and I don’t think you should dismiss them out of hand. They stay clean inside, they don’t have spiders (either the animal or the optical kind) to affect the image, and the coatings do not corrode rapidly (this latter factor I find to be a huge issue in a polluted city for open-tube scopes). Dewing of the corrector is an issue, but can be greatly slowed with a dew shield, which can be a flexible piece of plastic. The ‘large central obstruction’ is a bit of an over-done preoccupation of some people, in my view. The great telescopes of the world (and in space) all have obstructions of 30-40% of the diameter, and no astronomer ever thought that made them bad telescopes. Contrast comes from many factors, including cleanness of the optics and darkness of the tube (baffling). SCTs tend to score well on these. The central obstruction throws a bit more light into the first diffraction ring, and if observing close double stars in fantastic seeing it is an effect you might possibly detect, but it doesn’t seem to damage planetary detail. I’ve been happy enough with Celestron SCTs to have owned 5 different ones.

My other thought on all this is that, to save weight to be carrying, you could consider: do you really need a German equatorial? As Peter says, they imply that annoying counterweight. There’s an increasing selection of altazimuth mounts, manual and driven, available now. Most of them, again, I haven’t tested, so how well they might do in your context I don’t know. But another correspondent of mine is currently having a lot of fun with a Skywatcher GTi altazimuth GOTO (but only with a 75mm short-tube refractor).

As far as the 2nd hand market goes, I’d recommend UK Astronomy Buy & Sell for bargains. I’ve bought loads of things off there over the years, and rarely had any problems.