Mak Newt vs Apo Refractor?

[Jove]

A bit of a hypothetical one this, given available finances, but I can dream so i have one for the scope experts here:

I have had a lot of fun the last few years with my Skymax 127. One thing that sometimes I wish I could change would be its very narrow field of view - for looking at open clusters, star fields and so on. So, the latest Sky & Telescope has a review of a 6" f/4.8 Mak-Newt from Explore Scientific that is marketed as a 'rich field' scope and gives a near 3degree FOV with a 30mm eyepiece (about 25x). I have also read reports that similar Mak-Newts give as good a view as an apo refractor of the same aperture... which would make them a bargain if true. So, if a couple of thousand were to fall into my lap and I were to decide to splash out on a wide-field scope, how would the MN and an apo compare?

[Ben Ritchie]

I've been impressed with the optics of the Mak-Newts i've seen (mainly an Intes MN86, briefly the Skywatcher 190). "Apo-like" is a rather overused term, not least because refractors themselves vary widely in performance (i've seen a couple of "apochromats" that set the bar very low in performance terms!), but from what i've seen the performance of the Mak-Newt design is very good.

Downsides to me would be:

- on the Intes 'scopes i've used, focus travel was very limited and occasionally problematic for imaging

- like the conventional Newtonian, the focuser tends to end up in strange positions when mounted on a GEM, "straight-through + diagonal" with a refractor is generally a lot easier. Rotating rings can help with the Newt/Mak-Newt, but the eyepiece still tends to end up awkward near the zenith.

- the Mak-Newt corrector can be a dew magnet. Dew shields and heaters can help, but it's generally easier to keep a refractor dew-free.

Still, I think the MN is a great design, with good optics and at larger apertures offers a lot of bang for the buck compared to a comparable refractor.

[ollypenrice]

I'd agree with Ben. I suppose the other thing to look at would be the threads regarding optical and mechanical hiccoughs. Those afflicting MNs and other kinds of reflector greatly outnumber those afflicting refractors, but when reflectors and Cats are working to spec they are wonderful and great value. In visual use many little gremlins have no significant effect, however.

And as the big Chinese optical firms move upmarket apos are getting, if not cheaper, at least less expensive!

Olly

[John]

This is exactly the topic I'm interested in investigating over the coming months having been lucky enough to be able to buy both an Intes (Russian) 6" F/5.9 maksutov-newtonian and, recently, a Skywatcher ED120 Pro refractor. The previous owner of these 2 scopes felt that their performance was extremely close so I'm going to enjoy trying them "back to back" on the same objects and under the same conditions

So far August has been very uncooperative re: clear skies so I've barely managed 1st light with the refractor. I've owned the mak-newtonian for a while now so I've some experience with it - it's very impressive and versatile so the ED120 is going to have it's work cut out I feel

I'll post some reports when I've some experience under my belt with both.