Newbies need to consider many things before buying an expensive apo refractor for astronomical viewing. What I write is for them.
If using a Contrast Booster filter that essentially removes blue light and using a good 1/10 wave dielectric diagonal, a much cheaper achromat will basically perform as an apo that is similarly filtered, and save a bunch of money. If you want the full color spectrum, it's a different issue. I use filters anyway when doing high power planetary work, so an apo is not an essential upgrade. The tiny bit of residual astigmatism in my Stellarvue NH II probably does more image damage after being minus blue filtered than the fact it isn't apo. Also, upgrading the diagonal gave a HUGE gain in image quality. If observing from town and using Broadband, Contrast Booster, UHC or similar radical filters anyway, an apo is extra money down a rathole, like a Ferrari doing a heavy traffic urban comute. My 80mm NH II with Contrast Booster shows the Cassini Division very clearly when observing in town.
I love my refractor because it is small, light, rugged (for banging in the brush, ruggedness is an absolute essential) and works well as a long range terrestrial scope when filtered for that purpose. Minus blue filtration is necessary to cut through haze in the daytime. I always use at minimum a Fringe Killer, but usually a more radical Contrast Booster. Birding fanatics doing short range work at high power have a different need entirely, and an apo works better for them. My NH II goes lower power than a Mak and does not cause blackout problems in daytime with big exit pupils (you generally go lower, not higher mag, for long range terrestrial work). A big Mak or SCT scope is lighter and cheaper than a refractor, so you can buy more aperture for deep sky. My LOMO 102MN Mak-Newt actually is less affected by stray streetlight glare than my NH II, and that's WITHOUT a lens shade on the 102MN and using the lens shade on the NH II, so the old saw that refractors always have more contrast is pure horse manure, at least in my high glare situation. The NH II has internal baffling, and the 102MN does not. In direct glare situations with stray light hitting the lens directily, optical figure, polish and coatings are all important, not tube baffling.
I bought my Stellarvue refractor based on views of refractor lovers, and in real world use against excellent LOMO Mak optics in astro use, their opinions of refractors vs. Maks has not panned out for me. My preferred use of a refractor scope remains with daylight terrestrial viewing, where I see real solid and easily differentiated reasons for using them instead.
For any newbies out there, before you drop a load on an apo refractor because of what you read, know that most EXPERIENCED astro observers use reflectors or CAT's of some sort that do better overall for less money if any deep sky work at all is factored into the mix of targets.....and it usually is. Also know that a Mak is a "semi-refractor" and that thick meniscus lens may actually have more glass in it than a two-element ED or achromat refractor. Small central obstructions reduce contrast and resolution losses to insignificant levels in real world conditions with high quality Mak scopes. The greater aperture you can buy usually more than makes up for that anyway. If you have enough aperture in a refractor for true general purpose astro use, it will be bigger and/or heavier and/or costlier than anything else you might buy. Remember, as you raise magnification relative to aperture, contrast goes down in refractors just as in any other scope. The extra aperture you get in nonrefractors for the same price should more than make up the difference in lost contrast since you will be running a lower mag relative to aperture and have a bigger exit pupil with a brighter image. So in a dollar for dollar situation, the lost contrast by using something besides a refractor doesn't really exist. It's hogwash promoted by apo refractor lovers and manufacturers that compare aperture to aperture, which for any set amount of money spent will be VASTLY different anyway. So in the end it's often BS, except in certain situations where cost has little consideration. A fool and his money are soon parted. I have major cost considerations. I'm a refractor user, not a refractor lover.
In the end, I have seen higher quality of construction generally win out over type of scope for astro use. Witness the LOMO 102MN over the Stellarvue NH II. They are similarly priced on the open market, but the optical quality and aperture are quite different. I can usually get more quality for less money in a reflector or CAT of some sort. I'm not against apo refractors, but be very, very careful before parting with any money and know the few areas where they actually excel over other optical types. It isn't in general purpose visual astronomy at anywhere near the cost and practicality of other types. Astrophotography can be a different issue, and if you do that you know why that is.
I took my new Mak-Newt down to the river and observed water birds to compare it against my refractor. Except for the fact the birds were upside down, there was no contrast loss in the Mak-Newt that I could tell. I used a star diagonal in the refractor, not an Amici prism, in order to make it a fair test. Outside of the fact the Mak-Newt produced inverted images, I liked its images better for optical quality just as with my Mak-Cass scope. However, I will be using the refractor for general terrestrial viewing because of it's erect images and ability to do low powers better than a Mak-Cass. You CAN buy image erectors for Newtonians, and Siebert optics sells them. The view through the LOMO Mak-Newt finder was erect and quite good. Before the refractor guys cry foul because I did not use an apo in comparison, this was more a dollar for dollar value comparison, which is more real world in nature. A guy with mainly astro intentions that did birding occasionally on the side with limited funds would be better off with the Mak-Newt and a Newtonian image erector.
I have found that ordinary image erector prisms cause such noticeable loss of image quality that buying an apo for birding and using one on it would be more money down a rathole. Baader is said to make a good 1/10 wave erector prism for around $300 with adapters. I use a star diagonal on my Mak-Cass for occasional birding and got used to the left-right reversed image. You soon get used to it when scanning and never know the difference until written text is in the view. This is a poor man's way to get apo quality at a reflector price point. An 80mm triplet apo (doublets are NOT true apo refractors) at 100X will never have the brightness and visual punch of my 150mm LOMO Mak-Cass at that mag, which I probably paid considerably less for.
