Alan64

An 180mm Maksutov-Cassegrain would make for a splendid celestial "microscope"; for the Moon and the planets and double-stars, and would simulate a 140mm f/19 refractor. Observing quite a few of the smaller, single deep-sky objects should be possible, too. Now, a 30mm ocular, which gives a wide-field low-powered view at 25x via my 6" f/5 Newtonian, would realise 90x with said Maksutov: a considerable magnification, and one of the lowest practical powers. Perhaps more people than we know look upon the short tubes of the Cassegrains thinking that one would make for a capable deep-sky instrument, until it's there before them. Notice how the 2700mm focal-length of the 180mm Maksutov is folded into three sections within the optical tube... Therein, its true nature is revealed.

Physics is incapable of being "unfair". It is what it is.... I have an 80mm f/6 achromat. It even came with its own vampire-star... At f/6, the aberration is well controlled, up to a moderate magnification... However, research the colour-suppression performance of the faster Synta 80mm f/5 achromats(Orion, Sky-Watcher, iOptron, et al). Then, add an extra 40mm to said f-stop. The aberration increases with aperture when the same f-stop is maintained. Again, a 120mm f/5 achromat should offer, at times, wonderful if not stellar deep-sky performance, and that is its strong suit.

A 120mm f/5 achromat is going to exhibit oodles and gobs of false colour on every bright object you observe. Do you remember kaleidoscopes as a kid, and it gets worse as the magnification is increased. A fast achromat however excels at observing the dimmer deep-sky objects; not too terribly bright, mind you. If you want to observe mostly at higher magnifications, then go with either a 150mm f/12 Maksutov, or a 150mm f/5 Newtonian combined with a barlow. The Maksutov would be a near-simulation of a 120mm f/15 planetary refractor, and perfect for observing everything up close. Similarly, a 127mm Maksutov would mock a 90-100mm long-focus refractor. On the other hand, a 150mm f/5 Newtonian would imitate a 120mm f/6 apochromatic refractor... http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-ds-ota.html Newtonians are apochromatic, meaning "totally without colour"; that being false colour, or chromatic aberration. With a better-quality 2x barlow, the 150mm f/5 would enable magnifications up to 250x and beyond, in good and better seeing conditions; and all the way down to 23x with a 32mm ocular for wide-field deep-sky objects and vistas.

I'm near-sighted, and have worn glasses since my relative youth. In any event, what I had meant by my statement regarding the camera's shortcomings, is in that it fails to capture the sharpness of a live view. This is a photograph I took with the Tanzutsu 60mm f/15... It appears nice and sharp, eh? Ah, but not nearly as sharp as the live view at the time the photograph was taken. Here's a close-up... During the live view, within the circled portion, I saw what appeared to be dozens if not hundreds of what I term "hills and dales", within that ridge. The event has me almost convinced that the achromatic doublet was not manufactured by Tanzutsu, but by the Japanese optical house, Towa, instead. The two companies were in collaboration with one another at some point in the past. I wouldn't be surprised if the doublet was a part of Towa's old stock, and possibly from at least a decade prior to the refractor's manufacture.

A 5" Zeiss apochromat might exhibit only one thing: perfektion.

At f/6, 480mm, the Antares will indeed exhibit its fair share of false colouration, and the camera only accentuates it further in the resulting photograph. I've been told that the camera itself, even, will introduce colours, particularly when held at an angle. Here's another shot through the Antares, and at a higher magnification. However the colour wasn't as strong when observing with the eye...

The Moon was almost full, waning I think, when I took that photograph, thus the use a variable polariser to dim down the brightness.

Refractive family portraits... Takahashi FS-102, a 102mm f/8 apochromat... Purchased new in 2003, it is a consummate "pupil", my having split Sirius in the same year when it and its companion, "The Pup", were practically adjacent to each other; said companion having blinked in and out, but never having disappeared entirely within the Dog's intense glare. The separation between the two has steadily increased since that time. I attribute said feat to the refractor's exquisite calcium-fluorite doublet, known for its relative absence of light-scattering... Tanzutsu 60mm f/15 achromat, and upgraded to a 1.25" focusser... Made in Japan in 1987 or '88, this example was purchased as new old-stock earlier this year. Almost 5" had to be cut off of the optical tube, from the front, and in order to effect the new 1.25" format. An extra tube-baffle was added, and ultra-flat black spray paint applied throughout the optical path where necessary, from the front edge of the dew shield to the 1.25" visual back. I had always wanted a long-focal achromat, albeit only a 60mm. Lastly, the most recent acquisition: an Antares 805 80mm f/6 fast-achromat... It, too, will need enhancing, but as it stands I was able to view the Airy disc of the brightest star within Orion's Trapezium, designated "C", rather distinctly and under high magnification. Nonetheless I consider it to be little better than a guidescope with less than stellar optical quality. An afocal image via the Takahashi, and simply by holding a point-and-shoot camera up to the eyepiece... Likewise, via the Tanzutsu... ...and via the Antares... Chromatic abberation is well-controlled with this example, but present nevertheless. In every instance, the Canon S110 always falls short of that seen during a live session.